Investigation and control of a large outbreak of multi-drug resistant tuberculosis at a central Lisbon hospital

An increase in the number of new cases of tuberculosis (TB) combined with p oor clinical outcome was identified among HIV-infected injecting drug users attending a large HIV unit in central Lisbon. A retrospective epidemiologi cal and laboratory study was conducted to review all newly diagnosed cases of TB from 1995 to 1996 in the HIV unit. Results showed that from 1995 to 1 996, 63% (109/173) of the Mycobacterium tuberculosis isolates from HIV-infe cted patients were resistant to one or more anti-tuberculosis drugs; 89% (9 5) of these were multidrug-resistant, i.e., resistant to at least isoniazid and rifampicin. Eighty percent of the multidrug-resistant strains (MDR) av ailable for restriction fragment length polymorphism (RFLP! DNA fingerprint ing clustered into one of two large clusters. Epidemiological data support the conclusion that the transmission of MDR-TB occurred among HIV-infected injecting drug users exposed to infectious TB cases on open wards in the HI V unit. Improved infection control measures on the HIV unit and the use of empirical therapy with sis drugs once patients were suspected to have TB, r educed the incidence of MDR-TB from 42% of TB cases in 1996 to 11% in 1999. (C) 2001 The Hospital Infection Society.