Abstract
Stringent COVID-19 control measures were imposed in Wuhan between January 23 and April 8, 2020. Estimates of the prevalence of infection following the release of restrictions could inform post-lockdown pandemic management. Here, we describe a city-wide SARS-CoV-2 nucleic acid screening programme between May 14 and June 1, 2020 in Wuhan. All city residents aged six years or older were eligible and 9,899,828 (92.9%) participated. No new symptomatic cases and 300 asymptomatic cases (detection rate 0.303/10,000, 95% CI 0.270–0.339/10,000) were identified. There were no positive tests amongst 1,174 close contacts of asymptomatic cases. 107 of 34,424 previously recovered COVID-19 patients tested positive again (re-positive rate 0.31%, 95% CI 0.423–0.574%). The prevalence of SARS-CoV-2 infection in Wuhan was therefore very low five to eight weeks after the end of lockdown.
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Introduction
The Coronavirus Disease 2019 (COVID-19) was first reported in December 2019, and was classified as a pandemic by the World Health Organization on March 11, 20201. Following strict lockdown measures, the COVID-19 epidemic was generally under control in China, and the whole country has progressed into a post-lockdown phase. In this phase, countries face new problems and challenges, including how to accurately assess the post-lockdown risk of the COVID-19 epidemic, how to avoid new waves of COVID-19 outbreaks, and how to facilitate the resumption of economy and normal social life. As the city most severely affected by COVID-19 in China, Wuhan had been under lockdown measures from January 23 until April 8, 2020. During the first 2 months after city’s reopening, there were only a few sporadic COVID-19 cases in Wuhan (six newly confirmed cases from April 8 to May 10, 20202). However, there was still concern about the risk of COVID-19 in Wuhan, which seriously affected the resumption of industrial production and social services, and hampered the normal lives of residents. In order to ascertain the current status of the COVID-19 epidemic, the city government of Wuhan carried out a comprehensive citywide nucleic acid screening of SARS-CoV-2 infection from May 14, 2020 to June 1, 2020.
The citywide screening of SARS-CoV-2 infection in Wuhan is a mass screening programme in post-lockdown settings, and provided invaluable experiences or lessons with international relevance as more countries and cities around the world entering the post-lockdown phase. In this study, we report the organisation process, detailed technical methods used, and results of this citywide nucleic acid screening.
Results
There were 10,652,513 eligible people aged ≥6 years in Wuhan (94.1% of the total population). The nucleic acid screening was completed in 19 days (from May 14, 2020 to Jun 1, 2020), and tested a total of 9,899,828 persons from the 10,652,513 eligible people (participation rate, 92.9%). Of the 9899,828 participants, 9,865,404 had no previous diagnosis of COVID-19, and 34,424 were recovered COVID-19 patients.
The screening of the 9,865,404 participants without a history of COVID-19 found no newly confirmed COVID-19 cases, and identified 300 asymptomatic positive cases with a detection rate of 0.303 (95% CI 0.270–0.339)/10,000. The median age-stratified Ct-values of the asymptomatic cases were shown in Supplementary Table 1. Of the 300 asymptomatic positive cases, two cases came from one family and another two were from another family. There were no previously confirmed COVID-19 patients in these two families. A total of 1174 close contacts of the asymptomatic positive cases were traced, and they all tested negative for the COVID-19. There were 34,424 previously recovered COVID-19 cases who participated in the screening. Of the 34,424 participants with a history of COVID-19, 107 tested positive again, giving a repositive rate of 0.310% (95% CI 0.423–0.574%).
Virus cultures were negative for all asymptomatic positive and repositive cases, indicating no “viable virus” in positive cases detected in this study.
All asymptomatic positive cases, repositive cases and their close contacts were isolated for at least 2 weeks until the results of nucleic acid testing were negative. None of detected positive cases or their close contacts became symptomatic or newly confirmed with COVID-19 during the isolation period. In this screening programme, single and mixed testing was performed, respectively, for 76.7% and 23.3% of the collected samples. The asymptomatic positive rates were 0.321 (95% CI 0.282–0.364)/10,000 and 0.243 (95% CI 0.183–0.315)/10,000, respectively.
The 300 asymptomatic positive persons aged from 10 to 89 years, included 132 males (0.256/10,000) and 168 females (0.355/10,000). The asymptomatic positive rate was the lowest in children or adolescents aged 17 and below (0.124/10,000), and the highest among the elderly aged 60 years and above (0.442/10,000) (Table 1). The asymptomatic positive rate in females (0.355/10,000) was higher than that in males (0.256/10,000).
The asymptomatic positive cases were mainly domestic and unemployed residents (24.3%), retired older adults (21.3%), and public service workers (11.7%) (Fig. 1).
Note: Others included the self-employed, military personnel, and so on. (Source data are provided as s Source Data file.).
The asymptomatic positive rate in urban districts was on average 0.456/10,000, ranging from 0.317/10,000 in Hongshan to 0.807/10,000 in Wuchang district. A lower rate of asymptomatic positive cases was found in suburban districts (0.132/10,000), ranging from 0.047/10,000 in Xinzhou to 0.237/10,000 in Jiangan district (Fig. 2).
Note: 1 represents Jianghan district; 2 represents Qiaokou district. (Source data are provided as s Source Data file.).
Among the 7280 residential communities in Wuhan, asymptomatic positive cases were identified in 265 (3.6%) communities (only one case detected in 246 communities), while no asymptomatic positive cases were found in other 96.4% communities.
