Although tuberculosis (TB) is on the wane in the U.S., there’s little chance that the nation will eliminate the disease before the end of the 21st century, according to a new study from Harvard T.H. Chan School of Public Health.
But the study also found that intensifying TB control efforts could substantially accelerate its decline.
The study was published online May 14 in the American Journal of Epidemiology.
“The risk of developing TB is much higher for some people, particularly those born in countries where TB prevalence is high. These individuals could be infected with TB before coming to the U.S., but if we can treat their latent infection this can prevent them from progressing to active disease,” said Dr. Nicolas Menzies, assistant professor of global health at Harvard Chan School and lead author of the study.
TB is one of the world’s deadliest diseases, according to the U.S. Centers for Disease Control and Prevention. In 2016, 10.4 million people around the world became sick with TB and there were 1.7 million TB-related deaths. The number of TB cases in the U.S. has declined over the last seven decades, but these declines have flattened in recent years. Most new TB cases in the U.S. now occur among people born outside the U.S., where TB incidence is much higher.
The researchers, including collaborators from Yale University and the U.S. Centers for Disease Control and Prevention, used a mathematical model to estimate future TB outcomes in the U.S. under various scenarios. The model took into account factors such as historical data on the prevalence, spread, and treatment of TB; patterns of drug resistance; how HIV affects TB spread; risk levels among both U.S.-born and non-U.S.-born populations; and immigration trends.
The study found that if the U.S. makes no changes in how it prevents and treats TB, incidence is projected to decline to 14 cases per million by 2050, a 52 percent reduction from 2016. But strengthening TB control could accelerate declines—reducing incidence by 77 percent—with a combination of measures, including broader access to preventive and treatment services and improvements in the effectiveness of diagnosis and treatment.
The researchers predicted that, by 2100, TB may be eliminated among those born in the U.S. but not among the non-U.S.-born, who will account for an estimated 87 percent of TB cases at that time and thus be the dominant driver of future U.S. TB trends. “A long-term forecast like this is highly uncertain, but in all of the scenarios we looked at, it was clear that TB elimination would not be happening any time soon,” Dr. Menzies said.
Given that both TB incidence and latent TB infection—infection that is present in people’s bodies but not causing disease—is most prevalent among migrants, focusing prevention and treatment efforts on that population would be most effective, the scenarios showed. The authors also suggested that efforts to reduce the TB burden abroad could help reduce the disease’s incidence not only in other countries but also in the U.S.