Region-specific improvisation on WHO case definition and environmental risk factors associated with dengue: a case-control analysis from Kerala, India.

Abstract

Region-specific variations may occur in symptomatic manifestations that need to be addressed by dynamic case definitions. Environmental risk factors for dengue also vary widely across geographic settings. Our aim was to study the test positivity rate of the World Health Organization (WHO) 2009 probable dengue case definition and to suggest region-specific improvisations to it. The study also analyses the sociodemographic and environmental risk factors of dengue fever in South Kerala, India. A case-control study was conducted in South Kerala from 2017 to 2019. Dengue reverse transcription polymerase chain reaction (RT-PCR)-positive and RT-PCR-negative 'probable dengue' patients were compared to identify significant symptoms for a modified definition of dengue. A group of afebrile community controls was compared with RT-PCR-positive dengue cases to study the environmental and behavioural risk factors. Arthralgia, palmar erythema and rashes have high discriminatory power (odds ratio [OR] >3) for identifying dengue. Redness of eyes, altered consciousness, abdominal distension and chills were found to moderately discriminate (OR 2-3) dengue. The adjusted analysis showed the presence of mosquito breeding sites (indoor p=0.02, outdoor p=0.03), solid waste dumping (p<0.001) and open water drainage in the compound (p=0.007) as significant predictors. Regional modifications should be considered when using the WHO definition in endemic settings. Control of mosquito breeding at the household level is the key towards dengue prevention.