Nasal S aureus Carriage Linked to Surgical Infections

Nasal Staphylococcus aureus (SA) carriage is associated with SA surgical site and bloodstream infections following a surgical procedure, according to findings from a new prospective, multicenter clinical study published in the August issue of Open Forum Infectious Diseases.

“This was a pan-European study with many hospitals, many different clinical settings, and as far as I’m aware, it hasn’t been done before. [The new study] covers a lot of European countries and a lot of surgical specialties,” said lead author Jan Kluytmans, MD. The study also captures the current state of preventive strategies in surgery, such as changes in air flow, dress, and skin preparation, he added.

The study included 5004 patients from 33 hospitals in ten European countries, of whom 67.3% were found to be SA carriers. The median age was 65 years, and 49.8% of patients were men. Open cardiac and knee and hip prosthesis surgeries made up the largest fraction, but there were 12 types of surgery included in the study.

There were 100 SA surgical site or blood infections. The researchers found an association between surgical site or blood infection and SA carriage at any site (adjusted hazard ratio [aHR], 4.6; 95% CI, 2.1-10.0) and nasal SA carriage (aHR, 4.2; 95% CI, 2.0-8.6). Extranasal SA carriage was not associated with an increased infection risk.

One unit increase in nasal bacteria was associated with an increase in infection risk (aHR, 1.23; 95% CI, 1.05-1.43).

A strength of the study is that it is the largest prospective study yet conducted on SA carriage in surgical patients, but the researchers were unable to do a subgroup of methicillin-resistant SA (MRSA) due to small numbers of infections.

The World Health Organization (WHO) has endorsed nasal decolonization with the highest level of scientific evidence. The WHO strongly recommends decolonization for cardiothoracic and orthopedic surgery using intranasal applications of mupirocin 2% ointment with or without a combination of chlorhexidine gluconate bodywash. It has a conditional recommendation for a similar procedure before other types of surgery.

However, “It is not widely practiced, and although that was not a surprise to me, I think it’s really disappointing to see that proven effective strategies are not being practiced,” said Kluytmans, who is a professor of medical microbiology at University Medical Center Utrecht, Utrecht University, Utrecht, Netherlands. “If I would come into surgery being a carrier and not be decolonized, I would really be quite angry because it puts you at risk, which is preventable. I think that’s something we owe to our patients,” he said.

He said that some may have concerns about the potential for decolonization to contribute to antibiotic resistance, but the short-term prophylaxis — typically for a few days — should not foster resistance, according to Kluytmans. “If you use it short-term, just before surgery, it has been shown in many studies that resistance isn’t a big problem.”

The link specifically to SA nasal carriage is a mystery, said Kluytmans. “It puzzles me still how it gets from the nares to the wound during surgery. So that’s my one million dollar question that I would like to resolve. We would like to study it, but we haven’t quite a bright idea how to do that,” he said.

The results are compelling, according to Heather Evans, MD, who was asked for comment. “On the face of it, this looks like a no brainer. We should be decolonizing all patients that go to the operating room, and it’s not a terribly unpleasant thing for a patient to undergo to have decolonization done. Particularly for patients who are at higher risk for having a severe complication, like someone that has an operation that’s involving an implant, for example, I think it really makes a lot of sense to do this low-cost intervention for those patients,” said Evans, who is a professor of medicine at The Medical University of South Carolina as well as the president of the Surgical Infection Society.

She also noted that many facilities test for MRSA but usually not SA more broadly. “This is a very interesting and compelling study that makes us rethink that, and maybe it isn’t even worth testing to see if you have S aureus, maybe we should just be putting betadine in everyone’s nostrils when they come to the operating room. It just seems like it would be a pretty low-cost intervention and something that could potentially have a big impact,” said Evans.

Although she was impressed by the study, Evans noted that the researchers tested for carriage at sites unrelated to the surgical site. “It really made me wonder if it would have added even more credibility to the study if there had been a sample taken after surgical prep was done to demonstrate that there is actually no S aureus present on the skin at the time that the wound was made,” she said.

The question ties into the recent “trojan horse” hypothesis, which suggests that endemic carriage of bacteria is responsible for most surgical site infections, rather than the long-held belief that operating room contamination is to blame. “That would sort of fly with this study that the patient is walking around with S aureus and not necessarily on their skin or at their surgical site, but it’s endemic in their body,” said Evans.

Kluytmans and Evans had no relevant financial disclosures.