Salmonella is a type of bacterium which can cause food poisoning (‘gastro’) when a person eats or drinks food or water contaminated with the bacterium. The resultant food poisoning is often called ‘salmonella’ or ‘salmonellosis’. It is a notifiable disease in Australia, and usually causes sudden fever, diarrhoea and abdominal pain.
There are around 2500 different strains of Salmonella. The 2 main types are non-typhoidal and typhoidal Salmonella. Salmonella poisoning refers to the gastroenteritis caused by non-typhoidal Salmonella, whereas typhoidal Salmonella causes typhoid fever. Most people with non-typhoidal salmonella poisoning usually get better in 3-7 days without any antibiotics.
The symptoms of salmonella poisoning include:
- loose stools, sometimes bloody;
- stomach pain or cramps;
- nausea and sometimes vomiting;
- fever and chills; and
Symptoms of salmonella poisoning usually start 6 to 72 hours after getting infected, and normally last 4 to 7 days. Symptoms can vary from mild to severe – depending on your general health and age. Young children and the elderly are usually the worst affected. The number and strain of bacteria you are infected with, also play a part in how severe your symptoms are.
You may need urgent medical care if you have any of these symptoms:
- dehydration (increased thirst, peeing less, weight loss, tiredness, sunken eyes);
- diarrhoea more than 9 to 10 times a day;
- high fever (more than 38 degrees C); or
- severe abdominal pain.
If you suspect your baby is infected with Salmonella, you should urgently consult a doctor.
What causes salmonella poisoning?
Salmonella bacteria live in the intestines of both humans and other animals and are shed in the droppings or poo. They are found in domestic and wild animals, including birds. Agricultural animals, such as pigs, cows, goats, sheep, and chickens may carry Salmonella. This is also true for some domestic pets, such as dogs, reptiles and fish. Animals that are commonly infected include reptiles, frogs, toads, poultry, birds, hamsters, guinea pigs and farm animals.
Salmonella poisoning occurs when you ingest Salmonella bacteria into your mouth. There are a few ways humans can get salmonella poisoning.
Food to humans: Salmonella infection is most commonly acquired by eating contaminated foods of animal origin. Commonly infected foods include undercooked poultry, eggs, meat, milk and seafood. The foods become contaminated with animal stool where they are being made or handled (such as in abbatoirs). Seafood may be grown in water contaminated by sewage, or milk may not have been pasteurised.
Fruits and vegetables may also be a source of Salmonella if water or manure containing Salmonella has been used to irrigate or fertilise them. Salmonella then infects people when they eat the soiled food.
Cross-contamination can happen when contaminated foods, such as raw chicken, come into contact with food that is ready to eat. Or when cutting boards, plates, utensils or countertops that have touched infected foods transmit Salmonella to uninfected food.
Salmonella can also be passed from person to person. This is because if you are infected, the bacteria will be found in your stool. If you do not wash your hands properly after using the toilet you may infect other people by touching them, or by contaminating their food. You can also infect others if you touch infected animals or their stool and then touch other people or their food.
Salmonella can be transmitted from animals to humans by touching an infected animal or its faeces and then touching your mouth. It could be your pet, an animal at a petting zoo or a farm animal – they can all carry Salmonella.
Anyone can get salmonella poisoning, but people with lowered general immunity are at higher risk and more likely to be infected. These include infants, elderly people, malnourished people, people with autoimmune diseases, people with diseases that affect the structure of their red blood cells (e.g. sickle cell disease, thalassaemia), and people on corticosteroids, chemotherapy or immunosuppressants.
People who have lowered local gut immunity are also at increased risk, e.g. if you have recently used antibiotics, have had bowel removal surgery, have inflammatory bowel disease or colorectal cancer, or are taking antacids (e.g. Gastrogel, Mylanta) or proton-pump inhibitors (e.g. Pariet, Nexium, Somac).
Healthy people who travel to less developed countries (e.g. Asia, Africa and Latin America) are also at risk of getting infected.
Diagnosis and tests
Your doctor will usually be able to diagnose gastroenteritis without having to do tests. They will want to know what symptoms you have, how long you have had them, and if you have any risk factors.
If your doctor is concerned about salmonella poisoning or another serious infection, they will ask you to provide a stool sample, which will be sent to a laboratory for a faecal PCR (polymerase chain reaction) test. This test detects DNA from Salmonella and other bacteria in your stool and can also detect DNA from some parasites. The presence of specific DNA indicates which bacteria or parasites are in your stool.
Your doctor is likely to order a faecal PCR and blood tests if you have severe symptoms, lowered immunity, or if the infected person is a child less than 2 years old. The stool sample may also be examined under a microscope for parasites.
If you test positive for Salmonella, your result must be reported to the relevant authorities as salmonellosis is a notifiable disease. You will not need to do this yourself. The lab that has tested your stools or your doctor will report the results.
An outbreak (foodborne or waterborne) will be declared if there are more than 2 infected people in your local community in 24 hours who have eaten or drunk something from a common source. Public health officials will then look for and try to control the source of the outbreak. You can help to locate the source by keeping any leftover food at home for testing. You should be cautious about spreading the infection to your family and friends.
