Purpose: The object of this study was to identify patients with diagnosed dengue infection, who were positive
for both dengue-specific NS1 antigen and IgM antibody.
Method: From January 2013 to December 2016, in Central Kolkata in West Bengal in India, patients with
symptoms of dengue infection, were sent to the laboratory by the physicians for confirmatory diagnosis of
dengue infection. A total of 4762 patients were seen, and serum samples tested and distributed into seven
panels, according to the investigations requested. 1436 patients were tested positive.
Results: 1053 cases were tested for both NS1 and Ig M antibody, 835 for dengue-specific NS1 antigen, IgM and
IgG antibodies and 218 for NS1 dengue-specific antigen and IgM antibody. Of these, dengue was confirmed in
34.3 %, with 16.6% positive for both NS1 antigen and IgM antibody. Eleven were diagnosed, with late dengue
infection, thirty-nine with late primary infections and ten with late secondary dengue infection.
Conclusions: Many of the patients were reactive for both NS1 antigen and IgM antibody, and they required
proper attention and strict vigilance with effective monitoring and treatment, not of early dengue infection,
but of late dengue infection. Unless the serological tests for Ig M and IgG antibodies, and the dengue specific
viral antigen NS1 are performed simultaneously, these types of cases would not all be detected.