Mycobacterium tuberculosis Transmission in Healthcare Settings: A Systematic Review of Frequency, Risk Factors, and Exposure Conditions

Abstract Background Uncertainty regarding the factors that govern M.tuberculosis transmission in healthcare settings leads to broad and variable exposure definitions and low-yield contact investigations. We systematically reviewed data on M.tuberculosis transmission in healthcare to inform risk-stratification and exposure definitions. Methods We searched MEDLINE, EMBASE, CINAHL and Cochrane databases from inception through December 2024 for studies describing M.tuberculosis transmission from adult patients to healthcare personnel (HCP) or patients. We tabulated data on transmission frequency, circumstances, and risk factors. Results Of 6,695 studies screened, 86 met inclusion criteria, encompassing 1,083 source patients, 35,698 exposed individuals, and 2,517 secondary cases (7.1% overall transmission risk, 3.8% amongst studies published since the US Centers for Disease Control and Prevention last updated healthcare ventilation standards in 2005). Transmission was associated with prolonged contact between HCPs and source patients (median duration 24h, IQR 24-25h) and between patients in shared rooms (median duration 24h, IQR 12-24h), clinical care without a N95 respirator (1,232 transmissions/10,149 exposures that included data on face covering use, 12.1%), frequent direct care (185 transmissions/410 exposures, 45.1%), and lack of negative-pressure ventilation (1,906 transmissions/5,670 exposures, 33.6%). Only 8/116 (6.9%) transmissions with documented exposure durations were associated with 8h cumulative exposure and all in poorly ventilated spaces. Conclusions M.tuberculosis transmission in healthcare is uncommon, particularly in spaces that meet current healthcare ventilation standards. Risk factors for transmission include prolonged exposure, close contact, lack of respirators, and poor ventilation. Defining exposures as 8h without a respirator should identify most transmissions and could improve the efficiency of contact investigations.