Outbreak of multiple drug-resistant tuberculosis in Lisbon: detection by restriction fragment length polymorphism analysis

SETTING: Multidrug-resistant tuberculosis (MDR-TB) mainly among human immunodeficiency virus (HIV) seropositive patients in Lisbon hospitals in 1996–1997.

OBJECTIVE: Detection of transmission of MDR-TB strains and epidemic outbreaks in several hospital units in the city of Lisbon, including a prison hospital.

DESIGN: Use of restriction fragment length polymorphism (RFLP) to fingerprint isolates of Mycobacterium tuberculosis resistant to isoniazid, rifampicin, and one other drug.

RESULTS: A total of 43 MDR-TB strains were typed. Sixty-seven per cent of the patients were HIV positive, 12% were HIV negative, and the remainder had unknown HIV status. About 88% of the isolates were grouped in three genetically similar clusters, suggesting possible recent transmission. A predominant cluster (cluster A), corresponding to 72% of the cases, was found, 45% of which came from the prison hospital. Strains from this cluster were resistant to isoniazid, rifampicin, streptomycin, and sometimes ethambutol. A retrospective epidemiological investigation was conducted with respect to all patients in cluster A, and epidemiological links were established between them.

CONCLUSION: Our results suggest recent transmission of MDR-TB, mainly in HIV-positive patients, in Lisbon hospitals. Moreover, the predominant MDR-TB clustered strains were not confined to HIV-infected individuals, as they were also isolated in some immunocompetent patients.