Dengue: Lessons of an Outbreak.

Area of Science:

• Medical Entomology
• Infectious Diseases
• Public Health

Background:

• Dengue outbreaks have been recurrent in Delhi since 1967.
• The year 2015 saw one of Delhi's most severe dengue outbreaks, with over 15,000 confirmed cases and 60 deaths.
• This highlights the persistent public health challenge posed by dengue in the region.

Purpose of the Study:

• To assess the current status of dengue cases in Delhi compared to the preceding six years.
• To determine the ratio of primary versus secondary dengue infections.
• To evaluate the efficacy of a single-test diagnostic strategy (NS1 antigen or IgM antibody) for dengue confirmation.

Main Methods:

• A cross-sectional study was conducted in 2015, analyzing 7,177 serum samples from suspected dengue cases.
• Dengue NS1 antigen and IgM antibody ELISA tests were employed for acute and convalescent samples, respectively.
• IgG Avidity ELISA was used on 76 dengue-positive samples to differentiate primary and secondary infections.

Main Results:

• Out of 7,177 samples, 2,358 tested positive for dengue.
• Positivity rates were 37.1% for NS1 antigen and 24.8% for IgM antibody.
• IgG Avidity ELISA revealed that 68.4% of dengue cases were secondary infections, indicating a high prevalence of prior dengue exposure.

Conclusions:

• Dengue cases in Delhi show a consistent increasing trend since 2011.
• A dual-test strategy, including both NS1 antigen and IgM antibody detection, is crucial for accurate dengue diagnosis.
• The rising incidence of secondary dengue cases is attributed to the increased prevalence of past dengue infections in the population.