Tuberculosis, 2012

In 2012, 162 cases of tuberculosis (TB) disease (3.0 cases per 100,000 population) were reported in Minnesota, compared to 137 cases in 2011. Although this represents an 18% increase in the number of cases and a 15% increase in the incidence rate compared to 2011, the number of cases reported annually has decreased 32% since 2007, when 238 cases (the highest number in the past decade) were reported. Furthermore, although Minnesota’s TB incidence rate in 2012 was higher than in 2011, it was still below the national rate of 3.2 cases per 100,000 population. Four (2%) of the TB cases reported in Minnesota in 2012 have died due to TB or TB-related causes.

Twenty (23%) of the state’s 87 counties reported at least 1 case of TB disease in 2012. The large majority (85%) of cases occurred in the metropolitan area, primarily in Hennepin (44%) and Ramsey (24%) counties. Seventeen percent of TB cases in 2012 were reported from the other five metropolitan counties (i.e., Anoka, Carver, Dakota, Scott, and Washington). The remaining 15% of cases were reported from outside the metropolitan area. Among the metro area counties, the highest TB incidence rate in 2012 was reported in Ramsey County (7.6 cases per 100,000 population), followed by Scott County (6.8 cases per 100,000 population) and Hennepin County (6.1 cases per 100,000 population). The TB incidence rate for all Greater Minnesota counties combined was 1.0 per 100,000 population.

The majority (79%) of TB cases reported in Minnesota during 2012 were identified as a result of individuals seeking medical care due to symptoms of TB disease. Various targeted public health interventions identified the remaining 21% of cases. Such methods of case identification traditionally are considered high priority, core TB prevention and control activities; they include TB contact investigations (6%), domestic refugee health assessments (6%), and follow-up evaluations subsequent to abnormal findings on pre-immigration exams performed overseas (2%). Notably, however, an additional 7% of TB cases were identified through a variety of other means (e.g., occupational screening) that typically are considered lower priority activities.

The incidence of TB disease is disproportionately high in racial minorities in the United States and in Minnesota. In 2012, 12 TB cases occurred among non-Hispanic whites (incidence rate: 0.3/100,000 population). In contrast, 90 TB cases occurred among blacks (incidence rate: 28.2/100,000), 42 among Asians (incidence rate: 17.5/100,000), and 3 among American Indians (incidence rate: 3.8/100,000). The majority (86%) of black TB cases reported in Minnesota in 2012 were foreign-born.

The most distinguishing characteristic of the epidemiology of TB disease in Minnesota continues to be the large proportion of cases occurring among persons born outside the United States. Eighty-four percent of cases reported in 2012 occurred among foreign-born persons. In contrast, 63% of TB cases reported nationwide in 2012 were foreign-born. The 136 foreign-born TB cases reported in Minnesota during 2012 represented 33 different countries of birth; the most common region of birth among these patients was sub-Saharan Africa (56% of foreign-born cases), followed by South/Southeast Asia (25%), and Latin America (including the Caribbean) (11%) (Figure 7). Among U.S.-born pediatric TB cases (less than 15 years of age at TB diagnosis), 90% (9/10) had at least one foreign-born parent. The ethnic diversity among foreign-born TB cases in Minnesota reflects the unique and constantly changing demographics of immigrants and other foreign-born populations arriving in the state.

Among the foreign-born TB cases reported in Minnesota during 2012, 22% were diagnosed with TB disease less than 12 months after arriving in the United States, and an additional 11% were diagnosed 1 to 2 years after their arrival. Many of these cases likely represent persons who acquired TB infection prior to immigrating and began progressing to active TB disease shortly after arrival. Of the 21 TB cases 15 years of age or older who arrived as immigrants or refugees and were diagnosed in Minnesota within 12 months of arriving in the United States, only two had any TB-related condition noted in their pre-immigration medical examination reports. 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.

Over half (54%) of foreign-born and 23% of U.S.-born TB cases reported in Minnesota in 2012 had an extrapulmonary site of disease, or TB found outside the lungs. Among extrapulmonary TB cases, by far the most common site of TB disease was lymphatic (59%), followed by pleural (13%), and bone/joint (9%).

Aside from foreign-born persons, individuals with other risk factors comprise a much smaller proportion of the TB cases in Minnesota. Among cases reported in 2012, 12% occurred among persons with certain medical conditions (excluding HIV infection) that increase the risk for progression from latent TB infection (LTBI) to active TB disease (e.g., diabetes, prolonged corticosteroid or other immunosuppressive therapy, end stage renal disease, etc.). Following the presence of these underlying medical conditions, the next most common risk factor was substance abuse (including alcohol abuse and/ or illicit drug use), with 4% of TB cases reported in 2012 having a history of substance abuse during the 12 months prior to their TB diagnosis. Six (4%) were infected with HIV. The percentage of new TB cases with HIV co-infection in Minnesota remains less than that among TB cases reported nationwide in 2012 (nationally, 7.7% of those with an HIV test result were coinfected). Other high risk groups, such as homeless persons and residents of nursing homes, each represented around 1% of the TB cases reported in Minnesota during 2012.

In 2012, of 123 culture-confirmed TB cases with drug susceptibility results available, 23 (19%) were resistant to at least one first-line anti-TB drug (i.e., INH, rifampin, pyrazinamide, or ethambutol), including 12 (10%) cases that were resistant to INH. There was one case (0.8%) of multidrug-resistant TB (MDR-TB, or resistance to at least INH and rifampin) reported in 2012. The proportion of drug resistance among TB cases decreased from 2011, when 22% of culture-confirmed cases with susceptibility results available were resistant to at least one first-line anti-TB drug, and 3 (3%) had MDR-TB.

Figure 7: Foreign-Born Tuberculosis Cases by Region of Birth and Year of Report, Minnesota, 2008-2012

Updated Thursday, May 29, 2014 at 01:24PM