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Release: June 13, 2002

(Photo: Loreen Herwaldt, M.D., UI associate professor of internal medicine and public health)

NOTE TO EDITORS: Parts of this release are adapted from a release issued by Johns Hopkins Medical Institution.

Nasal antibiotic ointment reduces hospital-acquired, post-surgery infections

A new study conducted by researchers from the University of Iowa and Johns Hopkins Medical Institution finds that applying an antibiotic ointment inside the noses of surgery patients helps protect them from acquiring a post-operative infection. The study is published in the June 13 issue of the New England Journal of Medicine.

The antibiotic ointment, mupirocin, is effective for treating a bacterium known as Staphylococcus aureus (S. aureus), which resides in the nostrils of an estimated 25 to 30 percent of the general population. Usually, S. aureus nasal colonization is temporary and harmless, but bacteria from the nose can contaminate surgical sites, causing severe and often deadly infections. S. aureus causes one fourth of all hospital-acquired infections, which can result in prolonged hospital stays and substantially increased health care costs.

"It has been known for a while that patients who have S. aureus in their nose have a substantially higher risk of getting a S. aureus surgical wound infection after a surgical procedure than patients who don't have the bacteria in their noses," said Loreen Herwaldt, M.D., UI associate professor of internal medicine and public health and an author on the study. "Mupirocin really is the most effective agent that we have for eliminating S. aureus bacteria from the nose."

The study known as MARS (Mupirocin and the Risk of Staphyloccus aureus infections) may be the largest trial to date to investigate the effectiveness of an antibiotic in preventing post-operative infection. More than 4,000 adult patients undergoing elective surgery at UI Hospitals and Clinics and the Veteran Affairs Medical Center (VAMC) in Iowa City were enrolled.

The study had several goals. It aimed to find out if using mupirocin to kill nasal bacteria in patients before they had surgery would reduce S. aureus surgical-site infections. The study also examined whether mupirocin treatment could reduce surgical-site infections caused by other kinds of bacteria. Finally the study investigated whether mupirocin could reduce the overall incidence of hospital-acquired infection caused by S. aureus, including surgical site infection, pneumonia, bloodstream infections, and urinary tract infection.

Patients were randomly assigned to one of two groups. One group had mupirocin ointment applied to the inside of their nostrils twice daily for five days before surgery. The other group received a placebo treatment, which consisted of an ointment that did not contain the antibiotic substance. Neither patients nor physicians knew who received the mupirocin and who got the placebo. The patients were assessed for an average of 30 days after their operations to determine whether they acquired infections. Study participants included general surgery patients, neurosurgery patients, gynecology patients and cardiothoracic patients.

"When we looked at all S. aureus hospital-acquired infections, there was a significant decrease in infection rates for the treated group compared with the non-treated group," Herwaldt said.

The study also showed nearly a 50 percent decrease in surgical-site infections in the patients who received the mupirocin. Herwaldt commented that the researchers believed that this decrease was clinically important, but added that due to several factors in the study, the result was not statistically significant.

"We are excited to find that mupirocin did decrease the overall rate of S. aureus hospital-acquired infection," Herwaldt said. "However, we think that it is too early to say which patients are going to benefit the most, and we have to use mupirocin cautiously to protect against the development of antibiotic resistance."

Antibiotic resistance is a problem associated with increased use of any antibiotic. Although the research team found that a short, carefully planned mupirocin treatment, like that used in the study, did not appear to contribute to antibiotic resistance, Herwaldt explained that targeting mupirocin treatment only to patients most likely to benefit would also help prevent antibiotic resistance. The researchers hope to identify risk factors that increase patients' likelihood of carrying S. aureus in their nose so they can identify the patients who are at highest risk of acquiring an infection after an operation.

"Mupirocin is the only drug of its kind," Herwaldt said. "We don't want to lose it by causing antibiotic resistance through overuse. We definitely need to use mupirocin wisely."

Lead author on the study Trish Perl, M.D., associate professor of medicine, director of Hospital Epidemiology and Infection Control at Johns Hopkins, was at the University of Iowa when the study was done. In addition to Herwaldt and Perl, other UI authors of the study include

Joseph Cullen, M.D., associate professor of surgery, Michael Pfaller, M.D., professor of pathology and public health, M. Bridget Zimmerman, Ph.D., Deborah Sheppard, and Jennifer Twombley. Richard Wenzel, M.D., professor and head of internal medicine at Virginia Commonwealth University, Richmond Va., and Pamela French, M.D., at GlaxoSmithKline, also were authors. Herwaldt, Cullen and Pfaller all hold physician appointments at the VAMC.

Mupirocin ointment is made by GlaxoSmithKline. The study was funded by a research grant from GlaxoSmithKline, and both Herwaldt and Perl have consulted for the company.

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