Elderly, diabetics, women at risk for post-surgery infection

06/10/04

DURHAM, N.C. -- A Duke University Medical Center study of patients who undergo cardiothoracic surgery found the elderly, people with diabetes and women were more likely to develop a serious, potentially fatal chest infection caused by drug-resistant bacteria.

"The infection occurs infrequently, but when it does occur, it is extraordinarily devastating," said Vance Fowler, M.D., assistant professor of medicine in the division of infectious diseases at Duke University Medical Center. "It's catastrophic for the patient and expensive for the health-care system."

People who develop this chest infection after cardiothoracic surgery have an 11-fold increase in risk of death and accrue about $41,000 more in hospital costs, found a previous Duke study. Identifying the risk factors for infection is critical because the U.S. population is aging and becoming more overweight, with complications such as diabetes and cardiovascular disease, Fowler said. "Identifying the risk factors could help facilitate the design and implementation of preventive strategies. Our study may be a useful first step in this process," he said.

The research was published in the June 1, 2004, issue of the journal Clinical Infectious Diseases. Funding was provided by Duke University Medical Center.

The bug at fault is methicillin-resistant Staphylococcus aureus, a microbe impervious to the effects of methicillin antibiotics. This antibiotic-resistant staph strain had long been a problem in medical settings such as hospitals, but is increasingly the source of outbreaks in communities. The virulence of the microbe is also increasing; a new antibiotic-resistant strain appeared from an unknown source last year and has caused outbreaks throughout the U.S., Fowler said.

The standard treatment for the chest infection, called postoperative mediastinitis, is radical surgery, said Fowler, who specializes in the study of S. aureus strains. "Mediastinitis is a surgical disease, and surgery for mediastinitis is an ugly affair. In some cases, the sternum has to be completely cut out."

Lead author Elizabeth Dodds Ashley said the antibiotics typically given to patients just before surgery don't target the resistant pathogen. "What we give to all our patients doesn't hit these bugs," said Ashley, who holds a doctor of pharmacy degree and is with the division of infectious diseases at Duke University Medical Center.

Before Duke doctors and pharmacists could zero in on the best antibiotic to prevent methicillin-resistant S. aureus (MRSA) infection, they had to identify who was most at risk for the disease. "We don't want to give everyone these antibiotics because the drugs have a lot of toxicities," Ashley said.

The case-case-control study analyzed 223 patients at Duke University Medical Center who underwent surgery that involved opening the chest through incision. The majority of patients -- 92 percent -- had undergone coronary artery bypass surgery. More than 95 percent of the patients received prophylactic antibiotics -- cephalosporins -- just before surgery to help prevent infection. Cephalosporins are not effective against methicillin-resistant S. aureus.

The patients were divided into three groups: a control group of 80 randomly selected people who developed no post-surgical infection; a group of 79 people who developed chest infection caused by methicillin-susceptible S. aureus; and a group of 64 people who developed chest infection caused by methicillin-resistant S. aureus.

The study found patients who have diabetes, are female or more than 70 years old were more likely to develop postoperative mediastinitis caused by methicillin-resistant S. aureus. Obesity was also associated with infection, but not as strongly.

As a result of the study, physicians at Duke University Medical Center, which performs about 3,000 cardiothoracic surgeries annually, now consider giving antibiotics effective against methicillin-resistant S. aureus to certain patients before surgery.

"We've identified our elderly and diabetic patients as particularly at risk, so those patients receive a revised prophylactic regime, which includes 3-lactam, vancomycin and rifampin," said Keith Kaye, M.D., director of infection control at Duke University Hospital and assistant professor in the division of infectious diseases at Duke University Medical Center. "As a result, we've seen a drastic reduction in MRSA mediastinitis."

In addition to using prophylactic antibiotics, Duke doctors are also helping to lower the infection risk in patients with diabetes by developing algorithms to tightly control glucose levels before and after surgery, Kaye said. High blood sugar increases the risk of postoperative mediastinitis.

Other members of the research team include Doug Carroll, assistant professor at the University of Oklahoma College of Pharmacy; John Engemann, M.D., associate in the Duke department of medicine; Anthony Harris, M.D., assistant professor at the University of Maryland School of Medicine; and Dan Sexton, M.D., professor of medicine in the Duke division of infectious diseases.

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