Listeriosis
A food-borne infection caused by the bacterium listeria. In a healthy person it usually passes as a short bout of upset stomach, or causes nothing at all.
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Medicines commonly prescribed for Listeriosis
For informational purposes only. Always consult a doctor before using any medicine.
Dosage form: ORAL SOLUTION/SUSPENSION, 250 MGActive substance: amoxicillinManufacturer: Sandoz Farmaceutica S.A.Prescription requiredDosage form: TABLET, 750 mgActive substance: amoxicillinManufacturer: Sandoz Farmaceutica S.A.Prescription requiredDosage form: TABLET, 1000 mgActive substance: amoxicillinManufacturer: Laboratorios Combix S.L.U.Prescription required
A food-borne infection caused by the bacterium listeria. In a healthy person it usually passes as a short bout of upset stomach, or causes nothing at all. But in pregnant women, newborn babies, older people and anyone whose immunity is weakened, the same bacterium can leave the gut and cause blood poisoning or inflammation of the membranes around the brain.
It is caught rarely, far less often than salmonella. What makes it dangerous is not how common it is but how it ends: among those in whom the infection reaches the bloodstream, severe illness is the rule rather than the exception. Listeriosis is therefore worth knowing about in advance, especially if you are pregnant or belong to one of the vulnerable groups.
What sets listeria apart from other food bacteria
Ordinary gut bacteria multiply in warmth, and the fridge stops them. Listeria does not stop. It grows quite happily at refrigerator temperature, slowly but steadily building up its numbers in something that has been sitting there for a week. That is why the danger lies not in hot dishes but in chilled food eaten without any heating.
It has two further inconvenient habits. It tolerates salt, smoking and curing — the very treatments that finish off many other microbes. And it does not spoil food: contaminated food does not smell, does not taste different and looks perfectly normal. Nose and eyes are no help here; only temperature, dates and keeping things apart do any work.
Heat, on the other hand, leaves listeria defenceless. Warm the food through properly, until it is steaming and hot right the way through, and the bacterium dies. That is the whole logic of prevention: cold does not kill it, heat does.
Where it comes from
Almost always from food, and almost always from chilled items eaten without cooking:
- sliced cooked and cured meats, sausages and deli products;
- smoked and lightly salted fish, including the kind used in sushi;
- soft mould-ripened cheeses and blue cheeses, and any cheese made from unpasteurised milk;
- unpasteurised milk and everything made from it;
- pâtés of every kind, vegetable ones included;
- ready-made salads and sandwiches, pre-packed cut fruit and vegetables;
- frozen vegetables, which many people treat as ready to eat and add to dishes without cooking.
Less often the infection arrives another way: on the hands of somebody who prepared food without washing after the lavatory, or through close contact with farm animals during lambing and calving. The bacterium is widespread in soil, water and plants, so removing it from the food chain altogether is impossible; what can be done is to stop it multiplying.
It is worth keeping the risk in proportion, too. Those foods are by no means always carrying listeria. If you have eaten one of them recently and feel well, there is nothing you need to do.
How it shows itself
In most healthy people it comes to a few days of feeling unwell: a temperature, shivering, aching muscles, sometimes nausea, vomiting and diarrhoea. It cannot be told apart from other food poisoning, and as a rule nobody ever establishes the cause.
The timing is a difficulty in itself. Anything from a few days to several weeks can pass between the meal and the illness, sometimes more than a month: by then the food has been forgotten and the link is lost. So when a doctor asks about meals over recent weeks, the question is not idle.
The severe form develops when the bacterium leaves the gut for the bloodstream. High fever with shivering, marked weakness and confusion follow. Listeria has a particular liking for the nervous system: it inflames the membranes around the brain and, quite characteristically for this organism, attacks the brainstem. That produces an unusual set of signs — double vision, slurred speech, difficulty swallowing, unsteadiness and weakness of the facial muscles.
In pregnancy the picture is deceptive. The woman herself usually has a mild illness: a temperature, aching, the feeling of flu coming on, sometimes abdominal pain. The danger is not to her but to the baby, because listeria crosses the placenta and can lead to miscarriage, premature labour or stillbirth. Any fever in pregnancy is therefore a reason to contact a doctor the same day rather than to wait it out.
In a newborn the illness appears either right after birth as severe blood poisoning, or a week or two later as meningitis. The baby is listless or, on the contrary, unsettled, feeds poorly, has a raised temperature or — more worrying still — a low one, breathes rapidly and looks greyish.
Who is genuinely at risk
For most adults listeriosis is an episode of stomach upset and no more. Severe illness falls on particular groups, and it is worth knowing whether you are in one of them:
- pregnant women, whose risk is many times the average, and mainly through the danger to the baby;
- newborn babies;
- older people, with severity becoming more likely as age advances;
- people with weakened immunity: cancer patients on chemotherapy, transplant recipients, people living with HIV, and anyone taking corticosteroids or other immune-suppressing drugs long term;
- people with cirrhosis or other liver disease, with chronic kidney disease or with diabetes;
- people with iron overload — in haemochromatosis listeria multiplies more readily;
- people taking medicines that reduce stomach acid, since gastric juice acts as a natural barrier and without it the bacteria reach the gut more easily.
