The source of an emerging gastro-causing bacterium remains unknown, and UNSW researchers say better testing could help provide answers.
Most bacterial gastrointestinal illnesses in Australia are thought to be caused by two pathogens, Campylobacter and Salmonella.
But an emerging pathogen, Aeromonas, is much more common than previously thought, with UNSW researchers revealing more than two years ago that it is the second-most common bacterial intestinal pathogen in Australia.
Aeromonas infection causes gastrointestinal symptoms including diarrhoea, abdominal pain, nausea, and may also present as colitis. In severe cases, it can progress to blood infections, which are more common in older patients, and may also promote the development of inflammatory bowel disease (IBD).
In new research published in the journal Eurosurveillance , the researchers examined 90,000 faecal samples using two types of testing tools (PCR and bacterial culture), confirming the high prevalence of the bacteria in the community.
Across the 90,291 samples analysed, Aeromonas was detected in 3125 cases in total (479 by culture and 2646 by PCR), representing roughly 3.5% of all patients tested.
By comparison, Campylobacter was detected in 6571 samples and Salmonella in 1411, placing Aeromonas among the most frequently identified bacterial causes of gastroenteritis in this dataset.
This surprised the researchers because Aeromonas infections typically occur in developing countries after contact with dirty water, and researchers don't know what's driving it in Australia.
The authors also note that older people seem to harbour more Aeromonas bacteria.
"This remains a neglected research area, despite being highly relevant to the health of the Australian population," says the study corresponding author, Associate Professor Li Zhang from the UNSW School of Biotechnology & Biomolecular Science.
Mysterious origins
In their previous studies, the team sequenced 92 Aeromonas genomes and found three species of Aeromonas pathogens are causing the bulk of the infections, and that each species appears to play a different role in contributing to the three age-related infection peaks observed in Australia.
For example, most of the infections in young adults are caused by one species, while another is relatively more common in young children and older adults.
They also noted increased infections during periods of warm weather, suggesting the burden of disease may increase as climate change increases temperatures.
A/Prof. Zhang is calling for support to investigate the sources of infection, which she hopes will help reduce infections, which her research shows are consistently high across hundreds of thousands of samples spanning nearly a decade.
"Most Australian patients who tested positive for Aeromonas enteric infections did not have a recorded recent overseas travel history," says Christopher Yuwono, a UNSW PhD student and the first author of the newly published research.
"This suggests that infections are being acquired locally, possibly from domestic sources or imported food."
The team believes there are multiple sources for the infections but can't be sure at this stage.
To be certain of the sources of these infections, researchers would need to isolate and analyse a large number of Aeromonas strains from water, food, fish, and other possible sources, and compare their genomes with those isolated from patients.
"Identifying the sources of infection could support refinements in food and water safely policies, critical for reducing transmission and future cases," A/Prof. Zhang says.
"Aeromonas pathogens should be treated more seriously from a policy perspective," she says.
...infections are being acquired locally, possibly from domestic sources or imported food.
Improved testing
The team also compared the efficacy of the two main methods used to test which pathogen was causing illness and found discrepancies in the results.
The researchers say that dual testing is much more effective at detecting Aeromonas pathogens, as well as Campylobacter and Salmonella in faecal samples.
"This insight is important not only for improving surveillance and clinical practice in Australia, but also for strengthening pathogen surveillance systems globally," says A/Prof. Zhang.
A/Prof. Zhang wants to see dual testing become the norm for gastrointestinal bacterial pathogens, though not all diagnostic laboratories currently have the capacity.
