Researchers have called for more focus on Vibrio infections in Australia because of the potential impact of climate factors and a growing industry.
Australia currently produces almost 8,900 tons of oysters per year with expanded production expected in the next few years.
Vibrio infection is not a nationally notifiable disease which may mean cases go undetected. All Vibrio infections are notifiable in Tasmania; but there are varying requirements in other jurisdictions. A notifiable disease means infections must be reported by law to the relevant agency.
“A national discussion to consider Vibrio parahaemolyticus infection as a nationally notifiable disease is warranted,” said researchers.
Infections may be acquired through consumption of seafood or exposure to contaminated water.
Vibrio infection was rarely reported in Tasmania before 2016, when a multistate outbreak of Vibrio parahaemolyticus associated with Tasmanian oysters sickened 11 people. Since then, sporadic cases have been identified following consumption of commercially- and recreationally-harvested oysters, commonly eaten raw.
Also in 2016, Western Australia investigated nine cases of locally-acquired Vibrio parahaemolyticus that were likely linked to oysters grown in South Australia.
From 2003 to 2020, 55 cases of vibriosis were reported in Tasmania, with 22 foodborne and 32 non-foodborne infections. Most were reported from 2016 onward and 33 of 43 cases were Tasmanian-acquired infections.
Industry controls are being implemented in Tasmania that aim to minimize the risk of cases and foodborne outbreaks.
Varied national picture and factors increasing risk
Individual cases of locally-acquired foodborne vibriosis have been reported from states where Vibrio infections are notifiable, with oyster consumption frequent in food histories.
Vibriosis linked to oysters has occurred elsewhere but notification requirements vary, making case and outbreak detection difficult and potentially hampering public health response. It is also assumed that outbreaks of gastroenteritis are often not reported to health authorities, resulting in under-representation of the true number of patients, according to the study published in the journal Communicable Diseases Intelligence.
Environmental factors can lead to increased amounts of Vibrio species in the water and changes in the prevalence of pathogenic strains. Numbers are usually highest when water temperatures are 20 degrees to 30 degrees C (68 degrees to 86 degrees F).
Increases in both foodborne and non-foodborne Vibrio infections in Tasmania are likely associated with higher sea water temperatures. It is thought the combined growth in the oyster industry and climate-related factors will increase the incidence of vibriosis in Australia, said researchers.
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