Avoiding soft cheeses, deli meats and dressings like mayonnaise is well known to pregnant women to avoid contracting the bacterium, Listeria monocytogenes. But rockmelons are less well known for causing Listeria outbreaks.
One of the largest outbreaks of Listeria in rockmelons was in the US in 2011, where 33 people died. Since then, food microbiology research on Listeria in rockmelons ramped up globally to try and understand more about how it can grow in produce.
The incidence of Listeriosis (the bacterial infection caused by eating food contaminated by Listeria) is comparable in Australia to other western countries – we have around 60-70 cases per year. We had an outbreak linked to cheese in late 2012-early 2013 and that was our last large-scale Listeria incident. Listeria monocytogenes, along with Salmonella, is responsible for more deaths in Australia than any other foodborne disease, each accounting for about 15 deaths per year.
Listeria is generally only contracted by a fairly small, vulnerable group of people – the elderly, unwell and pregnant women – but it is fatal for about 1 in 5 of those who contract it. Compared to other pathogens ( microorganisms that make humans sick or is fatal) like Salmonella or E coli, Listeria has a high mortality rate among the risk groups. The three people who have unfortunately passed away this week from infected rockmelons were over 65.
Listeria is abundant in the environment and therefore it’s difficult for food producers and processors to control it. It’s commonly found in the soil which, of course, is where horticultural crops like rockmelons happen to grow. Listeria can go from the soil to the melon skin and although it doesn’t grow on the skin, when we slice the melon to eat it that can introduce it into the flesh. Then, we mightn’t eat it all at once but a few days later cut it up some more and put it out to eat at a picnic, and the bacteria has grown even more. Or if you leave it out of the fridge, it can grow faster. Listeria grows at four degrees but keeping it in the fridge will help slow the growth.
Because rockmelon is less acidic than say tomatoes, there’s more chance of microbes surviving.
So, should we wash rockmelons at home before eating them? It’s not necessary because they’ve already undergone a cleaning process. Australia’s food safety procedures are among the best in the world and in this case, the NSW Food Authority has advised that fruit currently available on supermarkets shelves are not implicated in this outbreak.
What can we do at home to reduce our risk of food-borne illness? Key food safety tips include washing your hands, storing food that is meant to be chilled (like salad bags) at 5 degrees or colder, cooking food properly and keeping raw and cooked foods separate during storage and preparation.