1 figure omitted
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.
This report is based, in part, on contributors by T Douglas, MD, Epidemiology
Program Office, CDC.
References: 3 available
Brief Report: Tuberculosis Outbreak in a Low-Incidence State—Indiana, 2001-2004. JAMA. 2005;293(3):290. doi:10.1001/jama.293.3.290