Under the Health (Protection) Amendment Act 2016, the medical ofﬁcer of health is given wide powers to investigate and control all TB cases and their contacts, while district health boards are required to make provision for the treatment and supervision of patients and their contacts.
BCG is a relatively minor component of TB control programmes, which rely primarily on case finding of active disease, contact tracing and selective screening, and treatment of active disease and LTBI (using directly observed therapy, if necessary). The local medical ofﬁcer of health can advise on local TB control programmes, including BCG immunisation policies.
Both TB infection and BCG immunisation lead to the development of a cellular immune response, which can be detected by measuring dermal induration after the injection of tuberculin-puriﬁed protein derivative (eg, via the tuberculin skin test). A positive response to a tuberculin skin test may be an indication of current infection, previous natural infection or prior BCG immunisation.
In vitro tests have been developed to measure the release of interferon-gamma from host lymphocytes in response to well-defined antigens. The antigens used are not present in BCG strains of M. bovis or most non-tuberculous mycobacteria. Interferon gamma release assay (IGRA) has the advantage of greater specificity and convenience, but it is more expensive.25 These tests, their use and interpretation are discussed fully in the Ministry of Health publications Guidelines for Tuberculosis Control in New Zealand 20101 and Technical Guidelines for Tuberculin Testing and BCG Vaccination 1996.17 For further information, refer to these Ministry of Health publications (or the most recent editions) or the Communicable Disease Control Manual 2012.26