Denise Cullen
Coming from health authorities, it was an unusual order: Don’t eat your greens.
It came just before Christmas last year after dozens of people began presenting to hospitals with an odd grab-bag of symptoms, including rapid heartbeat, hallucinations, delirium, blurred vision, dilated pupils, flushed faces and fever.
It was a case for the ‘food detectives’ to get to the cause. Authorities weren’t certain, but it seemed the common factor was – contaminated baby spinach.
Food Standards Australia New Zealand issued a national recall for several spinach-based food items, including bagged salad leaf blends, and pre-prepared salads.
Supermarkets in at least four states were caught up in the recall.
And with several cases identified in the nation’s capital, ACT Health issued an urgent public health alert.
“The products are not safe to consume and people who have these products should throw them out or return them to the place of purchase for a full refund,” the directorate said in a statement.
This was serious. There are an estimated 4.67 million cases of food poisoning in Australia each year which results in 47,900 hospitalisations.
And 38 deaths.
Unusual symptoms
Identifying the cause of food-borne illness, whether it’s gastroenteritis, or something more puzzling, is no easy task, says Jenny Post, an epidemiologist with ACT Health.
However, the “quite unusual” symptoms suffered by affected individuals in the spinach case, particularly the visual disturbances, were suggestive of anticholinergic syndrome, she adds.
According to clinical guidelines released by the Royal Children’s Hospital Melbourne, this syndrome can be caused by the ingestion of several prescription and over-the-counter medications, or the consumption of plants including deadly nightshade, jimsonweed, mandrake root, lupin beans, and angel’s trumpet.
“It took a bit of work to get there, but it was quite clear that the syndrome was not likely to be caused by spinach,” says Post.
The culprit, it turns out, was a weed that was growing alongside the spinach and harvested with it – Datura stramonium (jimsonweed).
Cracking this or any case of foodborne illness typically involves a lot of legwork by a large team of food detectives, including epidemiologists, microbiologists, public health nurses and environmental food safety officers.
It was quite clear that the syndrome was not likely to be caused by spinach.
Jenny Post
“It’s always a collaboration and the team can expand in times of outbreak,” says Post.
The ACT with a population of a little under 450,000 typically sees around 1000 cases a year of enteric infection – viruses, bacteria and parasites that cause intestinal illness.
Normally, these open with some sort of notification and it is the job of the staff from ACT Health to determine if any of these could be caused by contaminated food.
The notification might come from a hospital that is caring for someone who has contracted a notifiable disease such as salmonella infection, or a member of the public who learns their colleagues also developed diarrhoea and vomiting after that end-of-year work function.
“Once we receive that notification or complaint, we start to investigate, and that looks different depending on the nature of the notification,” Post says.
Usually, affected individuals will be interviewed in detail about what they’ve eaten and when.
“People often think the last thing you ate before you got sick (is what caused it), but the incubation period is often quite a bit longer than they expect,” Post says.
“For example, for salmonella, it can be up to seven days.”
Although there are at least 200 known pathogens that can cause food poisoning, there are several usual suspects, such as listeria or cryptosporidiosis.
Clusters of symptoms may provide clues about which bacteria, virus or other agent might be responsible.
Under the microscope
Once potential culprits have been identified, samples of food, swabs from cooking equipment, or even patients’ faeces, can help crack the case.
Back in the laboratory, microbiologists will use several tests, including PCR testing and bacterial culture (trying to grow the bacteria) to identify pathogens in the sample.
“They might do further typing, such as whole genome sequencing, to try to make sure that … even though it might be the same bacteria, it’s the same type of that bacteria,” Post says.
Cathy Moir, chair of the Food Safety Information Council, says genome sequencing is become more important.
“More recently whole genome sequencing has emerged as a highly accurate tool, supported by interview information, to identify the viruses, bacteria, fungi and parasites that cause foodborne diseases,” she says.
“All of these pathogens have unique DNA patterns that can be compared among infected people and with a suspected food source, if positive samples have been isolated from food.”
It’s rarely an overnight process, however.
One example of this food detective work was an investigation into a 2016-2020 outbreak of Listeria monocytogenes in enoki mushrooms in Australia and several other countries, including the United States, Canada and France. Epidemiologic, laboratory, and traceback evidence identified that the contaminated mushrooms came from a single source.
The 6 Australian cases notified between October 2017 and March 2020 were identified by whole genome sequencing as being related to the international outbreak, according to Food Standards Australia New Zealand. The mushrooms were recalled in April 2020..
Whole genome sequencing has emerged as a highly accurate tool.
Cathy Moir
The results demonstrated the importance of international collaboration, and of food sampling, testing, and integration of sequencing results into surveillance databases, according to a 2023 article in the Journal of Food Protection.
There have been several subsequent recalls of enoki mushrooms in Australia, most recently in June 2023, says Lydia Buchtmann, Communication Director with the Food Safety Information Council. Other recent cases to hit the headlines have included a multi-state listeria outbreak where ‘DNA fingerprinting’ linked nine cases to the same supplier of shredded chicken, and gastroenteritis caused by the bacterium Vibrio parahaemolyticus in raw Pacific oysters.
In 2021, six genetically identical instances of a unique strain of hepatitis A not previously detected in Australia were found to be caused by the consumption of fresh Medjool dates.
Safety starts at home
According to the World Health Organization (WHO), whole genome sequencing holds the potential to “revolutionise” the control and prevention of foodborne diseases through enhancing routine surveillance, outbreak detection, outbreak response and source identification.
Earlier this year WHO published guidelines for countries in the initial stages of laboratory-base surveillance for selected foodborne pathogens for how whole genome sequencing could be used to support foodborne disease outbreak investigations.
It notes that the global sharing of genome sequencing data from multiple countries could enhance the response to foodborne outbreaks, and help identify a particular source of contamination.
But food safety really starts at home, particularly in the hotter summer months, Post says.
“My advice is the same at any time of the year – which is to keep hot foods hot, and cold foods cold, until you’re ready to eat them,” she says.
“Wash your hands, chopping boards and knives before preparing food and between handling raw and ready-to-eat foods.
“We also recommend that people don’t wash their poultry – chicken or turkey – before they cook it.
“The risk is that the washing process will spread the bacteria around your kitchen, and then it can come into contact with other foods that you’re not going to cook.
“You don’t need to wash (the poultry) because the cooking process will kill the bacteria.”
Post also urges people who have a serious illness, or who are managing health conditions that affect their immune system, to avoid eating certain foods such as soft cheese, deli meats, pre-made salads or cut fruit.
“Their immune systems can put them at greater risk, so they need to be aware that these foods might be harmful to them,” she says.