title: Estimation of the burden of pandemic(H1N1)2009 in developing countries: experience from a tertiary care center in South India.
abstract: BACKGROUND
  The burden of the pandemic (H1N1) 2009 influenza might be underestimated if detection of the virus is mandated to diagnose infection. Using an alternate approach, we propose that a much higher pandemic burden was experienced in our institution.
  
  
  RESULTS
  Consecutive patients (n = 2588) presenting to our hospital with influenza like illness (ILI) or severe acute respiratory infection (SARI) during a 1-year period (May 2009-April 2010) were prospectively recruited and tested for influenza A by real-time RT-PCR. Analysis of weekly trends showed an 11-fold increase in patients presenting with ILI/SARI during the peak pandemic period when compared with the pre-pandemic period and a significant (P<0.001) increase in SARI admissions during the pandemic period (30 ± 15.9 admissions/week) when compared with pre-pandemic (7 ± 2.5) and post-pandemic periods (5 ± 3.8). However, Influenza A was detected in less than one-third of patients with ILI/SARI [699 (27.0%)]; a majority of these (557/699, 79.7%) were Pandemic (H1N1)2009 virus [A/H1N1/09]. An A/H1N1/09 positive test was correlated with shorter symptom duration prior to presentation (p = 0.03). More ILI cases tested positive for A/H1N1/09 when compared with SARI (27.4% vs. 14.6%, P = 0.037). When the entire study population was considered, A/H1N1/09 positivity was associated with lower risk of hospitalization (p<0.0001) and ICU admission (p = 0.013) suggesting mild self-limiting illness in a majority.
  
  
  CONCLUSIONS
  Analysis of weekly trends of ILI/SARI suggest a higher burden of the pandemic attributable to A/H1N1/09 than estimates assessed by a positive PCR test alone. The study highlights methodological consideration in the estimation of burden of pandemic influenza in developing countries using hospital-based data that may help assess the impact of future outbreaks of respiratory illnesses.
authors.affiliation: Department of Clinical Virology, Christian Medical College, Vellore, Tamil Nadu, India.
authors.forename: Mahesh
authors.initials: M
authors.lastname: Moorthy
authors.forename: Prasanna
authors.initials: P
authors.lastname: Samuel
authors.forename: John Victor
authors.initials: JV
authors.lastname: Peter
authors.forename: Saranya
authors.initials: S
authors.lastname: Vijayakumar
authors.forename: Dipika
authors.initials: D
authors.lastname: Sekhar
authors.forename: Valsan P
authors.initials: VP
authors.lastname: Verghese
authors.forename: Indira
authors.initials: I
authors.lastname: Agarwal
authors.forename: Prabhakar D
authors.initials: PD
authors.lastname: Moses
authors.forename: Kala
authors.initials: K
authors.lastname: Ebenezer
authors.forename: Ooriapadickal Cherian
authors.initials: OC
authors.lastname: Abraham
authors.forename: Kurien
authors.initials: K
authors.lastname: Thomas
authors.forename: Prasad
authors.initials: P
authors.lastname: Mathews
authors.forename: Akhilesh C
authors.initials: AC
authors.lastname: Mishra
authors.forename: Renu
authors.initials: R
authors.lastname: Lal
authors.forename: Jayaprakash
authors.initials: J
authors.lastname: Muliyil
authors.forename: Asha Mary
authors.initials: AM
authors.lastname: Abraham
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D002648:Child; D002675:Child, Preschool; D003140:Communicable Disease Control; D003906:Developing Countries; D005260:Female; D006760:Hospitalization; D006801:Humans; D007194:India; D007223:Infant; D007231:Infant, Newborn; D053118:Influenza A Virus, H1N1 Subtype / Q000378:metabolism*; D007251:Influenza, Human / Q000453:epidemiology* / Q000821:virology*; D007362:Intensive Care Units; D008297:Male; D008875:Middle Aged; D058873:Pandemics; D060888:Real-Time Polymerase Chain Reaction / Q000379:methods; D062606:Tertiary Care Centers; D013997:Time Factors