Testing of antibody against SARS-CoV-2 virus was positive IgG (+) in 190 of the 300 asymptomatic cases, indicating that 63.3% (95% CI 57.6–68.8%) of asymptomatic positive cases were actually infected. The proportion of asymptomatic positive cases with both IgM (−) and IgG (−) was 36.7% (95% CI: 31.2–42.4%; n = 110), indicating the possibility of infection window or false positive results of the nucleic acid testing (Table 2).
Higher detection rates of asymptomatic infected persons were in Wuchang, Qingshan and Qiaokou districts, and the prevalence of previously confirmed COVID-19 cases were 68.243/10,000, 53.767/10,000, and 100.047/10,000, respectively, in the three districts. Figure 3 shows that districts with a high detection rate of asymptomatic positive persons generally had a high prevalence of confirmed COVID-19 cases (rs = 0.729, P = 0.002).
a The prevalence of previously confirmed patients of COVID-19 in each district in Wuhan. b The detection rate of asymptomatic positive cases of COVID-19 in each district in Wuhan. (Source data are provided as s Source Data file.).
Discussion
The citywide nucleic acid screening of SARS-CoV-2 infection in Wuhan recruited nearly 10 million people, and found no newly confirmed cases with COVID-19. The detection rate of asymptomatic positive cases was very low, and there was no evidence of transmission from asymptomatic positive persons to traced close contacts. There were no asymptomatic positive cases in 96.4% of the residential communities.
Previous studies have shown that asymptomatic individuals infected with SARS-CoV-2 virus were infectious3, and might subsequently become symptomatic4. Compared with symptomatic patients, asymptomatic infected persons generally have low quantity of viral loads and a short duration of viral shedding, which decrease the transmission risk of SARS-CoV-25. In the present study, virus culture was carried out on samples from asymptomatic positive cases, and found no viable SARS-CoV-2 virus. All close contacts of the asymptomatic positive cases tested negative, indicating that the asymptomatic positive cases detected in this study were unlikely to be infectious.
There was a low repositive rate in recovered COVID-19 patients in Wuhan. Results of virus culturing and contract tracing found no evidence that repositive cases in recovered COVID-19 patients were infectious, which is consistent with evidence from other sources. A study in Korea found no confirmed COVID-19 cases by monitoring 790 contacts of 285 repositive cases6. The official surveillance of recovered COVID-19 patients in China also revealed no evidence on the infectiousness of repositive cases7. Considering the strong force of infection of COVID-198,9,10, it is expected that the number of confirmed cases is associated with the risk of being infected in communities. We found that asymptomatic positive rates in different districts of Wuhan were correlated with the prevalence of previously confirmed cases. This is in line with the temporal and spatial evolution (especially the long-tailed characteristic) of infectious diseases11.
Existing laboratory virus culture and genetic studies9,10 showed that the virulence of SARS-CoV-2 virus may be weakening over time, and the newly infected persons were more likely to be asymptomatic and with a lower viral load than earlier infected cases. With the centralized isolation and treatment of all COVID-19 cases during the lockdown period in Wuhan, the risk of residents being infected in the community has been greatly reduced. When susceptible residents are exposed to a low dose of virus, they may tend to be asymptomatic as a result of their own immunity. Serological antibody testing in the current study found that at least 63% of asymptomatic positive cases were actually infected with SARS-CoV-2 virus. Nonetheless, it is too early to be complacent, because of the existence of asymptomatic positive cases and high level of susceptibility in residents in Wuhan. Public health measures for the prevention and control of COVID-19 epidemic, including wearing masks, keeping safe social distancing in Wuhan should be sustained. Especially, vulnerable populations with weakened immunity or co-morbidities, or both, should continue to be appropriately shielded.
Findings from this study show that COVID-19 was well controlled in Wuhan at the time of the screening programme. After two months since the screening programme (by August 9, 2020), there were no newly confirmed COVID-19 cases in Wuhan. Further testing of SARS-CoV-2 in samples collected from market environment settings in Wuhan were conducted, and found no positive results after checking a total of 52,312 samples from 1795 market setting during June 13 to July 2, 202012.
This study has several limitations that need to be discussed. First, this was a cross-sectional screening programme, and we are unable to assess the changes over time in asymptomatic positive and reoperative results. Second, although a positive result of nucleic acid testing reveals the existence of the viral RNAs, some false negative results were likely to have occurred, in particular due to the relatively low level of virus loads in asymptomatic infected individuals, inadequate collection of samples, and limited accuracy of the testing technology13. Although the screening programme provided no direct evidence on the sensitivity and specificity of the testing method used, a meta-analysis reported a pooled sensitivity of 73% (95% CI 68–78%) for nasopharayngeal and throat swab testing of COVID-1914. Testing kits used in the screening programme were publicly purchased by the government and these kits have been widely used in China and other countries. Multiple measures were taken to possibly minimise false negative results in the screening programme. For example, standard training was provided to health works for sample collection to ensure the sample quality. The experiment procedures, including specimen collection, extraction, PCR, were according to official guidelines (Supplementary Note 1). For the real-time RT-PCR assay, two target genes were simultaneously tested. Even so, false negative results remained possible, particularly in any mass screening programmes. However, even if test sensitivity was as low as 50%, then the actual prevalence would be twice as high as reported in this study, but would still be very low. Around 7.1% of eligible residents did not participate in the citywide nucleic acid screening and the screening programme did not collect detailed data on reasons for nonparticipation, which is a limitation of this study. Although there were no official statistics, a large number of migrant workers and university students left Wuhan before the lockdown, joining their families in other cities or provinces for traditional Chinese New Year. Therefore, it is likely that most nonparticipants were not in Wuhan at the time of the screening. The main objective of the screening programme was to assess the risk of COVID-19 epidemic in residents who were actually living in the post-lockdown Wuhan. Therefore, the estimated positive rates are unlikely to be materially influenced by nonparticipation of residents who were not in Wuhan or some residents who did not participate in the screening for other reasons. Moreover, people who left Wuhan were the target population for monitoring in other provinces and cities and were required to take nucleic acid testing. Although there was no official statistics showing the positive rate of nucleic acid testing in this population, there was no report that shown a higher positive rate of nucleic acid testing than our findings.
