Tuberculous infection in nursing students. Prevalence and conversion during a 3 years follow-up

BACKGROUND: The aim of this study was to ascertain the positive tuberculin prevalence among the nursing students at the beginning of their studies; to assess the annual tuberculin conversion rate during their studies; to obvi ate the possibility of false conversions, studying the booster effect. PATIENTS AND METODS: Cohort study, prospective, 3 groups not parallels (n = 316), 32 months follow-up in all students. Mean age 21 years (SD = 4; rang e = 17-39). First phase: before beginning clinical practice, a tuberculin t est was undertaken by Mantoux technique with PPD type RT-23 with Tween 80 o f 2 TU; this was repeated after 7-10 days, to BCG vaccinated and PPD negati ve on the first one, to study the booster effect. Second phase: at 18 month s we repeated the tuberculin test to PPD negatives including the vaccinates with booster effect but PPD negative. The end of the study was at 32 month s, repeating the test to PPD negatives at the end of their nursing studies. RESULTS: Tuberculin prevalence of 12% (38/316); CI 95%: 8.4%-15.6%. There w ere no significant differences of prevalence between vaccinated and unvacci nated nurse students. The prevalence in women was 8.9% (24/267) and 28.6% ( 14/49) in men, The only variables with statistical significance for being t uberculin positive were, age (p = 0.002) and sex (p = 0.003). 3/42 vaccinat ed with BCG (7%) had initial PPD (+); 2/39 of the remaining (5%) showed to be tuberculin positive after the booster effect and 37 tuberculin negative and booster negative. In the conversion study there were 259 valid students at the end of 3 years; there were 14 (5.4%) converters in the second year and 9 (3.5%) in the third year. Tuberculin conversion annual rate was 3.8 p er 100 people/year. CONCLUSIONS: The tuberculous infection prevalence in nursing students was 1 2% (38/316). The annual frecuency of tuberculin conversion (3.8 per 100 peo ple/year) was higher in our students than in the general population, reinfo rcing the suitability of making periodical tuberculin control tests in PPD negative student nurses with continuous hospital contact.