Evaluation of NS1 Antigen Detection for Early Diagnosis of Dengue in a Tertiary Hospital in Southern India.

INTRODUCTION: Dengue is a mosquito-borne disease affecting mainly tropical and subtropical regions of the world. The early diagnosis of dengue is required for identifying an epidemic and also for implementing effective vector control measures.

AIM: To evaluate NS1 antigen assay as an alternative to RT-PCR for the early diagnosis of Dengue.

MATERIALS AND METHODS: A comparative study was conducted to evaluate NS1 antigen assay in clinically suspected dengue cases admitted to JIPMER hospital from January to November 2011. Serum samples were tested for NS1 antigen, IgM and IgG antibodies by ELISA and RT-PCR.

RESULTS: Out of total 112 clinically suspected dengue, 94 were laboratory-confirmed dengue cases (positive by one or more of the following tests - IgM ELISA, NS1 antigen ELISA and RT-PCR). NS1 was detectable from day 1 to day 12 of fever. The positive detection rate of NS1 antigen ELISA, RT-PCR and IgM ELISA were 80.9%, 68.1% and 47.9% respectively. NS1 antigen ELISA was evaluated using RT-PCR as the reference standard and showed a sensitivity of 96.8%, specificity of 53.3%, positive predictive value of 81.6% and negative predictive value of 88.9% with a likelihood ratio of 2.1 by Fisher's-exact test. The combination of NS1 and IgM had the highest sensitivity of 97.8%. DEN-3 was the serotype identified by RT-PCR for 24 randomly selected samples. NS1 antigen detection had the highest sensitivity in the early stages while IgM detection was more sensitive in the later half of the illness.

CONCLUSION: Both NS1 and RT-PCR are useful for early dengue diagnosis, although in terms of cost, ease of performance and rapidity, NS1 is superior to RT-PCR. NS1 in combination with IgM assay offers the most sensitive and cost-effective diagnostic modality for dengue.