J. Am. Med. Assoc. 14, 1406–1407 (2020).

N. Engl. J. Med. 382, 970–971 (2020)

Containment of COVID-19 is made difficult because, unlike SARS-CoV and MERS-CoV, SARS-CoV-2 is commonly spread by people showing no symptoms.

Two early reports monitoring contacts of people who traveled from the initial epicenter of the epidemic (Wuhan, China) sounded the alarm. Five family members in Anyang, China, were diagnosed with COVID-19 following the return of a relative from Wuhan. The index case tested positive for SARS-CoV-2 by PCR but did not develop symptons, indicative of asympomatic transmission fom this person. A different cluster, in Germany, was seeded by a traveller from Wuhan who was not symptomatic during her stay in Germany but later developed fever and a cough indicative of presymptomatic transmission.

While the relative role of asymptomatic and presymptomatic transmission in SARS-CoV-2 spread remains contentious, spread by people showing no symptoms is a hallmark of COVID-19.