There’s more bad news on the antibiotic resistance front.
A new study reveals that strains of tuberculosis that evade most of the drugs typically used to treat the bacterial infection have been spreading in South Africa, which already has a high rate of tuberculosis infection.
Extensively drug-resistant tuberculosis — known by the short form XDR TB — is highly concerning to health authorities because of the way tuberculosis spreads. Infected people expel bacteria from their lungs when they cough, sneeze, even speak. The bacteria can float for hours under the right conditions, infecting people who breathe them in.
About half of South Africa’s cases were in KwaZulu-Natal, a coastal province that includes the city of Durban.
The research, published Wednesday in the New England Journal of Medicine, does not suggest that extensively drug-resistant tuberculosis is spreading rapidly. But it does suggest that, of those tuberculosis cases in South Africa, far more are the result of transmission from person to person than previously known, rather than the result of improper medical treatment. The scientists — from the US and South Africa — found that in about 400 people studied, most had become infected by contracting the bacteria from someone else.
“We all know that tuberculosis is something that spreads between people, but it just hasn’t been as big a focus with XDR and MDR [multi-drug resistant] TB because there’ve been so many treatment failures that have caused [new] cases,” said Dr. Michael Gardam, who runs a TB clinic at Toronto’s University Health Network. Gardam was not involved in the study.
“But this case is showing this can spread quite nicely between people, and that’s even more terrifying in a way. Because you could just be in the wrong place at the wrong time.”
Extensively drug-resistant tuberculosis is still rare in the US, with fewer than five cases a year in the country, said Dr. Peter Cegielski, team lead for TB at the Centers for Disease Control and Prevention.
Several of the scientists responsible for the study work in Cegielski’s department. Cegielski and his colleague, Dr. Sarita Shah, reported the first cases of extensively drug-resistant tuberculosis TB in 2005, and Shah is the lead author on the new study.
Extensively drug-resistant TB is both difficult and costly to treat and treatment is often not successful. The fatality rate is between 50 percent and 80 percent, the study noted. The combination of XDR TB and HIV is particularly deadly.
Even though XDR TB is highly concerning to health authorities, TB is not as contagious as some other airborne pathogens, things like measles or chickenpox. Still, it is a major global threat, and one of the top 10 causes of death worldwide, according to the World Health Organization.
Tuberculosis is a bacterial infection that most often attacks the lungs. Most infections are latent; the bacteria are harbored in the body but don’t cause disease. The WHO estimates that about a third of the world’s population has latent TB.
People with latent tuberculosis have a 1 in 10 risk of developing active disease at some point. Symptoms of active disease are initially mild and include coughing, fever, night sweats, and weight loss. But untreated tuberculosis can be fatal.
The WHO estimates that in 2015, 10.4 million people were sickened by tuberculosis and 1.8 million died.
In this study, researchers from the CDC and a number of universities investigated 404 XDR TB patients to see if they were infected by others or had developed the resistance on their own. The scientists searched medical records and studied the genetic sequences of samples of bacteria collected from the patients. Closely related bacteria indicate transmission, not acquired resistance.
Inadequate treatment accounted for at most 31 percent of the cases, they reported. Some of the XDR TB transmission occurred in hospitals — a known risk — but some occurred in the community, they noted.
“It’s not a surprise that there’s so much transmission of tuberculosis, even highly drug-resistant tuberculosis going on in institutions. But I think it’s very important that they were able to quantify it using these state of the art scientific methods,” Cegielski said of the study.
He said a lot of work is underway to develop better methods of treating XDR TB cases and preventing transmission of this infection in hospitals. The findings, he noted, suggest “we need to redouble our efforts.”
That is true not just about XDR TB but tuberculosis in general, said Dr. Philip Lederer, an infectious diseases specialist at Massachusetts General Hospital and Harvard Medical School.
“This study points to the critical importance of transmission and the critical need for more funding and resources at all levels, from WHO to national TB programs, to research, to advocacy,” Lederer said. “It’s very neglected by the global health community.”