Bacterial gastroenteritis is a common condition seen in Aotearoa New Zealand, which is typically diagnosed by PCR testing on a stool sample. Most causes of bacterial gastroenteritis (e.g. Campylobacter spp, Salmonella spp, Yersinia spp) cause a self-limiting illness and antibiotic therapy is not required. Indeed, guidelines available for community healthcare providers in Aotearoa (e.g. Community HealthPathways, recently released national antimicrobial guidelines Te Whata Kura) recommend against antibiotic therapy for the vast majority of cases.

A recent internal analysis at Awanui Laboratories of community faecal pathogen PCR testing revealed that antibiotic prescribing was very common after a positive result (ranging between 20-40% for the various individual pathogens), which suggests many community healthcare providers may not be following the recommended approach for the management of these infections. Given how common infectious gastroenteritis is in Aotearoa, and the volume of tests performed (approximately 100,000 through the Awanui network per year), this prescribing behaviour may represent a large volume of unnecessary antibiotic use in our communities, with resultant potential harmful effects at the individual patient level and population level via side effects, disruption to the faecal microbiome, and impacts on antimicrobial resistance (AMR).

In previous work we have demonstrated that interpretive comments, when added to laboratory reports, can have a significant positive effect on prescriber behaviour (https://doi.org/10.1093/jac/dkad384), but this has not been examined in relation to faecal pathogen testing.

This is a cluster randomised crossover trial, where four laboratories within the Awanui Labs network in Aotearoa New Zealand will act as the clusters. Each laboratory will be assigned four intervention levels, which will be implemented in random order over the course of the 12 month study period (i.e. 3 months per intervention).

The intervention will consist of interpretive comments that are appended to laboratory reports where a stool sample has been submitted for faecal bacterial pathogen detection (predominantly tested via multiplex PCR methodology) and one of the target organisms has been detected. The target organisms are Campylobacter spp, Shigella spp/Entero-invasive Escherichia coli, Salmonella spp, Yersinia spp, and Aeromonas spp.

There will be four different intervention levels: 1. a comment that reminds requesters that most acute bacterial gastroenteritis does not require antibiotic treatment, as per local guidelines; 2. the same comment as 1 is used, plus an additional comment is added reminding requesters of the negative effects of antibiotic over use at the population level (i.e. AMR); 3. the same comment as 1 is used, plus an additional comment is added reminding requesters of the negative effects of antibiotic overuse at the individual patient level e.g. harms due to side effects; 4. is a the control group, where no comment is appended.

The four levels will be auto added by each lab, each for a three month period, in the random order allocated at the beginning of the study.

Outcome measures will relate to antibiotic use in the time period following the laboratory report, plus unplanned hospitalisation out to 30 days post report.

Inclusion Criteria:

• Age over six months
• Stool sample submitted to Awanui Labs for faecal bacterial pathogen testing from a community health provider during the study period
• Test results report the detection of: Campylobacter spp, Shigella spp/Entero-invasive Escherichia coli, Salmonella spp, Yersinia spp, or Aeromonas spp.

Exclusion Criteria:

• Samples where only Clostridioides difficile or Helicobacter pylori testing has been requested will be excluded
• Samples sent for Public Health testing (e.g. testing for clearance of Salmonella spp) will be excluded.