Testing a School After TB Exposure: How One Illinois County Reached 92% of Contacts, 2025

Summary

• Finding and testing the contacts of someone with infectious tuberculosis (TB) is how new cases are caught and latent TB infection (LTBI) is kept from progressing.
• In March 2025, the Lake County Health Department and Community Health Center in Illinois learned of a case of pulmonary TB in a person who had been at a local school while infectious.
• Guided by the school, it tested 143 of 155 school contacts (92%), finding eight with LTBI and no TB disease. A flexible, trust-building approach made it work.

The case and the community

The case was reported on March 18, 2025; the person had been at the school from November 6, 2024, through March 17, 2025. Lake County's TB rate in 2024 (2.5 per 100,000) was below Illinois's (2.7) and the nation's (3.0). The school is in a federally designated medically underserved area, where 30.9% of residents are foreign-born, 17.3% live in poverty and 15.5% lack health insurance; 94% of households have computers but 14% lack internet. During COVID-19, shifting guidance, limited bilingual communication and unequal resources had deepened mistrust of government.

Finding the contacts

The investigation identified 166 close contacts: 156 at the school (148 students and eight staff), four in the household and six health care workers.

• Household: one moved out of state and couldn't be found; the other three had LTBI (one already treated, two started treatment).
• Health care workers: all six tested negative through their employer.

Working with the school

The department first planned to test at the school, but the school warned that families worried about stigma and privacy, and that visible signs — staff in respirators, health department vehicles — could cause panic. So testing moved to the health department. Emails drew few replies, but on the school's advice staff phoned and texted families, and almost every contact was scheduled. The TB clinic also offered appointments outside the testing events.

Two rounds of testing

Following CDC recommendations, contacts who first tested negative were tested again, so that everyone had a result at least 8 weeks after exposure.

• First event, April 2–3: one school contact was already on LTBI treatment, leaving 155 to test. 147 (95%) were tested: 140 negative and seven positive by interferon-gamma release assay (IGRA), who began LTBI treatment.
• Second event, May 13, 14 and 19: of 148 people due for testing (the 140 negatives and eight missed the first time), 136 (92%) were tested — 135 negative, one positive.
• Overall: 143 of 155 school contacts had results at least 8 weeks after exposure, beating CDC's 90% target. Eight (5.2%) had LTBI and began treatment; no one had TB disease. Of the other 12, two samples deteriorated, and ten refused retesting or didn't respond.

Contact identification, testing and results. Figure from the CDC report.

What made it work

Recognizing barriers to parents' engagement, staying flexible, and persistent, respectful outreach with transparent communication — including bilingual messages, spoken education, testing away from the school and flexible hours — built the trust that got families tested.

Sources

Based on Amy Zun, Nicolette Meyer, Denise Flores and others (Lake County Health Department and Community Health Center), "Notes from the Field: Maximizing Tuberculosis Testing After a School-Based Exposure — Lake County, Illinois, 2025," MMWR, Centers for Disease Control and Prevention; published by CDC and in the public domain; rewritten in hubnx's own words.