Development of tuberculin reactivity and sensitization to M. Scrofulaceum and M. Fortuitum in children BCG-vaccinated at birth

Since the incidence of tuberculosis is steadily declining in Finland and in fections by environmental mycobacteria may be increasing, the aim of the pr esent study was to evaluate the development of tuberculin reactivity and se nsitization to environmental mycobacteria, Healthy Finnish schoolchildren aged 10.4-12.4 yrs (n=201) were tested with tuberculin purified protein derivative RT23, Mycobacterium scrofulaceum RS9 5 and M. fortuitum RS20 sensitins, The same children had been previously te sted with the same antigens and methods at the age of 4-6 yrs in 1989. Rapi d waning of tuberculin reactivity and decrease in sensitization to environm ental mycobacteria were observed between 4-6 yrs. Both tuberculin and sensitin skin reaction sizes decreased significantly ov er the 6-yrs period. The mean tuberculin skin reaction size was 3.2 mm in d iameter, which was significantly (p<0.001) smaller than the mean induration size (4.8 mm) at the age of 4-6 yrs. Similarly, the mean skin reaction siz es to M. scrofulaceum and M. fortuitum sensitins were 3.4 and 1.7 mm, respe ctively, which were significantly (p<0.001) smaller than 6 yrs earlier (mea n 4.5 and 3.1 mm), The number of zero reactions to all antigens increased s ignificantly during the follow-up period. Contacts with pets or farm animal s were associated with larger reactions. In contrast, children suffering fr om allergic symptoms had smaller reactions. Contacts with mycobacteria, either with Mycobacterium tuberculosis or envir onmental mycobacteria, seem to be too rare to maintain tuberculin responsiv eness and a high sensitivity to other mycobacteria. Different bacille Calme tte-Guerin vaccine products and dosages used, the declining incidence of tu berculosis and geographical factors, which can influence environmental myco bacterial exposure, may explain the disparity between the present and previ ous Finnish studies.