Routine two-step skin testing for tuberculosis in the staff of a geriatrichospital in Israel: booster and conversion rates

The objective of this study was to determine the prevalence of positive ski n tests amongst the staff of a 200 bed geriatric hospital in Haifa, Israel. By comparing the findings with those of a study performed five years previ ously, we hoped to ascertain the number of conversions which had occurred i n the period studied. This was undertaken in order to assess a new policy f rom the Israel Ministry of Health regarding skin testing for health care wo rkers. We also hoped to decide upon the frequency of skin testing required and to compare data from recent immigrants from countries with a high preva lence of TB. In 1997, we performed two-step skin testing (TSST) on 318 heal th care workers. We ascertained the number of positive reactions on the fir st and second testing and calculated the number of subjects who showed sign ificant boosting. We also compared the results to those obtained in a study in 1992 and calculated the rate of conversion. We used multivariate analys is to examine the effects of age, gender, country of origin, years in Israe l, previous BCG vaccination, previous exposure to contagious TB, work site and area of residence in the city, on the response to TSST. Between 1990 an d 1996, 655 000 immigrants from the former USSR arrived; 'recent immigratio n' was defined from that date onward. The final number of positive reaction s out of 282 subjects, who were either positive or negative on step 1 and p resented for step 2, was 171 (60%). Booster effect was not significantly associated with any of the variables e xamined. The size of reaction in TSST was related to country of origin and recent immigration. The 83 recent immigrants from the former USSR had more frequent (61%) and larger reactions (mean (sD): 9.0 (6.46)mm) than the 114 native-born Israelis with 39% positive reactions (6.2 (5.89) P=0.009). Comp arison with 1992 revealed 26 (31%) of previous negatives as positive. Conve rsion was associated with age. All conversions save one were in individuals younger than 50 years (P=0.07). In conclusion, TSST, performed to enable d etection of recent infection after exposure to contagious TB, was relevant for 40% of health care workers (HCWs). Second step testing contributed an a dditional 23% positive reactions. New immigrants had larger initial reactio ns. Conversion occurred mostly in younger workers and could be either due t o unrecognized TB in the hospital or to exposure in the community. (C) 2000 The Hospital Infection Society.