Epidemiology of a tuberculosis outbreak in a rural Missouri high school

1) Demonstrate the importance of maintaining a tuberculosis (TB) control program even in low-incidence areas by studying a TB-contact investigation of a highly infectious high school student in rural Missouri, and 2) discuss factors that perpetuated or contained this school-based outbreak.

A case review of the index patient, a 15-year-old high school student, established estimates of his level and duration of infectiousness. Contact investigations of his household (n = 5), high school (n = 781), and school bus (n = 67) were administered according to guidelines established by the Centers for Disease Control and Prevention. High school students were stratified further based on classroom exposure, and relative risks were calculated for each risk group.

The case review revealed that the index patient had evidence of a pulmonary cavity on chest radiograph 6 months before his TB diagnosis. Of the 5 household contacts, all were infected and 3 (60%) had developed active TB disease. Of the 781 high school students sought for TB screening, 559 (72%) completed testing, and 58 (10%) were PPD-positive. Sixty-seven bus riders were sought for testing and 7 (19%) were purified protein derivative (PPD)-positive, with 1 bus rider subsequently diagnosed with active disease. Risks were calculated based on classroom and bus exposure to the patient. The relative risks for a positive PPD were 3.2 for attending any class with the patient (n = 25), 4.2 for classes with less ventilation (n = 21), and 5.7 for > or =3 classes (n = 7) with the patient. A total of 62 students started treatment for latent TB infection, and 49 have completed it. Forty-two of these students received directly observed therapy through the local public health agency and the high school.

This investigation demonstrated widespread adult-type transmission from a pediatric TB case with a 6-month delay in diagnosis. Several actions contributed to the success of this investigation, including rapidly mobilizing the public health system, centralizing follow-up, and on-site testing and treatment with directly observed therapy. Pediatricians need to maintain awareness of TB and risk factors in children, even in low-incidence areas. Prompt diagnosis would have reduced the severity of illness in the patient and potentially prevented widespread school-based transmission. Public health authorities must maintain an infrastructure to respond to large TB outbreaks.