A study led by Macquarie University researchers has found that Salmonella poisoning (salmonellosis), one of the key causes of gastroenteritis, dropped off markedly in 2020, coinciding with COVID-19 restrictions.
Keep it clean post-COVID: If we keep washing our hands and wiping down surfaces, it goes a long way to preventing Salmonella poisoning, says Professor Amin.
There are about 90,000 cases of salmonellosis in Australia in an ordinary year, costing the economy an estimated $140 million in healthcare and lost productivity. In 2020, there were nearly 66,000 cases.
Common all over the world, Salmonella is a mostly foodborne pathogen, but it may also be present in the environment, for example in water, and it is commonly found in all sorts of wild and domestic animals and birds, including in chickens.
Most people who contract salmonellosis suffer from fever, diarrhoea and vomiting for about a week, but death is a very real risk for children under the age of five, elderly people, and the severely immunocompromised.
In NSW, between 2000 and 2017, about 54 per cent of outbreaks were linked back to restaurants.
The under-fives are also the most likely to be infected, as they are less conscious of hygiene than older children and adults.
Professor Janaki Amin from the Department of Health Sciences, Associate Professor Paul Beggs and Barbara Davis from the School of Natural Sciences, and Neil Franklin from the Australian National University's Centre for Epidemiology and Population Health and OzFoodNet at the NSW Ministry of Health, collaborated to publish an article in Communicable Diseases Intelligence on the findings.
Professor Janaki Amin says cases of salmonella Australia-wide dropped by 27 per cent in 2020 compared to the previous five-year median.
"Victoria recorded a larger drop than other states, which is likely to be associated with that state's longer lockdown," she says.
Super spreaders: The under-fives are also the most likely to be infected, as they are less conscious of hygiene than older children and adults.
"Simply put, we all washed our hands thoroughly, paid more attention to keeping surfaces clean, and ate our meals at home.
"Household cases of salmonellosis are common, but in NSW, between 2000 and 2017, about 54 per cent of outbreaks were linked back to restaurants, a figure that was mirrored in other states and territories. Large gatherings, like weddings and parties, are also sources of outbreaks.
"As we all know, restaurants were closed or operating at reduced capacity throughout much of 2020, and weddings and large gatherings were either not happening at all or on a drastically reduced scale.
The real key to keeping our gastroenteritis levels lower lies in not abandoning those simple public health measures.
Salmonella is nothing if not opportunistic, so if there is Salmonella present and it's left unrefrigerated in the right conditions, it will multiply, Amin says.
"There are also the so-called 'paddock-to-plate' factors. Chicken, for example, is a common source of Salmonella, which is why we need to ensure we cook it properly, but you may also see lettuces, for example, being irrigated or washed with contaminated water.
"These factors are unlikely to have changed dramatically, even taking into consideration improved hygiene in packing plants due to COVID-19.
"The real key to keeping our gastroenteritis levels lower lies in not abandoning those simple public health measures even as we come out of the pandemic, and eat out more and attend large gatherings again.
"There are other ways to reduce risk, but if we keep washing our hands and wiping down surfaces, it goes a long way to preventing Salmonella poisoning."
The summer factor
The study found that while states like the Northern Territory also had lockdowns and border closures that limited the number of interstate visitors, they did not see as marked a drop in cases as in the southern states.
Warning: Chicken is a common source of Salmonella, which is why we need to ensure we cook it properly.
The Northern Territory started from a much higher base than any other state, as it already had the highest rate of salmonellosis in the country, with up to 47 cases per 100,000 people each month.
"Salmonellosis rates are also consistently higher in summer and in warm states such as the NT and Queensland, indicating that there are environmental factors at play", Associate Professor Paul Beggs says.
Barbara Davis, who is doing her Master of Research at Macquarie University on the link between Salmonella and climate factors, first noticed the marked drop in salmonellosis in 2020.
"I was looking at 29 years of data, and 2020 just jumped out at me," she says. "The change was so obvious, and it couldn't be explained any other way than being a result of the pandemic public health measures.
"This pathogen is a real survivor and can tolerate a wide range of temperatures, from five to 45 degrees Celsius, but it really thrives in warmer environments.
"The basis of my Masters investigation is that because Salmonella loves warmer environments, we will see an increase in cases as the climate warms."
Seven ways to reduce your risk of getting salmonellosis ...
- Wash your hands well before preparing food or eating. Ordinary soap and water are enough – there is no need for antibacterial washes.
- Wash utensils like knives and cutting boards between uses and keep surfaces clean.
- Avoid cross-contamination between uncooked meat and cooked food and anything that will be served raw, like salads.
- Cook chicken and other poultry thoroughly – rare is OK for steak as bacteria tend to be present only on the outside, but this is not the case with chicken or anything that has been minced.
- Ensure food is stored at the correct temperature, refrigerated promptly, and reheated thoroughly.
- Wash raw fruit and vegetables before eating – even the bagged lettuce that say they've been pre-washed.
- Ensure your dish sponge dries after use, is replaced regularly and is not used for any other purpose than washing dishes.
Professor Janaki Amin is a public health researcher at Macquarie University's Department of Health Sciences. Associate Professor Paul Beggs is an environmental health scientist, and Barbara Davis is a Master of Research candidate, both at Macquarie University's School of Natural Sciences.
