Salmonella Infection

What is salmonella infection?

Salmonella infection, also called salmonellosis, is an illness caused by a group of bacteria named Salmonella. These bacteria live in the intestines of many animals and people and are passed out in stool (feces). When a person swallows food, water, or other material contaminated with the bacteria, the germs can settle in the gut and cause an infection. In most cases the result is a form of gastroenteritis, which means inflammation of the stomach and intestines, with diarrhea, cramping, and fever.

Understanding what is salmonella infection helps to know that there are many different types, or serotypes, of Salmonella. The most common types cause food poisoning that usually clears on its own. A smaller group, called Salmonella Typhi and Salmonella Paratyphi, cause typhoid and paratyphoid fever, which are more serious illnesses that are more often seen in regions with limited access to clean water and sanitation. This page focuses mainly on the common, non-typhoidal form of salmonella infection, while noting where typhoid fever differs.

Salmonella infection can affect anyone. Most healthy adults recover within about a week without specific treatment. However, infants, adults over 65, pregnant women, and people with weakened immune systems are more likely to become seriously ill and may need medical care. In a hospital setting, digestive infections of this kind are often managed by a gastroenterology department, sometimes together with infectious disease specialists.

Salmonella infection symptoms

Salmonella infection symptoms usually begin between six hours and six days after exposure, although in many cases they appear within 12 to 72 hours. The illness typically lasts four to seven days. Common symptoms include:

• Diarrhea, which may be watery and, in some cases, contain blood
• Stomach cramps or abdominal pain
• Fever, often mild to moderate
• Nausea and sometimes vomiting
• Headache
• Chills
• Loss of appetite
• Signs of dehydration, such as dry mouth, dizziness, passing little urine, or feeling very tired

In most people the symptoms are unpleasant but not dangerous. Diarrhea can be heavy for a day or two and then gradually settles. A small number of people continue to have loose stools or altered bowel habits for several weeks after the infection itself has passed.

Symptoms can differ depending on the type of infection and how far it has spread:

• Uncomplicated gastroenteritis: diarrhea, cramps, and fever that improve within a week.
• Invasive infection: in some people, especially those with weakened immunity, the bacteria pass from the gut into the bloodstream. This is called bacteremia. It may cause high fever, shaking chills, and a general feeling of being very unwell. From the blood, the bacteria can occasionally reach bones, joints, the lining of the heart, or the covering of the brain.
• Typhoid fever: caused by Salmonella Typhi, this illness develops more slowly, often over one to three weeks. It tends to cause a sustained high fever, weakness, headache, abdominal pain, and sometimes constipation rather than diarrhea early on. A faint rash of rose-colored spots may appear on the trunk in some patients.
• Carrier state: a small proportion of people continue to pass Salmonella in their stool for weeks or months after they feel well. They have no symptoms but can still spread the bacteria to others.

After the infection, some people develop reactive arthritis, which is joint pain and swelling that appears weeks after the gut illness. This can also involve eye irritation and pain when urinating. It usually improves over months, though it may last longer in some cases.

Causes and risk factors

Salmonella infection causes almost always involve swallowing the bacteria. Salmonella lives in the intestines of animals such as chickens, cattle, pigs, reptiles, and amphibians, and in infected people. Contamination can happen at many points between farm and table. Common sources include:

• Raw or undercooked poultry, meat, and seafood, where bacteria from the animal’s gut have reached the flesh during processing.
• Raw or lightly cooked eggs and foods made with them, such as homemade mayonnaise, some sauces, or uncooked batter.
• Unpasteurized milk and dairy products, since pasteurization (heating milk to kill germs) is what normally destroys Salmonella.
• Fruits and vegetables washed or irrigated with contaminated water, or handled by an infected person.
• Cross-contamination in the kitchen, for example using the same cutting board or knife for raw chicken and then salad without washing it.
• Contact with animals, particularly reptiles such as turtles, snakes, and lizards, amphibians such as frogs, live poultry including backyard chickens, and some pets and their food.
• Person-to-person spread when hands are not washed properly after using the toilet or changing a diaper.

