Background & Objective: Control of TB is regarded as a health priority program in underdeveloped countries, and Iran in no exception in this regard. Annual risk of infection (ARI) is an important index in this program. This index shows the percentage of people in a society who have been contaminated, and consequently their skin test has changed from negative to positive. In this study, Tuberculin skin test is conducted on Ardabil primary school students and its changes, if any, after one year have been regarded using renewed skin test in order to show ARI in this age group.

 Methods: 780 students were selected from among 17 primary schools using simple random sampling method. They were 8-14 years old, (mean 9.92). Tuberculin skin test was performed on all subjects two times with a one- year interval (May 1998-1999). The test results were recorded and analyzed. In this study PPD over 10 mm was considered positive.

 Results: In 55 (7.1%) students the test was positive in both tests, and in 33 (4.2%) students, PPD changed from negative (first time) to positive (second time) and in 78 subjects the results were doubtful. 765 students (98.1%) had history of BCG vaccination.

 Conclusions: This study indicated that, firstly, over the time, BCG has little effect on Tuberculin skin test, and secondly, the high rate of tuberculin skin test changes from negative (first time) to positive (second time) represents probability of severe contamination in this area.

  Background & Objectives: Since 1985 because of increasing incidence of tuberculosis (TB) in HIV background, the outbreaks of TB have been reported in different parts of the world. From 1985 to 1991 the incidence of TB increased by 18% in United States and Europe. In Multi Drug Resistant outbreaks of TB in United States 18 to 35% of heath care workers (HCW) who had exposure to TB patients had PPD Converted to positive test (Seroconversion). That is why the risk of TB incidence in health care workers has been put forward again. This study was designed to determine the rate of Buali hospital HCW exposure to mycobacterium tuberculosis.

 Methods: All 96 HCW of Buali hospital took part in this cross-sectional and analytical study. No PPD test was performed for HCW in this hospital in the beginning of their employment. For this reason 30 officers who had not previously worked in hospital wards and 60 medical students who had not started their clinical course were selected to obtain an estimation of PPD test before starting professional nursing.

  Results: Out of 96 subjects, 72 were female and 24 were male. Rate of positive PPD was 50% in general. Data analysis showed that PPD positivity was in direct relationship with number of working years in hospital. In 60 university students whose mean age was 21.6± 0/2.9 PPD positivity rate was 13.3%. I the third group consisting of 30 office workers (mean age=333±6.5) it was 23.3%.

 Conclusion: This study shows that HCW with 50% of PPD positivity are in exceeding probability of mycobacterium tuberculosis exposure, which is almost twice as much as the other office workers, possibility of exposure.

  Background and Objective: Intradermal Purified Protein Derivative PPD test is a reliable test assessment of primary mycobacterial infection. In this test the specific antigen is Purified Protein Derivative (PPD). The reaction were assessed by touching, the induration's diameter after 48 &48hours. We compared the induration's size 48 and 72 hour in this study.

  Methods: At this semi experimental study a 5 unit PPD was administered to 120 healthy medical students.

  Results: The measurements made at 72 h were significantly (4.22 mm) (p<0.001) higher than those made at 48h (2.79 mm). The reading taken at 72 h were 1.47mm larger than at 48 h recovery. There were significant differences between induration size of 48 and 72h between male and female.

  Conclusion: This study demonstrates that, in adults, the size of the 5 U Monteux reaction is significantly larger at 72h compared to the reaction at 48h. We suggest to read PPD after 72 hours if the PPD is negative after 48 hours.