Nonstationary and Mediated Dynamics between Climate and Cholera Incidence in Piura, Peru, 1991-2001

In Peru, it was hypothesized that epidemic cholera in 1991 was linked to El Niņo, the warm phase of El Niņo-Southern Oscillation. While previous studies demonstrated an association in 1997-98, using cross-sectional data, they did not assess the consistency of this relationship across the decade. Thus, how strong or variable an El Niņo-cholera relationship was in Peru or whether El Niņo triggered epidemic cholera early in the decade remains unknown. In this study, wavelet and mediation analyses were used to: characterize temporal patterns among El Niņo, local climate variables (rainfall, river discharge, and air temperature), and cholera incidence in Piura, Peru from 1991-2001; and estimate the mediating effects of local climate on El Niņo-cholera relationships. The study hypothesis is that El Niņo-related connections with cholera in Piura were transient, and interconnected via local climate pathways. Overall, our findings provide evidence that a strong El Niņo-cholera link, mediated by local hydrology, existed in the latter part of the 1990s, but found no evidence of an El Niņo association in the earlier part of the decade, suggesting that El Niņo may not have precipitated cholera emergence in Piura. Further examinations of cholera epicenters in Peru are recommended to support these results in Piura. For public health planning, the results may improve existing efforts that utilize El Niņo monitoring for preparedness during future climate-related extremes in the region.