In summary, the detection rate of asymptomatic positive cases in the post-lockdown Wuhan was very low (0.303/10,000), and there was no evidence that the identified asymptomatic positive cases were infectious. These findings enabled decision makers to adjust prevention and control strategies in the post-lockdown period. Further studies are required to fully evaluate the impacts and cost-effectiveness of the citywide screening of SARS-CoV-2 infections on population’s health, health behaviours, economy, and society.
Methods
Study population and ethical approvals
Wuhan has about 11 million residents in total, with seven urban and eight suburban districts. Residents are living in 7280 residential communities (or residential enclosures, “xiao-qu” in Chinese), and each residential community could be physically isolated from other communities for preventing transmission of COVID-19.
The screening programme recruited residents (including recovered COVID-19 patients) currently living in Wuhan who were aged ≥6 years (5,162,960 males, 52.2%). All participants provided written or verbal informed consent after reading a statement that explained the purpose of the testing. For participants who aged 6–17 years old, consent was obtained from their parents or guardians. The study protocol for an evaluation of the programme based on anonymized screening data was approved by the Ethics Committee of the Tongji Medical College Institutional Review Board, Huazhong University of Science and Technology, Wuhan, China (No. IROG0003571).
Organizational guarantee and community mobilization
A citywide nucleic acid screening group was formed, with specialized task teams contributing to comprehensive coordination, technical guidance, quality control, participation invitation, information management, communication, and supervision of the screening. The city government invested 900 million yuan (RMB) in the testing programme. From 14 May to 1 June 2020, in the peak time, up to 2907 sample collection sites were functioning at the same time in Wuhan. Each sample collection site had an assigned sample collection group, including several health professionals (staffed according to the number of communities’ residents), 2–4 community managers, 1–2 police officers, and 1–2 inspectors. The sampling sites were set up based on the number and accessibility of local residents. Local community workers were responsible for a safe and orderly sampling process to minimise the waiting time. In addition, mobile sampling teams were formed by primary health care professionals and volunteers to conduct door-to-door sampling for residents who had physical difficulties or were unable to walk.
About 50,000 health professionals (mainly doctors and nurses from community health centers) and more than 280,000 person-times of community workers and volunteers contributed to sample collection, transport of equipment and samples collected, arrangement of participation process, and maintaining order of sampling sites. Public information communication and participant invitation were implemented through mass media, mobile messages, WeChat groups, and residential community broadcasts, so as to increase residents’ awareness and the participation.
Acquisition, preservation, and transport of samples
All sampling personnel received standard training for the collection of oropharyngeal swab samples. To minimise the risk of cross-infection, the sampling process strictly followed a disinfection process and environmental ventilation were ensured. The collected samples were stored in a virus preservation solution or immersed in isotonic saline, tissue culture solution, or phosphate buffer (Supplementary note 1). Then, all samples were sent to testing institutions within 4 h using delivery boxes for biological samples refrigerated with dry ice to guarantee the stability of nucleic acid samples.
Technical methods for laboratory testing of collected samples
A total of 63 nucleic acid testing laboratories, 1451 laboratory workers and 701 testing equipment were involved in the nucleic acid testing. Received samples were stored at 4 °C and tested within 24 h of collection. Any samples that could not be tested within 24 h were stored at −70 °C or below (Supplementary note 1). In addition to “single testing” (i.e., separate testing of a single sample), “mixed testing” was also performed for 23% of the collected samples to increase efficiency, in which five samples were mixed in equal amounts, and tested in the same test tube. If a mixed testing was positive for COVID-19, all individual samples were separately retested within 24 h15.
Details regarding technical methods for sequencing and virus culture were provided in Supplementary note 1. Real-time reverse transcriptase-polymerase chain reaction (RT-PCR) assay method was used for the nucleic acid testing. We simultaneously amplified and tested the two target genes: open reading frame 1ab (ORF1ab) and nucleocapsid protein (N) (Supplementary Note 1). A cycle threshold value (Ct-value) less than 37 was defined as a positive result, and no Ct-value or a Ct-value of 40 or more was defined as a negative result. For Ct-values ranging from 37 to 40, the sample was retested. If the retest result remained less than 40 and the amplification curve had obvious peak, the sample was classified as positive; otherwise, it was reported as being negative. These diagnostic criteria were based on China’s official recommendations16.
For asymptomatic positive cases, virus culture was carried out in biosafety level-3 laboratories. The colloidal gold antibody test was also performed for asymptomatic positive cases (Supplementary note 1). All testing results were double entered into a specifically designed database, and managed by the Big Data and Investigation Group of the COVID-19 Prevention and Control Centre in Wuhan, which was established to collect and manage data relevant to the COVID-19 epidemic.
