Prevalence of sensitivity to tuberculin and histoplasmin among high school students in Montgomery County, Maryland.

Skin testing with tuberculin and histoplasmin was combined with the annual roentgenographic examination of high school students in Montgomery County, Maryland, during the spring term of 1957. More than 3,200 students participated in the program. The tests were given by intracutaneous injection of a 5 TU dose of standardized tuberculin and a 1:100 dilution of histoplasmin H-42. Reactions were read in 48 to 72 hours by measuring the transverse diameter of induration. Photofluorograms of the chest were read without knowledge of the results of the skin test. The prevalence of tuberculin sensitivity was found to be very low among white students throughout the county. It was estimated that only about 3% of the students had reactions indicative of a tuberculous infection. Histoplasmin sensitivity was many times more prevalent than tuberculin sensitivity and, moreover, showed striking differences in sections of the county no more than 20 miles apart, ranging from about 14% in the suburban schools in the southeast to more than 60% in the rural northwest. Pulmonary calcifications were most frequently associated with sensitivity to histoplasmin, occasionally with sensitivity to both histoplasmin and tuberculin and in no instance with sensitivity to tuberculin only.