Diabetes a Big Risk Factor for Surgical Site Infections

Becky McCall

December 31, 2015

Diabetes is a risk factor for surgical site infection, even after controlling for hyperglycemia, shows a new systematic review. The results suggest a need for continued efforts to improve surgical outcomes for patients with diabetes.

Specifically, patients with diabetes had a risk of surgical site infection that was 50% higher than patients without diabetes, lead author Emily Martin, PhD, assistant professor, epidemiology, University of Michigan School of Public Health, Ann Arbor, told Medscape Medical News.

The study confirms an association between both pre- and postoperative hyperglycemia and surgical site infection, but the authors also note that a "history of diabetes remained a significant risk factor in meta-analyses of studies that controlled for hyperglycemia." The results are published in the January issue of Infection Control and Hospital Epidemiology.

Based on the findings, Dr Martin said, "People with diabetes [undergoing surgery] can be proactive in talking to their doctors about strategies to reduce their risk of infection. Care providers should also provide support to patients with diabetes to help them manage their disease well throughout their daily life."

Commenting on the study, Aaron Glatt, MD, chair of the department of medicine at South Nassau Communities Hospital, New York, said, "It's a valuable study and confirms — with a great deal of statistical might behind it — that patients with diabetes are at increased risk of infection."

Thus, there is a need to "minimize this risk in terms of optimizing patients' diabetic control and being extra careful to identify infection when they do get it and recognize they are more likely to get it.

"I think physicians need to be aware of this, especially for elective surgery, and to aggressively treat hyperglycemia postoperatively," he added.

Meanwhile Dane Wukich, MD, orthopedic surgeon, University of Pittsburgh Medical Center (UPMC) Mercy Health Center, Pennsylvania, noted that the increased risk of surgical site infection associated with diabetes has been reported multiple times, but this study demonstrates anew that it is not diabetes per se but the complications of diabetes that increase the risk.

"Poor glycemic control, both short term, as measured by serum glucose, and long term, as measured by HbA1c, is associated with increased rates of surgical site infection," he explained.

"Also, readers of the paper should recognize that well-controlled...patients without complications of diabetes have lower rates of infection than those with poorly controlled diabetes and complications."

Understanding Link Might Improve Safety and Reduce Costs

The new study was partly motivated by the fact that the annual US healthcare cost of surgical site infections is $3 billion. Also, many hospitals are very focused on reducing surgical site infections as a way to improve patient safety, explained Dr Martin.

And the prevalence of hospital-associated infections because of antibiotic resistance highlights the importance of prevention in high-risk individuals, she and her colleagues note.

From 3631 abstracts published between December 1985 (the start date of the Centers for Disease Control and Prevention surgical site infection surveillance guidelines) and July 2015, 94 eligible studies involving adult patients undergoing any type of surgical procedures were evaluated for association between diabetes and surgical site infection. The included studies did not make any distinction between type 1 and type 2 diabetes.

Specific estimates for diabetes, blood glucose levels, and body mass index (BMI) were sourced from the data, and a random-effects meta-analysis was used to generate pooled estimates. Confounding was adjusted for according to surgery type, study type, inclusion of BMI, and diabetes prevalence in the study population. Patients who had undergone all types of surgical procedures were included and all comparative study designs were considered.

Risk Highest for Cardiac Surgeries

The results show a significant association between diabetes and surgical site infection that was consistent across multiple types of surgeries and remained after controlling for BMI.

Patients with diabetes had a risk of surgical site infection with an odds ratio (OR) of 1.53 compared with patients without diabetes.

"By looking at the results of 94 studies, we were able to take a 60,000-ft view of the connection between diabetes and surgical site infection," remarked Dr Martin. "We found that diabetes raises the risk of infection across many types of surgery."

Specifically, findings were significant for arthroplasty, breast, cardiac, and spinal surgeries, but the actual pooled estimate was found to be highest among those who had undergone cardiac surgery (pooled estimate OR 2.03 compared with surgeries of other types [P = .001]).

"We were surprised at how the rates of infection were consistently higher across multiple surgery types. This potentially indicates that diabetes is a risk factor overall," highlighted Dr Martin.

Diabetes Raises Risk of Infection Independently

A few studies included both glucose levels and history of diabetes in the multivariate analysis, and the findings from these support the hypothesis that diabetes is a significant contributor to surgical site infection risk through mechanisms other than hyperglycemia at the time of surgery.

Dr Martin said that they did not know the mechanism driving the higher surgical site infection rates in those with diabetes.

"We did look at glucose control during surgery and that did not explain it," she said. "Many of the studies we looked at used appropriate procedures to manage glucose during surgery. The connection was with people with a history of diabetes, above and beyond what a patient's glucose levels are right at the time of surgery."

"With regard to other explanations, my group is very interested in continuing to look at what bacteria cause these infections and whether that may impact risk of infection in diabetics," she continued.

Furthermore, she and her colleagues suggest the possibility that diabetes is a marker for other conditions that may put a patient at risk of infection, including vascular changes and white blood cell dysfunction.

Dr Glatt added that the contribution of each factor to overall risk remains unknown. "A diabetic who is well-controlled will do better than a diabetic who is not well-controlled, and a nondiabetic will be at less risk than a diabetic, whether the hyperglycemia is controlled or not," he said.

"I can't dismiss the hyperglycemia aspect, but it is important to note that diabetes itself seems to be a risk."

Dr Wukich added it is important to note that "other complications of diabetes such as neuropathy, peripheral artery disease, and end-stage renal disease also contribute to higher rates of infection."

Still Beware of Hyperglycemia in Nondiabetic Patients

One expert contacted by Medscape Medical News takes a slightly different view, however.

Patchen Dellinger, MD, professor of surgery, University of Washington, Seattle, says, "What is much more recent and still often misunderstood is that hyperglycemia is the risk factor and not diabetes."

He asserts that data show that perioperative hyperglycemia in nondiabetics actually causes a greater increase in risk of surgical site infection than in diabetics.

Dr Dellinger argues that because perioperative hyperglycemia in nondiabetics is less common than in diabetics, if a comparison were made between diabetics and nondiabetics there would be more perioperative hyperglycemia in diabetics and, in turn, more surgical site infections.

"However, because there are many more nondiabetics than diabetics in the world, between 25% to 50% of all episodes of hyperglycemia actually occur in nondiabetics when careful monitoring is done," he noted, adding that nondiabetics were less likely to be monitored and treated for raised glucose levels.

Surgical Site Infection Guidelines

A spokesperson for the Infectious Disease Society of America, Dale Bratzler, DO, associate dean of the University of Oklahoma College of Public Health, Oklahoma City, is an author of the surgical site infection guidelines and addressed this issue.

He asserted that "guidelines for the prevention of surgical site infection now recommend perioperative glucose control as an intervention to reduce the risk [of infection], and draft guidelines from the Healthcare Infection Control Practices Advisory Committee provide a strong recommendation to control glucose in all patients undergoing surgery."

He added that in a study in colorectal surgery, a bundle approach to surgical site infection prevention — including glucose control as a component — reduced rates of surgical site infection in all patients.

Finally, he added that, as noted by Dr Martin and colleagues, there has not been consensus on the best target for blood glucose (or HbA1c) in surgery.

Dr Martin and Dr Glatt declared no relevant financial relationships. Dr Wukich is a consultant for Arthrex and Stryker, but had no disclosures relevant to this topic. Dr Bratzler had no relevant financial relationships.

Infect Control Hosp Epidemiol. 2015;37:88-99. Abstract

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