Mycobacterium tuberculosis transmission among high school students in Greece

Background: The aim of this study was to investigate the requirements and practical steps for screening of Mycobacterium tuberculosis (MTB) transmission among high school student populations in two regional high schools of central Greece. Case-matched control populations from other regional schools were included. Methods: Case study of two indexed cases, 61 close contacts, 212 casual contacts and 369 controls were investigated. Detailed questionnaires, tuberculin-skin test (PPD test), chest radiography, medical evaluation and DNA fingerprinting of sputum isolates were used. Results: In case A, three (1.97%) of 152 close and casual contacts developed tuberculosis, and a further 25 (16.4%) were classified as infected. In contrast, none of the 121 close or casual contacts investigated for Case B developed tuberculosis or were classified as infected. None of the control populations contained infected individuals. Contacts of case A had a much higher risk (3.08 < RR = 22.29 < 161.69, P < 0.001) of being infected than contacts of case B. Two different strains of MTB were found responsible for these outbreaks. Conclusion: There was a considerable difference in the infectivity of the two cases presumably due to environmental and clinical factors, although two different MTB strains were responsible. It is proposed that the extent of case investigation should be individualized with particular emphasis placed among close contacts