Salmonellosis: Causes, Symptoms, and Prevention

Salmonellosis is one of the most widespread bacterial foodborne infections globally. It is caused by Salmonella bacteria – a group of gram-negative, rod-shaped organisms that live primarily in the intestinal tracts of animals and humans. Every year, this infection affects millions of people worldwide, and it remains a leading cause of food poisoning-related hospitalisations and deaths. Understanding how salmonellosis occurs, recognising its symptoms early, and knowing how to prevent it are essential – whether you’re a food science student, a food handler, or simply someone who wants to eat safely.

What is salmonellosis? 🔗

Salmonellosis is a gastrointestinal infection caused by ingesting food or water contaminated with Salmonella bacteria. The WHO identifies Salmonella as one of four key global causes of diarrhoeal diseases. Within the two known species – Salmonella enterica and Salmonella bongori – more than 2,500 serotypes have been identified, though fewer than 100 are responsible for most human illness.

The two most common serotypes linked to foodborne salmonellosis are Salmonella Enteritidis and Salmonella Typhimurium. According to the USDA Food Safety and Inspection Service, these two serotypes alone account for roughly half of all human Salmonella infections in the United States. Notably, S. Enteritidis is closely associated with poultry and egg products, while S. Typhimurium is more commonly linked to pork and other meats.

It is important to distinguish salmonellosis (nontyphoidal Salmonella infection) from typhoid fever, which is caused by a different set of Salmonella serotypes (Salmonella Typhi and Paratyphi) and produces a more severe systemic illness.

Causes and sources of salmonellosis 🔗

Salmonella bacteria are primarily transmitted to humans through the faecal-oral route – most commonly by eating food contaminated with animal faeces. The bacteria reside in the intestines of many animals, including poultry, cattle, pigs, and reptiles. A particularly concerning aspect is that contaminated food usually does not look, smell, or taste any different from safe food, making it impossible to detect contamination without laboratory testing.

Common food sources 🔗

The foods most frequently linked to salmonellosis include:

Poultry and eggs: Chicken is one of the most significant sources. The CDC estimates that more than 1 in every 25 packages of chicken at the grocery store may be contaminated with Salmonella. Eggs can be contaminated externally through shell contact with faeces, or internally through vertical transmission from infected hens before the shell is formed.

Raw and undercooked meat: Beef, pork, turkey, and other meats can carry Salmonella if not cooked to the proper internal temperature.

Unpasteurised dairy products: Raw milk and cheeses made from raw milk are potential vehicles for Salmonella.

Fruits and vegetables: Produce can become contaminated through contact with contaminated irrigation water, manure-based fertilisers, or during handling and processing.

Processed foods: Several outbreaks have been traced to peanut butter, nut products, frozen meals, flour, and even spices.

Non-food sources 🔗

Salmonella does not spread only through food. The CDC notes that people can also contract the infection through direct contact with animals – particularly reptiles, amphibians, baby chicks, and ducklings – as well as through contaminated water or contact with infected individuals via the faecal-oral route.

Pathogenesis: how Salmonella makes you sick 🔗

When a person consumes food containing a sufficient number of Salmonella organisms, the bacteria pass through the acidic environment of the stomach and reach the small intestine. Here, they invade and destroy the cells lining the intestinal wall. This invasion triggers an inflammatory response, disrupting the intestine’s normal ability to absorb water and nutrients.

The result is the hallmark symptoms of salmonellosis – diarrhoea, abdominal cramps, and nausea. The infective dose (the number of bacteria needed to cause illness) can vary depending on the person’s health and the Salmonella serotype, but in general, it ranges from 10⁵ to 10⁸ cells. In immunocompromised individuals, as few as 1,000 cells may be sufficient to cause infection.

Factors that lower stomach acidity – such as taking antacids or certain medications – can make a person more susceptible, since stomach acid is one of the body’s first defences against ingested pathogens.

Symptoms and incubation period 🔗

The incubation period for salmonellosis – the time between ingesting the bacteria and the onset of symptoms – typically ranges from 6 to 72 hours, though most people develop symptoms within 12 to 36 hours. According to the Mayo Clinic, common signs and symptoms include:

Diarrhoea (which can sometimes be bloody), fever, abdominal cramps, nausea, vomiting, headache, and chills.

In most healthy adults, symptoms resolve within 4 to 7 days without the need for antibiotics. However, diarrhoea can persist for up to 10 days, and it may take several months for bowel habits to fully return to normal. The illness is self-limiting in most cases, meaning the body clears the infection on its own.

When salmonellosis becomes serious 🔗

While most people recover without complications, salmonellosis can become life-threatening in certain populations. According to the USDA FSIS, those at highest risk for severe outcomes include infants and young children, pregnant women, older adults (over 65), and people with compromised immune systems due to conditions like HIV/AIDS, cancer, diabetes, or organ transplants.

