HOW TO SCREEN CONTACTS OF A TUBERCULOSIS CASE

Ln France, where the annual risk of infection has become relatively low, screening for secondary cases of tuberculosis or recent tuberculous infections among persons in contact with a tuberculosis case may be efficient, provided it is well targetted. The investigation should be guided by the following elements : 1) contagiosity of the case : pulmonary tuberculosis cases with positive sputum smears (direct microscopy) are the most contagious; 2) closeness of contacts : subjects in close contact with the case have a high risk of being infected and of developing disease; 3) characteristics of contact subjects : young children, adolescents and immunosuppressed (particularly HIV-infected) persons are the most susceptible subjects. Looking for the source of infection is also warranted if the tuberculosis case is Likely to have developed following a recent infection (tuberculosis in a young child or adolescent). Close contacts should be investigated first. Screening tools include clinical examination, chest X-ray (for screening of tuberculosis) and tuberculin skin test (for screening of tuberculous infection). When a tuberculinic conversion (i.e., an increase in induration size of at least 10 mm within 2 years) cannot be demonstrated, a 10 mm cut-off point can be used as an argument in favour of a tuberculous infection for patients in contact with a contagious case of tuberculosis. These results together with other elements (characteristics of the contact subject, epidemiological factors) can be used to discuss the usefulness of prescribing preventive chemotherapy.