The number of cases of tuberculosis (TB) disease reported in the United States has decreased each year since 1992, although the decline slowed to its smallest annual percent change (1.4%) with the 14,871 TB cases reported in 2003. The incidence of TB in Minnesota also declined for several years following a peak of 165 new cases in 1992. In 1999, however, the number of TB cases reported in Minnesota began a dramatic increase, reaching a new high of 239 cases in 2001. In 2003, 214 cases of TB disease (4.4 cases per 100,000 population) were reported in Minnesota. The incidence of TB in Minnesota exceeds the national objective of 3.5 cases per 100,000 population that was established as an interim goal for the year 2000. In 2003, 24 U.S. states reported TB incidence rates that met the 2000 national objective.
In many ways, the epidemiology of TB in Minnesota is distinct from other states and has been a precursor of trends that now are emerging nationally. The most significant such factor is the very large proportion of TB cases reported among foreign-born persons in Minnesota, which has averaged 80% over the past 5 years. In 2003, 173 (81%) TB cases in Minnesota occurred in persons born outside the United States. In contrast, 53% of TB cases reported nationwide in 2003 were born outside the United States, although that percentage has been increasing steadily for several years.
The 173 foreign-born TB cases reported in Minnesota during 2003 represent persons from 26 different countries of birth. These epidemiologic characteristics directly reflect the unique and constantly changing demographics of immigrant and other foreign-born populations arriving in Minnesota. The most common regions of birth among foreign-born TB cases reported in 2003 were sub-Saharan Africa (53%, n = 92) and South/ Southeast Asia (27%, n = 47) (Figure 5). In particular, 58 case-patients from Somalia who were diagnosed with TB in Minnesota comprised 55% of all Somali TB cases reported nationwide in 2003. The age distribution of TB cases in Minnesota differs by country of birth, with the largest age group among foreign-born cases in 2003 being young adults 25 to 44 years of age (47%). The proportion of TB patients who were 65 years of age or older was higher among U.S.-born cases than among foreign-born cases (17% versus 7%). Although the proportion of patients who were less than 5 years of age was higher among U.S.-born cases than among foreign-born cases (17% versus 2%), approximately 90% of these young, U.S.-born, pediatric cases occurred in households with foreign-born parents or other family members.
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 159 foreign-born persons 15 years of age or older who were diagnosed with TB disease in Minnesota during 2003 and whose date of arrival in the United States was known, more than half (55%) were diagnosed fewer than 5 years after arriving in the United States. Of 26 TB case-patients diagnosed within 12 months of their arrival in the United States, only seven (27%) had any TB-related conditions noted in their pre-immigration medical exams. 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. 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.
While the total number of TB cases reported in Minnesota declined 10% from 2002 to 2003, the decline was focused among U.S.-born persons; during this period, the number of foreign-born TB cases decreased 4%, whereas the number of U.S.-born cases declined 27% (Figure 6). Combined with the fact that the vast majority of TB cases in Minnesota occur among foreign-born persons, these data highlight the need to support global TB elimination strategies as well as local TB prevention and control activities targeted to foreign-born persons in order to control TB effectively in Minnesota. MDH is among 22 sites funded by the CDC through a TB Epidemiologic Studies Consortium to conduct a study, beginning in 2004, that is designed to identify missed opportunities for preventing TB disease among foreign-born populations in the United States and Canada.
Aside from country of birth, other less common risk factors among TB cases reported in Minnesota during 2003 included homelessness (5%), HIV infection (4%), incarceration in a correctional facility (2%), and residence in a nursing home (1%). Twentythree (26%) of the state’s 87 counties reported at least one case of TB disease in 2003, with the majority (79%) of cases occurring in the Twin Cities metropolitan area, particularly among residents of Hennepin (53%) and Ramsey (14%) counties. Notably, while the numbers of TB cases reported in Hennepin County, Ramsey County, and Greater Minnesota each decreased from 2002 to 2003, the number of cases reported in the suburban metropolitan counties of Anoka, Carver, Dakota, Scott, and Washington increased 53%.
Drug-resistant TB is a critical and growing 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 2003, 42 (24%) cases of drug resistant TB were reported in Minnesota among 172 culture-confirmed cases, including 30 (17%) cases resistant to INH and five (3%) cases of multidrug-resistant TB (MDR-TB) (i.e., resistant to at least INH and rifampin) (Table 5). This is the highest prevalence of INH-resistance and MDR-TB reported statewide since MDH began collecting such data in 1992. Drug resistant TB in Minnesota is approximately twice as common among foreign-born TB cases compared to U.S.-born cases. Thirty-seven (88%) of the 42 patients with drug-resistant TB reported in 2003 were born outside the United States, including 26 (87%) of the 30 INH-resistant cases and four (80%) of the five MDR-TB cases. The one U.S.-born MDR-TB case was a child living in a household with a foreign-born grandparent with MDRTB. Of great concern, seven of 20 MDR-TB cases reported in Minnesota during the past 5 years have been resistant to all five first-line TB drugs (i.e., INH, rifampin, pyrazinamide, ethambutol, and streptomycin). These seven MDR-TB case-patients originated from six different countries (one each from Ethiopia, Laos, Moldova, Somalia, and Thailand, and two from the United States); one of the two U.S.- born MDR-TB case-patients had resided in Africa for more than 20 years, and the other was the previously described child in a household with foreign-born family members.
TB-related resources for patients and health care providers (including patient education materials translated in nine languages) are available on the MDH Tuberculosis (TB) Program's web site.
Note: For up to date information on Tuberculosis see Tuberculosis (TB)
Go to full issue: DCN, August 2004: Volume 32, Number 4