Contact screening procedures for tuberculosis in Auckland.

A five year audit of tuberculosis notifications for the three Auckland health districts revealed that 10.7% of notifications were the result of contact screening procedures. Most notifications from this source were children (73.2%) up to 16 years of age. By far the greatest yield from contact screening procedures was among contact of patients with infectious pulmonary tuberculosis (whose sputum is smear positive on direct microscopy): 78.8% of cases found by contact procedures were contacts of these infectious patients. The yield was particularly high for children who were close contacts of these cases: 23.8% of such children were considered to be infected by tubercle bacilli compared with only 1.1% of children who were casual contacts of these infectious cases. Few adults were found by contact procedures because: (a) only those with pulmonary disease were found, whereas among children all those who had been infected, the majority of whom had not developed tuberculous disease (so-called primary occult tuberculosis) were found, and (b) many adult contacts of smear positive pulmonary index cases were not followed with chest radiographs for long enough: only one half had six months of surveillance. By restricting contact screening procedures to contacts at highest risk the workload could be substantially reduced with minimal reduction in the yield of new cases.