You may want to think twice about eating apples dipped in caramel on Halloween.
A study has found the traditional treats can cause listeria – a potentially fatal food poisoning bug that can cause fever, vomiting, diarrhoea and even meningitis.
Scientists believe the wooden stick used in traditional caramel apples, along with the temperature the apples are stored at, can affect the amount of bacteria they harbour.
When the stick is inserted into the apple, it causes a small amount of juice to leak out of the fruit. This moisture is then trapped under the caramel layer, where it becomes a breeding ground for bacteria.
Heat can cause this bacteria to multiply even further so refrigerating caramel apples is essential, the study suggests.
To study the growth of listeria-related bacteria, the scientists dipped Granny Smith apples in caramel, some with wooden sticks inserted and some without.
The caramel-coated apples were then either stored at room temperature or in the refrigerator.
The amount of listeria bacteria increased by 1,000 times when the apples with sticks were stored at room temperature for three days, compared to the refrigerated apples without sticks.
The study, published this week in the journal mBio, was prompted by an outbreak of listeria in the US around the Halloween period last year.
The study states that 35 people became infected with listeria across 12 states in the autumn and winter of 2014.
A total of 34 people were admitted to hospital when their symptoms became severe and seven died. Listeria was listed as directly causing at least three of the deaths.
Lead researcher Dr Kathleen Glass, from the University of Wisconsin-Madison’s Food Research Institute told the BBC that more research is needed on the topic. The study only looked at caramel-coated apples, not toffee apples, which are slightly different.
“It’s low risk but it’s not no risk,” she added. “I don’t want people to be worried, but it can happen, depending on how they are stored.”
According to the NHS, the best way to reduce your chances of developing listeria is to “ensure you always practise good food hygiene”.
This means not using food past its “use by” date, following storage instructions on food labels, ensuring that the temperature of your fridge is 0° C to 5° C and always cooking food thoroughly.