Serological investigation of a febrile outbreak in Delhi, India, using a rapid immunochromatographic test.

In reference to the article by Vaughn et al. published in the January 1998 issue (6), we have also used the rapid immunochromatographic assay for detection of dengue immunoglobulin M (IgM) and IgG antibodies (PanBio, Brisbane, Australia) in the serologic evaluation of a febrile outbreak in Delhi, India, in 1997. India has witnessed dengue epidemics since the last century, but cases with hemorrhagic manifestations appeared in Calcutta in 1963 (5) and in Delhi in 1988, followed by dengue hemorrhagic fever (DHF) epidemics in Shahjahanpur, Surat, and Calcutta in the 1990s (1, 3). Delhi had another epidemic of DHF in 1996. A total of 189 acute-phase serum samples collected at a tertiary-care hospital from April to December 1997 were screened for the presence of antidengue IgM and IgG antibodies by the rapid immunochromatographic test. The results for 43 randomly selected serum samples were compared with results obtained by the Dengue Duo IgM and IgG capture enzyme-linked immunosorbent assay (ELISA) (PanBio), as shown in Table 1. The results of the rapid immunochromatographic test were graded as reactive (strong band seen), weakly reactive (faint band seen), or negative (no band seen). A total of 31 patients had evidence of dengue fever (including DHFdengue shock syndrome [DHF-DSS]). Of these patients, 4 had primary infection and 27 had secondary dengue. About 50% of DHF cases were seen in the age group below 15 years, unlike the situation with earlier epidemics, in which DHF mostly affected children and 95% of cases reported occurred in the age group below 15 years (2, 4). DSS occurred in four patients, three of whom were less than 15 years old. The mean age of the patients with evidence of antidengue antibodies was 21.5 years. Adults comprised 67.8% of the serologically confirmed dengue cases. The maximum number of cases occurred in the 11to 15-year age group (32.2%), followed by the 21to 25-year age group (29%). The maximum number of cases occurred in the month of October. For those sera showing weakly reactive results by the initial rapid test, the capture ELISA was found useful. Since virus isolation takes a long time, serology is carried out in most laboratories for rapid diagnosis of dengue infection. The rapid immunochromatographic assay takes 5 min only and is a useful screening test. A combination of this test with the IgM and IgG capture ELISA should be used for final serologic diagnosis and distinguishing between primary and secondary dengue infections.