Epidemiology of a tuberculosis outbreak in a South Carolina junior high school

A 13-year-old, female, seventh-grade student (the index patient) was found to have smear-positive, cavitary, pulmonary tuberculosis. Epidemiologic and contact investigation, involving skin testing over 900 people, revealed a 40 per cent tuberculin reactor rate for persons in the junior high school she attended compared to a 2 per cent rate for control schools. Repeat skin testing of initial non-reactors identified an additional 3 per cent of infected school children. School teachers showed a seven-fold increase in the prevalence of positive skin-test reactions following the outbreak. Tuberculin-reactor rates for seventh graders were substantially higher than for eighth graders. The more classes shared with the index patient, the higher the probability of being a reactor. Among students who shared no classes with the index patient, the highest rates of tuberculin reactions were found for those who had entered a classroom immediately after the index patient had left it. Evidence of transmission on the school bus and in the church choir was also suggested. Six secondary cases (three pulmonary) resulted from the outbreak. Identical phage types from the index and secondary patients suggest that this was a common-source outbreak. Follow-up of students who had left school during the term proved useful in determining when transmission began. The index case was found to be a missed contact of a previously identified case of tuberculosis. Since household contacts are at high risk for developing active disease, there is a need for meticulous and complete investigation and preventive therapy for all such persons, especially children.