Mapping Snakebite Epidemiology in Nicaragua – Pitfalls and Possible Solutions

Background: Snakebites are a public health problem in Nicaragua: it is a tropical developing country, venomous snakes are present and there are reports of snakebites treated both in the formal and informal health care system. We aimed to produce an incidence map using data reported by the health care system that would be used to allocate resources. However, this map may suffer from case detection bias and decisions based on this map will neglect snakebite victims who do not receive healthcare. To avoid this error, we try to identify where underreporting is likely based on available information. Method and Findings: The Nicaraguan municipalities are categorized by precipitation, altitude and geographical location into regions of assumed homogenous snake prevalence. Socio-economic and healthcare variables hypothesized to be related to underreporting of snakebites are aggregated into an index. The environmental region variable, the underreporting index and three demographic variables (rurality, sex and age distribution) are entered in a Poisson regression model of municipality-level snakebite incidence. In this model, the underreporting index is non-linearly associated with snakebite incidence, a finding we attribute to underreporting in the most deprived municipalities. The municipalities with the worst scoring on the underreporting index and those with combined low reported incidence and large rural population are identified as likely underreporting. 3,286 snakebite cases were reported in 2005–2009, corresponding to a 5-year incidence of 56 bites per 100,000 inhabitants (municipality range: 0–600 cases per 100,000 inhabitants). Conclusions: Using publicly available data, we identified areas likely to be underreporting snakebites and highlighted these areas instead of leaving them “white” on the incidence map. The effects of the case detection bias on the distribution of resources against snakebites could decrease. Although not yet verified empirically, our study provides an example of how snake bite epidemiology may be investigated in similar settings worldwide at a low cost. Author Summary: Snakebites have recently been recognized as a neglected cause of human suffering and death worldwide. Many bites are treated by traditional practitioners and thereby not recorded by the health care system. This leads to a lack of reliable epidemiological data and is identified as a major obstacle in dealing with this health problem. Household surveys are recommended for finding the true snakebite incidence, but the countries where snakebites are frequent are usually poor, meaning that this method is often too expensive. The usage of data reported by the health care system could then provide a necessary option when locating and estimating the snakebite problem. However, this data could be biased and lead to implementation of unfair policies. In this study, we use publicly available data about environmental, socioeconomic and health-care related variables and incidence reported from health care facilities to create a map of where underreporting could be suspected, either because of the presence of factors favouring underreporting or by a comparatively low reported incidence. By high-lighting these areas, the reported statistics are put into a context and the decision-maker is able to make a less biased decision on where to locate research, preventive and therapeutic resources.