title: Shared air: a renewed focus on ventilation for the prevention of tuberculosis transmission.
abstract: BACKGROUND
  Despite an improvement in the overall TB cure rate from 40-74% between 1995 and 2011, TB incidence in South Africa continues to increase. The epidemic is notably disquieting in schools because the vulnerable population is compelled to be present. Older learners (age 15-19) are at particular risk given a smear-positive rate of 427 per 100,000 per year and the significant amount of time they spend indoors. High schools are therefore important locations for potential TB infection and thus prevention efforts.
  
  
  RESULTS
  Using portable carbon dioxide monitors, we measured CO2 in classrooms under non-steady state conditions. The threshold for tuberculosis transmission was estimated using a carbon dioxide-based risk equation. We determined a critical rebreathed fraction of carbon dioxide (ƒ(c)) of 1 · 6%, which correlates with an indoor CO2 concentration of 1000 ppm. These values correspond with a ventilation rate of 8 · 6 l/s per person or 12 air exchanges per hour (ACH) for standard classrooms of 180 m(3).
  
  
  CONCLUSIONS
  Given the high smear positive rate of high-school adolescents in South Africa, the proposal to achieve CO2 levels of 1000 ppm through natural ventilation (in the amount 12 ACH) will not only help achieve WHO guidelines for providing children with healthy indoor environments, it will also provide a low-cost intervention for helping control the TB epidemic in areas of high prevalence.
authors.affiliation: Division of Infectious Diseases and Geographic Medicine, Stanford University School of Medicine, Stanford, California, United States of America; Department of Anthropology, Stanford University, Stanford, California, United States of America; Desmond Tutu HIV Centre, Institute of Infectious Diseases and Molecular Medicine, University of Cape Town, Cape Town, Republic of South Africa.
authors.forename: Eugene T
authors.initials: ET
authors.lastname: Richardson
authors.affiliation: Desmond Tutu HIV Centre, Institute of Infectious Diseases and Molecular Medicine, University of Cape Town, Cape Town, Republic of South Africa.
authors.forename: Carl D
authors.initials: CD
authors.lastname: Morrow
authors.affiliation: Desmond Tutu HIV Centre, Institute of Infectious Diseases and Molecular Medicine, University of Cape Town, Cape Town, Republic of South Africa.
authors.forename: Darryl B
authors.initials: DB
authors.lastname: Kalil
authors.forename: Samuel
authors.initials: S
authors.lastname: Ginsberg
authors.affiliation: Desmond Tutu HIV Centre, Institute of Infectious Diseases and Molecular Medicine, University of Cape Town, Cape Town, Republic of South Africa.
authors.forename: Linda-Gail
authors.initials: LG
authors.lastname: Bekker
authors.affiliation: Desmond Tutu HIV Centre, Institute of Infectious Diseases and Molecular Medicine, University of Cape Town, Cape Town, Republic of South Africa.
authors.forename: Robin
authors.initials: R
authors.lastname: Wood
mesh_terms: D016902:Air Pollution, Indoor / Q000517:prevention & control; D002245:Carbon Dioxide / Q000032:analysis; D004784:Environmental Monitoring; D005260:Female; D006801:Humans; D008297:Male; D012574:Schools / Q000706:statistics & numerical data; D014376:Tuberculosis / Q000635:transmission*; D014691:Ventilation
chemical_list: D002245:Carbon Dioxide