Infection with influenza A(H1N1)pdm09 during the first wave of the 2009 pandemic: evidence from a longitudinal seroepidemiologic study in Dhaka, Bangladesh

Sharifa Nasreen, Mustafizur Rahman, Kathy Hancock, Jacqueline M Katz, Doli Goswami, Katharine Sturm-Ramirez, Crystal Holiday, Stacie Jefferson, Alicia Branch, David Wang, Vic Veguilla, Marc-Alain Widdowson, Alicia M Fry, W Abdullah Brooks

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BACKGROUND: We determined influenza A(H1N1)pdm09 antibody levels before and after the first wave of the pandemic in an urban community in Dhaka, Bangladesh.

METHODS: We identified a cohort of households by stratified random sampling. We collected baseline serum specimens during July-August 2009, just prior to the initial wave of the 2009 pandemic in this community and a second specimen during November 2009, after the pandemic peak. Paired sera were tested for antibodies against A(H1N1)pdm09 virus using microneutralization assay and hemagglutinin inhibition (HI) assay. A fourfold increase in antibody titer by either assay with a titer of ≥40 in the convalescent sera was considered a seroconversion. At baseline, an HI titer of ≥40 was considered seropositive. We collected information on clinical illness from weekly home visits.

RESULTS: We tested 779 paired sera from the participants. At baseline, before the pandemic wave, 1% overall and 3% of persons >60 years old were seropositive. After the first wave of the pandemic, 211 (27%) individuals seroconverted against A(H1N1)pdm09. Children aged 5-17 years had the highest proportion (37%) of seroconversion. Among 264 (34%) persons with information on clinical illness, 191 (72%) had illness >3 weeks prior to collection of the follow-up sera and 73 (38%) seroconverted. Sixteen (22%) of these 73 seroconverted participants reported no clinical illness.

CONCLUSION: After the first pandemic wave in Dhaka, one in four persons were infected by A(H1N1)pdm09 virus and the highest burden of infection was among the school-aged children. Seroprevalence studies supplement traditional surveillance systems to estimate infection burden.

Original languageEnglish
JournalInfluenza and Other Respiratory Viruses
Issue number5
Pages (from-to)394-398
Number of pages5
Publication statusPublished - 2017


  • Adolescent
  • Adult
  • Aged
  • Antibodies, Viral/blood
  • Bangladesh/epidemiology
  • Child
  • Child, Preschool
  • Cohort Studies
  • Female
  • Humans
  • Infant
  • Influenza A Virus, H1N1 Subtype/genetics
  • Influenza, Human/epidemiology
  • Longitudinal Studies
  • Male
  • Middle Aged
  • Pandemics
  • Seroepidemiologic Studies
  • Young Adult


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