Acta Tropica 153 (2016) 21–27 Contents lists available at ScienceDirect Acta Tropica journal homepage: www.elsevier.com/locate/actatropica An epidemiological study of dengue in Delhi, India Kumar Vikram a , B.N Nagpal a,∗ , Veena Pande b , Aruna Srivastava a , Rekha Saxena a , Anup Anvikar a , Aparup Das a , Himmat Singh a , Anushrita a , Sanjeev K. Gupta a , N.R. Tuli c , Olivier Telle d , N.K. Yadav c , Neena Valecha a , Richard Paul d a National Institute of Malaria Research (ICMR), Delhi, India b Kumaun University, Nainital, India c Municipal Corporation of Delhi, India d Institut Pasteur, Paris, France a r t i c l e i n f o Article history: Received 5 June 2015 Received in revised form 19 September 2015 Accepted 27 September 2015 Available online 1 October 2015 Keywords: Dengue Index case Asymptomatic infection Primary dengue infection Secondary dengue infection a b s t r a c t Delhi, the capital of India, is an important metropolitan hub for major financial and sociocultural exchanges, offering challenging threats to current public health infrastructure. In recent past, an upsurge of dengue cases in Delhi posed a significant menace to the existing dengue control policies. To reform the control strategies and take timely intervention to prevent future epidemics, an epidemiological study on the proportion of both asymptomatic and symptomatic dengue infections in selected population was conducted. The aim of the study was to investigate and assess the epidemiology of dengue infection and to estimate the proportion of asymptomatic and symptomatic dengue infections in Delhi. In this study, around 50 confirmed dengue cases, a total of 2125 individuals as household and neighbourhood contacts, with or without dengue febrile illness, were finger pricked and serologically detected as dengue positive or negative using SD Duo Bioline Rapid Diagnostic Test (SD Inc, Korea) with NS1, IgM & IgG combo test, which detected dengue virus antigen and antibodies to dengue virus in human blood. Out of 2125 individ- uals, 768 (36.1%) individuals showed positive dengue test with past (25.5%), primary (1.88%) or secondary (8.8%) dengue infections. Higher percentage of IgG was found in age groups 15–24 years and 25–50 years (36% each). Infants (<1 year) presented higher incidence of new infections (22% of NS1 + IgM positives) as compared to adults. Further analysis revealed that out of the 226 newly infected cases (including NS1 and IgM positives), 142 (63%) were asymptomatic and 84 (37%) were symptomatic, as per WHO guidelines. Our findings also suggest that out of the total population screened, 10.6% dengue infection was either primary or secondary. On the basis of these results, it may be hypothesized that there are large number of asymptomatic dengue infections in the community as compared to reported symptomatic cases in Delhi. For the effective control of dengue transmission in such community like Delhi where dengue epidemics have frequently been encountered, it is essential to ascertain the proportion of asymptomatic dengue infections which may act as a reservoir for dengue transmission, as well as threat for developing dengue haemorrhagic fever (DHF). © 2015 Published by Elsevier B.V. 1. Introduction Dengue infection is one of the most common arbo-viral diseases worldwide. It is prevalent in most of the tropical and sub-tropical countries and is caused by four serotypes (DEN-1, DEN-2, DEN-3 and DEN-4) in humans. All four serotypes can cause a spectrum of illness ranging from inapparent or mild febrile dengue fever to ∗ Corresponding author at: GIS, Taxonomy and OVBD Division, National Institute of Malaria Research, New Delhi – 110 077. E-mail address: bnnagpal57@gmail.com (B.N Nagpal). severe and fatal haemorrhagic disease (Gubler, 1998; Whitehorn and Farrar, 2010; Innis, 1995). It is transmitted mainly by Aedes aegypti mosquito and also by Aedes albopictus (Whitehorn and Farrar, 2010). Dengue fever represents high disease burden in endemic countries (Gubler and Meltzer, 1999; Beatty et al., 2011; Donald et al., 2013). An estimated 3.6 billion people live in high risk areas worldwide. It is also presumed that over 230 million bear the load of infection and approximately 2 million suffer with dengue fever and its severe forms with 21,000 deaths as reported (Beatty et al., 2008). The incidence of dengue fever (DF) and dengue hemor- rhagic fever (DHF) has increased dramatically over the last four http://dx.doi.org/10.1016/j.actatropica.2015.09.025 0001-706X/© 2015 Published by Elsevier B.V.