Dynamic patterns of circulating seasonal and pandemic A(H1N1)pdm09 influenza viruses from 2007-2010 in and around Delhi, India.

Shobha Broor,Ann Moen,Shivram Dhakad,Mandeep Chadha,Akhilesh C Mishra,Yashpal Singh,Renu B Lal,Samander Kaushik,Anand Krishnan,Muneer A Mir,Dipanjan S Roy

doi:10.1371/journal.pone.0029129

Abstract

Influenza surveillance was carried out in a subset of patients with influenza-like illness (ILI) presenting at an Employee Health Clinic (EHS) at All India Institute of Medical Sciences (AIIMS), New Delhi (urban) and pediatric out patients department of civil hospital at Ballabhgarh (peri-urban), under the Comprehensive Rural Health Services Project (CRHSP) of AIIMS, in Delhi region from January 2007 to December 2010. Of the 3264 samples tested, 541 (17%) were positive for influenza viruses, of which 221 (41%) were pandemic Influenza A(H1N1)pdm09, 168 (31%) were seasonal influenza A, and 152 (28%) were influenza B. While the Influenza viruses were detected year-round, their types/subtypes varied remarkably. While there was an equal distribution of seasonal A(H1N1) and influenza B in 2007, predominance of influenza B was observed in 2008. At the beginning of 2009, circulation of influenza A(H3N2) viruses was observed, followed later by emergence of Influenza A(H1N1)pdm09 with co-circulation of influenza B viruses. Influenza B was dominant subtype in early 2010, with second wave of Influenza A(H1N1)pdm09 in August-September, 2010. With the exception of pandemic H1N1 emergence in 2009, the peaks of influenza activity coincided primarily with monsoon season, followed by minor peak in winter at both urban and rural sites. Age group analysis of influenza positivity revealed that the percent positivity of Influenza A(H1N1)pdm09 influenza virus was highest in >5–18 years age groups (OR 2.5; CI = 1.2–5.0; p = 0.009) when compared to seasonal influenza. Phylogenetic analysis of Influenza A(H1N1)pdm09 from urban and rural sites did not reveal any major divergence from other Indian strains or viruses circulating worldwide. Continued surveillance globally will help define regional differences in influenza seasonality, as well as, to determine optimal periods to implement influenza vaccination programs among priority populations.

Highlights

Influenza is a widespread viral infection and a major cause of morbidity and mortality worldwide [1,2]
Age group analysis of influenza positivity revealed that the percent positivity of Influenza A(H1N1)pdm09 influenza virus was highest in .5–18 years age groups when compared to seasonal influenza
Influenza Surveillance Network has greatly contributed to the knowledge about circulating influenza viruses, including emergence of novel strains [3,4]

Summary

Introduction

Influenza is a widespread viral infection and a major cause of morbidity and mortality worldwide [1,2]. Influenza Surveillance Network has greatly contributed to the knowledge about circulating influenza viruses, including emergence of novel strains [3,4]. Improved understanding of temporal and geographic circulation of influenza viruses and the impact of influenza among populations living in tropical and subtropical regions is essential for the development of influenza prevention and control strategies for those areas [1,5,6]. The threat of an avian influenza virus (H5N1) pandemic and the emergence of pandemic Influenza, represented major stimuli for advances in knowledge about influenza in many countries [1,7]. Influenza activity in tropical countries usually in both 2009 and 2010, whereas A(H3N2) accounted for .35%. Influenza-like illness(ILI) presenting for care in urban and periurban sites in and around Delhi for the period 2007–2010, which includes surveillance during the Influenza pandemic and postpandemic periods

Results

Discussion

Materials and Methods