While the number of cases of tuberculosis (TB) disease reported nationally has decreased each year since 1993, the incidence of TB in Minnesota increased throughout much of the 1990s and peaked at 239 TB cases (4.8 cases per 100,000 population) in 2001. In 2005, 199 new cases of TB disease (3.8 cases per 100,000 population) were reported in Minnesota, which represents a plateau following a 3-year decline in the incidence of TB that occurred from 2002 through 2004. Although the statewide incidence of TB disease is less than the national rate (4.8 cases per 100,000 population in 2005), the incidence rate in Minnesota exceeds the U.S. Healthy People 2010 objective of 1.0 case per 100,000 population (Figure 5).
The most distinguishing characteristic of the epidemiology of TB disease in Minnesota is the very large proportion of TB cases reported among foreign-born persons, which has averaged 81% over the past 5 years. In 2005, 173 (87%) new TB cases in Minnesota occurred in persons born outside the United States. This exceptionally high percentage of foreign-born TB cases reported in 2005 represents the largest proportion of foreign-born cases reported in Minnesota since 1992, when MDH began collecting data on TB case-patients’ countries of birth. In contrast, 54% of TB cases reported nationwide in 2005 were foreign-born.
The 173 foreign-born TB case-patients reported in Minnesota during 2005 represent 31 different countries of birth. The most common region of birth among foreign-born TB cases reported in 2005 was sub-Saharan Africa (58%), followed by South/Southeast Asia (24%) (Figure 6). The ethnic diversity among these foreign-born TB cases reflects the unique and constantly changing demographics of immigrant and other foreign-born populations arriving in Minnesota. This diversity also poses significant challenges in providing culturally and linguistically appropriate TB prevention and control services for populations most affected by and at risk for TB in Minnesota.
Persons 15 years of age or older who arrive in the United States as immigrants or refugees receive a medical evaluation overseas that includes screening for pulmonary TB disease. Among 173 foreign-born persons who were diagnosed with TB disease in Minnesota during 2005, 119 (69%) were diagnosed less than 5 years after arriving in this country. Of 39 TB case-patients 15 years of age or older who were diagnosed within 12 months of their arrival in the United States and who arrived as immigrants or refugees, only seven (18%) had any TB-related conditions noted in their pre-immigration medical exams performed overseas. These findings highlight the need for clinicians to have a high index of suspicion for TB among newly arrived foreign-born persons, regardless of the results of medical exams performed overseas. Health care providers should pursue thorough screening, evaluation, and, if indicated, treatment of active TB disease or latent TB infection among patients who originate from regions where TB is endemic.
The majority (74%) of foreign-born TB case-patients reported in Minnesota in 2005 were 15 to 44 years of age, whereas only 30% of U.S.-born TB cases occurred among persons in this age category. In contrast, 47% of U.S.-born TB case-patients were 45 years of age or older. The proportion of pediatric patients (less than 15 years of age) was considerably larger among U.S.-born TB cases than among foreign-born cases (23% versus 8%, respectively), although most of the U.S.-born pediatric cases were children born in the U.S. to foreign-born parents (Figure 7). These first-generation U.S.-born children appear to experience an increased risk of TB disease that more closely resembles that of foreign-born persons. Presumably, these children may be exposed to TB as a result of travel to their parents’ country of origin and/or visiting or recently arrived family members who may be at increased risk for TB acquired overseas.
Aside from foreign-born persons, other high-risk population groups comprise much smaller proportions of the TB cases reported in Minnesota, each representing less than 10% of cases diagnosed statewide. Among TB cases reported in 2005, substance abuse (including alcohol abuse and/or illicit drug use) was the most common of these other risk factors, with approximately 7% of TB case-patients having a history of substance abuse during the 12 months prior to their TB diagnosis. The percentage of TB cases in Minnesota with HIV co-infection has increased over the past 5 years yet remains less than that among all TB cases reported nationwide. Twelve (6%) of the 199 TB cases reported in Minnesota during 2005 were infected with HIV; eight (67%) of those HIV-infected TB case-patients were foreign born, including five persons from Ethiopia and one person each from Cameroon, China, and Liberia. Other risk groups such as homeless persons, correctional facility inmates, and residents of nursing homes each represented only 1-2% of TB cases reported in 2005.
Twenty-three (26%) of the state’s 87 counties reported at least one case of TB disease in 2005, with the majority (83%) of cases occurring in the Twin Cities metropolitan area, particularly in Hennepin (50%) and Ramsey (18%) counties, both of which have public TB clinics. Fifteen percent of TB cases occurred in the five suburban Twin Cities metropolitan counties (i.e., Anoka, Dakota, Carver, Scott, and Washington). Olmsted County, which maintains a public TB clinic staffed jointly by the Olmsted County Health Department and Mayo Clinic, represented 5% of TB cases reported statewide in 2005. The remaining 12% of cases occurred in primarily rural areas of Greater Minnesota. In 2005, the highest TB incidence rate statewide (8.6 cases per 100,000 population) was reported in Hennepin County, followed by Olmsted County (7.3 cases per 100,000 population) and Ramsey County (7.0 cases per 100,000 population).
Drug-resistant TB is a critical concern in the prevention and control of TB in Minnesota, as well as nationally and globally. The prevalence of drug-resistant TB in Minnesota, particularly resistance to isoniazid (INH) and multi-drug resistance, exceeds comparable national figures. In 2005, 15 (10%) of 151 culture-confirmed TB cases were resistant to at least one first-line anti-TB drug (i.e., INH, rifampin, pyrazinamide, or ethambutol). In particular, 13 (9%) cases were resistant to INH, and four (3%) cases were multidrug-resistant (i.e., resistant to at least INH and rifampin). These data represent a decrease in the prevalence of any first-line drug resistance and INH-resistance in 2005. In comparison, from 2001 through 2004, the average annual prevalence of any first-line drug resistance among culture-confirmed TB cases in Minnesota was 17%, and the average prevalence of INH-resistance was 14%. In previous years, drug resistance has been considerably more common among foreign-born TB cases than among U.S.-born cases in Minnesota. In 2005, however, both INH resistance and multidrug-resistant (MDR)-TB were more common among U.S.-born TB cases than among foreign-born cases (10% versus 8%, and 5% versus 2%, respectively). Of particular concern, nine (38%) of 24 multidrug-resistant TB (MDR-TB) cases reported during the past 5 years (2001-2005) were resistant to all four first-line drugs. These nine pan-resistant MDR-TB case-patients represented seven different countries of birth (i.e., one each from Ethiopia, Laos, Moldova, South Korea, and Thailand, and two each from Somalia and the United States). One of the two U.S.-born pan-resistant patients had resided in Africa for several years; the other was a young child infected by a foreign-born family member.
The epidemiology of TB in Minnesota highlights the need to support global TB elimination strategies, as well as local TB prevention and control activities targeted to foreign-born persons. TB in Minnesota occurs primarily, although not exclusively, among foreign-born persons, with TB case-patients representing many countries of origin and varied cultural backgrounds. Although the incidence of TB in Minnesota is less than the national rate, the prevalence of drug-resistant TB in Minnesota is high and extrapulmonary sites of disease are common, especially among foreign-born cases. The proportion of TB cases occurring in persons under 15 years of age in Minnesota exceeds the comparable figure nationally, with many of these children being born to foreign-born parents. These trends suggest that the incidence of TB in Minnesota is not likely to decrease in the foreseeable future.
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- Full issue>> Annual Summary of Communicable Diseases Reported to the Minnesota Department of Health, 2005