By Stan Deresinski, MD, FACP, FIDSA
Clinical Professor of Medicine, Stanford University
Dr. Deresinski reports no financial relationships relevant to this field of study.
SYNOPSIS: The incidence of tuberculosis in the United States continues to decrease, but not at a rate sufficient to achieve elimination during this century.
SOURCE: Schmit KM, Wansaula Z, Pratt R, et al. Tuberculosis — United States, 2016. MMWR Morb Mortal Wkly Rep 2017;66:289-294.
A total of 9,287 newly diagnosed cases of tuberculosis (TB) were identified in the United States in 2016, a modest decrease from the 9,546 cases in 2015, resulting in a decrease in incidence from 3.0 per 100,000 persons to 2.0 per 100,000 persons. The incidence in 2016 ranged from 0.2 cases per 100,000 persons in Wyoming to 8.3 in Hawaii (median state incidence = 1.9). Alaska, Arkansas, California, Florida, Georgia, Hawaii, Maryland, Minnesota, New Jersey, New York, North Dakota, and Texas, as well as Washington, DC, had reported incidences that exceeded the overall national incidence. Four states accounted for 50.9% of all cases, with California reporting 2,130, Texas 1,333, New York 763, and Florida reporting 602 cases.
Two-thirds of cases in 2016 were in foreign-born individuals, and the incidence among the foreign-born (14.6 per 100,000) was 14 times greater than among individuals born in the United States (1.0 per 100,000). The incidence in foreign-born individuals nonetheless decreased by 3.2% compared to 2015, but the incidence also decreased 8.4% in U.S.-born individuals. Among U.S.-born individuals, the incidence has decreased or remained stable since 2013 in all racial and ethnic groups except native Americans (including Alaska natives and Hawaiian/Pacific Islanders, among whom the incidence had increased until 2016, when it decreased). Five countries of origin — Mexico, the Philippines, India, Vietnam, and China — accounted for 54.9% of all cases among foreign-born persons.
Among the individuals for whom the information was available, 5.7% were HIV-infected, 4.6% had been homeless at some point in the previous year, 1.8% resided in a long-term care facility, and 3.5% were confined to a correctional facility.
Susceptibility data for 2016 are not yet available, but in 2015, 0.4% of culture-confirmed cases in U.S.-born individuals were caused by multidrug-resistant (MDR) Mycobacterium tuberculosis (see Box), while among the foreign-born cases, 1.2% of isolates were MDR. One case was extensively resistant. Approximately four-fifths of MDR cases occurred in individuals without a known history of tuberculosis.
COMMENTARY
In addition to early recognition and treatment of patients with active tuberculosis, the cornerstone of control in the United States is identification and treatment of patients with latent tuberculosis infection (LTBI). Thus, the CDC and the U.S. Preventive Services Task Force (UPSTF) recommend screening with either the tuberculin skin test or an interferon-gamma release assay in individuals at increased risk of tuberculosis. Individuals at increased risk include those persons who were born in, or formerly resided in, countries with increased tuberculosis prevalence as defined by the World Health Organization (WHO) and persons who currently live in, or have lived in, high-risk congregate settings, such as homeless shelters, correctional facilities, and long-term care facilities.
Since, among foreign born individuals in the United States, 9 of 10 cases of tuberculosis are the result of reactivation of LTBI, targeting those born in high prevalence countries for testing and treatment of LTBI is an effective approach. Furthermore, since reactivation may occur at any time in a latently infected individual, the UPSTF recommends that testing should be performed on at-risk individuals even if they have resided in the United States for any period of time, no matter how prolonged.
Individuals, including healthcare workers, who work in high-risk settings with potential exposure to others with active tuberculosis, are considered to be at risk and also should be subject to testing and treatment. Additional persons considered to be at risk from either exposure or activation of latent infection should be tested similarly. These include:
- Close contacts of individuals with active infectious tuberculosis;
- Immunosuppressed persons;
- Those with other medical conditions associated with increased risk of tuberculosis reactivation, such as those with diabetes mellitus, chronic renal insufficiency, and silicosis; and
- Individuals with chest X-ray findings of fibrotic lesions suggestive of inactive tuberculous disease.
On March 24, 1882, Robert Koch announced the discovery of M. tuberculosis, and each year March 24 is recognized as World TB Day in commemoration. The theme of World TB Day is “Unite to End TB,” but the evidence is clear that in the United States, and despite the continued reduction in incidence, tuberculosis will not be eliminated during this century.
Figure. Tuberculosis Incidence Overall and Among U.S.-born and Foreign-born Persons — United States, 2002-2016
Source: Centers for Disease Control and Prevention
Box.
Multidrug resistant (MDR): Resistant to at least isoniazid and rifampin.
Extensively drug resistant (XDR): Resistant to at least isoniazid and rifampin among first-line drugs, resistant to any fluoroquinolone, and resistant to at least one of three second-line injectable drugs (i.e., amikacin, kanamycin, capreomycin).
The incidence of tuberculosis in the United States continues to decrease, but not at a rate sufficient to achieve elimination during this century.
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