Participant data collection and management
Before sample collection, residents electronically (using a specifically designed smartphone application) self-uploaded their personal information, including ID number, name, sex, age, and place of residence. Then, the electronic machine system generated a unique personal barcode and stuck it on the sample tube to ensure the match between the sample and the participant. Then trained staff interviewed each individual regarding the history of COVID-19 and previous nucleic acid testing. There was a database of confirmed COVID-19 cases in Wuhan, which can be used to validate the self-reported previous COVID-19 infection. All information was entered into a central database. The testing results were continually uploaded to the central database by testing institutions. Contact tracing investigations were conducted on participants who tested positive for SARS-CoV-2, to track and manage their close contacts. The pre-existing unique identification code for each resident was used as the programme’s identification number, to ensure information accuracy during the whole process of screening, from sampling, nucleic acid testing, result reporting, the isolation of detected positive cases, and tracing of close contacts of positive cases. All screening information was kept strictly confidential and was not allowed to be disclosed or used for other purposes other than clinical and public health management. Personal information of asymptomatic positive cases was only disclosed to designated medical institutions and community health centres for the purpose of medical isolation and identification of close contacts. Researcher was blind to the study hypothesis during data collection.
Biological security guarantee
Nucleic acid testing was performed in biosafety level-2 (BSL-2) laboratories, and virus culture was conducted in biosafety level-3 laboratories. Sampling and testing personnel adopted the personal protective measures according to the standard of biosafety level-3 laboratories. Participating laboratories implemented control measures to guarantee biological safety in accordance with relevant regulations17.
Result query and feedback
Two to three days after sample collection, participants could inquire about their test results using WeChat or Alipay application by their unique ID numbers. The results included text descriptions of nucleic acid testing and coloured health codes. A green coloured health code refers to a negative result, and a red coloured health code indicates a positive result.
Definition and management of identified confirmed cases and close contacts
In this study, all confirmed COVID-19 cases were diagnosed by designated medical institutions according to National Guidelines for the Prevention and Control of COVID-19 (Supplementary Note 2). Asymptomatic positive cases referred to individuals who had a positive result during screening, and they had neither a history of COVID-19 diagnosis, nor any clinical symptoms at the time of the nucleic acid testing. Close contacts were individuals who closely contacted with an asymptomatic positive person since 2 days before the nucleic acid sampling16. Repositive cases refer to individuals who recovered from previously confirmed COVID-19 disease and had a positive testing again in the screening programme. All repositive cases, asymptomatic positive persons, and their close contacts were isolated for at least 2 weeks in designated hotels managed by primary health care professionals, and they were released from isolation only if two consecutive nucleic acid tests were negative.
Statistical analysis
Detection rate of asymptomatic positive or repositive cases was calculated by dividing the number of individuals with a positive result of nucleic acid testing by the number of participants tested. Because of extremely low detection rates, we calculated 95% confidence intervals of estimated proportions using Pearson–Klopper exact method, implemented through R package “binom” version 1.1-118. SPSS version 22.0 was used for other statistical analyses. We analyzed the distribution of asymptomatic positive cases and assessed the Spearman correlation between the asymptomatic positive rate and the prevalence of previously confirmed COVID-19 cases in different districts of Wuhan. Differences in asymptomatic positive rates by sex and age groups were assessed using the χ2 test. ArcGIS 10.0 was used to draw a geographic distribution map of asymptomatic positive cases. A value of P < 0.05 (two-tailed) was considered statistically significant.
Reporting summary
Further information on research design is available in the Nature Research Reporting Summary linked to this article.
Data availability
Detailed data directly used to generate each figure or table of this study are available within the article, Supplementary Information andsource data are provided with this paper.
Change history
17 December 2020
The original version of this Article was updated shortly after publication, because the Peer Review file was inadvertently omitted. The error has now been fixed and the Peer Review file is available to download from the HTML version of the Article.
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Acknowledgements
We would like to thank all institutions and all citizens in Wuhan for their support for citywide nucleic acid screening work. We also would like to thank the Wuhan city government for this citywide nucleic acid testing, sampling and management, and thank the big data and investigation group of COVID-19 prevention and control institution in Wuhan (the data and investigation group of Wuhan Municipal Health Commission) for their efforts in the data collection. In addition, we would like to thank the National Social Science Foundation of China (Grant No. 18ZDA085) for supporting the fund.
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Authors and Affiliations
Contributions
S.Y.C., C.W., X.X.Y., and Z.X.L. conceived the study. C.W., Y.C.H., T.T.W., K.L., H.B.X., and X.S. participated in the acquisition of data. S.B.W. and J.G. were responsible for the on-site specimen collection, laboratory testing quality evaluation, and control. Y.C.H., T.T.W., and L.Q.L. analyzed the data. H.J., Y.H.G., and F.J.S. gave advice on methodology. Q.F.T. and C.Z.L. investigated the responses to the citywide nucleic acid testing among residents lived in outside of Wuhan city. S.Y.C., Y.G., C.W., and X.X.Y. drafted the manuscript, Y.G., M.B., and F.J.S. revised the manuscript, and M.B., C.Z.L., and F.J.S. critically commented and edited the manuscript. All authors read and approved the final manuscript. Z.X.L. is the guarantor of this study.
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Cao, S., Gan, Y., Wang, C. et al. Post-lockdown SARS-CoV-2 nucleic acid screening in nearly ten million residents of Wuhan, China. Nat Commun 11, 5917 (2020). https://doi.org/10.1038/s41467-020-19802-w
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DOI: https://doi.org/10.1038/s41467-020-19802-w
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Donal Garrahan
Brilliant study well done. Asymptomatic people do not spread even to close contacts . The overreaction of government and health authorities is proven to be all harm and no benefit. Stop all lockdowns now . Vaccines not necessary for healthy people . Adequate vitamin and mineral levels are important for Health as is normal blood sugar levels . Chronic ill health is a consequence of bad levels them and mostly ignored by health professionals.
