Clinical and Health Affairs
Tuberculosis at the University of Minnesota Medical Center, 2000 to 2006
A Brief Report
By Dan Fulton, M.D., and Susan Kline, M.D., M.P.H.
Abstract
For millions of people around the world, tuberculosis (TB) is a cause of significant morbidity and mortality. It continues to affect the well-being of Minnesotans as well. This article reviews one Minnesota hospital’s experience with TB. Through retrospective reviews of charts at the University of Minnesota Medical Center, we found that patients who tested positive for TB were more likely to be foreign-born than U.S.-born, that foreign-born patients who tested positive for TB were younger than those who tested positive and were born in the United States, and that foreign-born patients were more likely to have extrapulmonary disease than pulmonary TB.
Tuberculosis (TB) affects 2 billion people throughout the world and is responsible for 2 million deaths per year.1,2 Caused by Mycobacterium tuberculosis, TB is often thought of as a disease of the developing world. However, we continue to encounter it here in Minnesota, especially in immigrant communities. One of the most important risk factors for TB is a patient’s country of origin.3 Although the TB rate among people born in the United States is declining, the rate among foreign-born individuals remains unchanged.4 Starting in the early 2000s, approximately 80% of TB cases in Minnesota involved people who were born outside of the United States, making Minnesota one of the states with the highest percentage of TB patients who are foreign-born.4,5 In 2008, the percentage dropped to 73%, but the state remains in the top 10 with regard to the percentage of individuals with TB who are foreign-born. One reason for that high percentage is the fact that Minnesota has experienced an influx of immigrants from sub-Saharan Africa as well as from Southeast Asia—two parts of the world that have a high incidence of TB.2,6 These trends have changed the characteristics of TB patients encountered in Minnesota hospitals.
Tuberculosis can present in the classic pulmonary fashion with a chronic cough, night sweats, fever, weight loss, and eventually hemoptysis.1 However, TB does not always present this way; indeed, extrapulmonary TB is often diagnosed without apparent pulmonary infection.7 Additionally, 43% of TB cases are diagnosed in individuals within the first four years after they immigrate.4 Because of constantly shifting populations and the different ways in which TB can present, we proposed studying the epidemiology of TB at the University of Minnesota Medical Center (UMMC).
The UMMC, which includes the University of Minnesota Medical Center, Fairview and the University of Minnesota Amplatz Children’s Hospital, is a tertiary care hospital located in the heart of Minneapolis. Not only is the UMMC a major center for referrals, it also serves a large population of immigrants who live in the community. Because of this, diseases otherwise considered rare in Minnesota are more commonly encountered here. One such disease with which the UMMC staff has had some experience is TB. Patients who are diagnosed with TB are tracked by the UMMC’s infection-control department.
We decided to observe epidemiologic trends among the TB patients at the UMMC to gain insight into their clinical presentation. We examined all cases that were tracked by the infection-control department between January 2000 and June 2006 that were AFB or culture positive. We performed a retrospective review of both electronic and paper charts.
This article describes the epidemiology and clinical presentation of our patient population.
Findings
We found 68 patients who were diagnosed with TB at the UMMC during the study period. Of those, 53 were foreign-born and 15 were born in the United States. Patients came from 13 countries, with the largest proportion coming from Somalia (39%), followed by the United States (23%) and Ethiopia (9%).
The average age of the foreign-born and U.S.-born patients was 32 and 47 years, respectively. In addition, the average length of time an immigrant had been in the United States at the time of presentation was 4.7 years.
We looked at the relative rates of pulmonary versus extrapulmonary versus mixed-disease TB. Altogether, the UMMC had 30 cases of pulmonary, 33 cases of extrapulmonary, and five case of mixed TB between 2000 and 2006. Foreign-born patients were more likely to present with extrapulmonary disease (52.8%), while U.S.-born patients were more likely to present with pulmonary disease (60%).
Musculoskeletal TB was the most common form of extrapulmonary disease (44% of cases). Other major extrapulmonary categories included lymphatic TB (13%) and abdominal TB (11%).
Regarding the amount of time patients had experienced symptoms, those with pulmonary TB experienced theirs for 15 days on average, while those with extrapulmonary TB experienced their symptoms for 110 days on average. A difference in time to presentation also was seen between foreign-born and U.S.-born patients. Patients born in the United States experienced symptoms for 38 days prior to the visit at which they were diagnosed, whereas foreign-born patients experienced symptoms for 72 days. Looking further at patients with extrapulmonary disease who are foreign-born or U.S.-born, we observed that U.S.-born patients with extrapulmonary disease took 52 days to be diagnosed, whereas foreign-born patients took 117 days.
