Influenza A Virus Shedding and Infectivity in Households

J Infect Dis. 2015 Nov 1;212(9):1420-8. doi: 10.1093/infdis/jiv225. Epub 2015 Apr 15.


Background: Viral shedding is often considered to correlate with the infectivity of influenza, but the evidence for this is limited.

Methods: In a detailed study of influenza virus transmission within households in 2008-2012, index case patients with confirmed influenza were identified in outpatient clinics, and we collected nose and throat swab specimens for testing by reverse-transcription polymerase chain reaction from all household members regardless of illness. We used individual-based hazard models to characterize the relationship between viral load (V) and infectivity.

Results: Assuming that infectivity was proportional to viral load V gave the worst fit, because it strongly overestimated the proportion of transmission occurring at symptom onset. Alternative models assuming that infectivity was proportional to a various functions of V provided better fits, although they all overestimated the proportion of transmission occurring >3 days after symptom onset. The best fitting model assumed that infectivity was proportion to V(γ), with estimates of γ = 0.136 and γ = 0.156 for seasonal influenza A(H1N1) and A(H3N2) respectively.

Conclusions: All the models we considered that used viral loads to approximate infectivity of a case imperfectly explained the timing of influenza secondary infections in households. Identification of more accurate correlates of infectivity will be important to inform control policies and disease modeling.

Keywords: infectiousness; influenza; isolation; public health.

Publication types

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

MeSH terms

  • Adolescent
  • Adult
  • Family Characteristics
  • Female
  • Humans
  • Influenza A Virus, H1N1 Subtype / isolation & purification*
  • Influenza A Virus, H3N2 Subtype / isolation & purification*
  • Influenza, Human / transmission*
  • Influenza, Human / virology
  • Linear Models
  • Male
  • Middle Aged
  • Nose / virology
  • Oseltamivir / therapeutic use
  • Pharynx / virology
  • Prospective Studies
  • Specimen Handling
  • Viral Load
  • Virus Shedding*
  • Young Adult


  • Oseltamivir