Since 2016, Ramsey County, Minnesota has been working to end a deadly outbreak of multidrug-resistant tuberculosis (MDR TB). So far, health officials have identified 17 cases of MDR TB. A total of six of these cases have died, but only three of these deaths are being attributed to MDR TB. The large number of MDR TB cases in Ramsey County is highly unusual and is being described as the largest outbreak of MDR TB in the country in recent years. That a single county in Minnesota is witnessing so many cases of MDR TB in such a short period of time is cause for concern. Below we review why.
Overview of Tuberculosis (TB) in the United States
Tuberculosis is a contagious illness caused by the bacterium Mycobacterium tuberculosis, and it is spread from person to person via the respiratory route. It is estimated that one third of the world is infected with TB. The majority of those infected with TB have what is called latent tuberculosis infection, meaning they are infected but not sick with the active form of TB disease. A portion (typically 5-10%) of those with latent TB—particularly those with certain risk factors such as HIV infection or diabetes—may develop active TB disease. Only those who have active TB disease can transmit their infection to others.
Both latent TB infection and active TB disease are typically curable with antibiotic regimens. Multidrug-resistant TB (MDR TB) occurs when a person is infected with TB that is resistant to the two drugs most commonly used to treat TB (isoniazid and rifampin). Extensively drug-resistant TB (XDR TB) occurs when someone is infected with TB that is resistant to all of the following: isoniazid, rifampin, any fluoroquinolone, and at least one of three injectable second-line drugs—amikacin, kanamycin, and capreomycin.
According to the US CDC, there were 9,287 new cases of TB in the US in 2016. A majority of these cases (68.5%) were born outside of the US. Although the number of cases reported in 2016 is the lowest ever recorded, this success is tempered by an understanding that the rate of decline in TB incidence in the US is slowing. Based on this trend, models have shown that the US will not meet its goal for TB elimination by the end of the 21st Century.
TB in Minnesota
In a typical year, Minnesota reports approximately 160 cases of TB, but usually only a very small number of them are resistant cases. Like most places in the US, the majority of cases of TB occur among the foreign-born. From 2006-2015, 81% of reported TB cases in Minnesota occurred among non US-born persons. In 2015, Minnesota’s highest incidence of TB (5.4 new cases per 100,000 population) occurred in Ramsey County.
Minnesota tests all of its culture-confirmed TB cases for drug resistance. During 2011-2015, only 5 out of the 558 TB cases that the state tested for drug resistance were found to be multidrug-resistant, which corresponds to fewer than 1% of all TB cases tested. More than 3 times as many cases of MDR TB have been identified in Ramsey County since 2016 than were reported in the entire state over the previous 5 years, which raises serious concerns about the current outbreak.
Most of the 17 MDR TB cases identified in the current outbreak in Ramsey County have been elderly members of the local Hmong community, and 10 of the 17 cases have been linked to a senior center in the community. It has been reported that the outbreak in the center likely began among a group of seniors who regularly played cards together. One of the card players is thought to have been infectious for 5 years before being diagnosed.
That so many of the identified cases have been linked to each other in time suggests that transmission of MDR TB was primary—that is, directly from an infected individual to others. Historically, the majority of drug-resistant TB cases have been thought to occur among those who have been improperly treated for an infection that was initially susceptible to TB drugs (ie, secondary resistance). However, a recent review of drug-resistant TB by the Lancet Respiratory Medicine Commission concluded that the “traditional view that acquired resistance to anti-tuberculous drugs is driven by poor compliance and programmatic failure is now being questioned”.
What is Being Done to Respond?
According to a news report, public health officials in Ramsey County have identified more than 350 potential contacts of the known cases. A contact investigation of this scale is no easy feat. TB contacts are typically tested for latent TB infection, and those who have symptoms will be evaluated for active TB disease. Health officials in Ramsey County report that that they had incomplete contact information for a large number of contacts (~150), highlighting the challenges facing public health investigations and the time and resources required to complete them.
Testing on the 125 potential contacts already located has identified 58 cases of latent TB infection. Testing for drug resistance is really only feasible for active TB patients, because the bacteria is present in their sputum. For latent TB infection, the body’s immune system seals off bacteria in the lungs, where they remain dormant and largely inaccessible for testing. This makes it difficult to tell if latent TB cases were infected during this outbreak or infected previously from some other source. Since public health officials cannot rule out that these individuals have MDR TB, these individuals will likely have to be treated as though they are infected with MDR TB. This means a much longer and more expensive course of treatment is required. According to the CDC, it typically takes 18-24 months to treat MDR TB (compared to 6 months for drug-susceptible TB) and costs as much as $134,000 (versus $17,000 for standard TB therapies).
Shrinking TB Budgets and Erosion of Capacities
To facilitate response to this outbreak, Minnesota has allotted nearly $225,000 in emergency funds to St. Paul, the largest city in Ramsey County. The Ramsey County Public Health Department has allocated additional public health workers to respond to the outbreak. This demand on public health resources comes after the state recently spent $2.3 million to battle a measles outbreak that sickened more than 70 people. Although it is hard to gauge how much the MDR TB outbreak will ultimately cost, there is evidence that the tab could exceed that of MN’s recent measles outbreak. In 2013, Wisconsin spent $5.6 million to control a TB outbreak in one county.
The high expected costs of this and other TB outbreaks is most worrisome. Despite the fact that all states in the US report TB each year, most states’ TB control budgets have been shrinking, and federal support for TB control has also been declining. A survey conducted by the National Tuberculosis Controllers Association found that 60 percent of TB control programs have had to eliminate staff as a result of shrinking budgets, and 25 percent of programs reported having to restrict some essential TB activities, such as provision of directly observed therapy and contact and outbreak investigations. These cuts make it difficult for state and local health agencies to engage in routine TB control activities--such as screening and treating high-risk groups for TB infection--and leave them more vulnerable to outbreaks like that which is occuring in Minnesota.
Photo: A 1938 poster illustrating tuberculosis transmission commissioned by the US National Tuberculosis Association (now the American Lung Association), on exhibition at the Victoria and Albert Museum, London, UK
Photo courtesy of Flickr / typofi.
Outbreak Observatory aims to collect information on challenges and solutions associated with outbreak response and share it broadly in near-real time to allow others to learn from these experiences in order to improve global outbreak response capabilities.