Effect of El Niño Southern Oscillations on the incidence of enteric fever in Ahmedabad, India from 1985 to 2017

Objective: To explore the relationship between climate variables and enteric fever in the city of Ahmedabad and report preliminary findings regarding the influence of El Nino Southern Oscillations and Indian Ocean Dipole over enteric fever incidence. Method: A total of 29 808 Widal positive enteric fever cases reported by the Ahmedabad Municipal Corporation and local climate data in 1985-2017 from Ahmedabad Meteorology Department were analysed. El Nino, La Nina, neutral and Indian Ocean Dipole years as reported by the National Oceanic and Atmospheric Administration for the same period were compared for the incidence of enteric fever. Results: Population-normalized average monthly enteric fever case rates were the highest for El Nino years (25.5), lower for La Nina years (20.5) and lowest for neutral years (17.6). A repeated measures ANOVA analysis showed no significant difference in case rates during the three yearly El Nino Southern Oscillations categories. However, visual profile plot of estimated marginal monthly means showed two distinct characteristics: an early rise and peaking of cases in the El Nino and La Nina years, and a much more restrained rise without conspicuous peaks in neutral years. Further analysis based on monthly El Nino Southern Oscillations categories was conducted to detect differences in median monthly case rates. Median case rates in strong and moderate El Nino months and strong La Nina months were significantly dissimilar from that during neutral months (P Conclusions: El Nino Southern Oscillations events influence the incidence of enteric fever cases in Ahmedabad, and further investigation from more cities and towns is required.