Factors Associated With Tuberculin Conversion Among Staff at a University-Affiliated Hospital

To the Editor:Early identification of tuberculosis (TB) conversion among hospital workers is the cornerstone by which the quality of TB control measures can be evaluated.Moreover, regular screening identifies newly infected individuals, who are most likely to develop the disease during the 2 years following infection, 1 allowing timely chemoprophylaxis.The aim of this study was to determine the incidence of, and factors associated with, tuberculin conversion at a university-affiliated hospital.A retrospective cohort was compiled from staff at the University Hospital Puerta del Mar, Cadiz, Spain, from January 1989 through July 1996.This is an 850-bed tertiarycare facility with a staff of 2,700 and 24,000 admissions per year.Workers were classified as belonging to a high-risk work area if they had been employed for at least 1 year in the infectious diseases, pulmonary, or medicine unit; emergency department; adult intensive-care unit; pathology; or hematology.All 400 staff who were skin-test negative in January 1989 or who tested negative from that date through July 1996 were included in the study.The test was read by the presence or absence of induration, as determined by palpation, 72 hours after inoculation, and the diameter of the induration was measured.The tuberculin skin-test (TST) conversion rate was defined as representing an increase of 10 mm or more in induration, with respect to that of any test carried out in the previous 2 years.From this information, Kaplan-Meier curves were drawn for each of the independent variables.Log-rank testing was used to compare the incidence density of the conversion among the groups.Cox's