That last point is rarely known, and a great many people take such medicines for years. It is no reason to stop them, but it is a reason to treat the foods listed above with more care.
When emergency help is needed
Call an ambulance — across much of Europe on the single number 112 — if you or a child, alongside a fever, develops:
- severe headache together with a stiff neck, the chin not reaching the chest;
- real discomfort in bright light;
- confusion, odd behaviour, marked drowsiness or an inability to wake the person;
- a seizure;
- double vision, slurred speech, choking on swallowing or sudden unsteadiness;
- in a baby: floppiness, refusing feeds, a high or, conversely, a low temperature, fast breathing, an unusual high-pitched cry or a bulging fontanelle.
These are signs that the infection has reached the brain and its coverings, and they have to be treated immediately and in hospital.
Seek a doctor the same day, though without an ambulance, if you have a temperature and are pregnant; if a fever lasts more than two or three days while your immunity is weakened; if diarrhoea and vomiting have not settled in several days, or signs of dehydration appear such as a dry mouth, passing little urine or dizziness on standing. In pregnancy there is a further reason to be seen urgently: abdominal pain, or a sense that the baby is moving less than usual.
How it is diagnosed and treated
Listeriosis is confirmed by a blood culture and, where the nervous system is suspected, by examination of the spinal fluid. A stool test is of no use for this. That is why in a mild bout of gastroenteritis the diagnosis is usually never pursued: there would be no practical point.
Tell the doctor plainly if you are pregnant, if you take medicines that suppress immunity, or if you have recently eaten anything from the list above. This is not a formality: listeria does not respond to some of the common antibiotics given blindly in a serious infection, and suspecting it changes the choice of drug.
Treatment depends on severity. A healthy person with mild bowel symptoms needs no antibiotics: rest and plenty of fluid in small amounts are enough, preferably as rehydration solutions. If, on the other hand, the infection has entered the blood or reached the nervous system, or if the patient is pregnant or in a risk group, antibiotics are given — from a particular group, and usually intravenously in hospital. In pregnancy, starting in time can protect the baby, which is one more argument against putting off the call.
How to avoid it
The rules are simple and all follow from what the bacterium is like: it grows in the cold and dies with heat.
- Keep the fridge genuinely cold, around five degrees or below, and check it with a thermometer: domestic fridges often run warmer than the dial suggests.
- Go by the use-by date, not by smell and appearance. Food past its date can smell perfectly good and still be dangerous.
- Finish an opened pack of ready-to-eat food within a day or two rather than stretching it to the date printed for the unopened pack.
- Do not leave chilled ready-to-eat food standing in the warm; take it out of the fridge shortly before eating.
- Reheat until steaming and hot right through, not merely warm. This applies to frozen vegetables too if they are going into a dish uncooked.
- Keep raw meat and fish away from ready-to-eat food, give them the bottom shelf and a board of their own.
- Wash hands, boards and knives with soap, and wipe down the fridge shelves regularly.
For anyone in a risk group, and above all in pregnancy, there is an additional list of foods best avoided: soft mould-ripened and blue cheeses, any unpasteurised cheese or milk, pâtés, lightly salted and cold-smoked fish, ready-made salads and sliced cold meats from the counter. There is one exception to the rule: all of it is safe once heated until hot right through — baked soft cheese, for instance, poses no danger.
Hard cheeses, cottage and cream cheese made from pasteurised milk, mozzarella, processed cheese and yoghurt are not on that list and stay in the normal diet. Pregnant women should also stay away from lambing and calving and keep their distance from newborn lambs and calves.
Online consultation
With a food-borne infection a remote appointment is most useful for sorting the situation out: working out what is going on and deciding whether care at home is enough. The doctor will ask about the fever, the timing, what you have eaten in recent weeks and about your long-term conditions and medicines, and will explain how to replace fluids properly, what you can eat, when to expect improvement and which signs mean waiting is no longer safe.
There is another very common reason to get in touch: worry after a meal. "I am pregnant and I have eaten a piece of blue cheese, what now?" is exactly the question best answered remotely. The doctor will judge the real risk, say which signs to watch for and for how long, and spare you pointless investigations. Online is also the place to work out how to adjust your eating during pregnancy or during treatment that lowers immunity.
But a high temperature in pregnancy, any suspicion that the brain is involved and any illness in a newborn need face-to-face care, and often hospital. In those cases do not spend time writing messages — go straight for help.
This material is for information only and does not replace medical advice.
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Online doctors for Listeriosis
Discuss your symptoms and possible next steps for Listeriosis with a doctor online.
