The Impact of Ventilation and Early Diagnosis on Tuberculosis Transmission in Brazilian Prisons

Abstract

Prisoners have among the highest incidence of tuberculosis (TB) globally. However, the contribution of the prison environment on transmission is not well understood and structural characteristics have received little attention as effective epidemiological interventions in TB control. We evaluated architectural characteristics and estimated ventilation rates in 141 cells in three prisons in central west Brazil using steady-state exhaled carbon dioxide (CO2) levels. We used a modified Wells-Riley equation to estimate the probability of infection for inmates sharing a cell with an infectious case and projected the impact of interventions, including early diagnosis and improved ventilation. Overall, prison cells were densely populated (mean 2.1 m(2) per occupant) and poorly ventilated, with only three cells meeting World Health Organization (WHO) standards for per-person ventilation (60 L/s) applied in infection control settings. In the absence of interventions, projected mean risk of infection was 78.0% during a 6-month period. Decreasing time-to-diagnosis by 25% reduced transmission risk by 8.3%. Improving ventilation to WHO standards decreased transmission by 38.2%, whereas optimizing cross-ventilation reduced transmission by 64.4%. Prison environments promote high infection risk over short-time intervals. In this context, enhanced diagnostics have a limited impact on reducing transmission. Improving natural ventilation may be required to effectively control TB in prisons.

© The American Society of Tropical Medicine and Hygiene.

Figures

Figure 1.

Ventilation (L/s/person) (colored dots) and mean value (dark solid line) in general population cells of three prisons, Mato Grosso do Sul, Brazil, 2013. The horizontal dashed line indicates the World Health Organization (WHO)-recommended 60 L/s/person for naturally ventilated, general wards (A). Overall floor plan of UPRB illustrating the distribution of ventilation (colored dots) in proportion to the number of inmates (B). Photograph of typical courtyard in Unidade Penal Ricardo Brandão (UPRB) (C).

Figure 2.

Projected probability of tuberculosis (TB) infection over time for each inhabitant of a prison cell in which one infectious case is present, in Estabelecimento Penal de Corumbá (EPC) (A), Penitenciária de Três Lagoas (PTL) (B), and Unidade Penal Ricardo Brandão (UPRB) (C), Mato Grosso do Sul, Brazil, 2013. The grey lines indicate TB transmission probability for individual prison cells. The dark red lines indicate the mean TB transmission probability for each prison.

Figure 3.

The effects of improving cell ventilation and time-to-diagnosis on tuberculosis (TB) transmission probabilities by the time of infectiousness up to 180 days. Two values of ventilation scenarios are shown (A): the current estimated mean absolute ventilation (m3/hour) and the mean of improving ventilation in all cells to ≥12 air changes per hour (ACH) as recommended for airborne infection isolation rooms (AIIR). The vertical dashed line represents a 25% reduction in time to diagnosis. Three values of ventilation scenarios are shown (B): the current estimated mean absolute ventilation (m3/hour); improved ventilation rate in all cells to 60 L/s/person; and improved ventilation rate in all cells to reflect ACH under a cross-ventilation design for naturally ventilated settings.