A Comparison of Two-Step Tuberculin Skin Test between Health-Care Workers and Nonhospital Employees

Background: The tuberculin test is widely used to identify tuberculosisinfection. Some individuals infected with Mycobacteriumtuberculosis may have an initial negative skin test reactionto tuberculin. The two step purified protein derivative skin testcan decrease misinterpretation of tuberculin test .This study wasaimed at comparing the two- step tuberculin skin test and boosterphenomenon in health care workers and non hospital employees.Methods: One hundred and eighty five health service employeesfrom Razi University Hospital and 181 non hospitalemployees were subjected to an initial tuberculin skin test.Those who were negative on the first test underwent a secondone 2 weeks later. The reactions to the tests were measured 72hours later. Tests with an induration of ≥ 10 mm was consideredpositive. Moreover, second tests with an induration of atleast 6 mm increase relative to the relevant first tests wereconsidered positive.Results: Compared to non hospital employees (n=79, 43.6%), asignificantly higher number of health care workers (n=113,61.1%) were positive on the first tuberculin test. 18.5 % of healthcare workers and 31.5% of non hospital employees demonstrateda boosted reaction after the second tuberculin test. The occurrenceof boosted reaction was significantly associated with ageboth groups. There was no association between the presence ofBCG scars and the occurrence of boosted reaction.Conclusion: the present study shows that the prevalence of TBwas higher among health care worker than non hospital employees.Moreover, it demonstrated that non hospital employeeshad a higher age-associated booster reaction to the second tuberculinskin test than health care workers. Therefore, to avoidmissing false negative cases, it would be necessary to do a secondtuberculin test for subjects with a negative reaction to theinitial test, especially in subjects older than 40 years