Reviewed by: Tyler Stephen, MD, University of Rochester Medicine
This systematic review analyzed 86 studies on the transmission of Mycobacterium tuberculosis in healthcare settings, encompassing 1083 index patients, 35,698 exposed individuals, and 2,517 secondary cases. The studies reviewed for this paper covered a diverse range of healthcare settings, though most were from acute care hospitals.
In their meta-analysis of 31 studies, the duration of exposure without PPE was associated with increased risk of transmission to both other patients and healthcare personnel (HCP). The median exposure time of HCP who developed secondary infections was 24 hours. The few studies that described shorter transmission times were all associated with “high-risk” scenarios such as rooms without any ventilation, thoracic surgery, bronchoscopy, and autopsy. Secondary cases amongst patients followed a similar pattern with duration of exposure. Secondary cases rarely occurred after less than 8 hours of exposure; 93% occurred after 8 or more hours.
Proximity of exposure was also associated with transmission in studies that reported this, with secondary cases amongst HCP more common in direct than in indirect patient care. Across all studies that reported on masking among HCP, the rate of secondary cases was similar among HCP who wore no mask and those who wore a surgical mask. One study comparing rates in units where surgical masks were common with those where they were not found fewer secondary cases when surgical masks were common. Overall, no HCP developed a secondary case while wearing a respirator. The frequency of room air changes was also noted to be protective, with no secondary cases reported in rooms with 12 or more air changes per hour.
From their analysis, the authors conclude that 8 hours of exposure may be a reasonable time frame for defining exposed persons in an exposure investigation and identify other key factors to consider. This time frame is similar to the period generally used for investigations of air travel exposure, as recommended by the WHO. The present paper otherwise provides an excellent review of existing studies on tuberculosis transmission in healthcare settings.
Reference:
Manzoor F, Rhee C, Baker MA, Klompas M. Mycobacterium tuberculosis Transmission in Healthcare Settings: A Systematic Review of Frequency, Risk Factors, and Exposure Conditions. Clin Infect Dis. 2026;82(5):799-807. doi:10.1093/cid/ciag053