title: Influenza A Virus Shedding and Infectivity in Households.
abstract: 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.
authors.affiliation: WHO Collaborating Centre for Infectious Disease Epidemiology and Control, School of Public Health.
authors.forename: Tim K
authors.initials: TK
authors.lastname: Tsang
authors.affiliation: WHO Collaborating Centre for Infectious Disease Epidemiology and Control, School of Public Health.
authors.forename: Benjamin J
authors.initials: BJ
authors.lastname: Cowling
authors.affiliation: WHO Collaborating Centre for Infectious Disease Epidemiology and Control, School of Public Health.
authors.forename: Vicky J
authors.initials: VJ
authors.lastname: Fang
authors.affiliation: Department of Microbiology, Li Ka Shing Faculty of Medicine, The University of Hong Kong, Hong Kong Special Administrative Region, China.
authors.forename: Kwok-Hung
authors.initials: KH
authors.lastname: Chan
authors.affiliation: WHO Collaborating Centre for Infectious Disease Epidemiology and Control, School of Public Health.
authors.forename: Dennis K M
authors.initials: DK
authors.lastname: Ip
authors.affiliation: WHO Collaborating Centre for Infectious Disease Epidemiology and Control, School of Public Health.
authors.forename: Gabriel M
authors.initials: GM
authors.lastname: Leung
authors.affiliation: WHO Collaborating Centre for Infectious Disease Epidemiology and Control, School of Public Health Centre of Influenza Research, Li Ka Shing Faculty of Medicine, The University of Hong Kong, Hong Kong Special Administrative Region, China.
authors.forename: J S Malik
authors.initials: JS
authors.lastname: Peiris
authors.affiliation: Mathematical Modelling of Infectious Diseases Unit, Institut Pasteur, Paris.
authors.forename: Simon
authors.initials: S
authors.lastname: Cauchemez
mesh_terms: D000293:Adolescent; D000328:Adult; D005191:Family Characteristics; D005260:Female; D006801:Humans; D053118:Influenza A Virus, H1N1 Subtype / Q000302:isolation & purification*; D053122:Influenza A Virus, H3N2 Subtype / Q000302:isolation & purification*; D007251:Influenza, Human / Q000635:transmission* / Q000821:virology; D016014:Linear Models; D008297:Male; D008875:Middle Aged; D009666:Nose / Q000821:virology; D053139:Oseltamivir / Q000627:therapeutic use; D010614:Pharynx / Q000821:virology; D011446:Prospective Studies; D013048:Specimen Handling; D019562:Viral Load; D017201:Virus Shedding; D055815:Young Adult
chemical_list: D053139:Oseltamivir
keywords: infectiousness; influenza; isolation; public health