Tuberculosis bacteria that resist two or more of the most potent drugs available have begun to emerge and spread worldwide, according to a study reported in tomorrow's New England Journal of Medicine. The study, conducted between 1994 and 1997, points out the need for effective tuberculosis control programs in every country, public health experts say.
Tuberculosis kills more people than any other infectious pathogen--3.1 million worldwide in 1995, according to the World Health Organization. Because the bacteria hide inside cells and rapidly evolve resistance to antibiotics, they are particularly hard to kill. Infected patients must simultaneously take three and sometimes four antibiotics for up to 8 months to beat back an infection. When patients don't finish their treatment, resistance to even two of these drugs--isoniazid and rifampin--can crop up and render a strain almost unstoppable. "If we lose these two drugs, then we're going to be in deep trouble," says study author Adalbert Laszlo, a microbiologist at the National Reference Center for Tuberculosis in Ottawa, Canada. "There's no replacement for them."
To find out just how far drug resistance had spread, the World Health Organization and the International Union against Tuberculosis and Lung Disease enlisted 25 reference laboratories worldwide; in 1994, these labs began testing samples of tuberculosis strains for resistance to various drugs.
In each of the 35 countries studied, strains that resisted both isoniazid and rifampin had appeared. Although 2.2% of all tuberculosis strains worldwide resisted both drugs, an alarming 13% of strains from patients treated for less than a month also resisted both drugs. Bacteria resistant to multiple drugs flourished in areas where antibiotics are freely available and tuberculosis control programs are weak, such as the former Soviet Union, says Laszlo.
Public health experts say the findings sound an alarm. "The data show that resistance to antituberculosis drugs is still a major threat to the global control of tuberculosis," says Dixie Snider of the U.S. Centers for Disease Control and Prevention in Atlanta. Now that public health workers know which drugs are easily resisted by tuberculosis bacteria, they can recommend drug combinations that work for strains that only resist one. Says Laszlo: "We are no longer blind."