Laboratory Investigation of a Nosocomial Transmission of Tuberculosis at a District General Hospital

BACKGROUND/PURPOSE: Nosocomial outbreak of tuberculosis (TB) is rarely documented and the transmission is usually difficult to confirm because of the long incubation period of the mycobacterial infection. In this report, we demonstrated the use of molecular genotyping methods together with contact tracing to identify the source case, the causative outbreak strain and transmission dynamics of Mycobacterium tuberculosis, and for the definite confirmation of a suspected outbreak. METHODS: M. tuberculosis strains were genotyped with IS6110 restriction fragment length polymorphism, spacer oligonucleotide typing and minisatellite interspersed repetitive unit–variable number tandem repeat methods. Clinical data and contact tracing results were collected from medical records and the National TB Registry. RESULTS: In this episode, 66 health care workers (HCWs) were notified as TB cases. A total of 18 M. tuberculosis isolates from HCWs and patients were collected. IS6110 RFLP results revealed that 9 out of 10 HCWs' and 7 out of 8 patients' isolates shared the same genotype. The causative isolate was identified as the Beijing genotype. The index case was a hospitalized respirator-dependent patient. CONCLUSION: Thorough collection along with molecular diagnosis and genotyping of all M. tuberculosis isolates are recommended for the confirmation of any suspected nosocomial TB outbreak.