Typhoid and paratyphoid fever spread only from person to person, usually through water or food contaminated with the stool or urine of an infected individual. They are most common in areas where sewage may mix with drinking water.

Anyone can get salmonella infection, but certain factors raise the risk of catching it or of becoming seriously ill:

• Age: infants and young children have immature immune systems; adults over 65 tend to have weaker defenses and are more prone to dehydration.
• Weakened immune system from conditions such as HIV, cancer treatment, organ transplant medicines, or long-term steroid use.
• Reduced stomach acid, because acid normally kills many swallowed bacteria. Antacids and acid-reducing medicines, and some stomach conditions, lower this protection.
• Recent antibiotic use, which can disturb the healthy gut bacteria that help resist infection.
• Inflammatory bowel disease, such as Crohn’s disease or ulcerative colitis, which may damage the lining of the intestine.
• Sickle cell disease, which is linked with a higher chance of Salmonella spreading to the bones.
• International travel to areas with limited sanitation, which raises exposure to both non-typhoidal Salmonella and typhoid.
• Pregnancy, during which dehydration and fever may carry added risks.

Salmonella infection diagnosis

Many people with mild diarrhea never see a doctor and are never formally diagnosed. When testing is done, salmonella infection diagnosis relies on identifying the bacteria in a sample rather than on symptoms alone, because many different germs cause a similar illness.

• Stool culture: this is the standard test. A small stool sample is sent to the laboratory, where technicians try to grow bacteria and identify them. Results usually take a few days. Once Salmonella is found, the laboratory may test which antibiotics it is sensitive to, which is called antibiotic susceptibility testing.
• Molecular stool tests: some laboratories use PCR (polymerase chain reaction) panels that detect the genetic material of several common gut germs at once. These can give faster results, though a culture is often still done to confirm and to check antibiotic sensitivity.
• Blood culture: if a person has a high fever, appears very unwell, or has a weakened immune system, doctors may take blood samples to check whether the bacteria have entered the bloodstream. Blood cultures are especially important when typhoid fever is suspected.
• Other blood tests: a complete blood count, kidney function, and electrolyte tests (which measure salts such as sodium and potassium) help assess dehydration and the body’s response to infection. They do not diagnose Salmonella by themselves.
• Urine or bone marrow cultures: these are occasionally used in suspected typhoid when other tests are unclear.
• Imaging: scans are not needed for ordinary salmonella infection. If a doctor suspects that the bacteria have spread to a bone, joint, or blood vessel, an ultrasound, X-ray, CT, or MRI scan may be arranged to look for a focus of infection.

Your doctor will also ask about what you have eaten recently, any travel, contact with animals, and whether others around you are ill. Confirmed cases are usually reported to public health authorities, who track outbreaks and try to trace the source. A confirmed diagnosis also matters for people who handle food or care for vulnerable individuals, since they may be advised to stay away from these duties until they are clear of infection.

Salmonella infection treatment options

For most otherwise healthy people, salmonella infection treatment options center on supportive care while the body clears the infection on its own. The main goals are to prevent dehydration and to relieve symptoms.

Fluids and rest

Diarrhea and vomiting cause the body to lose water and salts quickly. Drinking plenty of fluids is the most important part of care. Water, diluted juices, broth, and oral rehydration solutions, which are drinks containing a balanced mix of salts and sugar available from pharmacies, help replace what is lost. Small, frequent sips are often easier to keep down than large amounts. Eating can continue as tolerated; bland foods are often better accepted at first. Rest allows the body to recover.

Intravenous fluids

If a person cannot keep fluids down, shows signs of significant dehydration, or is very young, elderly, or otherwise vulnerable, a doctor may arrange fluids given directly into a vein in a clinic or hospital. This restores fluid balance more quickly and safely than drinking alone.

