The Infectiousness of Tuberculosis Patients Coinfected with HIV

Department of Infectious Diseases and Immunity, Imperial College London, United Kingdom.
PLoS Medicine (Impact Factor: 14.43). 10/2008; 5(9):e188. DOI: 10.1371/journal.pmed.0050188
Source: PubMed


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.
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.
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.

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    • "resistant TB among previously treated patients are treated with category 2 regimens instead of agents designated for treating MDR-TB; this anomaly is responsible for resistant TB transmission (Escombe et al., 2008). Drug resistant TB is high among previously treated TB patients (Andrews et al., 2010) and especially previously treated HIV infected TB patients (Seithi et al., 2013) and this is capable of worsening disease progression and subsequently raising TB mortality rates. "

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    • "Quanta values are typically calculated from past outbreaks, which may be based on unreliable outbreak or ventilation data. While there are several studies that report quanta values for TB (Nardell et al. 1991; Beggs et al. 2003; Escombe et al. 2007, 2008), there are limited data for other pathogens. Values have been reported for influenza (Rudnick and Milton 2003; Liao et al. 2005), measles (Riley et al. 1978), and SARs (Liao et al. 2005), which could, with appropriate UV susceptibility data, be used to conduct preliminary assessments into effectiveness against these pathogens. "
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