The infectiousness of tuberculosis patients coinfected with HIV
A Roderick Escombe1, David A J Moore, Robert H Gilman
1Department of Infectious Diseases and Immunity, Imperial College London, United Kingdom. rod.escombe@imperial.ac.uk
Background:
The current understanding of airborne tuberculosis (TB) transmission is based on classic 1950s studies in which guinea pigs were exposed to air from a tuberculosis ward. Recently we recreated this model in Lima, Perú, and in this paper we report the use of molecular fingerprinting to investigate patient infectiousness in the current era of HIV infection and multidrug-resistant (MDR) TB.
Methods And Findings:
All air from a mechanically ventilated negative-pressure HIV-TB ward was exhausted over guinea pigs housed in an airborne transmission study facility on the roof. Animals had monthly tuberculin skin tests, and positive reactors were removed for autopsy and organ culture for M. tuberculosis. Temporal exposure patterns, drug susceptibility testing, and DNA fingerprinting of patient and animal TB strains defined infectious TB patients. Relative patient infectiousness was calculated using the Wells-Riley model of airborne infection. Over 505 study days there were 118 ward admissions of 97 HIV-positive pulmonary TB patients. Of 292 exposed guinea pigs, 144 had evidence of TB disease; a further 30 were tuberculin skin test positive only. There was marked variability in patient infectiousness; only 8.5% of 118 ward admissions by TB patients were shown by DNA fingerprinting to have caused 98% of the 125 characterised cases of secondary animal TB. 90% of TB transmission occurred from inadequately treated MDR TB patients. Three highly infectious MDR TB patients produced 226, 52, and 40 airborne infectious units (quanta) per hour.
Conclusions:
A small number of inadequately treated MDR TB patients coinfected with HIV were responsible for almost all TB transmission, and some patients were highly infectious. This result highlights the importance of rapid TB drug-susceptibility testing to allow prompt initiation of effective treatment, and environmental control measures to reduce ongoing TB transmission in crowded health care settings. TB infection control must be prioritized in order to prevent health care facilities from disseminating the drug-resistant TB that they are attempting to treat.
Insights
A small number of inadequately treated multidrug-resistant tuberculosis (MDR TB) patients, often with HIV, caused most airborne TB transmission. Rapid testing and treatment are crucial for infection control in healthcare settings.
Area of Science:
- Infectious Diseases
- Microbiology
- Public Health
Background:
- Classic 1950s studies informed current understanding of airborne tuberculosis (TB) transmission.
- This study recreated a guinea pig model to investigate TB transmission in the era of HIV and multidrug-resistant TB (MDR TB).
Purpose of the Study:
- To investigate patient infectiousness in airborne tuberculosis transmission using molecular fingerprinting.
- To identify factors contributing to TB spread in healthcare settings.
Main Methods:
- Air from a negative-pressure HIV-TB ward was exhausted over guinea pigs.
- Molecular fingerprinting (DNA fingerprinting) and tuberculin skin tests identified infectious patients and TB transmission events.
- The Wells-Riley model was used to calculate relative patient infectiousness.
Main Results:
- A small fraction of patients (8.5%) caused 98% of secondary TB cases in guinea pigs.
- Inadequately treated MDR TB patients accounted for 90% of TB transmission.
- Three highly infectious MDR TB patients generated significant airborne infectious units per hour.
Conclusions:
- A few inadequately treated MDR TB patients coinfected with HIV were the primary source of TB transmission.
- Highlights the critical need for rapid drug-susceptibility testing and effective treatment initiation.
- Emphasizes the importance of environmental controls and prioritizing TB infection control in healthcare facilities to prevent dissemination of drug-resistant TB.
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