Circulation of Dengue virus-1 (DENV-1) serotype in Delhi, during 2010-11 after Dengue virus-3 (DENV-3) predominance: a single centre hospital-based study

Delhi, a city in north India, has so far witnessed several reported outbreaks of dengue. Dengue in Delhi from being epidemic is slowly changing towards being endemic and hyper-endemic. Circulating type of the virus is also changing over the years. In the absence of an effective vaccine, dengue prevention to a major extent relies on virological surveillance, and development of effective, locally adapted control programmes. In the present study, we tried to identify the between-year non-epidemic serotype of dengue virus circulating in Delhi, during 2010-11. Acute-phase samples were collected from the patients attending the Institute of Liver & Biliary Sciences, New Delhi, India. Dengue diagnosis was done using WHO case definitions. All the samples were subjected to Dengue NS1 Ag ELISA and modified nested RT-PCR. A total of 75 acute-phase samples were received, of which 19 (25.3%) were positive for dengue NS1 antigen. Dengue RT-PCR was positive in 14.6% (11/75) samples. All the RT-PCR isolates were of DENV-1 serotype. No case of concomitant infection with more than one serotype was observed. Median age of involvement was 23 yr (range10-86). Maximum number of cases were seen in the age group of 21-30 yr. Male to female ratio was 1.2 : 1. Maximum number of suspected dengue cases (n=79) was seen during September and October. DENV-1 was circulating in Delhi in the year 2010-11 in non-epidemic period following reported predominance of DENV-3 and co-circulation of all dengue serotypes in the epidemic years 2003, 2006 and 2007.