Water-borne Outbreaks and Climate: a Meta-analysis Approach

Seasonality is universal phenomenon for many infectious diseases with a strong environment component that affects the probability of exposure and transmission. The global synchronization of spatio-temporal patterns has been noted for water-borne infections worldwide. Rotaviral infection is most prominent in colder weather; peaks of cryprosporidiosis fluctuate and may exhibit one or two seasonal spikes: in summer and late fall; seasonality of cholera correlates with changes in aquatic environment. A meta-analysis was conducted to examine how patterns of waterborne infections, including cryptosporidiosis and rotavirus, relate to vegetation, ambient temperature, and precipitation on a global scale. This presentation introduces the notion of seasonality by outlining several of its essential terms and factors, provide comparisons of current methods for assessing seasonality, and illustrate synchronization of waterborne infections with respect to climatic regions. Incidence data were abstracted from published epidemiological studies and related to temporally aggregated ambient temperature and precipitation for each study location using non-linear mixed effects models. Vegetation was measured by using remote sensing, which has a great potential for developing a unifying approach to comprehensively study seasonal patterns across various climatic zones and vulnerable populations. In temperate, tropical and humid mid-latitude climates, low temperature and precipitation levels are significant predictors of an increase for both infections. In South Asia, for example, the highest incidence of rotavirus is seen in the colder, drier months. A lagged structure is well pronounced for different strains and an increase in the proportion of undetects is indicative for emergence of a new strain in the next season. Seasonality of cryptosporidiosis varies by climate region. On a local scale, an event of hot weather in a temperate climatic region exhibits a time-distributed effect on the rate of cryptosporidiosis, characteristic to its incubation period. Given the strong lagged association with temperature, meteorological parameters can be used to strengthen public health prevention programs. In this communication we argue, that seasonal patterns depicted globally are not necessarily a simple sum of patterns observed locally. Deviations from seasonality, or a break out from an expected pattern, might be indicative of various environmental, demographic and social changes affecting exposure and transmission of waterborne infections.