Linking disease surveillance figures from health centres to data obtained from geographic information system (GIS), a study in two urban slums of Kolkata has found that typhoid fever struck the poor and less literate people more than their comparatively affluent, more literate counterparts in the same community1. People with bigger households and those living close to water bodies were also found to be more at risk of getting the debilitating enteric fever.

The researchers in a Kolkata slum. Credit: NICED
The study, carried out during 2003-04, found significantly safer toilet use in the high risk areas for typhoid fever as compared to the low risk areas. The source of drinking water also seemed to affect the risk for enteric fever. Poor food hygiene was identified as a risk factor for enteric fever. "Food prepared and sold on the streets of resource-poor countries are particularly hazardous as often there is no water and soap to clean plates and utensils. Tropical climates can transform a food stall into an incubator," says Mohammad Ali, one of the authors of the paper.

The subpopulation with the lowest socio economic status of this impoverished population appeared to be at highest risk for enteric fever. "It is impractical to think of any immediate solution to overcome the risks for controlling the disease. Alternatively, we can think of introducing typhoid vaccine in public health programs, as the vaccine has become increasingly available and inexpensive", Ali says.

A baseline census of the population was conducted with concomitant collection of demographic and socio-economic data. Each household and important landmark in the study area was digitally mapped. The residents were encouraged to consult at a study treatment centre for any episode of fever. The authors then analyzed factors associated with high and low risk areas of enteric fever incidence.

"The method of comparison is statistically powerful and holds promise in detecting risk factors associated with diseases using digital mapping," says Sujit Kumar Bhattacharya, a co-author.

The authors of this study are from: National Institute of Cholera and Enteric Diseases, Kolkata, India; International Vaccine Institute, Seoul, Korea; London School of Hygiene and Tropical Medicine, London, UK.