title: Clinical differences between influenza A (H1N1) pdm09 & influenza B infections identified through active community surveillance in North India.
abstract: OBJECTIVE
  Most studies on the clinical presentation with influenza viruses have been conducted in outpatient or inpatient medical facilities with only a few studies in community settings. Clinical differences between influenza A (H1N1) pdm 09 and influenza B virus infections have importance for community-based public health surveillance. An active community surveillance at the time of emergence of pandemic influenza provided us with an opportunity to compare the clinical features among patients infected with influenza A (H1N1) pdm09 virus and those with influenza B virus co-circulating in an active community-based weekly surveillance in three villages in Faridabad, Haryana, north India.
  
  
  METHODS
  Active surveillance for febrile acute respiratory infection (FARI) was carried out in a rural community (n=16,182) in the context of an inactivated trivalent influenza vaccine trial (among children <11 yr). Individuals with FARI were assessed clinically by nurses and respiratory samples collected and tested for influenza viruses by real time RT-PCR from November 2009 to August 2010. Clinical symptoms of patients with influenza A (H1N1) pdm 09 and influenza B infection were compared.
  
  
  RESULTS
  Of the 4796 samples tested, 822 (17%) were positive for influenza virus. Of these, 443 (54%) were influenza A (H1N1) pdm09, 373 (45%) were influenza B and six were other subtypes/mixed infections. The mean age was lower for patients with influenza B (16.4 yr) than influenza A (H1N1) pdm09 infection (18.7 yr; P=0.04). Among children aged 5-18 yr, chills/rigours (OR 4.0; CI 2.2, 7.4), sore throat (OR 6.8; CI 2.3, 27.3) and headache (OR2.0; CI 1.3, 3.3) were more common in influenza A (H1N1) pdm09 infection than in influenza B cases. Chills/rigours (OR 2.4; CI 1.4, 4.0) and headache (OR 1.7; CI 1.0, 2.7) were associated with influenza A (H1N1) pdm09 infection in those >18 yr. No significant differences were seen in children <5 yr.
  
  
  CONCLUSIONS
  Our findings show that the differences in the clinical presentation of influenza A(H1N1)pdm09 and influenza B infections are not likely to be of clinical or public health significance.
authors: Debjani Ram
authors: DR
authors: Purakayastha
authors: Vivek
authors: V
authors: Gupta
authors: Shobha
authors: S
authors: Broor
authors: Wayne
authors: W
authors: Sullender
authors: Karen
authors: K
authors: Fowler
authors: Marc-Alain
authors: MA
authors: Widdowson
authors: Renu B
authors: RB
authors: Lal
authors: Department of Microbiology, Centre for Community Medicine, All India Institute of Medical Sciences, New Delhi, India.
authors: Anand
authors: A
authors: Krishnan
mesh_terms: D000293:Adolescent; D000328:Adult; D002648:Child; D005260:Female; D006801:Humans; D007194:India; D053118:Influenza A Virus, H1N1 Subtype / Q000302:isolation & purification / Q000472:pathogenicity*; D009981:Influenza B virus / Q000472:pathogenicity*; D007251:Influenza, Human / Q000453:epidemiology* / Q000473:pathology / Q000821:virology; D008297:Male; D008875:Middle Aged; D058873:Pandemics; D012141:Respiratory Tract Infections / Q000453:epidemiology* / Q000473:pathology / Q000821:virology; D012424:Rural Population; D012621:Seasons