Dengue and Chikungunya virus illness affects tropical and subtropical regions around the world including India. In Delhi,a highly populous city, as recently as in the year 2010, several cases of fever with clinical picture similar to that of dengue and chikungunya virus infection eported in our Vardhman Mahavir Medical College & associated Safdarjang Hospital, New Delhi. Cases of fever started reporting in late June, 2010 but fromSeptember onwards also emerged cases of chikungunya. On clinical basis alone, especially during mixed outbreaks, it is generally difficult to differentiate between the two, in particular when dengue fever does not manifest as DHF. Serology
for dengue and chikungunyawas performed byMacELISA test with the aim as detection of specific IgM antibodies. In cases of dengue fever from late June till end August โ€“ 2010, the IgM seropositivitywas found to be 38.3%. From September, 2010 onwards and till December end, in cases of chikungunya virus fever the IgM seropositivity was found to be 65.11% and that of dengue as 37.86%. Also, in cases from Sep to Dec, 2010, which presented with clinical pictures suggestive of both types of viral infections, revealed that the seropositivity for dengue declined to 8.36%, and for Chikungunya increased to 41.46%. In conclusion, the dengue outbreak, especially in city Delhi, may get overwhelmingly replaced by chikungunya virus fever cases with both the dominant viruses’ co circulating in the community. Detection of IgM antibodies against dengue and chikungunya by ELISA during the mixed outbreak appears to play important role for distinguishing the two, and reinforces clinical diagnosis, and, hence, helps initiate proper medical care.