Salmonella infection: symptoms, how long it lasts and treatment

The symptoms of food poisoning listed by the NHS are feeling or being sick, diarrhoea, tummy pain, a high temperature and feeling generally unwell. NHS inform adds stomach cramps, loss of appetite, aching muscles, chills and weakness, and says the diarrhoea may contain blood or mucus. It gives a fever as a temperature of 38C or above.

UKHSA gives the usual window for salmonella as 12 to 72 hours after infection, with illness lasting around 4 to 7 days. The NHS points out that food poisoning symptoms can start within a few hours, a few days, or occasionally not for a few weeks, so the meal you suspect is not always the last one you ate.

• Watery diarrhoea, sometimes with mucus or blood.

• Stomach cramps and tummy pain.

• Nausea, with or without vomiting.

• A fever, chills and aching muscles.

• Tiredness and loss of appetite that can linger for a few days after the bowels settle.

The main job is to replace the fluid you lose. The NHS suggests small, frequent sips of water or squash if you feel sick, rest, and eating when you feel able, avoiding fatty or spicy foods. It advises against fruit juice and fizzy drinks, which can make diarrhoea worse. NHS inform suggests bland foods such as toast, crackers, banana and rice as appetite returns and says to avoid alcohol and caffeine.

A pharmacist can recommend oral rehydration powder if you show signs of dehydration, such as dark, smelly urine or passing less than usual. The NHS says a pharmacist can also suggest loperamide to stop diarrhoea for a few hours, but it is not suitable for children under 12, and it advises that children under 16 should not be given aspirin. NICE CKS notes that antibiotics, anti-diarrhoeal, anti-emetic and probiotic treatment are not routinely recommended for gastroenteritis.

Salmonella is not a single germ. UKHSA describes more than 2,500 strains of the bacteria, which live naturally in the guts of domestic and wild animals. When a strain reaches the human gut, it can irritate the lining and cause the diarrhoea and cramps that most people think of as food poisoning.

The NHS says campylobacter is the most common cause of food poisoning in the UK, with salmonella, E. coli and norovirus also on its list. NICE Clinical Knowledge Summaries make a useful distinction: gastroenteritis in general is usually caused by viruses, so a bout of diarrhoea and vomiting is not automatically salmonella. A stool test is the only way to know which germ is responsible, and it is not needed for most mild illnesses.

According to UKHSA, foods such as eggs, chicken, pork and dairy produce can carry salmonella. Fruit and vegetables can also become contaminated if they have been in contact with livestock, manure or untreated water. The NHS adds the general ways any food becomes unsafe: it is not cooked or reheated thoroughly, it is stored incorrectly, it is left out for too long, it is handled by someone who is ill or has not washed their hands, or it is eaten after its use-by date.

Animals are the other route. UKHSA names snakes and lizards among the animals that carry the bacteria, and publishes separate guidance on reducing the risk of infection from reptiles. Contact with someone who has diarrhoea, or with an unwell animal, can also pass the infection on, because the bacteria are shed in faeces.

Salmonella spreads easily in a home with one shared toilet. NHS inform advises washing hands often with soap and warm water, especially after using the toilet and before preparing food, and warns that alcohol gels are not always effective. It recommends cleaning surfaces and objects that could be contaminated with a bleach-based household cleaner, and washing soiled clothing and bedding separately on a hot wash.

It also advises not sharing towels, flannels, cutlery or utensils while you are ill, avoiding preparing food for other people if possible, and keeping contact with very young or elderly people to a minimum. Exclusion rules can be stricter for people who work with food or care for vulnerable people, so ask your employer or the local health protection team if that applies to you.

The NHS says to call 111 if you are worried about a baby under 12 months, if a child stops feeding, if there are signs of dehydration that persist after oral rehydration sachets, if vomiting stops you keeping fluids down, if there is bloody diarrhoea or bleeding from the bottom, or if diarrhoea lasts more than 7 days or vomiting more than 2 days.

NHS inform also lists a recent return from a part of the world with poor sanitation, and conditions such as kidney disease, inflammatory bowel disease or a weakened immune system, as reasons to call 111 or contact the GP practice urgently.

Call 999 or go to A&E for vomit that looks like blood or coffee grounds, green or yellow-green vomit, a stiff neck with pain in bright light, a sudden severe headache or tummy ache, blue, grey or blotchy skin, severe difficulty breathing, or confusion. NICE CKS lists dehydration, electrolyte disturbance, acute kidney injury, sepsis and haemolytic uraemic syndrome among the complications of infectious diarrhoea. They are uncommon, but they are the reason very young, older and immunosuppressed people are advised to seek advice early.

Most people never have a test. NICE CKS describes arranging a stool culture when someone is systemically unwell, has possible dysentery (painful diarrhoea with blood, mucus or pus), has diarrhoea that goes on, or has recently travelled to an at-risk destination. Testing may also be considered after contact with an affected person or an outbreak. A confirmed result lets the clinician decide whether antibiotics are needed in a specific case and whether the local health protection team should be told.

Care usually starts with self-care, then a pharmacist, then the GP or NHS 111. Private services can arrange a stool test, but the result seldom changes home treatment for a mild illness. Where an illness is linked to a restaurant or shared meal, the local authority food safety team and the Food Standards Agency are the bodies that investigate.