Salt Lake City, UT—Severe illness caused by the bacteria Clostridium difficile is now the most common hospital acquired infection in the United States.

A new study published online by JAMA Internal Medicine suggests, however, that C difficile is not always being treated optimally. A study team led by researchers from the Veterans’ Salt Lake City Health Care System (VA) and University of Utah report that patients with the infection were less likely to die when treated with the antibiotic vancomycin compared to the standard treatment of metronidazole.

One of the challenges in treating C difficile is the high mortality rate. In 2011, almost half a million Americans, mostly 65 or older, developed C difficile infection, and 83,000 of them experienced recurrence of infection within 30 days of completing the standard course of antibiotics, according to the CDC.

“This is a very real problem that impacts the patients’ quality of life,” explained lead author Vanessa Stevens, PhD, a research assistant professor in the department of internal medicine and an investigator at the IDEAS 2.0 Center at the VA.

Overall, the research indicated an up to 20% mortality risk within 30 days of a C difficile diagnosis.

Two antibiotics—metronidazole or vancomycin—are recommended in practice guidelines to treat the condition, although metronidazole has tended to be favored over the past few decades because of its lower cost and because of concerns about vancomycin resistance in other hospital-acquired infections.

“For many years the two antibiotics were considered to be equivalent in their ability to cure C. diff and prevent recurrent disease,” noted Stevens, whose report pointed out that the study guidelines are based on small clinical trials from about three decades ago. “Our work and several other studies show that this isn’t always the case.”

For the current study, researchers sought to determine the effectiveness of the two drugs by focusing on the risk of mortality after treatment. To do that, investigators examined the data from more than 10,000 patients treated for C difficile in the VA’s healthcare system from 2005 to 2012.

For purposes of the research, a severe case of C difficile infection (CDI) was defined as elevated white blood cell count or serum creatinine within 4 days of the CDI diagnosis, while a mild- to-moderate case of CDI was defined as normal white blood cell counts and creatinine levels.

With about 35% of the cases considered severe, those patients had lower mortality rates when treated with vancomycin compared to metronidazole—15.3% versus 9.8%. In fact, researchers calculated that only 25 patients with severe CDI would need to be treated with vancomycin instead of metronidazole to prevent one death.

Yet only 15% percent of CDI patients, including severe cases, received vancomycin at the VA at the time of the study.

“That is a powerful, positive outcome for our patients’ well-being,” Stevens emphasized, although she added that the study team does not fully understand why the difference in the antibiotic affects mortality rates.

Study results did not show a difference in the rate of the illness recurrence, no matter the antibiotic treatment or illness severity. In addition, no difference in mortality rates was identified for mild-to-moderate CDI cases treated with either antibiotic.

Research limitations include its observational nature and that study subjects were primarily male, according to Stevens, who called for more research. “The optimal way to move forward is to do decision analysis that allows us to weigh the pros and cons of the various treatment strategies,” she said.

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