Epidemiology of malaria outbreak years in India provides key insights into malaria elimination

In-depth analysis of distributions of historical malaria outbreak years is crucial for evaluating progress in malaria control, understanding the impact of previous interventions, and identifying regions that remain highly susceptible to outbreaks. Numerous methodologies, including the 95% CI method, the Cullen method, the quartile method, and the C-sum method, have been documented in the literature as potential approaches for calculating malaria outbreaks, each with its pros and cons. Data from the past decade was used to establish a robust criterion to define a malaria outbreak year, i.e., if the number of malaria cases in a specific year surpassed the value derived from the sum of the last three years' moving average and 2.5 times the last three years' moving standard deviation. Over the past decade, India has grappled with 402 outbreak years of malaria in various districts. Notably, the years 2011, 2014, and 2015 stand out due to their high frequency of case upticks, marking peak periods in the country's recent epidemiological history. Subsequently, there was a sharp decline in the number of district-wise outbreak years after 2015, with 2020 recording the lowest number of outbreaks to date. Among 28 states, seven—Mizoram, Tripura, Jharkhand, Odisha, Madhya Pradesh, Uttar Pradesh, and Meghalaya—have been identified as "more outbreak-prone states" because over 70% of their districts experienced at least one outbreak year between 2011 and 2020. The frequency of outbreak years in India has decreased over the last decade. Districts susceptible to case upticks require specific, heightened, new modes of surveillance and targeted interventions to address future occurrences of malaria outbreaks in India.