Skin tuberculin test (STT) for screening tuberculosis in contacts of tuberculosis patients

INTRODUCTION: Many studies have underlined the theorical and practical role of Skin Tuberculin Test (STT) as an important tool for the diagnosis and for the screening of tuberculosis in the population. PATIENTS AND METHOD: This prospective study evaluated STT in 51 smear positive tuberculosis patients and 108 contacts tuberculosis patients apparently in a good health condition. Twenty seven patients have disappeared before the end of the study and 7 patients were excluded for non suitable results. So we analysed only 73 cases. RESULTS: The mean age was 34 years, with extreme of 1 and 77 years. There were 33 male and 40 female patients for a sex-ratio of 0,8. BCG vaccination scar was found in 64% of patients. We calculated the Body-Mass-Index and we found a proteinocaloric malnutrition (BMI<18,5) in 30%. The mean diameter of STT induration was 12,3mm with extremes of 7 and 20mm. Considering a STT < 7 mm as negative, 4 patients (5%) had a negative STT and 69 (95%) a positive STT. 13 of these 69 patients had a STT > 15mm. The age group of the 10 to 50 years had more positive STT. Meanwhile, according to the sexe and to the nutritional status, there was no statistical difference. All patients with a negative STT received BCG vaccination after 2 months of follow-up. Those with STT>15mm were examinated and had a chest X-ray the day of their enrolment, at the second month and at the sixth month and we didn't find any evolutive tuberculosis. CONCLUSION: According to these results, we can conclude that STT is not an important test for the screening of pulmonary tuberculosis in contact patients. Clinical examination, chest X-ray and sputum smear remain very important for the diagnosis. Despite these results, STT remain the only validated technic between the different tuberculin tests. Its interest was twofold: the research of an acquired immunity against tuberculosis after BCG immunisation and it is clinical test for the diagnosis of tuberculosis in children.