El Nino southern oscillation predicts vibriosis risk in the United States

Purpose: While epidemics of diarrhea caused by toxigenic strains of Vibrio cholerae are of global public health concern, non-toxigenic strains of V. cholerae and non-cholera Vibrio (NCV) species are also important causes of human disease, including foodborne illness, skin and soft tissue infection, and sepsis. These bacteria are abundant in ocean waters, and climate change (and associated ocean warming) could lead to increased incidence of NCV infection. Methods & Materials: We obtained United States monthly national vibriosis case counts by digitizing annual reports from the U.S. Cholera and Other Vibrio Illness Surveillance (COVIS) surveillance system from 1999 to 2014. Monthly population denominators were derived from census data. Oceanic conditions for the Pacific and North Atlantic Ocean, respectively, were modeled based on the Multivariate El Nino Index (MEI) and the North Atlantic Oscillation Index (NAO). The irregular nature of fluctuations in MEI, and the similarity of El Nino-like conditions to projected future climatic change conditions, have led to its use as a natural experimental exposure that may predict future climate change effects. We constructed distributed nonlinear lag models that estimated integrated risk of vibriosis based on integrated effects of lagged oceanic conditions over a 12 month period. Results: Poisson models of temporal trend demonstrated significant seasonal oscillation (P-value for Fast Fourier Transform component < 0.001) and an 8% annual increase in disease risk (annual IRR 1.079, 95% CI 1.074–1.084). Distributed nonlinear lag models showed a strong association with El Nino-like Pacific Ocean conditions over the subsequent 12 months (RR associated with MEI = 3, 1.708, 95% CI 1.285–2.272) but not North Atlantic Conditions (RR associated with NAO = 3, 0.879, 95% CI 0.581–1.330). Conclusion: While the lack in geographic specificity of cases in this national dataset limits our ability to identify oceanic effects on vibriosis risk with precision, we find that the past 15 years have witnessed a marked increase in vibriosis risk in the United States. This trend is explained at least in part by oceanic conditions that anticipate those that will be accentuated by global climate change.