Medicines for symptoms

Acetaminophen (paracetamol) may be used for fever and aches. Anti-diarrhea medicines such as loperamide are generally not recommended, particularly if there is blood in the stool or a high fever, because slowing the gut may prolong the infection or worsen complications. Your doctor can advise whether they are appropriate in your case.

Antibiotics

Antibiotics are medicines that kill bacteria or stop them multiplying. For uncomplicated salmonella gastroenteritis in healthy adults, antibiotics are usually not prescribed. They do not shorten the illness much and may increase the length of time a person carries the bacteria in the stool afterward. Antibiotics are, however, commonly used when:

• The infection has spread to the blood or other organs.
• The patient has a weakened immune system, is an infant under a few months old, or is elderly.
• The patient has severe or prolonged symptoms.
• Typhoid or paratyphoid fever is diagnosed, since these always need antibiotic treatment.

The choice of antibiotic depends on the laboratory susceptibility results, local resistance patterns, and the patient’s age and health. Antibiotic resistance, where bacteria no longer respond to certain drugs, is a growing concern with Salmonella, which is one reason unnecessary use is avoided.

Treatment of complications

If the bacteria have caused an infection in a bone, joint, blood vessel, or other deep site, treatment may involve a longer course of antibiotics, often given intravenously at first. In some situations a procedure may be needed to drain an abscess (a pocket of pus) or to remove infected material. Surgery is uncommon but can be required for complications such as an infected aneurysm (a weakened area of a blood vessel) or, in severe typhoid, a perforation of the intestine. Reactive arthritis, when it occurs, is generally managed with anti-inflammatory medicines and physical therapy rather than with antibiotics.

Follow-up

People who work with food, in health care, or in childcare may be asked to provide follow-up stool samples to confirm that the bacteria have cleared before returning to work. Long-term carriers, especially of Salmonella Typhi, may be offered a course of antibiotics to clear the bacteria, and in rare cases gallbladder problems that harbor the germ are addressed.

Living with salmonella infection and outlook

For the great majority of people, salmonella infection is a short, self-limiting illness. Diarrhea usually eases within a week, and energy and appetite return over the following days. It is common for bowel habits to take a few weeks to settle completely, and this alone is not usually a cause for concern.

While recovering, careful hygiene protects others. Washing hands thoroughly with soap and water after using the toilet and before preparing food is the most effective step. Sharing towels should be avoided, and surfaces in the bathroom should be cleaned regularly. Because the bacteria may remain in the stool for a time after symptoms stop, these habits should continue for several weeks. Children may be advised to stay out of daycare until diarrhea has resolved.

The outlook is less predictable for people at higher risk. Invasive infection, typhoid fever, and complications such as bone or heart infections are serious and require prompt treatment; with appropriate care most people recover, but recovery can be slow and some complications can be life-threatening if not treated. Older adults and infants are more vulnerable to the effects of dehydration, which is why early medical review is encouraged for these groups.

A previous salmonella infection does not provide reliable long-term protection, so the same preventive measures apply afterward: cooking meat, poultry, and eggs thoroughly, keeping raw and ready-to-eat foods separate, refrigerating food promptly, washing hands after handling animals, and being cautious with food and water while traveling. Vaccines exist for typhoid fever and may be recommended before travel to certain regions; there is no vaccine for common non-typhoidal Salmonella. Digestive symptoms that persist beyond a few weeks may warrant assessment by a gastroenterology specialist to rule out other causes.

Frequently asked questions

How long do salmonella infection symptoms last?

In most people, salmonella infection symptoms last four to seven days. Diarrhea is often heaviest in the first two or three days and then gradually improves. A minority of people notice loose or irregular stools for several weeks afterward. If symptoms are getting worse rather than better after a few days, or if there is high fever or blood in the stool, a medical assessment is advisable.

