Microbiological stewardship: redefining antibiotic use through lab leadership

Examining how our laboratories can provide stewardship on the appropriate use of antibiotics is the topic of a recently published research paper authored by a team of microbiologists led by Dr Max Bloomfield.

The team included Awanui microbiologists Michelle Balm and Tim Blackmore, Head of Department Koen Van Der Werff, and Wellington-based GP Sue Todd.

Their paper titled ‘Post-report antibiotic initiation following community non-sterile-site microbiology results: an opportunity for labs to lead stewardship?’ examined whether specimens collected from non-sterile sites, such as skin, mouth or a wound, are resulting in the unnecessary prescription of antibiotics and possible preventative measures.

“These specimens are the majority of community samples sent for microbiology testing because they are easy to collect. The key is they should generally be collected only if the patient has clear signs of an infection, but this often is not the case,” says Max Bloomfield.

“Test results, known as positive culture results, show these non-sterile sites usually have bacteria living in them under normal circumstances, but not whether the patient has an infection or not. However, from discussions with requestors, we know the results are often interpreted by clinicians as indicating infection and the need for antibiotics. Therefore, we suspect much of this prescribing is unnecessary.”

Max says because positive culture results from non-sterile sites are a poor indicator of clinical infection, the research sought to quantify their influence, and get more data on how often the results generate an antibiotic prescription.

Understanding potential unnecessary prescribing 

The team selected 65,000 wound and skin swabs, and just over 8,000 sputum samples, collected from patients from February 2017 to July 2022 as part of their research. They also drew on the National Minimum Dataset showing hospital discharge data reported to the Ministry of Health for the demographic breakdown.

“This data enabled us to determine patients who had been prescribed antibiotics at the same time as their sample was taken, which we called ‘Test and Treat,’ and those who had a sample taken but no antibiotics started.

“We were particularly interested in this second group who we identified as ‘Test and Wait.’ The fact these patients had not been started on antibiotics at the time of sampling made us suspect they did not have clear signs of an infection.

“If they had started on antibiotics after we issued their culture report, we called this ‘post-report antibiotic initiation’ (PRAI). This raised the further possibility our lab reports may have generated unnecessary antibiotic use for them because they were only started on antibiotics after we reported a result.”

Max says the research found ‘Test and Wait’ was common, occurring in about one third of patients having a wound swab collected, and about a half of those having a sputum sample collected.

He says this was a concern as it showed there may be a large number of patients with limited clinical evidence of infection having microbiological samples collected.

“PRAI occurred in just over 43 percent of cases when an organism was reported, as opposed to almost 11 percent for a ‘no growth’ report for wound and skin swabs. For the same comparison with sputum swabbing, PRAI occurred in almost 48 percent of cases, against nearly 11 percent.

“Overall, the findings show wound and sputum sampling in cases where the evidence for infection is likely to be low is common, and our lab reporting may be inadvertently driving quite a lot of unnecessary antibiotic use.”

Opportunities for laboratory guidance

So what opportunities are there for laboratories to provide guidance and leadership in this area?

“Microbiologists and laboratory scientists have an important role for interpretating patient test results. Therefore, developing strategies to reduce PRAI can support laboratories in offering meaningful antimicrobial stewardship and guidance given to clinicians on how they can interpret the results,” says Max.

“As a result of this research, Awanui Labs Wellington has made some significant changes to the reporting of wound swab results, and early analysis of these results show they have significantly reduced PRAI. We still need to do some more work and research, but it looks like our new reporting method has significantly improved prescribing in patients with an initial test and wait approach and their overall care.”

The paper is published in the Journal of Antimicrobial Chemotherapy and to read online – click here

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