Treatment for salmonella poisoning
Salmonella poisoning usually gets better by itself in a few days. Your main goal should be to keep yourself hydrated by drinking lots of water. People who become dehydrated may need to be hospitalised.
Children become dehydrated more easily than adults, and oral rehydration solutions (such as Hydralyte and Gastrolyte) may be helpful. Some rehydration products come as ice blocks and ready-made solutions. Adults can also use these rehydration products, but they are often not needed.
Anti-diarrhoea or anti-vomiting medications should not be taken as they may be harmful. They should definitely not be used for children, people with bloody diarrhoea or where a person has a fever.
Infants and children with acute diarrhoea should NEVER be given anti-diarrhoea medicines.
If your symptoms do not resolve in a few days, you should go to your local GP or emergency department. You should also be seen by a doctor if you have severe symptoms or many risk factors.
Do you need antibiotics for salmonella poisoning?
Most of the time, healthy people do not need antibiotics for salmonella poisoning. They don’t shorten the length of symptoms and might even make a person infectious for longer.
Antibiotics may be needed if symptoms are severe. If the fever lasts more than 72 hours or if you have a lowered immunity, antibiotics are needed. If the Salmonella bacteria get into your bloodstream or any of your organs, you may also need antibiotics.
If you cannot take tablets or if you have a serious infection, you may be given intravenous (into the vein through a drip) antibiotics. Your doctor will decide how long you need to stay on antibiotics based on the severity of your infection and your symptoms.
How long will you be contagious?
If you have salmonella poisoning, you are infectious while you have symptoms. If you work with food, you should not go to work until you have not had diarrhoea for more than 48 hours. Similarly, if you work with patients, children or the elderly, you should stay away from work until 48 hours has passed since you last had diarrhoea.
Children who have salmonella poisoning should not go to school, pre-school or child care until there has not been a loose bowel motion for 24 hours.
Some people who have salmonella poisoning may still excrete bacteria in their stools months later (meaning they are still infectious) and fewer than 1 per cent will carry it permanently.
Some potential complications of salmonella poisoning include:
- bacteraemia (bacteria in your blood), which may possibly lead to sepsis (a defective response to bacteria in your blood)
- endocarditis (infection of the innermost layer of your heart, usually affecting your heart’s valves)
- mycotic aneurysm (abnormal dilation of an artery)
- visceral abscesses (collections of pus in your organs)
- osteomyelitis (infection in your bone)
- reactive arthritis (or Reiter’s arthritis) causing joint pain, painful urination and conjunctivitis (redness, itchiness and tearing of your eyes).
Outlook and prognosis
Your symptoms should start to get better after a few days and you should be back to normal in a week.
The main complication of salmonella poisoning is dehydration, so it’s important to keep your hydration levels up. The other complications of salmonella poisoning are very rare, and are unlikely to happen in most people with salmonella poisoning.
Salmonella poisoning usually does not have long-lasting effects. There is a small risk that you might be a long-term carrier of Salmonella but it is unlikely to have a major impact on your health.
Reactive arthritis is an uncommon complication of some bacterial infections, such as salmonella poisoning. Reactive arthritis is a type of temporary arthritis triggered by a bacterial infection in another part of your body. The symptoms are joint inflammation and swelling and eye inflammation (conjunctivitis).
How do you prevent salmonella poisoning?
It’s very important to follow safe food handling and food preparation practices. Contaminated food mostly looks, smells and tastes the same as normal food, so you won’t know if it’s infected with Salmonella.
At home, you can do these things to prevent salmonella poisoning:
- Avoid consuming raw eggs, meat, or seafood
- Avoid drinking unpasteurised milk
- Do not use dirty or cracked eggs
- Wash fruits and vegetables well
- Wash your hands with soap and warm water before and after preparing food
- Wash your hands after touching raw meat, petting animals, cleaning up pet faeces, going to the toilet and changing nappies.
- Use a different cloth to dry your hands to the cloth you use to dry dishes.
- Make sure your fridge is set below 5 degrees C
- Store your raw meat and seafood at the bottom of the fridge away from cooked food
- Don’t mix cooked food and raw food
- Don’t use utensils used on raw food to then prepare cooked foods.
- Wash your hands between handling different types of food, e.g. meat and vegetables
- Wash and dry cutting boards between preparing different types of food, e.g. meat or fish, and vegetables or fruit. Or use different cutting boards.
- Always clean your plates, utensils and cutting boards after using them.
When travelling there are some simple measures you can take to avoid travellers’ diarrhoea caused by Salmonella. One precaution is to boil water or only drink clean bottled water. As foods are easily contaminated, only eat freshly cooked hot food. Avoid food that has been at room temperature for long periods and food that has been exposed to flies.
If you have many risk factors, your doctor might give you a prescription for antibiotics to fill before you travel. Usually, you only need to take the antibiotics if you get food poisoning while you are overseas, but for some people at very high risk, the doctor may advise taking the antibiotics anyway for a certain period.
If you are healthy you should not need antibiotics. Doctors avoid giving unnecessary antibiotics as it can make bacteria harder to kill. This process is known as antibiotic resistance.