An outbreak of multidrug-resistant tuberculosis involving HIV-infected patients of two hospitals in Milan, Italy

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To describe an outbreak of multidrug-resistant tuberculosis (MDR-TB), amongst HIV-infected patients, spread from one hospital in Milan to another. Descriptive epidemiological investigation and molecular typing. All cases identified by intensive case-finding were described in terms of clinical characteristics, previous nosocomial exposure to an infectious MDR-TB patient, previous stays in other institutional settings where exposure to MDR-TB could have occurred, and restriction fragment length polymorphism (RFLP) pattern. Between October 1991 and July 1995, 116 cases of MDR-TB were identified (85 at hospital A and 31 at hospital B). A single case patient, infected at hospital A, introduced the strain into hospital B. Eighty-two of the 92 strains available for fingerprinting revealed an identical pattern; 10 strains had unique RFLP patterns. Nosocomial exposure to an infectious MDR-TB patient was ascertained for 39 of the 56 patients with the 'outbreak' RFLP strain at hospital A (69.6%) and for 24 of the 26 patients at hospital B (92.3%). The median duration of exposure was 32 days at hospital A and 40 days at hospital B. For eight patients with the outbreak strain, exposure was determined to have probably occurred in other hospitals, in the community or in prison. This is the largest nosocomial outbreak of MDR-TB reported in Europe. Exposure to MDR-TB cases in other institutions caring for HIV-infected patients probably contributed to the spread of this epidemic. Strict control measures should be immediately adopted in order to prevent the spread of TB amongst HIV-infected patients in institutional settings in Europe.