The incidence of tuberculosis in the U.S. continues to fall, as it has since 2000, but the disease disproportionately affects people born outside the country, the CDC reported.
The incidence rate was three cases per 100,000 population, which represents a decrease of 4.2% from 2012, the report said.
The proportion of cases occurring in foreign-born people continued to rise, reaching 64.6% in 2013, although the absolute numbers are falling.
That's because the number of cases among native-born Americans is falling more quickly, the agency report said.
However, revised technical instructions for testing immigrants and refugees, started in 2007, appear to be cutting the number of people diagnosed with TB after they arrive in the U.S., the agency said in a separate report.
The analyses, in the March 21 issue of Morbidity and Mortality Weekly Report, appeared just days before World TB Day.
The World Health Organization, in a release to mark the annual March 24 event, noted that nine million people a year fall ill with TB, and three million are missed by health systems.
But fewer are being missed during the immigration and refugee process, the CDC report said, noting that every year about 450,000 people come to the U.S. on an immigrant visa, and between 50,000 and 70,000 arrive as refugees.
In 2007, the agency's technical instructions for TB testing of those people added a requirement for sputum cultures as well as smears.
Some 1,100 cases were detected in 2012, the most recent year with available data, of which 60% were smear-negative but culture-positive and so they would not have been detected using the earlier guidelines.
The increase in diagnoses coincided with a decline in the proportion of newcomers diagnosed with TB after their arrival in the U.S. -- from about 7% to between 1% and 2%, the CDC report said.
One implication of the finding is that referring people for treatment in their home country saved state and local health authorities in the U.S. about $15 million, the agency report argued.
"This program has been one of the largest and most successful interventions in U.S. tuberculosis control during the past decade," said Martin Cetron, MD, director of CDC's Division of Global Migration and Quarantine.
"In addition to creating major savings in healthcare costs," Cetron said in a statement, "the program ensures that immigrants and refugees get prompt care and correct treatment, which is vital to their health, the health of their loved ones, and the U.S. communities where they settle."
In its report on the decline in TB in the U.S., the CDC analyzed provisional surveillance data for 2013, which showed a total of 9,588 new TB cases reported.
The 3,377 TB cases among U.S.-born people -- representing 35.4% of all cases with a known national origin -- was down by 7.6% from the number reported in 2012 and 61% fewer than the number reported in 2000.
The rate among U.S.-born people was 1.2 per 100,000 population -- down 8.4% over 2012 and down 64.7% since 2000.
At the same time, 6,172 cases were reported among foreign-born people -- 64.6% of cases with a known national origin -- which represented a 1.6% decrease since 2012 and a 19% decrease since 2000.
The rate of 15.6 cases per 100,000 population was a 2.1% decrease since 2012 and a 41.1% decrease since 2000.
California, Texas, New York, and Florida combined reported 51.3% of all TB cases reported in 2013, the agency report said.
The agency cautioned that the data underlying the analysis are provisional and that incidence rates are based on population estimates.
North American Correspondent for MedPage Today, is a three-time winner of the Science and Society Journalism Award of the Canadian Science Writers' Association. After working for newspapers in several parts of Canada, he was the science writer for the Toronto Star before becoming a freelancer in 1994. His byline has appeared in New Scientist, Science, the Globe and Mail, United Press International, Toronto Life, Canadian Business, the Toronto Star, Marketing Computers, and many others. He is based in Toronto, and when not transforming dense science into compelling prose he can usually be found sailing.MOST READ IN Infectious Disease
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