Listeria in pregnancy: foods, symptoms and what to do

Listeriosis is caused by the bacterium Listeria monocytogenes, which survives and slowly multiplies even at fridge temperatures. The NHS describes it as a rare illness that usually goes away on its own but can make some people seriously ill. Pregnant women are about the same as other healthy adults in how unwell they feel, but the infection can reach the baby through the placenta.

That is the reason it features in every list of pregnancy food advice, even though the number of cases is small.

The NHS lists a high temperature, aches and pains, chills, feeling sick and diarrhoea, usually lasting a few days. In pregnancy the illness can be mild and look like flu, which is why it can be missed.

Symptoms can appear anywhere from a few days to several weeks after eating contaminated food, so the link to a particular meal is often unclear. Any fever in pregnancy without an obvious cause is worth reporting.

The NHS names miscarriage, stillbirth, sepsis and meningitis as potential complications for high-risk groups. A baby infected before birth may be born unwell, sometimes prematurely, and needs prompt antibiotic treatment in a neonatal unit.

The NHS pregnancy infections page does not cover listeria in detail, so the main source of advice is the foods-to-avoid page and the general NHS listeriosis page. Most women who eat a risky food will not become infected, and most who do are not seriously affected, but the consequences when they are can be severe.

The NHS says the foods associated with listeria include certain cheeses and chilled cooked and prepared items, and adds that these foods do not always contain it. Pregnancy advice is to avoid or heat them.

• Mould-ripened soft cheeses such as brie and camembert, and soft blue cheeses, unless cooked until steaming hot.

• Pâté of any type, including vegetable pâté.

• Cold cured, ready-to-eat meats such as salami, parma ham and chorizo, which are not cooked.

• Cold-smoked or cured fish such as smoked salmon, unless cooked until steaming hot.

• Unpasteurised milk and products made from it.

• Pre-packed sandwiches and salads, which should be kept chilled and eaten before the use-by date.

The NHS recommends keeping the fridge at 5 degrees Celsius or lower, eating ready-to-eat items within 4 hours of removing them from the fridge, keeping raw and ready-to-eat foods apart, and washing hands thoroughly. Check use-by dates strictly, because listeria can grow to harmful levels before food looks or smells off.

Wash fruit and vegetables, cook meat and ready meals until hot all the way through, and reheat leftovers only once. A fridge thermometer is a cheap way of checking the temperature, since many domestic fridges run warmer than expected.

Listeriosis is diagnosed by culturing the bacterium from blood or other samples. The NHS says most healthy people recover with rest and fluids, while antibiotics are used for those at higher risk, which includes pregnant women. If you have symptoms and have had a risky food, a prompt blood test and early antibiotics are the safest course.

After birth, newborns with possible exposure are watched closely. The treating team will explain what checks are needed for the baby.

The NHS advises contacting NHS 111 or your GP if you are pregnant or have a weakened immune system and develop symptoms. Also call NHS 111 if food poisoning symptoms last longer than 48 hours in pregnancy, as the foods-to-avoid page advises. Call 999 for signs of meningitis, which include severe headache, neck stiffness, confusion or a rash that does not fade under pressure. Tell your midwife as well, and report any reduction in baby movements immediately.