NS1 antigen as an early diagnostic marker in dengue: report from India

Detection of specific IgM antibodies by ELISA forms the mainstay for diagnosis of dengue infection. However, IgM antibodies develop after 4 to 5 days of infection. The methods for early diagnosis include virus isolation and reverse transcriptase polymerase chain reaction (RT-PCR) which need a sophisticated laboratory. Another alternative that has recently come up is NS1 antigen detection. The present study compared IgM antibody detection with NS1 antigen for the diagnosis of acute dengue in 87 samples. NS1 antigen could be detected with good sensitivity (71–100%) till day 3 of fever, whereas IgM had a sensitivity of 0% to 50% at this time. On day 4 of illness, both the tests had comparative sensitivity. Beyond day 4, IgM antibody detection was superior to NS1. Both these diagnostic modalities were also compared with RT-PCR in 40 acute samples. NS1 detected additional 15 samples, which were missed by PCR. NS1 antigen is an early diagnostic marker that is feasible in a routine diagnostic laboratory.