Tesla Coil Replied to Donal Garrahan
You misinterpret the study. The positively tested persons were not actually having an active infection, but were examples of the rare case of viral RNA shedding many weeks or even months after the infection. This is completely different from active infections that are asymptomatic, or, as is more often the case, pre-symptomatic. The literature is very clear that asymptomatic or presymptomatic transmission is very common and may even be more common than symptomatic transmission (as patients are less careful when not showing symptoms).
jUlie Replied to Tesla Coil
Asymptomatic is not the same as pre-symptomatic and should not be interchanged which causes confusion. The fact is none of these asymptomatic people had any viable virus per cell culture so they are not infecting anyone. Should these people be called asymptomatic at all?! When the CT values are set so high that virus is not infectious why do we call this asymptomatic, they are simply showing viral particles that make up less than one percent of the actual virus. We have lots of viral particles so who cares if it isn't making anyone sick? I have read that CTs of more than 33 are extremely difficult to find any active virus yet many tests have CT's 35-45!!!! We are locking down entire economies for this nonsense and ruining lives. Why isn't there transparency and why aren't we demanding tests that directly correspond to transmission and illness? And why in the world were those "asympotomatic" people quarantined at all with a negative viral cell culture?!
Andrew Iannaccone
"There were no positive tests amongst 1,174 close contacts of asymptomatic cases."
How is this possible? Even if all those contacts were indeed uninfected, where are the false positive tests? Even assuming just a 1% false positive rate, the chance of getting zero positives out of 1,174 is less than 1 in 100,000. In the "source data" section, there's an even more improbable claim: zero positive results out of 85,884 tests conducted in East Lake Scenic Area of Wuhan.
Isn't this clear evidence that the data being used is unreliable?
EDIT: Tesla Coil resolved this for me below!
Tesla Coil Replied to Andrew Iannaccone
No, it is evidence that your assumption of "just a 1% false positive rate" is wrong. In fact, this test shows that at least in a low-incidence situation, the false-positive rate is at most 0.002%. Australia's and New Zealand's numbers for community transmission are consistent with that.
brandom moron Replied to Tesla Coil
I agree. But FPR probably depends on sample community prevalence rate as cross contamination is significant potential mechanism. Therefore China/Australia/NZ can achieve these ultra-low FPR's, but probably not most labs in countries processing samples with high positivity rates.
Tesla Coil Replied to brandom moron
Absolutely. I think there is tiny amount of real false positives, plus an amount from contamination that is somehow positively correlated with the current prevalence. In either case, however, false positives are either extremely low in absolute terms, or the number of false positives in relation to true positives is very low.
Andrew Iannaccone Replied to Tesla Coil
I believe I understand. Thanks. Can you point me to the AU/NZ data you're referring to?
Tesla Coil Replied to Andrew Iannaccone
The idea is: Look at a low-incidence population with many tests (a recent example would probably be community transmission in Victoria in the last four weeks). You can then calculate an upper bound for the false-positive rate by looking at the actual positive rate. I made the calculations a while ago with the numbers from South Australia in June, but let's look at Victoria. Covidlive dot com dot au has nicely compiled data showing that there were zero cases and 399,561 tests in Victoria in the last 28 days. This gives us a 95% Clopper-Pearson confidence interval of [0.00000%;0.00092%] for the true proportion of positive tests, which serves as an upper bound for the true amount of false positives. This implies a specificity of 99.999% or higher for the testing protocol in practice.
Note that such a high specificity does not necessarily hold when there is a higher incidence as this would increase the chance of contamination. But even then, false positives would only be a small fraction of true positives. In a nutshell: False positives from PCR tests basically never matter.
Andrew Iannaccone Replied to Tesla Coil
That's really interesting and helpful. Thanks!
brandom moron
A minority of patients go on shedding non-viable viral material that can be detected on PCR weeks or months after recovery from COVID-19 infection. Subjecting positive cases to needing two negative tests in a row will pick up most of these cases, but using the referenced PCR sensitivity rate of 73% means that even ignoring intermittent shedding, 7.3% of cases of prolonged PCR shedding will be slip through.
The 107/34,424 "re-positives" identified are likely a mix of some false positives in amongst a group of prolonged shedders, who passed two negative tests, but were picked up on this screening in May. None harboured viable virus and no comparison could be made with previous infection.
As for the 300/9,865,404 asymptomatic positive cases found, 110 were completely seronegative, so likely mostly false positives. None were IgM+/IgG-, and most were IgM-/IgG+ implying an old infection, which was not recognised as many COVID-19 infections are known to be asymptomatic. Again no viable virus was detected.
The finding of these missed asymptomatic infection prolonged shedders concentrated in areas which experienced higher rates of COVID-19 in the previous months would be expected.
At the end of June further screening of 52,312 samples detected zero cases. The pick-up rate in May would have predicted 1.6 positives in this sample. As this was 1 month later there would be far fewer prolonged shedders and given the small sample, a detection rate of zero is not unexpected (false positive rates aside).
Therefore this study simply proves what we probably know already, that the extreme Wuhan lockdown halted the spread of the virus regionally, and a minority of symptomatic and some asymptomatic patients will go on shedding non-viable viral RNA particles for up to a couple months or so, with no significant risk to others.
It does not say anything about risks of spread by asymptomatics/pre-symptomatics in populations where viable SARS-CoV-2 is still circulating.
Antiestablishmentarianism
Okay, so now COVID-19 has turned into the milk studies of 2020. One person says it does 'x', another person says it does 'y'.
Those who let science guide their behavior and thoughts on something are going to be whiplashed by this given numerous studies that DO show asymptomatic spread.
But this is a large study so let's assume for the moment that it's true.
But when someone is presymptomatic and the virus is in its incubation stage, or even just beginning to replicate on a larger scale - before they start feeling "sick." These people DO spread COVID, regardless of the merits of this study.
