On the eve of World TB Day, the CDC says there is good news and bad news about tuberculosis in the U.S.
On one hand, TB incidence in 2016 was the lowest seen since reporting began in 1953, with a provisional count of just 9,287 new cases, the agency reported in the March 24 issue of Morbidity and Mortality Weekly Report.
On the other hand, unless TB incidence starts to fall at a much faster rate, it will take decades to eliminate the disease, according to Kristine Schmit, MD, and colleagues at the CDC's division of tuberculosis elimination.
"Epidemiologic modeling demonstrates that if similar slow rates of decline continue, the goal of U.S. TB elimination will not be reached during this century," Schmit and colleagues reported.
The case count is down 2.7% from 2015, when some 9,486 cases were reported. And the rate is also down -- to 2.9 cases per 100,000 persons, from 3.0 per 100,000 in 2015.
The key to eliminating TB is to find and treat people with latent disease, according to Philip LoBue, MD, director of the TB elimination division.
Programs aimed at preventing TB transmission remain "essential" but are not sufficient, LoBue said in a statement. "More than 85% of U.S. TB cases are associated with reactivation of latent TB infection," he said, noting that the CDC estimates up to 13 million people in the U.S. have a latent TB infection.
Without treatment, he said, between 5% and 10% will go on to develop active TB.
Schmit and colleagues noted that 2016 recommendations from the U.S. Preventive Services Task Force (USPSTF) call for screening for latent TB, using either a tuberculin skin test or interferon-gamma release assay, among people at increased risk for TB.
Those individuals were defined by the task force as:
In the current analysis, Schmit and colleagues said, incidence varied on a state-by-state basis, from a low of 0.2 cases per 100,000 people in Wyoming to a high of 8.3 per 100,000 in Hawaii. The median state incidence was 1.9 per 100,000 people.
Twelve states -- Alaska, Arkansas, California, Florida, Georgia, Hawaii, Maryland, Minnesota, New Jersey, New York, North Dakota, and Texas -- and the District of Columbia had incidences higher than the national average.
And four states -- California, Florida, New York, and Texas -- each reported more than 500 cases, accounting for 50.9% of the national total.
As in previous years, people born in the U.S. accounted for a smaller number of cases than those born elsewhere -- 2,935 cases versus 6,307, with 45 cases in which the place of birth was not known.
Incidence among U.S.-born people was 1.1 cases per 100,000, down 8.4% from 2015, while the rate among foreign-born people was 14.6 cases per 100,000, down 3.2% from 2015.
The researchers said in 2015 -- the most recent year for which complete drug-susceptibility data are available -- there were 88 cases of multidrug-resistant (MDR) TB, defined as a bacterial isolate resistant to at least isoniazid and rifampin, the main first-line drugs.
Multidrug-resistant TB accounted for 0.4% and 1.2% of cases among U.S.- and foreign-born persons, respectively. Among the 88 cases, 72 occurred in people with no reported history of TB.
CDC identified one case of extensively drug-resistant (XDR) TB, defined as resistance to isoniazid and rifampin among first-line drugs, resistance to any fluoroquinolone, and resistance to at least one of three second-line injectable drugs.
The CDC report comes as international researchers warned online in The Lancet Respiratory Medicine that TB drug resistance threatens progress against the disease.
Around the world, about 5% of new cases are either MDR or XDR, according to Keertan Dheda, PhD, of the University of Cape Town in South Africa, and colleagues.
Both are associated with high mortality, with death rates of roughly 40% for MDR-TB and 60% for XDR-TB, the researchers noted. And the resistant disease is expensive to treat -- of the $6.3 billion available for TB response in 2014, about $1.8 billion was applied to MDR-TB.
Resistance "threatens to derail efforts to eradicate" TB, Dheda said in a statement.
"Even when the drugs work, TB is difficult to cure and requires months of treatment with a cocktail of drugs," he said. "When resistance occurs the treatment can take years and the drugs used have unpleasant and sometimes serious side effects."
He and colleagues called for community-based case finding, combined with better drugs and diagnostic methods.
Importantly, they argued that there is increasing evidence that the development of resistance -- long thought to be simply a matter of poor adherence to treatment -- is actually a more complicated phenomenon that requires intensive study.
The report by Schmit and colleagues was supported by the CDC. Authors are employees of the agency.
Dheda and colleagues did not report support for their analysis. Dheda reported grants from Foundation of Innovative New Diagnostics, eNose Company, Statens Serum Institut, bioMeriux, ALERE, Oxford Immunotec, Cellestis (now Qiagen), Cepheid, Antrum Biotec, and Hain Lifescience, as well as several patents.
Primary Source
Morbidity and Mortality Weekly Report
Source Reference: Schmit KM, et al "Tuberculosis -- United States, 2016" MMWR Morb Mortal Wkly Rep 2017;66:289-294.
Secondary Source
The Lancet Respiratory Medicine
Source: MedPage Today