title: Quantification of shared air: a social and environmental determinant of airborne disease transmission.
abstract: BACKGROUND
  Tuberculosis is endemic in Cape Town, South Africa where a majority of the population become tuberculosis infected before adulthood. While social contact patterns impacting tuberculosis and other respiratory disease spread have been studied, the environmental determinants driving airborne transmission have not been quantified.
  
  
  METHODS
  Indoor carbon dioxide levels above outdoor levels reflect the balance of exhaled breath by room occupants and ventilation. We developed a portable monitor to continuously sample carbon dioxide levels, which were combined with social contact diary records to estimate daily rebreathed litres. A pilot study established the practicality of monitor use up to 48-hours. We then estimated the daily volumes of air rebreathed by adolescents living in a crowded township.
  
  
  RESULTS
  One hundred eight daily records were obtained from 63 adolescents aged between 12- and 20-years. Forty-five lived in wooden shacks and 18 in brick-built homes with a median household of 4 members (range 2-9). Mean daily volume of rebreathed air was 120.6 (standard error: 8.0) litres/day, with location contributions from household (48%), school (44%), visited households (4%), transport (0.5%) and other locations (3.4%). Independent predictors of daily rebreathed volumes included household type (p = 0.002), number of household occupants (p = 0.021), number of sleeping space occupants (p = 0.022) and winter season (p<0.001).
  
  
  CONCLUSIONS
  We demonstrated the practical measurement of carbon dioxide levels to which individuals are exposed in a sequence of non-steady state indoor environments. A novel metric of rebreathed air volume reflects social and environmental factors associated with airborne infection and can identify locations with high transmission potential.
authors.affiliation: Desmond Tutu HIV Centre, Institute of Infectious Diseases and Molecular Medicine, and Department of Medicine, University of Cape Town Faculty of Health Sciences, Cape Town, South Africa.
authors.forename: Robin
authors.initials: R
authors.lastname: Wood
authors.affiliation: Desmond Tutu HIV Centre, Institute of Infectious Diseases and Molecular Medicine, and Department of Medicine, University of Cape Town Faculty of Health Sciences, Cape Town, South Africa.
authors.forename: Carl
authors.initials: C
authors.lastname: Morrow
authors.affiliation: Department of Electrical Engineering, Faculty of Engineering & the Built Environment, University of Cape Town, Cape Town, South Africa.
authors.forename: Samuel
authors.initials: S
authors.lastname: Ginsberg
authors.affiliation: Desmond Tutu HIV Centre, Institute of Infectious Diseases and Molecular Medicine, and Department of Medicine, University of Cape Town Faculty of Health Sciences, Cape Town, South Africa.
authors.forename: Elizabeth
authors.initials: E
authors.lastname: Piccoli
authors.affiliation: Desmond Tutu HIV Centre, Institute of Infectious Diseases and Molecular Medicine, and Department of Medicine, University of Cape Town Faculty of Health Sciences, Cape Town, South Africa.
authors.forename: Darryl
authors.initials: D
authors.lastname: Kalil
authors.affiliation: Desmond Tutu HIV Centre, Institute of Infectious Diseases and Molecular Medicine, and Department of Medicine, University of Cape Town Faculty of Health Sciences, Cape Town, South Africa.
authors.forename: Angelina
authors.initials: A
authors.lastname: Sassi
authors.affiliation: Center for AIDS Research, Harvard Medical School, Boston, Massachusetts, United States of America.
authors.forename: Rochelle P
authors.initials: RP
authors.lastname: Walensky
authors.affiliation: Division of Infectious Diseases and Geographic Medicine, Stanford University School of Medicine, Stanford, California, United States of America.
authors.forename: Jason R
authors.initials: JR
authors.lastname: Andrews
mesh_terms: D000293:Adolescent; D000328:Adult; D000388:Air / Q000032:analysis*; D002245:Carbon Dioxide / Q000032:analysis; D005260:Female; D006801:Humans; D007398:Interpersonal Relations; D008297:Male; D008875:Middle Aged; D010865:Pilot Projects; D012119:Respiration; D013019:South Africa; D013997:Time Factors; D014376:Tuberculosis / Q000503:physiopathology / Q000635:transmission*; D055815:Young Adult
chemical_list: D002245:Carbon Dioxide