title: Modes of transmission of influenza B virus in households.
abstract: BACKGROUND
  While influenza A and B viruses can be transmitted via respiratory droplets, the importance of small droplet nuclei "aerosols" in transmission is controversial.
  
  
  RESULTS
  In Hong Kong and Bangkok, in 2008-11, subjects were recruited from outpatient clinics if they had recent onset of acute respiratory illness and none of their household contacts were ill. Following a positive rapid influenza diagnostic test result, subjects were randomly allocated to one of three household-based interventions: hand hygiene, hand hygiene plus face masks, and a control group. Index cases plus their household contacts were followed for 7-10 days to identify secondary infections by reverse transcription polymerase chain reaction (RT-PCR) testing of respiratory specimens. Index cases with RT-PCR-confirmed influenza B were included in the present analyses. We used a mathematical model to make inferences on the modes of transmission, facilitated by apparent differences in clinical presentation of secondary infections resulting from aerosol transmission. We estimated that approximately 37% and 26% of influenza B virus transmission was via the aerosol mode in households in Hong Kong and Bangkok, respectively. In the fitted model, influenza B virus infections were associated with a 56%-72% risk of fever plus cough if infected via aerosol route, and a 23%-31% risk of fever plus cough if infected via the other two modes of transmission.
  
  
  CONCLUSIONS
  Aerosol transmission may be an important mode of spread of influenza B virus. The point estimates of aerosol transmission were slightly lower for influenza B virus compared to previously published estimates for influenza A virus in both Hong Kong and Bangkok. Caution should be taken in interpreting these findings because of the multiple assumptions inherent in the model, including that there is limited biological evidence to date supporting a difference in the clinical features of influenza B virus infection by different modes.
authors.affiliation: School of Public Health, Li Ka Shing Faculty of Medicine, The University of Hong Kong, Hong Kong Special Administrative Region, China.
authors.forename: Benjamin J
authors.initials: BJ
authors.lastname: Cowling
authors.affiliation: School of Public Health, Li Ka Shing Faculty of Medicine, The University of Hong Kong, Hong Kong Special Administrative Region, China.
authors.forename: Dennis K M
authors.initials: DK
authors.lastname: Ip
authors.affiliation: School of Public Health, Li Ka Shing Faculty of Medicine, The University of Hong Kong, Hong Kong Special Administrative Region, China.
authors.forename: Vicky J
authors.initials: VJ
authors.lastname: Fang
authors.affiliation: Queen Sirikit National Institute of Child Health, Bangkok, Thailand.
authors.forename: Piyarat
authors.initials: P
authors.lastname: Suntarattiwong
authors.affiliation: Influenza Program, Thailand MOPH-US CDC Collaboration, Nonthaburi, Thailand; Influenza Division, US Centers for Disease Control and Prevention, Atlanta, Georgia, United States of America.
authors.forename: Sonja J
authors.initials: SJ
authors.lastname: Olsen
authors.affiliation: Influenza Program, Thailand MOPH-US CDC Collaboration, Nonthaburi, Thailand.
authors.forename: Jens
authors.initials: J
authors.lastname: Levy
authors.affiliation: Influenza Division, US Centers for Disease Control and Prevention, Atlanta, Georgia, United States of America.
authors.forename: Timothy M
authors.initials: TM
authors.lastname: Uyeki
authors.affiliation: School of Public Health, Li Ka Shing Faculty of Medicine, The University of Hong Kong, Hong Kong Special Administrative Region, China.
authors.forename: Gabriel M
authors.initials: GM
authors.lastname: Leung
authors.affiliation: School of Public Health, Li Ka Shing Faculty of Medicine, The University of Hong Kong, Hong Kong Special Administrative Region, China; Centre for 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: Queen Sirikit National Institute of Child Health, Bangkok, Thailand.
authors.forename: Tawee
authors.initials: T
authors.lastname: Chotpitayasunondh
authors.affiliation: Graduate School of Medicine, The University of Tokyo, Bunkyo-ku, Tokyo, Japan.
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Nishiura
authors.affiliation: Epidemiology and Medical Affairs, Sanofi Pasteur, Bangkok, Thailand.
authors.forename: J Mark
authors.initials: JM
authors.lastname: Simmerman
mesh_terms: D000293:Adolescent; D000328:Adult; D002648:Child; D002675:Child, Preschool; D003371:Cough / Q000821:virology; D005260:Female; D006235:Hand Disinfection; D006801:Humans; D009980:Influenza A virus / Q000235:genetics; D009981:Influenza B virus / Q000235:genetics*; D007251:Influenza, Human / Q000635:transmission* / Q000821:virology; D008297:Male; D008397:Masks; D008875:Middle Aged; D008962:Models, Theoretical; D012367:RNA, Viral / Q000032:analysis; D020133:Reverse Transcriptase Polymerase Chain Reaction; D055815:Young Adult
chemical_list: D012367:RNA, Viral