Controlling dengue, an urban pandemic – a case study of Delhi, India

Abstract Globally, more than 3.5 billion people are at risk of dengue infection and an estimated 390 million cases are detected annually. The pandemic has brought with it the simultaneous circulation of multiple serotypes and in its aftermath, endemic dengue haemorrhagic fever/dengue shock syndrome (DHF/DSS). Nearly 3 million children were hospitalized with this syndrome in the past 3 decades, mainly in South-East Asia. Recent outbreaks in the Pacific Islands, China, India, Sri Lanka, Cuba and Venezuela indicate that the high intensity and rapid spread of dengue transmission which is closely connected with urbanization factors, increase with temperature and precipitation and changes in spatial patterns.Since the mid-1990s, India has been experiencing frequent dengue epidemics. The overall cost of dengue in India in 2016 was about US$5.71 billion. Over the years, dengue has transitioned into an urban pandemic, largely as an epidemic starting in urban centres and gradually expanding to surrounding peri-urban and rural areas. Urban areas are characterized by relatively higher temperature (Urban Heat Island), and higher concentration of population, and are more favorable for the transmission of Aedes aegypti mosquito. The vector thrives in areas with standing water, including puddles, water tanks, containers and old tires. Lack of reliable sanitation and regular garbage collection and water storage practices contribute to the breeding and spread of the mosquitoes.Delhi is hyperendemic with a frequent occurrence of concurrent infections with multiple DENV serotypes. The first severe outbreak took place in the state during 1996 with 10253 cases and 253 deaths. Since then, outbreaks in the city have been reported during 2006, 2010, 2013 and 2015, indicating the decreasing gap between the outbreaks. Dengue cases in the city show an increasing trend in the past decade with 2015, the most recent incidence of outbreak reporting 15857 cases and 60 deaths as reported under the National Vector Borne Disease Surveillance Programme (NVBDSP). A lag period of two months has been observed between the peaks of rainfall and dengue cases in Delhi indicating a lack of sufficient and timely preventive and public health efforts by the local health administration alongside other systemic challenges to be responsible for the outbreaks. However, since 2015, the reported dengue-related cases and deaths are showing steady decline with 80% reduction in reported cases.The municipality and other urban local bodies are taking several measures for dengue control and prevention. Several fever clinics have been opened up in the government hospitals, dispensaries and mohalla (community) clinics. The private hospitals have also been permitted to increase the bed strength by 20% during the season only for fever patients. To coordinate the efforts of the Delhi government and the civic bodies, a dengue control cell is also created. In addition, an intensive anti dengue campaign has been launched to increase awareness and public participation is contributing to improved disease control. Several studies have emphasized on the need for epidemiological and entomological surveillance to monitor trends in dengue distribution, seasonal patterns and circulating serotypes to guide dengue control activities with efforts currently being made to ensure early warning signals for timely detection of outbreaks.