Salmonella

What is Salmonella?

Salmonella is a type of bacteria named after D.E. Salmon, the American scientist who first discovered it in a pig’s intestine in 1884. This bacteria is known for several features – it falls into the category of Gram-negative bacteria, it can move on its own, it produces hydrogen sulfide, and it doesn’t survive well in acidic conditions. Salmonella often causes a stomach illness known as gastroenteritis and can spread between people and animals.

Many types of animals can carry and spread Salmonella, including chickens. If a person eats undercooked chicken, they can get sick with a type of Salmonella infection called Salmonella enteritidis, which results in an inflammation of the intestines leading to diarrhoea. This bacteria can also cause serious localized infections in people with weakened immune systems. There are over 2,500 different variations, known as serovars, of Salmonella bacteria identified all over the world.

What Causes Salmonella?

Salmonella is a type of bacteria that exists in two primary forms, known as Salmonella enterica and Salmonella bongori. There’s also a third form, called Salmonella subterranea, that’s pending approval to be classified as a separate species.

Each of these forms, particularly Salmonella enterica, has several subtypes also known as subspecies. Think of these like different branches of the same family tree, each having its own characteristics. Some of the subspecies are named Enterica, Salamae, Arizonae, Diarizonae, Houtenae, and Indica.

Within these subspecies, there are even more specific forms called serovars. Again, think of these as distinct family members. The Salmonella enterica subspecies “Enterica” has the most serovars, and is most commonly associated with infections in people.

It includes common serovars like Enteritidis, Typhimurium, Newport, and Javiana. Importantly, the serovars Typhi and Paratyphi lead to a condition called typhoidal salmonella, which causes typhoid fever and paratyphoid fever. Together, these fevers are known as enteric fever. Typhoidal salmonella typically only affects humans.

Other Salmonella enterica serovars can lead to nontyphoidal Salmonella (NTS), which can affect a wide range of vertebrate species, including humans. Some serovars are specific to nonhuman vertebrate species.

Risk Factors and Frequency for Salmonella

In places like the United States, which are considered developed countries, the most usual type of Salmonella infection leads to an inflammation of the stomach and intestines. Every year, the US sees over 1 million cases of this form of salmonella infection, also known as NTS. Enteric fever, another kind of Salmonella infection, is unusual in the US and typically comes from outside the country. Nevertheless, like NTS, enteric fever is a huge concern worldwide; there are over 20 million new cases every year, and it results in more than 200,000 deaths.

This type of Salmonella infection, also known as typhoid fever, is particularly common in South Asia and Sub-Saharan Africa, with numbers sometimes reaching over 100 cases per 100,000 people each year. It’s worth noting the higher risk of infection in these areas, especially in countries with low to middle incomes. This is primarily due to inadequate sanitation, as well as contaminated food and water arising from infected human waste.

Signs and Symptoms of Salmonella

Salmonella is a type of bacteria that can cause a range of infections, such as bloodstream infections (bacteremia), bone infections (osteomyelitis), inflammation of the brain and spinal cord fluid (meningitis), inflammation of the stomach and intestines (gastroenteritis), and urinary tract infections. People with sickle cell disease may particularly develop bone infections.

Symptoms of a Salmonella infection vary based on the specific type of the disease. One form, Non-Typhoidal Salmonella (NTS), often leads to gastroenteritis which involves diarrhea, fever, and stomach cramps. Activities that increase the odds of getting an NTS infection can include handling reptiles like those often found in zoos or homes. Consuming undercooked chicken, eggs, meat, dairy can also cause infection, and this might be something you recall doing if you become infected.

Those with weaker immune systems, such as children under the age of one, long-term steroid users, people with cancer, organ recipients, or people with acquired immunodeficiency syndrome (AIDS), are more likely to get Salmonella infections.

On the other hand, enteric fever, another type of Salmonella infection, starts slowly and features symptoms including fever, headache, weakness, tiredness, stomach pain, joint swelling, an enlarged liver or spleen, and a flat, rose-colored skin rash. It can present with either diarrhea that looks like pea soup or constipation. Severe cases can progress to sepsis, shock, and altered mental state due to potential meningitis. A small group of enteric fever patients may also have bloody diarrhea. Related to the fever, patients may also experience relative bradycardia, a slower than expected heart rate. Enteric fever has the potential to become a long-term condition turning individuals into chronic carriers of the bacteria. These bacteria reside in the gallbladder of chronic carriers leading to gallbladder cancer.

