Tuberculin reactivity in a chest clinic: the effects of age and prior BCG vaccination.

Heaf tests were performed in 834 adults and children seen during one year in a tuberculosis contact clinic in Edinburgh. All subjects with a past history of tuberculosis, or who subsequently developed evidence of tuberculous infection and 63 subjects of Asian origin were excluded to leave 749 'healthy' adults and children broadly representative of the local caucasian population. All Heaf tests in 178 children without BCG vaccination were negative or grade I whereas 16 (73%) of the 22 children with a history of previous BCG vaccination were positive grade I or II. A strongly positive Heaf test (grade III-IV) in any child with or without previous BCG vaccination seen as a tuberculosis contact implies recent infection and merits consideration for chemoprophylaxis or prolonged follow-up. Two hundred and seventy adults without previous BCG vaccination showed an increasing incidence of strongly positive Heaf tests (grade III or IV) with age reaching a peak of 55% in the 45-65 age group; beyond the age of 65 this fell to 37%. Two hundred and eighty-one adults with previous BCG vaccination showed significantly more Heaf grades I and II, fewer negatives and fewer strong positives than the unvaccinated group. A strongly positive Heaf test (III-IV) is a frequent finding in a healthy adult and has little discriminatory value in the diagnosis of active tuberculosis infection in Edinburgh, and by implication elsewhere in the United Kingdom. Positive tuberculin tests should be viewed in the context of the tuberculin profile of the local population.