The impact of meteorological variables on Salmonella bacteraemia in Mysuru District, Karnataka State, India: a retrospective time-series analysis.

Background: Salmonella species are major pathogens responsible for gastroenteritis and typhoid fever. In 2017, Salmonella enterocolitis caused over 95 million cases of diarrhoea and 50,000 deaths globally, with India bearing more than 50% of the typhoid burden. Objectives: To test the association of monthly mean and maximum temperature, precipitation and absolute humidity with the incidence of Salmonella bacteraemia in a metropolitan city in South India. Design: A retrospective time-series analysis. Methods: This study employed a retrospective time-series analysis to evaluate the influence of meteorological variables, including temperature, absolute humidity and precipitation, on Salmonella bacteraemia in a metropolitan city in South India. Results: Between 2014 and 2019, a total of 492 blood culture-confirmed cases of Salmonella bacteraemia were identified in Mysuru, India. S. typhi was predominantly among younger patients, while non-typhoidal Salmonella was more frequent in older age groups. Resistance was highest to nalidixic acid (84%), with a rising trend in ciprofloxacin resistance. Increased mean temperature (lags 1-3 months) and absolute humidity were positively associated with Salmonella bacteraemia, while temperature variability was protective, and monsoon rainfall significantly increased the risk. Cumulative exposure-response analyses further showed elevated risks at higher humidity (>26 g/m³), temperatures (>34°C) and extreme precipitation (>250 mm), although confidence intervals were wide and most associations did not reach statistical significance. Conclusion: This single-centre retrospective time-series analysis has demonstrated that meteorological variables impact the incidence of Salmonella bacteraemia, which could lead to increased antibiotic use and contribute to the development of resistance.