Tuberculosis, 2001

While the number of tuberculosis (TB) cases reported nationally has decreased each year since 1993, the incidence of TB in Minnesota is increasing. In 2001, 239 new cases of TB disease (4.9 per 100,000 population) were reported statewide. This represents a 34% increase since 2000 (178 cases) and the largest number of cases reported since the early 1970s. For the third consecutive year, the incidence of TB disease in Minnesota remains at or above the national goal (for the year 2000) of 3.5 per 100,000 population.

The epidemiology of TB in Minnesota is distinct nationally, with the most significant factor being the very high percentage of TB cases that occur among foreign-born persons. In 2001, 194 (81%) cases occurred in persons born outside the U.S. (Figure 9). This trend reflects the unique and changing demographics of immigrant populations arriving in the state, particularly persons arriving from regions of the world where TB is prevalent. The most common regions of origin for foreign-born persons with TB disease reported in 2001 include sub-Saharan Africa (e.g., Somalia, Liberia, and Ethiopia) (61%) and South/Southeast Asia (e.g., Laos and Vietnam) (24%) (Figure 10). More than half (55%) of foreign-born TB cases were less than 30 years of age, while the most common (36%) age group among U.S.-born cases was those 60 years of age or older.

Among the 194 foreign-born persons diagnosed with TB disease in Minnesota during 2001, 60 (31%) were diagnosed within 12 months of arrival in the U.S., and an additional 37 (19%) were diagnosed 2 to 5 years after arriving in this country. All individuals who arrive in the U.S. as either immigrants or refugees receive a medical evaluation overseas to identify conditions (such as infectious pulmonary TB disease) of public health concern. In 2001, only seven (13%) immigrants/refugees diagnosed in Minnesota with TB disease within 12 months of their arrival in the U.S. had any TB-related conditions noted in the results of their pre-immigration medical exams. These findings highlight the need for clinicians not to rely exclusively on the overseas exam to identify TB disease among newly arrived foreign-born persons; providers should thoroughly pursue screening, evaluation, and, if indicated, treatment of active TB disease or latent TB infection among patients who originate from areas where TB is cases were less than 30 years of age, while the most common (36%) age group among U.S.-born cases was those 60 years of age or older.

Among the 194 foreign-born persons diagnosed with TB disease in Minnesota during 2001, 60 (31%) were diagnosed within 12 months of arrival in the U.S., and an additional 37 (19%) were diagnosed 2 to 5 years after arriving in this country. All individuals who arrive in the U.S. as either immigrants or refugees receive a medical evaluation overseas to identify conditions (such as infectious pulmonary TB disease) of public health concern. In 2001, only seven (13%) immigrants/refugees diagnosed in Minnesota with TB disease within 12 months of their arrival in the U.S. had any TB-related conditions noted in the results of their pre-immigration medical exams. These findings highlight the need for clinicians not to rely exclusively on the overseas exam to identify TB disease among newly arrived foreign-born persons; providers should thoroughly pursue screening, evaluation, and, if indicated, treatment of active TB disease or latent TB infection among patients who originate from areas where TB is endemic.

Other less frequent risk factors among TB cases in Minnesota included homelessness (5%), HIV infection (3%), incarceration in a correctional facility (1%), and residence in a nursing home (1%). Twenty-eight (32%) of the state's 87 counties reported at least one case of TB disease in 2001, with the majority (83%) of TB cases in the seven-county Twin Cities metropolitan area, particularly among residents of Hennepin (59%) and Ramsey (18%) counties. The incidence rate of TB disease increased 34% (from 9.3 to 12.5 cases per 100,000 population) in Hennepin County and 74% (from 4.7 to 8.2 cases per 100,000 population) in Ramsey County.

Drug-resistant TB is a critical public health and clinical concern, both globally and locally. The prevalence of drug resistance among TB cases reported in Minnesota exceeds comparable figures nationally. In 2001, 56 (29%) cases of drug-resistant TB were reported in Minnesota among 195 culture-confirmed cases for whom drug susceptibility results were available, including 23 (12%) cases resistant to isoniazid and four (2%) cases of multidrug-resistant TB (MDR-TB) (i.e., resistant to at least isoniazid and rifampin). National guidelines indicate initial four-drug therapy (i.e., isoniazid, rifampin, pyrazinamide, and ethambutol or streptomycin) for all TB cases in areas where the prevalence of INH resistance is 4% or greater; accordingly, all TB cases in Minnesota initially should receive a four-drug regimen, at least until drug susceptibility results are known.

These drug susceptibility data in Minnesota represent an increase in drug resistance overall and, most notably, among U.S.-born persons. The percentage of drug-resistance among foreign-born cases (29%) was relatively stable in 2001. However, among U.S.-born cases, the percentage of drug resistance more than tripled, from an average of 8% during 1997-2000 to 26% in 2001 (Table 5). Of the 10 U.S.-born drug-resistant cases reported in 2001, eight (80%) were resistant to streptomycin (which was the only anti-TB drug to which five of those cases were resistant). Although streptomycin is the least commonly used of the five first-line anti-TB medications, this trend is concerning and without explanation. Of 56 persons with drug-resistant TB disease reported in 2001, 46 (82%) were born outside the U.S., including all four MDR-TB cases, suggesting that the majority of drug-resistant TB in Minnesota (and all cases of MDR-TB reported to date) represent primary drug resistance acquired overseas, rather than secondary resistance resulting from nonadherence to prescribed therapy. However, the increasing prevalence of drug resistance among U.S.-born cases, in particular, raises concern that drug-resistant TB in Minnesota increasingly may be the result of transmission locally.

More detailed TB surveillance data and other TB-related resources (including patient education materials translated in nine languages) are available on the MDH TB Program's web site.

• For up to date information see>> Tuberculosis (TB)
• Full issue>> Annual Summary of Communicable Diseases Reported to the Minnesota Department of Health, 2001