Increased mortality rate associated with chikungunya epidemic, Ahmedabad, India

Abstract

In 2005–2006, Reunion Island in the Indian Ocean reported ≈266,000 cases of chikungunya; 254 were fatal (case-fatality rate 1/1,000). India reported 1.39 million cases of chikungunya fever in 2006 with no attributable deaths; Ahmedabad, India, reported 60,777 suspected chikungunya cases. To assess the effect of this epidemic, mortality rates in 2006 were compared with those in 2002–2005 for Ahmedabad (population 3.8 million). A total of 2,944 excess deaths occurred during the chikungunya epidemic (August–November 2006) when compared with the average number of deaths in the same months during the previous 4 years. These excess deaths may be attributable to this epidemic. However, a hidden or unexplained cause of death is also possible. Public health authorities should thoroughly investigate this increase in deaths associated with this epidemic and implement measures to prevent further epidemics of chikungunya. Chikungunya virus, an alphavirus of the family Togaviridae, is native to tropical Africa and Asia. This virus is transmitted to humans by mosquitoes. Aedes aegypti and Ae. albopictus are the 2 main vectors that transmit this disease. The first reported chikungunya outbreak occurred in Tanganyika (now Tanzania) in 1952–1953. The word chikungunya is derived from the Makonde language in southeastern Tanzania and means “bent down or become contorted,” which indicates the classic posture the patient adopts because of severe joint pain. Symptoms of chikungunya include sudden onset of fever, severe arthralgia, and maculopapular rash. A specific symptom is severe incapacitating arthralgia, often persistent, which can result in long-lasting disability. A major epidemic of this disease was reported in 2005–2006 in Réunion Island; ≈266,000 residents (34.3% of the population) of this Indian Ocean island were affected by chikungunya fever as of February 19, 2007. This epidemic also spread to France through imported cases from Réunion Island. Historically, chikungunya was considered self-limiting and nonfatal. However, 254 deaths on Réunion (case-fatality rate 1/1,000) that were attributed directly or indirectly to chikungunya during the epidemic changed this perspective. India reported a massive chikungunya epidemic in 2006. Chikungunya has reemerged in India since 1973, when the attack rate was 37.5%. However, in the 2006 epidemic, the attack rate increased to 45% in some places. More than 1.39 million cases across 151 districts and 10 states were reported during this period. However, unlike the epidemic on Réunion Island, no deaths directly attributable to this disease were reported. The dominant vectors are Ae. albopictus on Réunion Island and Ae. aegypti in India. However, Ae. albopictus was also implicated in Kerala State, India. Studies have indicated that the recent outbreak in the Indian Ocean islands was initiated by a strain related to East African isolates, from which viral variants have evolved with a traceable history of microevolution. This history could provide information for understanding the unusual magnitude and virulence of this chikungunya epidemic. The purpose of this study was to analyze the association between the chikungunya epidemic in India and the mortality rate in the city of Ahmedabad. Such findings could show correlations between reported genomic mutations in chikungunya virus and its increased virulence. Such information is valuable for public health systems in developing countries that frequently underreport or misreport epidemics.