There is scarcity of global data with regards to rates of asymptomatic carrier state due to 2009 pandemic H1N1 influenza virus. It will be interesting to study asymptomatic carrier state in the year 2012 when the global pandemic has been controlled. In this study we have attempted to evaluate the rates of asymptomatic carrier state due to this virus in a remote rural community from South India.
380 consecutive, asymptomatic, community living adults without history of respiratory illness in the last 30 days were studied. Demographic and clinical profile was noted. Throat swab was obtained and tested by RT-PCR (reverse transcriptase polymerase chain reaction) for swine influenza A (HINI) as per CDC (Centers for Disease Control) protocol. Participants who were positive in this test were followed weekly by clinical evaluation for a period of 4 weeks to look for onset of respiratory symptoms.
Mean age was 42.58 yrs. Males formed 48.3% of the cohort. Mean body mass index was 23.62 kg/m2. 16.3% and 10.5% were diagnosed to have diabetes mellitus and hypertension respectively. None of the study participants had received seasonal influenza vaccine or pandemic H1N1 influenza vaccine. RT-PCR identified asymptomatic infection in 41 participants (10.8%). In uni-variate and multi-variate logistic regression analysis there were no significant associations between having asymptomatic carrier state, diabetes diagnosis, gender, age, BMI, hemoglobin A1C%. On follow-up none of the 41 positive participants developed respiratory symptoms.
High prevalence of asymptomatic carrier state after 2009 H1N1 influenza virus pandemic was found in our study in the year 2012. The significance of asymptomatic infection remains unclear.