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. 2013 Jul 1:13:300.
doi: 10.1186/1471-2334-13-300.

Natural ventilation reduces high TB transmission risk in traditional homes in rural KwaZulu-Natal, South Africa

Melissa Lygizos  1 , Sheela V Shenoi, Ralph P Brooks, Ambika Bhushan, James C M Brust, Daniel Zelterman, Yanhong Deng, Veronika Northrup, Anthony P Moll, Gerald H Friedland
Affiliations

Natural ventilation reduces high TB transmission risk in traditional homes in rural KwaZulu-Natal, South Africa

Melissa Lygizos et al. BMC Infect Dis. .

Abstract

Background: Transmission of drug susceptible and drug resistant TB occurs in health care facilities, and community and households settings, particularly in highly prevalent TB and HIV areas. There is a paucity of data regarding factors that may affect TB transmission risk in household settings. We evaluated air exchange and the impact of natural ventilation on estimated TB transmission risk in traditional Zulu homes in rural South Africa.

Methods: We utilized a carbon dioxide decay technique to measure ventilation in air changes per hour (ACH). We evaluated predominant home types to determine factors affecting ACH and used the Wells-Riley equation to estimate TB transmission risk.

Results: Two hundred eighteen ventilation measurements were taken in 24 traditional homes. All had low ventilation at baseline when windows were closed (mean ACH = 3, SD = 3.0), with estimated TB transmission risk of 55.4% over a ten hour period of exposure to an infectious TB patient. There was significant improvement with opening windows and door, reaching a mean ACH of 20 (SD = 13.1, p < 0.0001) resulting in significant decrease in estimated TB transmission risk to 9.6% (p < 0.0001). Multivariate analysis identified factors predicting ACH, including ventilation conditions (windows/doors open) and window to volume ratio. Expanding ventilation increased the odds of achieving ≥12 ACH by 60-fold.

Conclusions: There is high estimated risk of TB transmission in traditional homes of infectious TB patients in rural South Africa. Improving natural ventilation may decrease household TB transmission risk and, combined with other strategies, may enhance TB control efforts.

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Figures

Figure 1
Figure 1
Two predominant types of traditional home construction in Tugela Ferry. A. Round-shaped home with thatched roof B. Box-shaped home with metal roof.
Figure 2
Figure 2
ACH and Estimated TB Risk under different ventilation conditions. Box-plot of ACH and estimated TB risk from the various ventilation conditions tested: (1) baseline with windows and door closed, (2) windows open, and (3) windows and door open. Mean ACH and TB risk for each condition is marked with “+”. Median ACH and TB risk is marked by the solid horizontal line, with the upper and lower ends of the box representing the limits of the interquartile range (IQR). The dotted lines represent the range of values. a. ACH b. Estimated TB Risk.
Figure 3
Figure 3
Estimated Risk of TB Infection by Exposure Time. Risk of TB infection after various durations of exposure to an active TB case under different ventilation conditions, as estimated using the Wells-Riley equation. Diamond: windows and door closed; Triangle: windows open; Circle: windows and door open together.
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References

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