Mycobacterium tuberculosis transmission from patients with drug-resistant compared to drug-susceptible TB: a systematic review and meta-analysis

The extent to which drug-resistant (DR) Mycobacterium tuberculosis strains cause infection and progression to tuberculosis (TB) disease in comparison to drug-susceptible (DS) strains is unknown. Studies in guinea pigs and in vitro experiments have suggested a reduced fitness of organisms that harbour mutations that confer drug resistance [1, 2]; it was therefore believed that transmitted drug resistance was a rare event. However, more recent work using molecular typing has shown transmission events occurring in the context of DR-TB [3]. Understanding the risk of transmission, infection and progression to disease in the context of DR-TB is important to guide control measures and help predict the evolution and magnitude of the multidrug-resistant (MDR)-TB epidemic. Hence, we performed a systematic review and meta-analysis to assess whether M. tuberculosis transmission and progression to TB disease (risk/rate of M. tuberculosis infection in all contacts, risk/rate of TB disease in all contacts and risk/rate of TB disease in infected contacts) differ between DR- and DS-TB.