Case finding during an outbreak of tuberculosis in a homeless shelter − Illinois, 2010

Background: Homeless shelters are high-risk settings for tuberculosis transmission and present unique challenges for outbreak control. From November 2009- May 2010, an outbreak of tuberculosis with a matching genotype pattern occurred among residents and staff of a homeless shelter in Illinois.

Methods: Outbreak associated cases were defined as cases with a genotype matching the outbreak strain and an epidemiologic link to the shelter. Culture negative cases with an epidemiologic link to the shelter were also classified as outbreak-associated. Strategies for identifying active cases included mass screenings, alerting of local physicians and laboratories, and ongoing “cough watch” by shelter staff. Direct costs of mass screening events were calculated using billing data and health department records.

Results: Among 760 exposed residents, 18 residents with active tuberculosis were identified. During three mass screenings, 481 residents and 137 staff were evaluated using symptom screen, QuantiFERON Gold in-tube assay, chest x-rays and sputum smear and culture. Sixteen cases had genotype-matched isolates. Two cases were culture negative. Two cases were identified at the screening events, seven through the cough watch and nine in the community. Four-hundred (52.5%) potentially exposed residents did not attend any screening, including two residents later identified as cases. The mass screenings cost approximately $40,000, excluding the cost of sputum testing and staff time.

Conclusion: Difficulty reaching exposed residents, due to transiency and low participation, reduced the yield of mass screening events. In this homeless shelter outbreak, well-informed local providers and symptom screening by shelter staff identified more cases than resource-intensive mass screenings.