Number of live organisms in BCG vaccine and other related factors in tuberculin skin reaction

Background: With respect to the prevalence of tuberculosis in our country, BCG vaccination at birth seems to be an effective means of prevention. The present study was designed to evaluate the efficiency of BCG vaccination and factors influencing the tuberculin skin reaction. Materials and methods: The inoculum of live BCG organisms in vaccinated infants was evaluated at birth and the correlation between the amount of CFU and PPD reaction was examined 3 months later. For this purpose, 854 newborn infants were included. PPD induration diameter was measured 72 hours after the tuberculin skin test. Results: Results have revealed that most of the vaccine samples contained more than 3 million live organisms. Vaccines showing more than 3×106 live organisms were associated with positive tuberculin skin test in more 93% of cases as compared with 69% positive induration of vaccines with less than 3×106 live organisms. Breast-fed infants showed more positive reaction to tuberculin skin test. Conclusion: The number of live organisms in vaccines can play an important role in the size of tuberculin skin reaction.