Malaria control - lessons learned from trends of Malaria indices over three decades in Karnataka, India.

Background: Karnataka is one of the largest states in India and has a wide range of geographical terrains, ecotypes, and prevalence of malaria. It experiences a voluminous influx and efflux of people across the state that affects the spread of malaria. The state deployed focused intervention measures keeping the national objective of malaria elimination as the foremost priority. This brought down malaria cases below a thousand by the year 2021. Furthermore, the state is motivated toward malaria elimination by 2025. This study analyzes the trends in malaria indices over the past three decades in the state and highlights the key intervention measures that impacted the reduction in the malaria burden.

Methods: Data from 1991 to 2021 at the district level was collected from the archives of Regional Office for Health & Family Welfare (ROH&FW), Bangalore. Time-tend analysis on this data was conducted after categorization into three decades. Sequence plots were then plotted on the moving average of Annual Parasite Index for all those three decades. Generalized estimating equation model with Poisson distribution were used to evaluate difference in these indicators with pre and post interventions like LLIN, RDT with ACT and Guppy and Gambusia fishes.

Results: Malaria burden across the state has consistently declined over the last three decades with few years of exception. This has coincided with the mortality also steadily declining from 2006 and culminating in zero malaria deaths reported from 2011 to 2019. Morbidity had drastically reduced from the hundred-thousand (1993-2003) to ten thousand (2004-2016) thousands (2017-2020) of cases in this period and less than thousand cases were reported by 2021. Generalized estimating equation (GEE) model revealed significant difference of incidence risk ratio of malaria incidence and deaths, post introduction of interventions like LLIN, RDT with ACT and Guppy and Gambusia fishes, indicating these three as important interventions for reducing the malaria burden. Time trend analysis revealed a linear decreasing trend in malaria cases during 2011-2021 decade.

Conclusions: A linear decreasing trend in malaria cases was observed during 2011-2021 decade. LLIN, RDT with ACT and Guppy and Gambusia fish's interventions significantly helped in reducing the state malaria burden.