What are the most common salmonella infection causes?

The most common salmonella infection causes are eating contaminated food, especially undercooked poultry, meat, and eggs, unpasteurized dairy, and produce washed in contaminated water. Cross-contamination in the kitchen, contact with animals such as reptiles and live poultry, and inadequate handwashing after using the toilet also spread the bacteria. Typhoid fever, a related illness, spreads from person to person through contaminated water or food.

How is salmonella infection diagnosis confirmed?

Salmonella infection diagnosis is confirmed by finding the bacteria in a laboratory sample, most often a stool culture. Some laboratories use faster molecular tests that detect the bacteria’s genetic material. If doctors suspect the infection has entered the bloodstream, or if typhoid is a possibility, blood cultures are taken. Symptoms alone cannot confirm the diagnosis because many other germs cause a similar illness.

Do salmonella infection treatment options always include antibiotics?

No. For otherwise healthy people with uncomplicated diarrhea, salmonella infection treatment options usually consist of fluids and rest, and antibiotics are not recommended because they offer little benefit and may prolong carriage of the bacteria. Antibiotics are used when the infection is severe, has spread beyond the gut, affects an infant, older adult, or person with weakened immunity, or when typhoid fever is diagnosed.

Is salmonella infection contagious?

Yes. A person with salmonella infection can pass the bacteria to others through stool, usually when hands are not washed properly and then touch food, surfaces, or another person. Some people continue to shed the bacteria for weeks after they feel better. Good hand hygiene, avoiding food preparation for others while ill, and staying home from work or school until diarrhea has stopped help reduce spread.

What is the difference between salmonella infection and typhoid fever?

Both are caused by Salmonella bacteria, but by different types. Common salmonella infection is caused by non-typhoidal strains found in animals and food, and it usually produces short-lived diarrhea and fever. Typhoid fever is caused by Salmonella Typhi, spreads only between humans, develops more slowly, causes prolonged high fever, and always requires antibiotic treatment. A vaccine is available for typhoid but not for non-typhoidal Salmonella.

Can salmonella infection cause long-term problems?

Most people recover fully. In a small number of cases, reactive arthritis with joint pain and swelling develops weeks after the infection and can last for months. Some people experience prolonged changes in bowel habit. Rarely, the bacteria spread to bones, joints, blood vessels, or the heart lining, which requires longer treatment. These complications are more likely in people with weakened immunity or other underlying conditions.

When to see a doctor

Most cases of salmonella infection can be managed at home with fluids and rest. However, medical review is recommended if diarrhea lasts more than a few days, if you belong to a higher-risk group such as infants, adults over 65, pregnant women, or people with weakened immune systems, or if you are unsure about the cause of your symptoms. Seek urgent medical attention if you or someone you are caring for has any of the following warning signs:

• Signs of severe dehydration: very little or no urine, dark urine, dizziness or fainting when standing, sunken eyes, dry mouth, or extreme drowsiness
• Inability to keep fluids down because of persistent vomiting
• High fever, for example above 102°F (38.9°C), or fever that does not come down
• Blood in the stool or black, tarry stools
• Severe or worsening abdominal pain, or a hard, swollen abdomen
• Diarrhea lasting more than three days without improvement
• Confusion, a stiff neck, severe headache, or difficulty staying awake
• Shaking chills, rapid heartbeat, or rapid breathing, which may suggest the infection has spread to the blood
• In infants: no wet diaper for several hours, no tears when crying, a sunken soft spot on the head, unusual sleepiness, or refusal to feed
• New joint pain or swelling, eye redness, or pain when urinating in the weeks after a gut illness
• Recent travel to an area where typhoid fever is common together with a persistent fever

Early assessment allows dehydration to be corrected and allows doctors to decide whether laboratory testing or antibiotics are needed. If symptoms are severe or rapidly worsening, emergency care should be sought without delay.