Demographic and Clinical Characteristics of Pandemic Influenza A (H1N1) 2009 Outbreak in Kerala, Southern India.

ABSTRACT

Aims: To study the clinical and epidemiological features in the affected individuals from different areas of Kerala, India. Study design: Population based cross sectional study. Place and Duration of Study Regional Facility for Molecular Diagnostics, Rajiv Gandhi Center for Biotechnology and Directorate of Health Services, Kerala, between August 2009 and September 2010. Methodology: We conducted active surveillance for referral hospitals with specialist inpatient care in Kerala during pandemic periods. Oropharyngeal or nasopharyngeal swabs were tested for influenza viruses by Real time reverse transcriptase PCR. Results: A total of 4252 samples were tested for H1N1 influenza virus, of which, 30.17% were positive for pandemic influenza A H1N1 and 10.49% were positive for Influenza A (seasonal flu). Severe disease and mortality in the pandemic influenza A (H1N1) 2009 infection predominantly affected relatively healthy adolescents and adults between the age of 10 and 50 years. Both Males (29.28%) and Females (31.15%) were equally effected even though we observed a significant difference (P=.02). 141 cases exhibited lower respiratory tract symptoms. Pneumonia alone accounted for 28% of complicated cases. It was observed that the majority of cases (29.28%) during the first outbreak season were imported from affected overseas regions. Conclusion: In this study, prevalence of Influenza A H1N1 was high in the healthy younger population and there wasn’t any sex related susceptibility for Influenza infection. Majority of districts showed a positivity of approximately 10-30%, few with high positivity of >30%. Our findings highlight the importance of regular influenza immunization as it is significant to understand that the H1N1 (2009) virus may still circulate for many years with similar high severity.