Introduction

Salmonella is a common foodborne bacterial infection that affects the gut health. It is frequently found in contaminated pork, meat and poultry.¹ While some people with mild infection do not present symptoms and hence do not require medical attention, most people often present with diarrhoea, stomach cramps, fever, or more serious issues.²

Salmonella infections (salmonellosis) are classified into two groups major and minor: minor salmonellosis is characterized by self-limiting diarrhoea and is usually caused by non-typhoid Salmonella strains,³ and major salmonellosis is represented by typhoid fever, which could be fatal if left untreated.⁴ 

Diagnosis

Clinical evaluation

Patient history and symptom assessment

A medical professional will take the patient’s history and assess their symptoms to narrow down the possible diagnosis. Recent travel histories, food intake, food purchases, specific symptoms and when the symptoms began, are some of the questions that can be asked. However, because Salmonella infection presents non-specific symptoms that are similar to other illnesses, the only way to confirm the diagnosis is through lab tests. 

Laboratory tests

Stool culture

A stool test can be done to look for the presence of blood in stool, which confirms whether an infection is causing the symptoms or if there are any other gastrointestinal abnormalities. Since there are two groups of Salmonella, a specific stool test is required to identify the type of Salmonella responsible for the symptoms. 

Blood tests 

Blood tests (including culture) are normally done if the healthcare provider suspects the bacteria has travelled into the bloodstream (bacteremia). Blood tests are also done when a patient complains of severe symptoms like vomiting and diarrhoea.

Serologic tests (Widal test)

There is an alternative test to diagnose typhoid and paratyphoid fever caused by Salmonella, called the Widal test. It may be used when a blood test for culture is unavailable, and it can detect the Salmonella antibody as early as the first week of infection.

Differential diagnosis

Common Conditions to Differentiate

Many other foodborne bacterial infections can be mistaken for Salmonella poisoning due to the similar symptoms presented by patients, for example, Escherichia coli (E. coli), Shigella, and Campylobacter. Furthermore, diagnosis of Salmonella infection may also be confused with alternative diseases and conditions including, but not limited to, malaria, tuberculosis, influenza, and dengue.⁵ Therefore, it is essential to provide a detailed and precise history and symptoms to narrow down the diagnosis pool. Travel history is especially important to consider for typhoid fever, as certain countries or areas are more prone to such disease.

Treatment

Supportive care

The key treatment restores fluids and electrolytes rapidly by drinking plenty of fluids, diluted fruit juices, sports drinks, and oral rehydration therapy (ORT) (usually prescribed by the healthcare provider). While most people with mild symptoms may choose to stay at home, it is possible to make your rehydration solution using:

• 1/2 teaspoon of salt
• 6 teaspoons of sugar
• 1 litre of water

It is advisable to have small meals throughout the day, preferably broth or liquid food. It is best to avoid spicy and greasy foods, sugary drinks (they fuel bacteria), caffeinated beverages, and alcoholic drinks. The BRAT diet may be a useful guide for a delicate stomach.

Pharmacological treatment

Antibiotic therapy

If your symptoms persist or worsen, or if you have underlying conditions or diseases that could affect your recovery, it is best to consult a doctor who promptly runs tests to confirm the diagnosis and prescribe suitable medications. 

Antibiotics are commonly used to fight off Salmonella infection. However, antibiotics are not used routinely for healthy patients with mild or moderate cases to avoid antibiotic resistance. It is only recommended for:

• People with severe symptoms such as high fever, severe diarrhoea, bacteremia (bacteria has spread into the bloodstream)
• Adults older than 50 years old (elderly), especially those with underlying conditions like heart disease
• Children under 6 months of age

Examples of antibiotics for the treatment of Salmonella are ciprofloxacin and azithromycin.⁶ It is important to complete the prescribed course of antibiotics and if any discomfort is experienced after starting the antibiotics therapy, it should be addressed immediately. 

Antipyretics and pain management

Enteric fever is the term used for both paratyphoid and typhoid fevers caused by Salmonella, as the clinical symptoms of both fevers are indistinguishable. In enteric fever, a specific fever pattern is noticed; begins with a low-grade fever (> 37.5°C to 38.2°C) in the first week and slowly onto a high-grade fever (> 38.2°C to 41.5°C) in the second week.⁷ 

Before diagnosis, antipyretics like acetaminophen can be obtained over the counter to manage fever symptoms, although, in most cases of minor salmonellosis, the fever usually subsides by itself. More severe cases of enteric fever; major salmonellosis, would require antibiotics to fight off the infection.

Over-the-counter painkillers, like Ibuprofen, may be useful to manage pain and reduce fever.

Alternative and complementary therapy

Probiotics are live bacteria that are already present in our gut, usually known as “good” bacteria. During infection, the gut health is compromised - probiotics may help to restore the natural balance of bacteria thus, reducing the frequency of diarrhoea or speeding up the recovery in mild to moderate cases. It is best to consult your doctor if you are immunocompromised or have any underlying conditions to ensure probiotics do not affect your health adversely.⁸ 

Complications

10-15% of major salmonellosis patients develop complications, although this value is largely based on endemic countries where the disease is consistently present. The most common complication is gastroenteritis (inflammation of the gastrointestinal tract) which includes:

• pancreatitis (inflammation of the pancreas) 
• hepatitis (inflammation of the liver tissue)
• cholecystitis (inflammation of the gallbladder) 

The most severe gastrointestinal complication is haemorrhage (internal bleeding), resulting in bloody diarrhoea.^9,10

Approximately 5% of minor salmonellosis patients develop bacteremia, which in severe conditions or if left untreated, can lead to septic shock with a high mortality rate. Other extraintestinal complications may occur, including cellulitis, urinary tract infections, pneumonia, endocarditis and meningitis; the lung is the most commonly compromised organ.¹¹

Prevention

Preventive measures for Salmonella involve all parties from agricultural production, to processing, manufacturing and preparation of food products similar to other foodborne bacterial diseases. There are national and regional surveillance systems in place to monitor statistical reports and take action accordingly. It is equally important to ensure foods are handled and cooked properly at home. Homes with pet animals require extra attention to ensure foods are not in contact with the animals that may be carrying Salmonella.

Besides food, Salmonella can also be found in water. Purification of water is essential to prevent transmission of the bacteria. Boiling water for at least 10 minutes before drinking is an easy way to get rid of the bacteria.¹²

Vaccination is currently available to prevent typhoid fever (not paratyphoid). It is advisable to get vaccinated if you are travelling to high-risk areas with poor sanitation and hygiene. Examples of high-risk areas are the Indian subcontinent, Africa, South and Southeast Asia, and South America. The vaccines are available as an injection (one shot) and orally (3 capsules to be taken on alternate days). Each vaccination lasts up to 3 years, and a booster dose is available after.¹³

Summary

Salmonella is a foodborne bacterial infection categorised into minor and major salmonellosis. Minor salmonellosis (non-typhoidal) is usually self-limiting while major salmonellosis (typhoid) is often fatal if left untreated. Common symptoms include diarrhoea, fever, and stomach cramps. Salmonella infection is often diagnosed through stool tests and blood cultures. Since the symptoms resemble many other foodborne diseases, history-taking and patient assessment are crucial to ensure accurate diagnosis and, hence effective and appropriate medical treatment. Antibiotics are indicated for certain groups of patients and are reserved for severe cases to avoid antibiotic resistance. Antipyretics and painkillers can be taken if necessary. The main focus of preventing Salmonella infection and transmission is good sanitation and hygiene practices, at the home and commercial levels. Vaccination is only available to prevent typhoid fever.