So now, we ask the question, how long before symptoms show up can that person spread it. We were saying cases of up to 32 days early on and as short as zero days.
So what's the timeframe here? You don't have symptoms but are infected. You then spread it for 'x' time prior to symptoms showing up.
And if the people in this study - the "asymptomatic people" - are testing negative....is it even accurate to claim they ever had it in the first place? So is this study merely calling people who didn't have COVID "asymptomatic"?
I didn't really see that question fleshed out here. Lots of questions.
Tesla Coil Replied to Antiestablishmentarianism
I believe a good interpretation is that those 300 patients that were tested positive but were asymptomatic were mostly old cases that were still shedding viral RNA. Probably none of them were still in the phase of an active infection, and presumably no viable virus was being shed.
rendy bella Replied to Antiestablishmentarianism
For those folks you mention to transmit the virus, you may need to do a lavage of the respiratory tissue affected, centrifuge it, and then carefully apply it to the prospect/recipient. A lot of people left their common sense they had in training for ideological-driven impossibilities.
S.K.
Hey all of you (Andrew Iannaccone, Antiestablishmentarianism, brandom moron, etc.)
Don't be so skeptical of findings and data that invalidate your beliefs!
Don't politicize science.
Don't involve science in ideological obsessions.
Meanwhile about asymptomatics...
Just hear Dr. Fauci...
https://www.youtube.com/wat...
brandom moron Replied to S.K.
By Sept 2020, Fauci had changed his view on asymptomatic spread in BMJ interview:
"Should we focus on people who are positive but asymptomatic? I’ve heard you say that they can’t be driving the pandemic because it’s pretty rare that they actually caused transmission. Was that wrong?
Yes, we were incorrect. What we did not know early on was that about 40-45% of the cases are asymptomatic. And recent modelling studies show that perhaps up to 50% of the transmissions occur from an asymptomatic person to an uninfected person. We cannot ignore asymptomatic infection, because that is a major component of the outbreak.
Sometimes you make a statement based on the data that you have. One of the things that I’ve learnt over the years is that you’ve got to be humble enough and flexible enough, as the data evolve, to change your guidelines and recommendations.
S.K. Replied to brandom moron
“La plus belle des ruses du diable est de vous persuader qu'il n'existe pas."
("The devil's finest trick is to persuade you that he does not exist.")”
―Charles Baudelaire, Paris Spleen
The oldest described chameleon is Anqingosaurus brevicephalus from the Middle Paleocene (about 58.7–61.7 mya) of China.
The youngest described chameleon is Fauci!
Colour change in chameleons has functions in camouflage, but most commonly in social signaling and in reactions to temperature and other conditions.
MIKE_THE_SKEPTIC Replied to brandom moron
recent modelling studies..... modelling is not scientific evidence
Tesla Coil
I have a humble request: Could the authors possible show for each of the four rows of the antibody results table, how many of the samples were from the 107 previously recovered COVID-19 patients that tested positive again, and how many from others? This way one could check how many of the 300 positively tested samples had either history of COVID-19 or positive antibody results.
brandom moron Replied to Tesla Coil
In the supplementary info, they only seem to mention that antibody testing was performed for the 300 asymptomatics, not the 107 repositives: "The colloidal gold antibody test was also performed for asymptomatic infected cases in conjunction with nucleic acid testing."
I would suspect a large majority of the repositives would still be antibody positive, so not tested, but would have been good to see the results.
Tesla Coil Replied to brandom moron
You are correct. It is actually clear from the second paragraph of the results section. There are two separate study populations: one without COVID-19 history (of which 300 tested positives), and one with COVID-19 history (of which 107 re-tested positive).
It would have been good to also do antibody testing on those 107 cases as this would have confirmed the proportion of COVID-19 cases that could still be picked up by antibody testing. This would then give an insight whether the 110 antibody-negative tests in the no-COVID-19-history group could partly be false negatives. Although the comparison may not be completely fair as the COVID-19-history group was presumably mostly symptomatic whereas the no-COVID-19-history group may have had asymptomatic infection, which might result in a different antibody response.
rendy bella
One of the most impossible and frankly scientifically ludicrous claims of this viral pandemic has been that asymptomatic carriers can transmit the disease. Regardless of this study, if this had been the case, by this time, we would have had almost a complete worldwide herd immunity; there would have been very few naive populations available to sustain the contagion. A lot of science has been jettisoned for the sole purpose of defeating Trump. Crazy times we are living.
Bill Crawford Replied to rendy bella
Unfortunately, the purpose was not to defeat Trump. We know this because after Trump's defeat, nothing has changed. And the insanity is even worse in the UK. University scientists are being told not to take a public stance contrary to erroneous CDC guidelines. Social media accounts are being terminated simply because people reference valid scientific research that refutes government guidelines.
Flint Westwood
Great to see people are out to undermine a ten million population study already. It's the clearest data to date.
It's proved just as anyone that's not lost their mind in the last year that asymptomatic cannot transmit viruses next to impossible.
The mass psychosis will try to trash this study as it's contrary to the covid storyline that's being pushed.
Absolutely no need for Vaccines.
Only thing I want to see now is a purified and isolated covid 19 and I'll be happy...
Sam Ottenhimer Replied to Flint Westwood
How do people who clearly don't support science end up on a science site finding the only article to go against the grain of all other research findings in the last 11 months?