• NTS infection symptoms: diarrhea, fever, and stomach cramps
• Risks for NTS infection: contact with reptiles, eating undercooked foods like chicken, eggs, meat, and dairy
• Infections most common in: children under one, long-term steroid users, people with cancer, organ recipients, people with AIDS
• Enteric fever symptoms: fever, headache, weakness, tiredness, other symptoms
• Risks for enteric fever: can become a long-term condition, especially for people with weak immune systems. Can lead to gallbladder cancer in chronic carriers.

Testing for Salmonella

The best way to confirm a Salmonella infection is by performing tests called cultures on various body fluids. Cultures involve trying to grow bacteria present in the sample provided, allowing doctors to identify the specific bacteria causing the infection. The type of culture used depends on where the infection is suspected, and can be from a variety of sources such as your stool (poop), blood, urine, bile (a substance your liver makes to help digest fats), cerebrospinal fluid (the fluid around your brain and spinal cord), and bone marrow (the spongy tissue inside your bones where blood cells are made).

If a Salmonella infection is affecting your intestines and causing diarrhea, the doctors usually test your stool. This stool test is often used to diagnose infections caused by non-typhoidal Salmonella, which mainly cause food poisoning.

However, if you show symptoms of typhoid or paratyphoid fever, more serious types of Salmonella infections, the doctors may choose to test your blood, bone marrow, or bile instead of stool. That’s because these types of bacteria don’t show up in the stool as often as they show up in the blood, bone marrow, or bile. If Salmonella bacteria are suspected to have spread to your brain causing a condition called meningitis, doctors may need to collect a sample of the cerebrospinal fluid that surrounds your brain and spinal cord for testing.

Once the culture sample is taken, it’s placed on a special dish which encourages the bacteria to grow. Salmonella bacteria can be identified by the black colonies that form on a specialized dish called Hektoen agar plates. This black color is due to the production of hydrogen sulfide by Salmonella bacteria. For those presenting with typhoid fever, bone marrow cultures tend to be more effective than blood cultures as these bacteria are often more concentrated in bone marrow than in blood.

Emerging diagnostic techniques, such as polymerase chain reaction (PCR) tests, use a small sample of DNA to detect the presence of specific bacteria, including Salmonella. Usually used in a research setting, these techniques are increasingly being used in clinical practice.

Treatment Options for Salmonella

The primary focus of treatment for most cases should be on addressing dehydration and issues with electrolytes. Care is needed to cope with symptoms of acute diarrhea and dehydration. If necessary, fever-reducing treatments can also be used.
In cases of Salmonella infection (NTS) that is restricted to gastroenteritis—meaning it’s causing stomach and intestinal inflammation—without signs of sepsis (a potentially life-threatening condition caused by the body’s response to an infection), antibiotics are not usually needed, except for patients less than 3 months old and those with weakened immune systems. Once a diagnosis of NTS gastroenteritis is confirmed, blood tests should be done.

If the NTS infection has spread to the blood or other parts of the body, initial treatment is typically done with a third-generation class of antibiotics such as ceftriaxone, for between 7 to 10 days. Once the bacterial susceptibilities (how the bacteria respond to different treatments) are known, the antibiotic treatment can be modified to azithromycin or a fluoroquinolone (classes of antibiotics). The length of treatment may be extended in certain infections such as meningitis (4 weeks) or osteomyelitis (an infection in the bone), which usually take 4 to 6 weeks to treat.

In the case of enteric fever, another disease caused by Salmonella infection, the preferred treatment is fluoroquinolone. However, a growing number of cases are found to be resistant to multiple drugs, which has led to an increased focus on testing the bacteria for susceptibility to different treatments, and also on the use of alternative antibiotics like third-generation cephalosporins and azithromycin. Fluoroquinolones are not as commonly used in children as in adults, and alternatives like azithromycin are often chosen. Treatment usually lasts between 10 to 14 days. In severe cases of enteric fever where symptoms include confusion, reduced awareness or a state of unconsciousness, or a severe drop in blood pressure (shock), additional treatment with corticosteroids—a class of drug that reduces inflammation in the body—may be considered. Chronic carriers of the bacteria require four weeks of fluoroquinolone therapy to clear the bacteria from their bodies. In adults, if therapy with antibiotics doesn’t work, a surgical procedure called cholecystectomy (removal of the gallbladder) might be considered due to the persistence of bacteria in the gallbladder.

What else can Salmonella be?

Salmonella infections can mimic many illnesses that cause fever. This can sometimes lead to confusion when diagnosing in regions where such infections are common. Other conditions could look similar, such as stomach flu, viral infections, infections caused by microorganisms inside cells, and different bacterial infections.

