Post-exposure rate of tuberculosis infection among health care workers measured with tuberculin skin test conversion after unprotected exposure to patients with pulmonary tuberculosis: 6-year experience in an Italian teaching hospital

BACKGROUND: This study assesses the risk of LTBI at our Hospital among HCWs who have been exposed to TB patients with a delayed diagnosis and respiratory protection measures were not implemented. METHODS: All HCWs exposed to a patient with cultural confirmed pulmonary TB and respiratory protection measures were not implemented were included. Data on TST results performed in the past (defined as T0) were recorded. TST was performed twice: first, immediately after exposure to an index patient (T1) and three months later (T2). The period of time between T0 and T1 was used to calculate he annual rate of tuberculosis infection (ARTI), while le period of time between T1 and T2 was used to calculate the post exposure annual rate of tuberculosis infection (PEARTI). RESULTS: Fourteen index patients were admitted; sputum smear was positive in 7 (58.3%), 4 (28.6%) were non-Italian born patients. 388 HCWs were exposed to index patients, a median of 27 (12-39) HCW per each index patient. One hundred eighty (46.4%) HCWs received BCG in the past. One hundred twenty two HCWs (31%) were TST positive at a previous routine screening and not evaluated in this subset. Among the remaining 255 HCWs with negative TST test in the past, TST at T1 was positive in 11 (4.3%). ARTI was 1.6 (95% CI 0.9-2.9) per 100 PY. TST at T2 was positive in 9 (3.7%) HCWs, that were TST negative at T1. PEARTI was 26 (95% CI 13.6-50) per 100 PY. At univariate analysis, older age was associated with post exposure latent tuberculosis infection (HR 1.12; 95% CI 1.03-1.22, p=0.01). CONCLUSIONS: PEARTI was considerably higher among HCWs exposed to index patients than ARTI. These data underscore the overwhelming importance of performing a rapid diagnosis, as well as implementing adequate respiratory protection measures when TB is suspected.