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TB Notes 4, 2004

No. 4, 2004


CDC Investigates Tuberculosis Outbreak in a Low-Incidence State— Allen County, Indiana, 2000–2004

Indiana is a low-incidence state for TB (i.e., case rate < 3.5 cases per 100,000 population), with a case rate of 2.3 cases per 100,000 population in 2003. From 2000 to 2002, Indiana’s Allen County exceeded the state TB case rate with a mean rate of 2.9 per 100,000 (range 2.7 to 3.0 per 100,000), but was still a low-incidence county. However, in 2003, Allen County reported 16 patients with TB (case rate 4.7 per 100,000 population), and in the first half of 2004, reported 12 patients with TB disease. In March 2004, the Allen County Department of Health (ACDH) and the Indiana State Department of Health (ISDH) requested DTBE assistance with an investigation of ongoing transmission of M. tuberculosis in Allen County that was thought to have started in 2001.

In March 2004, a team from CDC was sent to Indiana to assist state and county health officials with the epidemiologic investigation. The team consisted of Idalia M. González, Dawn Tuckey, Phyllis Cruise, and Kathrine Tan of DTBE, and Tanyanika Douglas, a medical student on an epidemiology elective. The objectives of the investigation were to define the scope and extent of M. tuberculosis transmission, assist in identifying and prioritizing contacts for investigation, and make recommendations to ACDH and ISDH for the control and prevention of TB transmission in Allen County. As part of the initial assessment, the CDC team reviewed patient medical records, reinterviewed TB disease patients, assisted with the contact investigation, and sent M. tuberculosis isolates for genotyping. Cases that had a matching M. tuberculosis genotype or, when no isolate was available for genotyping, an epidemiologic link to a previously identified case, were considered outbreak-related.

After the initial CDC team visit, Dawn Tuckey, the CDC state TB program consultant, and several public health advisors (PHAs)—Phyllis Cruise, Gabe Palumbo, Derrick Felix, Wendy Heirendt, and Tracina Cooper—have been sent to Allen County for continued technical and programmatic assistance. Additional outbreak-related cases of TB disease continued to be found, requiring a second follow-up investigation in July 2004. CDC continues to assist ACDH and ISDH with this ongoing TB outbreak, and the results of the investigation thus far are summarized below.

Twenty-six cases of TB disease from 2001 to present are thought to be outbreak-related. The median age of outbreak-related TB patients is 27 years, almost all are African-American, more than half are female, and 19 reside in two contiguous zip codes. Of the 16 patients tested for HIV, all were HIV negative. Pulmonary TB was present in 18 (69%) patients. Six patients (23%) were highly infectious, having acid-fast bacilli (AFB) identified on sputum smear and chest radiographs showing cavitary lesions.

All available M. tuberculosis isolates from TB patients reported from 1999 to 2004 in Allen County were genotyped. Of these 36 isolates, 16 had matching genotypes. Cross-matching of the spoligotype with the National TB Genotyping and Surveillance Network (NTGSN) database has determined that this spoligotype has been previously identified.

A total of 1096 contacts have been identified. Of the 749 (68%) patients that have been tested with at least an initial tuberculin skin test (TST, positive defined as induration > 5 mm), 130 (17%) had positive TST results. Of these 130 contacts, 16 (12%) developed TB disease, and the remainder were candidates for latent TB infection (LTBI) treatment. Seventy-seven (68%) of the LTBI treatment candidates started therapy; however, 18 (23%) defaulted. Three (17%) of the defaulters and one who refused treatment developed TB disease. Had these contacts completed LTBI treatment, 16 other TB cases may have been prevented. All contacts who defaulted identified lack of TB knowledge as a major barrier to completing LTBI treatment.

In summary, achieving TB control in this outbreak will require thorough contact investigations, TB education in health care workers (HCWs) and the community, and close patient management, which will include directly observed therapy for LTBI in patients who are at high risk of developing TB disease (i.e., children less than 5 years of age and immunosupressed persons). Recognizing an ongoing and increased need for TB services and education, ACDH is restructuring its TB program and increasing financial and personnel resources. Additionally, ACDH is working with CDC to develop educational programs for the TB clinic staff, local HCWs, and the community. Improved TB education and communication between HCWs and the community may help with prompt identification of TB disease and increased adherence of patients to LTBI treatment.

—Reported by Kathrine Tan, MD,
Epidemic Intelligence Service Officer

Div of TB Elimination


Released October 2008
Centers for Disease Control and Prevention
National Center for HIV/AIDS, Viral Hepatitis, STD, and TB Prevention
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