We identified several risk factors associated with TB in our patient population. They included being an immigrant from sub-Saharan Africa or Southeast Asia and being immunosuppressed. Of the U.S.-born patients, 40% of those who tested positive for TB were immunosuppressed compared with 11.3% of foreign-born patients. A patient who was considered immunosuppressed was defined as one with cancer, diabetes, end-stage renal disease, end-stage liver disease, or who was taking steroids, had a history of alcoholism, or was HIV-positive. Of the foreign-born patients in our study, 67% were tested for HIV while they were being evaluated for TB; of those born in the United States, 33% were tested for HIV. Of the U.S.-born patients who were tested for HIV, 6.7% were HIV-positive; of the foreign-born patients, 2% were HIV-positive.
In addition, 20% of the U.S.-born patients who tested positive for TB had experienced recent foreign travel. Intravenous drug use was reported in two of the 68 TB-positive patients. There also was one case of multidrug-resistant TB discovered between 2000 and 2006.
Discussion
Two different comparisons helped us understand the epidemiology of TB at the UMMC. The first was between foreign-born patients and U.S.-born patients; the second was extrapulmonary versus pulmonary disease. More foreign-born TB patients were seen during the study period than U.S.-born patients. The number of local immigrants from countries with a higher incidence of TB infection (both active and latent) likely helped explain this difference. Our data concurred with Rock et al.’s findings that foreign-born patients with active TB were younger than U.S.-born patients with active TB.8 It is likely that U.S.-born TB patients are older because their TB is reactivating from an exposure that occurred many years ago and was not acquired through a recent exposure; also, immigrants tend to be younger and present for health screenings, where they are tested for TB, soon after entering the United States. The average 4.7-year delay of disease onset after immigration was similar to CDC findings.4
A higher percentage of foreign-born patients than U.S.-born patients had extrapulmonary disease. Immigration screening procedures may help explain this difference. Prior to coming to the United States, immigrants receive a chest X-ray. If it is suspicious for TB, AFB sputum smears are done. If these are negative, it is presumed the TB is not active. If the smears are positive, the person is treated prior to immigrating. Therefore, people with untreated TB who enter the country are more likely to have latent TB or TB that is disseminated to extrapulmonary sites. There also may be population-specific reasons why foreign-born patients have a higher incidence of extrapulmonary TB. Yang et al. established that being a non-Hispanic black is an independent risk factor for extrapulmonary TB.7 Kempainen et al. found Somali immigrants in Minnesota had a significantly higher percentage (46%) of extrapulmonary TB than U.S.-born blacks (22%) or other foreign-born blacks (33%).9 The reasons for this difference are not well-understood.
Regarding the length of time patients experience symptoms prior to diagnosis, we found a big difference between foreign-born and U.S.-born patients. It is was not entirely clear why this was the case. Possible reasons are that foreign-born patients present later for medical evaluation because of lack of access to care or cultural reasons and because they are more likely to have extrapulmonary TB, which is difficult to diagnose. Our sample size was small, and further study is needed to verify the differences we found and to determine whether there are barriers to care or other reasons for them.
Summary
Tuberculosis continues to be a fascinating and dynamic disease. Its presentation and clinical characteristics have changed in Minnesota over time. We think several important lessons can be drawn from this retrospective look at TB at the UMMC.
First, in Minnesota, where welcoming immigration policies have helped create large immigrant communities, TB is largely a disease of foreign-born individuals. Thus, health care providers must have a high index of suspicion for TB when working with patients born in certain countries, especially during their first five years in the United States. However, because a portion of TB cases in Minnesota are diagnosed in U.S.-born patients, physicians need to consider TB among a broad spectrum of diseases when making a differential diagnosis, especially as more and more patients take immunosuppressive agents for chronic diseases.
Second, TB, while most often thought of as a pulmonary disease, can and will surprise providers by presenting solely in extrapulmonary sites. In foreign-born patients in particular, it may present as a backache, nausea, or a soft-tissue mass. Therefore, it is essential to keep an open mind and be persistent when making a diagnosis in a difficult case.
Third, we noted differences in how quickly foreign-born and U.S.-born patients are diagnosed. We cannot say why this was the case; however, a number of factors, including lack of access to care and language and cultural differences that make communication between patients and physicians challenging, may play a role. These need to be evaluated.
Tuberculosis is here to stay. Populations will continue to change, as will presentations, resistance patterns, and treatments. The challenge for providers is to stay one step ahead of a disease that can show up anywhere, even in Minnesota. MM
Dan Fulton is an intern in internal medicine at Hennepin County Medical Center. He conducted this research project with Dr. Kline when he was a third-year medical student at the University of Minnesota. Susan Kline is an assistant professor in the department of medicine’s division of infectious disease and international medicine at the University of Minnesota Medical School and medical director for infection control at the University of Minnesota Medical Center, Fairview.
The authors wish to thank Sandra Davis of the medical records department at the UMMC/CH, Kathy Billman in microbiology, and Sarah Cameron in the infection control department.