[Infectiousness and virulence of multidrug-resistant and drug susceptible tuberculosis in adult contacts].

Patients carrying multidrug-resistant (MDR) strains of Mycobacterium tuberculosis have been considered traditionally as presenting a diminished epidemiological risk according to animal experimentation results. The experience obtained from the MDRTB/AIDS related epidemics showed MDRTB transmission to immunocompetent health care workers and adults close contacts. In this retrospective study, the infectiousness (measured as the frequency of intradermal test with PPD 2TU over 10 mm) and virulence (cases bacteriologically confirmed) among close contacts of patients with MDR and susceptible TB were evaluated. A total of 97 contacts of 37 MDRTB patients vs. 356 contacts of 100 patients with susceptible TB were studied. No statistical differences were found in PPD 2 UT positivity and TB cases between both contact groups, nor in relation to HIV seropositivity of index cases. According to these observations, MDR strains of M. tuberculosis present similar infectiousness and virulence compared with susceptible strains.