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.