Pandemic H1N1 virus transmission and shedding dynamics in index case households of a prospective Vietnamese cohort

J Infect. 2014 Jun;68(6):581-90. doi: 10.1016/j.jinf.2014.01.008. Epub 2014 Feb 1.


Objectives: Influenza household transmission studies are required to guide prevention strategies but most passively recruit index cases that seek healthcare. We investigated A(H1N1)pdm09 transmission in a household-based cohort during 2009.

Methods: Health-workers visited 270 households weekly, and collected swabs from influenza-like-illness cases. If A(H1N1)pdm09 was RT-PCR-confirmed, all household members had symptoms assessed and swabs collected daily for 10-15 days. Viral RNA was quantified and sequenced and serology performed on pre-pandemic sera.

Results: Index cases were detected in 20 households containing 81 people. 98.5% lacked A(H1N1)pdm09 neutralizing antibodies in pre-pandemic sera. Eleven (18.6%, 95% CI 10.7-30.4%) of 59 contacts were infected. Virus genetic diversity within households was negligible and less than between households. Index and secondary cases were distributed between mothers, daughters and sons, and had similar virus-RNA shedding and symptom dynamics. Fathers were rarely infected. Five secondary cases (45%) had no apparent symptoms and three shed virus before symptoms. Secondary infection was associated with index case wet cough (OR 1.56, 95% CI 1.22-1.99).

Conclusions: In this cohort of A(H1N1)pdm09 susceptible persons, virus sequencing was capable of discriminating household from community transmission. Household transmission involved mothers and children but rarely fathers. Asymptomatic or pre-symptomatic shedding was common.

Keywords: Antibody; Household; Index; Influenza; Pandemic; Secondary; Serial interval; Shedding; Symptoms; Transmission.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adolescent
  • Adult
  • Aged
  • Aged, 80 and over
  • Antibodies, Viral / blood
  • Asian Continental Ancestry Group
  • Child
  • Child, Preschool
  • Cohort Studies
  • Family Characteristics*
  • Female
  • Genetic Variation
  • Humans
  • Infant
  • Infant, Newborn
  • Influenza A Virus, H1N1 Subtype / isolation & purification*
  • Influenza, Human / transmission*
  • Influenza, Human / virology*
  • Male
  • Middle Aged
  • Prospective Studies
  • RNA, Viral / genetics
  • Sequence Analysis, DNA
  • Viral Load
  • Virus Shedding*
  • Young Adult


  • Antibodies, Viral
  • RNA, Viral