Kinetics of pandemic influenza virus 2009 virus in Gujarat, Western India: An investigation of signature features

Context: Establishment and kinetics of pandemic H1N1 2009 virus in Gujarat. Aims: To assess epidemiological and clinical profile of pandemic H1N1 cases and to correlate findings with signature features of pandemic agent. Settings and Design: Study was performed at a tertiary care hospital in Ahmedabad, Gujarat. Patients attending various hospitals across Gujarat for influenza-like illness were tested. Materials and Methods: Nasopharyngeal or nasal swabs collected in viral transport medium were subjected to real-time reverse transcriptase PCR using CDC-validated and WHO-approved protocols. Results: A total of 5750 samples were tested: 2620 tested positive for influenza A. 1710 were positive for pandemic H1N1 2009 virus: 910 males and 800 females with maximum positivity in the age group 18 to < 36 yrs (13.6% of total tested and 45.7% of pandemic H1N1 positive) with cough being the major clinical feature. Three distinct peaks of pandemic H1N1 2009 were observed, outnumbering seasonal flu A virus by 1.9:1. In most districts, a positivity of approximately 10-30% was observed. However, some districts showed very high positivity of >30% while some showed little incidence. This new virus is at low activity since October 2010. Conclusions: Pandemic H1N1 2009 virus is presently circulating in almost all parts of Gujarat but has been unable to replace seasonal influenza A completely. The present study corroborates the signature features for pandemic H1N1 as there is greater affection of younger age groups, appearance of successive peaks, higher transmissibility than seasonal influenza A, and differing impacts in different geographic regions.