Dennis Yaste Replied to Sam Ottenhimer
This is not an opinion article. It is a scientific research report and meets all the criteria of "supporting science". If there is a research report in the last 11 months or otherwise that refutes these findings, then please post a link to the research report that is published for peer review in a professional journal with scientific design, method, analysis, and conclusions approved by an institutional review board. This is the way REAL science is supported. A communicable disease is not spread by healthy people who are not sick and are not about to be sick. What we have been told by the CDC and others is NOT science, it is bunk. Research that is scientifically designed, peer reviewed, and replicated, will continue to separate valid science from fictitious political assertions.
Sam Ottenhimer Replied to Dennis Yaste
I was talking about the commenters, not the authors.
I'm not an idiot. I know how science research works.
I'm not that big of a tool that I couldn't tell it was research. Jeez!
Sofie C Replied to Dennis Yaste
One of the greatest parts of science is the admissibility of critical analysis, whether or not anyone agrees. It would be better for everyone to critique their bias, of course, as that tends to foster better conclusions, but this take is just as flawed as the others.
'REAL science' is not what you think is 'true' or 'designed'. It is the conclusion accepted by the majority. Preferably, that would be corrected over time to be a reliable resolution with some form of integrity.
Avoiding politicization carries just as much danger of ignoring reality as does imposing it. Whether you like it or not, lives are at stake. To claim it shouldn't be politicized is to ignore that those peer reviewers are potentially all politicized themselves.. and if they aren't, they will be. Once they figure out that's how to take control :p
Due diligence on all fronts.
Ryan Matzke Replied to Sam Ottenhimer
So you support science? Does that include biology? How many genders are there?
Sam Ottenhimer Replied to Ryan Matzke
These days, gender is more of a social construct. However, biologically there are two sexes, male and female.
What does this have to do with anything? My science degree is in biology and Mathematics.
Raphael Wimmer Replied to Sam Ottenhimer
Actuallllllly - some animals have only one sex (and apparently, fungi have quite a lot).
Sam Ottenhimer Replied to Raphael Wimmer
That is all true. Some animals even have both sexes, but none of that was indicated in the original comment.
Also the argument of sex vs. gender has NOTHING to do with Sars-CoV-2.
Fujian Song
Thanks for commenting on this paper, and we are really grateful for Tesla Coil, Brandom Moron and others clarified some interesting questions. We are aware of some inappropriate understanding of the results regarding the asymptomatic cases identified in this study. To help appropriate interpretation of the results, we have posted some explanations online and on social media:
https://www.uea.ac.uk/news/...
Social media:
https://www.facebook.com/ue...
https://twitter.com/uniofea...
Raphael Wimmer Replied to Fujian Song
Thank you for these clarifications.
Two minor questions:
a) It seems that the source data (Excel file) and the data in Table 2 are slightly different. Which one is correct? And why the difference? (see https://uploads.disquscdn.c... )
b) You cite Ref. 5 for the claim that "asymptomatic infected persons generally have low quantity of viral loads and a short duration of viral shedding, which decrease the transmission risk of SARS-CoV-2". As far as I can tell, Ref. 5 does not contain any information that would support this claim. Could you clarify this?
Melissa
Hi, I'm Italian. I have submitted this article to some people but they are skeptical because they think that this study is valid only for Wuhan. Hence my question: can this study be considered true worldwide? Or only in Wuhan?
CanadaTruth Replied to Melissa
See my comments about this 'Study' above... Do question their methodolgy as to whether this conclusion is any way valid!
Inés Vidal
I do not comprehend how the authors could expect that patients with both negative cell culture and IgM would infect anyone. They didn't have an infection to transmit at all! They didn't have active viruses. Let's not forget that the PCR test detects virus' ARN fragments, but do not differentiate whether the virus is living or dead. Therefore, they weren't asymptomatic infected individuals, they just happened to have positive PCRs. 63% of those who had positive PCRs also had a positive IgG, which indicates that they had had the virus at some point in the past, probably during the last 3 months. Hence, it was to be expected they would have unviable viral remains.
Raphael Wimmer Replied to Inés Vidal
The authors are clearly aware of this fact and explicitly clarify this in their press release.
The goal of this study was not to make claims about asymptomatic transmission but instead to find out whether SARS-CoV-2 had really been eradicated from Wuhan.
Only some Corona 'skeptics' try to argue (incorrectly) that this study shows that asymptomatic transmission does not exist.
CrystalClearTruth Replied to Inés Vidal
PCR tests are useless to test for this virus as it has never been isolated to determine exactly which sequences to test for.
samnigromd
Not a word about mouth cleaning, mouth salting, pulmonary hygiene, best breathing, or SAMMO....which they all are doing as verbally instructed.
go4jazz
So. You did a research study when essentially the virus had burned through its first wave. You readily admit that in your paper. This in of itself is problematic as many studies/drug trials were cancelled due to insufficient numbers of currently infected persons.
Asymptomatic. What I didn't see is a definition of asymptomatic in regards to this study. Stupid comment/question? Even the symptoms have varied greatly with new impacts being discovered every week. (See the Italian study about COVID manifesting as measles) I think your study has completely failed to cover the true period of potential asymptomatic potential infections. In other words the time once infected to the time to showing symptoms. There is an incubation time whereby far more people would appear to be asymptomatic because the virus is ramping up its attack. I think it does a great disservice to people when this is at the very least not even mentioned. THIS is the very reason the virus exploded the way it did. People moving around unaware that they were infected (feeling asymptomatic) infecting people for possibly weeks only for symptoms to finally appear.
The incubation period during which eventually asymptomatic become symptomatic doesn't appear to be covered at all by this study and now you have your study being cited as proof that science conveniently lies where they feel justified. Thank you for at least mentioning that preventative measure should continue although I don't think many people will even read that far.
