Surgical infections could primarily be caused by bacteria that already live on your skin, rather than via external contamination, according to a study of just over 200 people who underwent spinal procedures.

Hospitals tend to have strict hygiene standards, including sterilising surgical clothing and equipment, to prevent such problems, but one US study found 3 per cent of people who have an operation are affected.

Instead of coming from the hospital environment, many post-surgery infections could stem from an individual’s skin microbiome, says Dustin Long at the University of Washington in Seattle.

To investigate that idea, Long and his colleagues collected skin swabs before and after 204 people underwent different types of spinal surgery.

Fourteen of the participants went on to develop wound infections. After analysing the microbes responsible, the team found that 12 of the cases involved bacteria that were already part of the individuals’ skin microbiomes before surgery.

“Virtually all of the SSIs [surgical site infections] we encountered originated from the patient’s own microbiome, rather than pathogens that were introduced from the hospital or the operating room,” says team member Stephen Salipante, also at the University of Washington.

The researchers expect similar results for any surgery that involves cutting the skin, says Long.

They also found that 59 per cent of the infection-causing organisms uncovered in the study were resistant to pre-surgery antibiotics given intravenously to all the participants, in an effort to prevent such infections. “By characterising the antibiotic resistance traits in the microbiome before surgery, antibiotic therapy could be tailored to each individual patient in order to make it as effective as possible,” says Salipante.

Future research could also look into the most effective methods for sterilising people’s skin before an operation, he says.

Despite the findings, a clean hospital environment and sterile surgical instruments are still essential, says Long.

“Much of the information on the importance of bacterial skin flora in surgical site infection, and particularly surgery involving implantable material, has been known for several decades,” says Roger Bayston at the University of Nottingham in the UK.