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Brief Report: Tuberculosis Outbreak in a Low-Incidence State --- Indiana, 2001--2004

States with fewer than 3.5 cases of tuberculosis (TB) per 100,000 population are designated as states with low incidence for TB, corresponding to CDC's interim target rate for 2000, with a goal to eliminate TB in the United States by 2010 (1). Indiana is a low-incidence state, with a TB case rate of 2.3 per 100,000 population in 2003. However, during 2000--2002, Allen County, Indiana, exceeded the state TB case rate with a mean case rate of 2.9 (range: 2.7--3.0) per 100,000 population. The TB case rate in Allen County increased to 4.7 per 100,000 population (with 16 patients reported with TB disease) in 2003 and to 7.0 per 100,000 population (with 12 patients reported with TB disease) during the first half of 2004. The Allen County Department of Health (ACDH), the Indiana State Department of Health, and CDC are investigating this ongoing TB outbreak. This report describes the preliminary results of the investigation, the efforts of ACDH to restructure its TB program, and the importance of maintaining TB-control efforts in low-incidence states.

During January 2001--June 2004, a total of 59 cases of TB disease were reported in Allen County. Cases in which patients had a matching Mycobacterium tuberculosis genotype or, when no isolate was available for genotyping, an epidemiologic link to a patient with TB disease, were considered outbreak related. Of the 59 cases investigated, 25 (42%) were outbreak related, 21 (84%) had epidemiologic links (Figure) and four (16%) had genotypic links only. The median age of outbreak-related TB patients was 27 years (range: 6 months--51 years). Nearly all patients (96%) were black, 14 (56%) were female, and 22 (88%) resided in four contiguous postal code areas. Of 16 patients who were tested for human immunodeficiency virus (HIV), all tested negative. Pulmonary TB was present in 18 (72%) patients. Six (24%) patients were highly infectious, with acid-fast bacilli (AFB) identified on sputum smear and cavitary lung lesions.

To examine whether other cases were outbreak related and to confirm the index patient, all available M. tuberculosis isolates from TB patients reported in Allen County from 1999 (the year the index patient first reported symptoms) through June 2004 were sent for genotyping by spoligotyping, mycobacterial interspersed repetitive unit (MIRU) typing, and IS6110-based restriction fragment-length polymorphism (RFLP) testing. Of these 38 isolates, 18 (47%) had matching spoligotypes and MIRU patterns, indicating that the 18 cases were likely outbreak related. RFLP testing on nine isolates confirmed a matching nine-band pattern in eight isolates, with a one-band shift in the remaining isolate. RFLP testing of the remaining available isolates is pending.

A total of 516 contacts of the 25 linked patients have been identified. Of these, 423 (82%) were tested with at least an initial tuberculin skin test (TST); the remaining 18% are either pending follow-up or cannot be found. Among the tested contacts, 85 (20%) had positive TST results (induration >5 mm) (2), and 13 other persons reported a previous positive TST result. Of these 98 contacts, 13 (13%) received a diagnosis of TB disease upon further evaluation. The remaining 85 (87%) were candidates for latent TB infection (LTBI) treatment; 49 (58%) of the candidates started therapy, but, of these, 12 (24%) defaulted. For two (17%) of the persons who defaulted (patients 3 and 7) and one LTBI candidate who refused treatment (patient 4), infection progressed to TB disease. Because of matching isolate genotypes and epidemiologic links to other patients, these three patients are suspected as the sources of TB infection for 16 of 24 patients (patients 6--21) with TB disease (Figure). Had the three patients completed LTBI treatment, 16 TB cases might have been prevented. Each contact who defaulted cited lack of TB knowledge as a major barrier to completing LTBI treatment.

ACHD and CDC continue to identify new cases and contacts related to this outbreak. Investigation is under way for approximately 600 additional contacts associated with one of the AFB sputum smear-positive, pulmonary TB case-patients with cavitary lesions.

Achieving TB control in this outbreak will require 1) continuing contact investigation, 2) successful treatment of patients with newly diagnosed TB disease or LTBI, 3) TB education for health-care workers (HCWs) and the community, and 4) close patient management that includes directly observed therapy for LTBI in patients at high risk for TB disease (2). Recognizing this increased need for TB services and education, ACDH is restructuring its TB program and increasing financial and personnel resources. In addition, CDC is working with ACDH to develop educational material and programs for the TB clinic staff, local HCWs, and the community. Improved TB education and communication between HCWs and the community might expedite TB disease detection and increase adherence of patients to LTBI treatment. This TB outbreak demonstrates the limitations of gains in TB control and the importance of continued resource commitment to and preparedness for TB resurgences, even in low-incidence states (3).

Reported by: D McMahan, MD, L Robertson, MS, M Benge Koch, A Lapsley, Allen County Dept of Health, Fort Wayne; R Teclaw, DVM, PhD, P Britton, Indiana State Dept of Health. J Massey, DrPH, L Mosher, MS, Bur of Laboratories, Michigan Dept of Community Health. I Gonzalez, MD, K Ijaz, MD, D Tuckey, MPH, P Cruise, G Palumbo, MPH, D Felix, W Heirendt, T Cropper, Div of Tuberculosis Elimination; K Tan, MD, EIS Officer, CDC.

Acknowledgment

This report is based, in part, on contributors by T Douglas, MD, Epidemiology Program Office, CDC.

References

  1. CDC. A strategic plan for the elimination of tuberculosis in the United States. MMWR 1989;38(No. S-3).
  2. CDC. Targeted tuberculin testing and treatment of latent tuberculosis infection. MMWR 2000;49(No. RR-6).
  3. CDC. Progressing toward tuberculosis elimination in low-incidence areas of the United States: recommendations of the Advisory Council for the Elimination of Tuberculosis. MMWR 2002;51(No. RR-5).

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