Risk map of cholera infection for vaccine deployment: the eastern Kolkata case.

Young Ae You,John Clemens,Mohammad Ali,Mahesh Puri,Suman Kanungo,Jacqueline L Deen,Byomkesh Manna,Matteo Convertino,Dipika Sur,G Balakrish Nair,Sujit Kumar Bhattacharya,Binod Sah,Anna Lena Lopez,Thomas F Wierzba

doi:10.1371/journal.pone.0071173

Abstract

BackgroundDespite advancement of our knowledge, cholera remains a public health concern. During March-April 2010, a large cholera outbreak afflicted the eastern part of Kolkata, India. The quantification of importance of socio-environmental factors in the risk of cholera, and the calculation of the risk is fundamental for deploying vaccination strategies. Here we investigate socio-environmental characteristics between high and low risk areas as well as the potential impact of vaccination on the spatial occurrence of the disease.Methods and FindingsThe study area comprised three wards of Kolkata Municipal Corporation. A mass cholera vaccination campaign was conducted in mid-2006 as the part of a clinical trial. Cholera cases and data of the trial to identify high risk areas for cholera were analyzed. We used a generalized additive model (GAM) to detect risk areas, and to evaluate the importance of socio-environmental characteristics between high and low risk areas. During the one-year pre-vaccination and two-year post-vaccination periods, 95 and 183 cholera cases were detected in 111,882 and 121,827 study participants, respectively. The GAM model predicts that high risk areas in the west part of the study area where the outbreak largely occurred. High risk areas in both periods were characterized by poor people, use of unsafe water, and proximity to canals used as the main drainage for rain and waste water. Cholera vaccine uptake was significantly lower in the high risk areas compared to low risk areas.ConclusionThe study shows that even a parsimonious model like GAM predicts high risk areas where cholera outbreaks largely occurred. This is useful for indicating where interventions would be effective in controlling the disease risk. Data showed that vaccination decreased the risk of infection. Overall, the GAM-based risk map is useful for policymakers, especially those from countries where cholera remains to be endemic with periodic outbreaks.

Highlights

John Snow’s cholera map of 1855 [1] is a disease map on which he plotted the households with cholera deaths in London
The study shows that even a parsimonious model like generalized additive model (GAM) predicts high risk areas where cholera outbreaks largely occurred
The GAM-based risk map is useful for policymakers, especially those from countries where cholera remains to be endemic with periodic outbreaks

Summary

Introduction

John Snow’s cholera map of 1855 [1] is a disease map on which he plotted the households with cholera deaths in London. The John Snow’s map revealed that families receiving water from the Broad Street hand pump were more likely to have cholera deaths, which helped the health authorities making appropriate area-based interventions for controlling the disease. One reason could be spatial patterns of risk for cholera in an endemic area are not clearly known, an effective control mechanism could have never established in a cholera endemic country. We investigated the data of a geographically referenced population-based surveillance from a cholera vaccine trial conducted in the area, and plotted the cases during the outbreak in the trial area. We evaluated the socioenvironmental characteristics between the high and low risk areas of the disease and the impact of the vaccination on spatial risk for cholera. We investigate socio-environmental characteristics between high and low risk areas as well as the potential impact of vaccination on the spatial occurrence of the disease

Methods

Results

Discussion

Conclusion