The rate of tuberculosis infection in the United States has been going down because of prevention and treatment efforts, but the country may now be more susceptible to new nastier drug-resistant form, according to Johns Hopkins researchers.

The researchers used computer modeling to show an increased risk for epidemics of multi-drug resistant tuberculosis, or MDR-TB. The model also showed that without proper treatment of TB cases, there is also an increased risk.

The results were published in the Sept. 22 journal PLoS ONE.

MDR-TB is a kind resistant to at least two of the primary antibiotics used to treat tuberculosis. It affects 500,000 to 2 million people a year, according to the World Health Organization. There were 111 cases in the United States in 2006.

“The ability of MDR-TB to spread depends on the prevalence of drug-susceptible TB,” said Dr. David Bishai, senior author of the study and associate professor in the departments of Population, Family and Reproductive Health and International Health at the Johns Hopkins Bloomberg School of Public Health, in a statement. “The most successful approach to reduce this risk for MDR-TB epidemics in the U.S. would be to ensure that populations around the world combine high rates of case findings that are tightly coupled to high compliance with directly observed drug therapy.”

David Bishai conducted the research with his brother Dr. William Bishai, professor with the Johns Hopkins School of Medicine and co-director of the Johns Hopkins Center for Tuberculosis Research, and David Bishai’s son Jason D. Bishai, an undergraduate student at Stanford University.

The research was funded with an award to Jason Bishai from the Robert Wood Johnson Foundation Young Epidemiology Scholars Contest and by the National Institutes of Health.