Finally we now know that the virus began its spread far before anyone had originally thought back into the fall of 2019. Not just in China but the US, India and Europe. This phenomenon alone should cause people to pause and to think about what constitutes "asymptomatic" when many symptoms are unknown/not defined or masquerade as other diseases.
Sofie C Replied to go4jazz
Assumedly, most individuals are asymptomatic until they can be declared as presymptomatic, once they become symptomatic.
Someone who does not ever become symptomatic cannot, obviously, become presymptomatic at any point.
CrystalClearTruth
This paper will have to be retracted. It does not go along with the mandated fake science narrative. These scientists will mysteriously be removed one by one.
CanadaTruth Replied to CrystalClearTruth
Not to mention... the asymptomatic spread likely occured in China well before Dec 2019! A retrospective study is not the way to study pre- or asymptomatic transmission of a virus prospectively! deCODE Genetics out of Iceland in April 2020 did it right after the 1st symptomatic person appeared there...
Sofie C Replied to CanadaTruth
Not sure why you are implying it was done before December. There can be asymptomatic cases after the fact, even slightly before becoming symptomatic. In no place did this state it was retrospective. The Wuhan lockdowns happened through the beginning of 2020, not the end of 2019.
Dr. van Nostrand MD PhD DDS
I did poorly in statistics but I did notice something strange in the abstract:
"107 of 34,424 previously recovered COVID-19 patients tested positive again (re-positive rate 0.31%, 95% CI 0.423–0.574%)."
How can the average be outside the confidence interval? The %age calculation, 0.31, is correct.
Jim
Facebook “Fact Checkers” have labeled this article when posted there as being “False Information”.
Wish one of the authors would set them straight.
CanadaTruth Replied to Jim
"set them straight'... and you are from?
CP Replied to CanadaTruth
He said he wished one of the authors (i.e., of the paper) would set them straight.
Sofie C Replied to Jim
Chances are, it's being reported elsewhere under false pretenses and used to champion the wrong cause.
It sounds like it from this post, anyway.
Sofie C
"The researchers said that their findings did not show that the virus couldn’t be passed on by asymptomatic carriers, and they didn’t suggest that their findings were generalisable.
They said that strict measures—such as mask wearing, hand washing, social distancing, and lockdown—were successful in reducing the virulence of SARS-CoV-2 in Wuhan and that asymptomatic people in Wuhan may have low viral loads. This means that the finding cannot be applied to countries where outbreaks have not been successfully brought under control.
Fujian Song, from UEA’s Norwich Medical School, who collaborated with colleagues in Wuhan on the research, said: “The asymptomatic cases identified in the screening programme were truly asymptomatic, as none of them showed clinical symptoms before or during their follow-up isolation.” But, he added, “there is plenty of evidence elsewhere showing that people infected with covid-19 may be temporarily asymptomatic and infectious, before going on to develop symptoms.”
Using antibody testing, the researchers found that almost two thirds of the asymptomatic cases had previously had covid-19. “With the centralised isolation and treatment of all covid-19 cases during the lockdown period in Wuhan, the risk of residents being infected in the community has been greatly reduced. When susceptible residents are exposed to a low dose of virus, they may tend to be asymptomatic as a result of their own immunity,” wrote the authors.
Song said, “It is very important to say that these asymptomatic cases were identified shortly after the relaxation of a very stringent lockdown in Wuhan that lasted more than 70 days. By then, the epidemic in Wuhan had been effectively brought under control. It is too early to be complacent, because of the existence of asymptomatic positive cases and high level of susceptibility in residents in Wuhan.”
Essentially: No, it doesn't prove you don't have to wear a mask or quarantine. It actually supports said measures.
CP Replied to Sofie C
"The researchers said that their findings did not show that the virus couldn’t be passed on by asymptomatic carriers"
Where exactly in the paper did they state this? You've got quotes on it, yet that statement does not appear as quoted.
However, in the last paragraph of the "Discussion" section, the researchers stated this (emphasis added):
"In summary, the detection rate of asymptomatic positive cases in the post-lockdown Wuhan was very low (0.303/10,000), and there was no evidence that the identified asymptomatic positive cases were infectious."
Obviously, this is the semantical opposite of the claimed statement I cited above.
Robert Eibl
This report is on screening data from May 14 to June 1st in 2020, i.e. long before the newer and current variants of concern developed, like the recent British (Alpha) and Indian (Delta). These new variants may be seen as totally NEW pandemics, since they may behave differently in many senses, including higher infectiosity and, perhaps, different symptoms and higher rates for need of hospitalisation. It may also mean that the findings and conclusions on the wild-type virus in early 2020 in Wuhan, are different. Currently, it is known that major production of virus is from pre-symptomatic people, i.e. 1-6 days before any symptoms. It is also quite possible that asymptomatic persons, i.e. those who won't get any symptoms, but also get infected, produce large amounts of virus, especially if the newer variants of concern are spreading so fast.
Chen
I have a question about the ethical integrity of this paper. In the Methods, the authors stated that "All participants provided written or verbal informed consent after reading a statement that explained the purpose of the testing.." However, as a local Wuhan resident, I was actually one of the participants being screened and tested on May 15th, 2020, BUT I was NEVER shown any informed consent, and had NEVER agreed to have my test result as part of a published work in any written or verbal form. As I underwent the test procedure at the same time with hundreds of thousands of other residents at the same location and I did not see any informed consent shown to them either, I believe that I was not the only one who was NEVER shown any form of informed consent for our own data to be included and published in the current study.
This could be a serious issue related to compromised scientific and ethical integrity. As such, I respectively but strongly ask that the author provide solid proof that they had received written or verbal informed consent from ALL participants, and provide such evidence to the public as soon as possible.