A community and workplace outbreak of tuberculosis in Hawke's Bay in 2002

To describe a community and workplace outbreak of tuberculosis in Hawke's Bay in 2002.

Contact tracing and case definitions used in this study followed New Zealand guidelines for tuberculosis control. DNA fingerprinting of Mycobacterium tuberculosis isolates was performed by restriction fragment length polymorphism (RFLP).

19 new cases of active tuberculosis disease (TBD) and 42 cases of latent tuberculosis infection (LTBI) were diagnosed. 55 family and close associates of the index case were investigated, of whom 9 (16.4%) had TBD disease and 11 (20.0%) had LTBI. 139 co-workers on the same work shift were investigated of whom 8 (5.8%) had TBD and 27 (19.4%) had LTBI. DNA typing of Mycobacterium isolates (from 4 TBD cases) confirmed that this was an outbreak of 'Rangipo'-strain TB.

High infection rates were observed among family, close associates, and workplace contacts. Several factors may have contributed to this high infection rate--ie, delays in presentation and contact tracing, the use of positive pressure ventilation and re-circulated unfiltered air, and virulence of this strain of Mycobacterium tuberculosis. Inadequate adherence to TBD treatment precipitated this outbreak and reinforces the recommendation that TBD cases (in whom risk factors for non-adherence are present) should receive directly observed therapy (DOT) or at least by close supervision. Further research into strain characteristics is required in order to determine if the Rangipo-strain of TB is truly more virulent and if contact tracing or treatment regimes need to be modified accordingly.