Screening Strategy Reduces Incidence of Immigration-Related Tuberculosis

By LabMedica International staff writers
Posted on 30 Mar 2015

Implementation of the culture-based algorithm may have substantially reduced the incidence of tuberculosis (TB) among newly arrived, foreign-born persons in the United States of America.

Immigration has a substantial effect on the incidence of TB, so immigrants and refugees bound for the USA are required to have overseas TB screening. Before 2007, a smear-based algorithm that could not diagnose smear-negative/culture-positive TB was used to screen this population.

Image: Mycobacterium tuberculosis culture revealing this organism’s typical morphologic characteristics of colorless rough surface, which are seen in M. tuberculosis colonial growth (Photo courtesy of Dr. George Kubica).

Scientists at the Centers for Disease Control and Prevention (CDC; Atlanta, GA, USA) revised the screening strategy to use a more inclusive culture-based algorithm. They reviewed health records to determine the increase of smear-negative/culture-positive Mycobacterium tuberculosis or TB cases diagnosed overseas between 2007 and 2012 and compared that figure with the decline of reported TB cases among foreign-born persons within one year after arrival in the USA.

Of the 3,212,421 arrivals of immigrants and refugees from 2007 to 2012, a total of 1,650,961 (51.4%) were screened by the smear-based algorithm and 1,561,460 (48.6%) were screened by the culture-based algorithm. Among the 4,032 TB cases diagnosed by the culture-based algorithm, 2,195 (54.4%) were smear-negative/culture-positive. Before implementation (2002 to 2006), the annual number of reported cases among foreign-born persons within one year after arrival was relatively constant (range, 1,424 to 1,626 cases; mean, 1,504 cases), but decreased from 1,511 to 940 cases during implementation (2007 to 2012). During the same period, the annual number of smear-negative/culture-positive TB cases diagnosed overseas among immigrants and refugees bound for the USA by the culture-based algorithm increased from 4 to 629.

The authors concluded that the increased annual number of TB cases detected in immigrants and refugees closely matched in magnitude a decrease in the number reported TB cases, suggesting that the culture-based algorithm effectively reduced TB incidence. To further reduce the TB incidence in foreign-born populations, consideration should be given to expanding TB screening to students, exchange visitors, and temporary workers from countries with a high incidence of TB, as well as finding novel strategies to address the large numbers of foreign-born persons with latent TB infection The study was published on March 17, 2015, in the journal Annals of Internal Medicine.

Related Links:
[US] Centers for Disease Control and Prevention