Public Health Dispatch: Tuberculosis Outbreak Among Homeless Persons --- King County, Washington, 2002--2003

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The Public Health--Seattle and King County (PH-SKC) Tuberculosis Control Program, with assistance from the Washington State Department of Health and CDC, is continuing to investigate an ongoing outbreak of tuberculosis (TB) disease among homeless persons in Seattle (1). This report describes patient characteristics, methods used to identify active TB cases and contacts at highest risk for exposure, and control measures under way to prevent further transmission of this outbreak strain of Mycobacterium tuberculosis.

During 1999--2001, PH-SKC reported an annual average of 13 cases of TB among the homeless population. In 2002, diagnosis of TB in 30 homeless patients prompted an investigation. As of September 30, 2003, PH-SKC had identified 44 outbreak-associated TB patients with dates of diagnosis during May 2002--September 2003. Outbreak-associated TB patients have been defined according to the following criteria: 1) having an M. tuberculosis isolate with a matching 15-band restriction fragment length polymorphism (RFLP) pattern (2) (n = 39) or 2) if RFLP analysis is pending, having an epidemiologic link to a patient whose isolate matched the outbreak pattern (n = five). All but three of the outbreak-associated patients were homeless at the time of diagnosis; 43 (98%) were born in the United States, 34 (77%) were male, 21 (48%) were American Indian/Alaska Native, and 17 (39%) were black. Of the 38 (86%) patients with pulmonary disease, 23 (61%) had acid-fast bacilli identified on sputum smear at diagnosis. Seven (16%) outbreak-associated patients also were infected with human immunodeficiency virus (HIV).

In January 2003, an investigation conducted by PH-SKC assisted in identifying contacts at highest risk for exposure. Investigators reinterviewed outbreak patients and health-care providers serving homeless facilities to identify additional patient contacts. Sites of transmission were determined by review of homeless facility intake registries for the presence of infectious patients and the rates of positive tuberculin skin testing (TST) results among staff and clients. Exposed cohorts were identified at three sites of transmission. The cohort prioritized for intensive screening included 385 contacts from three homeless facilities and 86 other contacts named by patients or health-care providers.

In February 2003, PH-SKC began an intensive effort to screen the high-priority cohort for TB disease and latent TB infection (LTBI) in the TB clinic and at homeless facilities, which included symptom review, chest radiograph, sputum examination and culture, TST, and voluntary HIV counseling and testing. During February 1--September 30, PH-SKC screened approximately 380 contacts with a chest radiograph and/or sputum culture. Of the 44 outbreak-associated patients, 20 were reported during this time, and 11 (55%) were identified through PH-SKC screening efforts, limiting the amount of time these patients were exposing others in the community. As of December 9, all homeless outbreak-associated patients with TB disease and some contacts with LTBI were receiving directly observed therapy.

Focused, intensified screening efforts for early detection and treatment of both TB disease and LTBI are under way to control transmission in the King County community (3). TB controllers, particularly those from western states, should consider the possibility of unrecognized TB outbreaks involving homeless persons in their communities.

Reported by: M Narita, MD, S Goldberg, MD, L Lake, MBA, Public Health--Seattle and King County; T Kuss, MPH, K Field, MSN, J Hofmann, MD, Washington State Dept of Health. P McElroy, PhD, P Tribble, MA, Div of Tuberculosis Elimination; B Metchock, DrPH, Div of AIDS, STD, and Tuberculosis Laboratory Research; M McConnell, MD, Global AIDS Program, National Center for HIV, STD, and Tuberculosis Prevention; K Lofy, MD, EIS Officer, CDC.

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