Doctors also need to consider numerous other illnesses when diagnosing Salmonella. These include:

• Malaria
• Tuberculosis
• Brucellosis
• Tularemia
• Leptospirosis
• Encephalitis (brain inflammation)
• Endocarditis (heart valve infection)
• Influenza (flu)
• Dengue fever
• Infectious mononucleosis (mono)
• Visceral leishmaniasis (parasitic infection)

Moreover, a patient’s travel history can be a big clue, especially considering illnesses like typhoid fever which is more common outside the United States.

What to expect with Salmonella

Most people who acquire NTS infection, a type of bacterial infection, usually recover fully with no lingering complications. However, individuals who are malnourished and don’t have adequate supportive care may face drawn-out symptoms such as prolonged diarrhea, dehydration, and other issues.

Some people who require antibiotics, usually infants or those with weakened immune systems, may experience a longer and more severe illness, often with the infection spreading to other parts of the body. However, in the case of enteric fever (a bacterial infection of the intestines), if caught and treated quickly and effectively, patients have a high likelihood of full recovery.

If the diagnosis of enteric fever is delayed or if inappropriate antibiotics are used, the outcomes can potentially be unfavorable. Malnourished patients infected with strains of bacteria resistant to multiple drugs tend to face more complications.

Sometimes, patients can become chronic carriers of the bacteria when they don’t respond to antibiotic treatment and continue to excrete the bacteria for more than three months. Being a chronic carrier is rare in children, but the likelihood increases with age and in patients with gallbladder disease. In addition, individuals can become chronic carriers in their urinary system when they have a coexisting infection with schistosomiasis (a disease caused by parasitic worms).

Possible Complications When Diagnosed with Salmonella

People suffering from NTS gastroenteritis, an inflammatory condition in the stomach and intestines, can become severely dehydrated if the condition isn’t managed well. This becomes more problematic when coupled with other illnesses. Particularly, those with weakened immune systems may experience a systemic infection where multiple organs are affected, leading to a severe, life-threatening condition, known as sepsis, shock, and could potentially cause death.

Typhoid fever has several complications that involve the nervous system, which can manifest as delirium, psychosis, acute cerebellar ataxia (a condition that affects coordination), and Guillain-Barré syndrome (a rare neurological disorder). In relation to the heart, typhoid fever can cause myocarditis (inflammation of the heart muscle) and pericarditis (inflammation of the lining around the heart). Digestive tract complications include intestinal bleeding and perforation (making a hole in the wall of the intestine). Finally, enteric fever can turn patients into chronic carriers of the disease if the treatment is ineffective or inappropriate.

Possible Complications:

• Severe dehydration
• Systemic infections affecting multiple organs
• Sepsis
• Shock
• Potential death
• Neurological complications including delirium, psychosis, acute cerebellar ataxia, and Guillain-Barré syndrome
• Cardiovascular complications including myocarditis and pericarditis
• Gastrointestinal pains including intestinal hemorrhage and perforation
• Patients becoming chronic carriers of the disease

Preventing Salmonella

There are several ways to prevent Salmonella infection, which include maintaining cleanliness, being mindful while caring for kids and pets, and getting vaccinated. One of the primary ways to prevent Salmonella is ensuring good cleanliness practices. This means making sure your water supply is clean and that food is handled correctly. Contaminated water can cause Salmonella, so it’s crucial to purify water with methods such as chlorination. When preparing food, it’s also important to wash hands thoroughly, especially after handling certain items like raw eggs, chicken, or uncooked meat. Even street foods like fruits and ice cream are potential carriers of the infection.

Pets, particularly reptiles and amphibians, can transmit Salmonella to people, which makes child care associated with these pets another important aspect of prevention. After petting these animals, wash your hands and don’t eat or drink around them. Younger children, especially those under five, or individuals with weakened immune systems should not handle these pets. In child care centers or schools, kids who have had a Salmonella infection can return once symptoms like diarrhea have ended. For specific types of Salmonella like typhi or paratyphi 3, it’s necessary for tests to confirm that the infection has cleared before a child returns to school.

To prevent typhoid fever, another disease caused by a type of Salmonella, vaccination can be a helpful method. There are two vaccines currently available which protect against the typhi type of Salmonella. These vaccines are suggested for individuals who are traveling, people in contact with those carrying typhoid fever, and workers in laboratories with exposure risk. The first vaccine is the Ty21a strain typhoid vaccine, which is a series of four doses taken orally on specific days (0, 2, 4, and 6). This vaccine should be finished at least a week before potential exposure and boosters, including all 4 doses, should be taken every 5 years. Certain medications, including specific antibiotics, should not be taken within three days of starting or finishing the vaccine. The second vaccine, called Vi capsular polysaccharide vaccine (ViCPS), is administered through a one-time injection and can be given to individuals two years and older. It should be given at least two weeks before potential exposure, and follow-up doses or ‘boosters’ should be given every 2 years.