Tuberculosis Outbreaks in the United States, 2009-2015.

Objectives: The Centers for Disease Control and Prevention provides on-site epidemiologic assistance for outbreak response when the health capacity of state, tribal, local, and territorial health departments has been exceeded. We examined recent outbreaks of tuberculosis (TB) for which health departments needed assistance.

Methods: We defined a TB outbreak as detection of ≥3 TB cases related by transmission, as suggested by routine genotyping and epidemiologic linkages. We conducted retrospective reviews of documentation from all 21 TB outbreak investigations in the United States for which the Centers for Disease Control and Prevention provided on-site assistance during 2009-2015. We abstracted data on patients' demographic characteristics and TB risk factors, as well as factors contributing to the outbreak from trip reports written by on-site investigators, and we compared these with outbreaks investigated during 2002-2008.

Results: The 21 TB outbreaks during 2009-2015 involved 457 outbreak patients (range, 3-99 patients per outbreak). Of the 21 outbreaks, 16 were first identified through genotype data. In sum, 118 (26%) patients were identified through contact investigations of other patients in the outbreak. Most outbreak patients (n = 363, 79%) were US born. Ninety-two (26%) patients had a mental illness, 204 (45%) had been homeless in the year before diagnosis, and 379 (83%) used alcohol excessively or used illicit substances. The proportion of patients experiencing homelessness doubled between 2002-2008 and 2009-2015; other characteristics were similar between the 2 periods. Delayed TB diagnosis contributed to unmitigated transmission in all but 1 outbreak.

Conclusions: TB outbreaks challenge frontline public health resources. Genotyping and contact investigations are important strategies for detecting and controlling TB outbreaks, particularly among people experiencing homelessness or those with mental illness.