Infectious disease dynamics and climate forcing in a megacity of the developing world: rotavirus as a case study

Background/Question/Methods

Several infectious diseases, especially those that are water-borne or vector-borne, have been shown to exhibit significant variation in the size of seasonal outbreaks, a pattern known as interannual variability. The role of climate forcing in driving this interannual variation has been addressed with retrospective records that typically aggregate cases over space, and therefore, over whole cities. Here, we distinguish between two distinct regions in the megacity of Dhaka (Bangladesh), a highly populated core and the more rural periphery, to examine the effect of flooding on rotavirus infections, which are the most common cause of gastroenteritis in infants and young children worldwide. With process-based models for the population dynamics of the disease that couple the two parts of the city, we address the role of flooding and the importance of spatial heterogeneity in the response to climate. The models are fitted with a maximum likelihood method based on an iterated filtering, to monthly time series of cases in the core and periphery that span 22 years.

Results/Conclusions

We find that 83.6% of the cases occur in the core region of the city and that cases in this region exhibit seasonality similar to that of tropical countries, with one peak during winter and another during the monsoon. In contrast, cases in the periphery exhibit a much weaker second peak. The best model incorporates flooding in the force of infection and captures the interannual variation of the disease in the core of the city. This model outperforms a linear seasonal autoregressive moving-average model (SARIMA). The inclusion of the two regions with differences in their response to climate helps elucidate the contribution of flooding and local susceptibility to exposure risk. This work together with previous results on cholera, another diarrheal disease, demonstrates the importance of considering the spatial structure of urban environments when considering the response of infectious diseases to climate forcing.