Individual Correlates of Infectivity of Influenza A Virus Infections in Households

PLoS One. 2016 May 6;11(5):e0154418. doi: 10.1371/journal.pone.0154418. eCollection 2016.


Background: Identifying individual correlates of infectivity of influenza virus is important for disease control and prevention. Viral shedding is used as a proxy measure of infectivity in many studies. However, the evidence for this is limited.

Methods: In a detailed study of influenza virus transmission within households in 2008-12, we recruited index cases with confirmed influenza infection from outpatient clinics, and followed up their household contacts for 7-10 days to identify secondary infections. We used individual-based hazard models to characterize the relationship between individual viral shedding and individual infectivity.

Results: We analyzed 386 households with 1147 household contacts. Index cases were separated into 3 groups according to their estimated level of viral shedding at symptom onset. We did not find a statistically significant association of virus shedding with transmission. Index cases in medium and higher viral shedding groups were estimated to have 21% (95% CI: -29%, 113%) and 44% (CI: -16%, 167%) higher infectivity, compared with those in the lower viral shedding group.

Conclusions: Individual viral load measured by RT-PCR in the nose and throat was at most weakly correlated with individual infectivity in households. Other correlates of infectivity should be examined in future studies.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adolescent
  • Adult
  • Family Characteristics*
  • Female
  • Hong Kong
  • Humans
  • Influenza A virus / pathogenicity*
  • Influenza, Human / virology*
  • Male
  • Middle Aged
  • Virulence
  • Virus Shedding

Associated data

  • Dryad/10.5061/dryad.1p3kn