Outbreak of tuberculosis in a closed setting: views on transmission based on results from molecular and conventional methods.

This study describes an outbreak of tuberculosis (TB) in a nursing home for men with mental disorders where residency is lengthy or permanent. This type of setting can provide a model of transmission as contact with the rest of society is extremely limited.To determine if cases of TB, diagnosed around the same time and in the same place, are linked based on results using molecular and conventional methods.The strains of Mycobacterium tuberculosis were analysed by drug resistance testing and mycobacterial interspersed repetitive units-variable number tandem repeats (MIRU-VNTRV). Microbiological results were related to clinical history and time of diagnosis.Nine patients were diagnosed with TB, and strains were recovered from seven of these patients. Unexpectedly, the strains with the same genotype showed different patterns of resistance, and only two strains demonstrated identical patterns. MIRU-VNTR analysis demonstrated that one patient was infected with two different strains.Variation between the strains indicates that the outbreak may have arisen from several sources of infection. The variation in resistance indicates that rapid emergence of antimicrobial resistance is possible. As such, several questions are raised concerning source of infection, development of disease, resistance and mixed infections.