Public Health Dispatch: Tuberculosis Outbreak in a Homeless Population --- Portland, Maine, 2002--2003

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During June 2002--July 2003, seven men with active pulmonary tuberculosis (TB) disease in Portland, Maine, were reported to the Maine Bureau of Health (MBH). Six were linked through residence at homeless shelters; four had matching Mycobacterium tuberculosis genotypes. Prompt investigation and identification of approximately 1,100 contacts likely prevented further spread of TB. This report summarizes preliminary results of the ongoing investigation and MBH efforts to work with health-care providers statewide to improve early detection of TB among homeless persons.

The median age of patients was 51 years (range: 39--66 years); all were U.S.-born. Six were non-Hispanic white, and one was American Indian. Culture specimens from all seven patients were positive for M. tuberculosis, and all isolates were susceptible to first-line drugs. Three (43%) patients had cavitary pulmonary disease, an indication of increased infectiousness (1). Three (43%) were infected with hepatitis C virus, and one of these also was infected with human immunodeficiency virus. Six (86%) patients had a history of alcoholism.

During the year preceding their diagnoses, five (71%) TB patients resided at the same homeless shelter in Portland; six (86%) had been incarcerated in the county jail. During the contact investigation for patient 1 in June 2002, patient 3 was screened and determined to have a productive cough and history of latent TB infection (LTBI). Medical records showed evidence consistent with active TB disease, including chest radiograph abnormalities; however, TB was not diagnosed in patient 3 until 9 months after the contact investigation. Patient 6 also had LTBI diagnosed during patient 1's contact investigation but was not treated; patient 6 had active TB disease diagnosed 1 year later. Medical records corroborated by genotyping results suggest that delayed diagnosis in patient 3 resulted in prolonged infectiousness and contributed to TB transmission to patients 4, 5, and 6. In February 2003, patient 2 had active TB disease diagnosed while residing at the shelter with patients 1, 3, and 6; patients 3 and 6 were determined to be infectious at that time. Patient 7 had active TB disease diagnosed while incarcerated in the county jail in July 2003.

M. tuberculosis isolates from all seven patients were genotyped by using spoligotyping, mycobacterial interspersed repetitive units analysis, and IS6110--based restriction fragment length polymorphism analysis. Patients 1, 2, and 7 had unique genotypes. Patient 3 (the presumed source patient) and patients 4, 5, and 6 had matching genotypes.

As of November 20, 2003, the investigation had identified 1,069 contacts, 36 (3.4%) of whom reported having a positive tuberculin skin test (TST) result previously. Among the 1,033 persons eligible for a TST, 648 (62.7%) received at least one test, and 56 (8.6%) of these had a positive result; 15 (26.7%) of the 56 are receiving, and one completed, therapy for LTBI. A total of 163 (15.2%) contacts had chest radiographs; no additional active cases were detected.

Active TB case-finding for this investigation is ongoing. MBH continues to work with health-care providers to improve early detection of TB among homeless persons and other populations at high risk, and to increase treatment for LTBI.

Reported by: N Nickerson, MSN, J Linder, MD, D Friou, PhD, Portland Public Health Div, Portland; K Gensheimer, MD, P Kuehnert, MSN, D Hubert, MPA, S Gunston, L Crinion, Maine Bur of Health. K Ijaz, MD, D Ruggiero, MPS, Div of TB Elimination, National Center for HIV, STD, and TB Prevention; B Metchock, PhD, L Diem, L Cowan, PhD, Div of AIDS, STD, and TB Laboratory Research, National Center for Infectious Diseases; H Dale, BVSc, L Simmons, Div of Applied Public Health Training, Epidemiology Program Office; V Gammino, PhD, EIS Officer, CDC.

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