BACKGROUND: Since the first years of antituberculosis chemotherapy, there has been controversy regarding the transmissibility, infectiousness, virulence and pathogenicity of susceptible and drug-resistant strains of Mycobacterium tuberculosis. OBJECTIVE: To determine the incidence of active tuberculosis (TB) among individuals cohabiting with patients infected with susceptible and multidrug-resistant tuberculosis (MDR-TB). METHODS: A case-control study was conducted. Cases of MDR-TB were defined as those infected with M. tuberculosis strains resistant to at least rifampin and isoniazid. Susceptible TB cases (controls) were defined as those first treated at approximately the same time as the first treatment of the MDR-TB cases - and cured by the time of the interview. Study cases were selected on the basis of the results of susceptibility tests, using the proportion method, carried out at the Central Laboratory of Public Health of the State of Ceará. The control group consisted of patients enrolled in the Tuberculosis Control Program between 1990 and 1999. RESULTS: We evaluated 126 patients and 176 controls. The number of individuals sharing the household with patients was 557 in the MDR-TB group and 752 in the controls. The average number of exposed individuals per index case was 4.42 and 4.27 among patients and controls, respectively. Of the 557 MDR-TB-exposed individuals, 4.49% (25) received antituberculosis treatment after the respective index case had begun treatment, compared to 5.45% (41/752) among the controls (p = 0.4468). Microepidemics of MDR-TB were confirmed in eight families. CONCLUSION: Our results suggest that the incidence of active TB is comparable between households inhabited by MDR-TB patients and those inhabited by susceptible-TB patients.
Tuberculosis, multidrug-resistant; Tuberculosis
