El Niño Southern Oscillation and Leptospirosis Outbreaks in New Caledonia

Leptospirosis is an important cause of seasonal outbreaks in New Caledonia and the tropics. Using time series derived from high-quality laboratory-based surveillance from 2000–2012, we evaluated whether climatic factors, including El Niño Southern Oscillation (ENSO) and meteorological conditions allow for the prediction of leptospirosis outbreaks in New Caledonia. We found that La Niña periods are associated with high rainfall, and both of these factors were in turn, temporally associated with outbreaks of leptospirosis. The sea surface temperature in El Niño Box 4 allowed forecasting of leptospirosis outbreaks four months into the future, a time lag allowing public health authorities to increase preparedness. To our knowledge, our observations in New Caledonia are the first demonstration that ENSO has a strong association with leptospirosis. This association should be tested in other regions in the South Pacific, Asia or Latin America where ENSO may drive climate variability and the risk for leptospirosis outbreaks.Author Summary: The El Niño Southern Oscillation is a major ocean – atmosphere phenomenon that strongly contributes to the timing and intensity of rainfall in the tropical Pacific islands and beyond. As a consequence, it also has a major effect on the number of cases of leptospirosis. By incorporating oceanographic parameters in models, we have been able to predict leptospirosis outbreaks in New Caledonia 4 months in advance. We discuss that this forecasting delay might be used to implement timely interventions prior to the occurrence of outbreaks. Possible interventions include controlling rodent reservoir populations before population growth and maintaining sewage networks or river banks. The major impact of El Niño on the climate of Pacific Islands Countries and Territories suggests that other countries might be able to build similar predictive models.