In severe cases, the bacteria can enter the bloodstream and spread to other organs – a condition known as bacteraemia – potentially leading to infections in bones (osteomyelitis), the heart lining (endocarditis), or the brain (meningitis). A small number of patients may also develop reactive arthritis (Reiter’s syndrome) weeks after the initial infection, causing joint pain, eye irritation, and painful urination.

Diagnosis and treatment 🔗

Salmonellosis is typically diagnosed through a stool culture – a laboratory test that identifies Salmonella bacteria in a patient’s faecal sample. In cases where the infection may have spread beyond the intestines, blood cultures may also be performed.

For most healthy individuals, treatment focuses on managing symptoms, primarily through adequate fluid intake to prevent dehydration. Oral rehydration solutions, clear broths, and electrolyte-containing drinks are recommended. Over-the-counter anti-diarrhoeal medications may provide relief for adults, but they should not be given to young children without medical advice.

Antibiotics are generally not required for uncomplicated cases. In fact, the WHO advises that routine antimicrobial therapy is not recommended for mild or moderate cases in healthy individuals. Antibiotics are reserved for severe infections, bacteraemia, or high-risk patients. When prescribed, common choices include ciprofloxacin, ceftriaxone, and azithromycin.

The growing concern of antimicrobial resistance 🔗

A significant challenge in treating salmonellosis is the rise of antimicrobial-resistant Salmonella strains. The overuse of antibiotics in both human medicine and livestock production has contributed to the emergence of resistant serotypes, making some infections harder to treat. This is recognised as a global public health concern by both the WHO and the CDC.

Prevention of salmonellosis 🔗

The good news is that salmonellosis is largely preventable. Effective prevention requires a farm-to-fork approach – involving everyone from farmers and food processors to retailers, food handlers, and consumers. The U.S. FoodSafety.gov outlines four fundamental principles: Clean, Separate, Cook, and Chill.

Proper cooking 🔗

Cooking food to safe internal temperatures is the single most effective way to kill Salmonella. Poultry should reach an internal temperature of at least 74°C (165°F), ground meats should reach 71°C (160°F), and eggs should be cooked until both the yolk and white are firm. Using a food thermometer is the only reliable way to confirm that food has been cooked sufficiently.

Avoiding cross-contamination 🔗

Cross-contamination occurs when juices from raw meat, poultry, or eggs come into contact with ready-to-eat foods like salads, fruits, or cooked dishes. To prevent this, keep raw meats separate from other foods during storage and preparation. Use separate cutting boards for raw meat and fresh produce, and wash all utensils, boards, and surfaces with hot soapy water after handling raw animal products.

Hand hygiene 🔗

Handwashing is one of the most effective and simplest prevention measures. Hands should be washed thoroughly with soap and water for at least 20 seconds before and after handling food, after using the toilet, after changing nappies, and after contact with animals – especially reptiles, poultry, and their habitats.

Safe storage and refrigeration 🔗

Salmonella multiplies rapidly at temperatures between 4°C and 60°C (the “danger zone”). Perishable foods should be refrigerated promptly – within two hours of preparation or purchase (one hour in hot weather). Leftovers should be stored in shallow containers for rapid cooling. Frozen foods should be thawed in the refrigerator, in cold water, or in the microwave – never at room temperature.

Choosing pasteurised products 🔗

Pasteurisation is a heat treatment process that kills harmful bacteria, including Salmonella, in milk and juice products. Always choose pasteurised dairy products and juices. Avoid consuming raw or unpasteurised milk and products made from it.

The role of food handlers and the food industry 🔗

Food handlers bear a critical responsibility in preventing salmonellosis outbreaks. An infected food handler – even one without visible symptoms – can contaminate food through poor hygiene practices. Regular hand washing, wearing clean protective clothing, and staying away from food preparation areas when ill are non-negotiable practices in any food service setting.

On the industry side, measures include maintaining hygienic conditions at slaughterhouses, testing livestock for Salmonella, implementing hazard analysis and critical control point (HACCP) systems, and ensuring proper cold chain management during transport and storage. Regulatory agencies such as the USDA’s FSIS and the FDA conduct inspections and set standards to minimise Salmonella contamination in the commercial food supply.

Global burden and public health significance 🔗

Salmonellosis is a disease of global significance. The WHO reports that almost 1 in 10 people fall ill from foodborne diseases each year, with 33 million healthy life years lost globally. Diarrhoeal diseases from unsafe food affect 550 million people annually, including 220 million children under five. In the United States alone, Salmonella causes an estimated 1.4 million foodborne illness cases, 26,500 hospitalisations, and over 400 deaths each year.

An important surveillance challenge is that the majority of cases go unreported. The CDC estimates that for every confirmed laboratory case, nearly 30 additional cases are never diagnosed because most affected individuals do not seek medical care.

In response, international organisations like the WHO and regional bodies such as the European Food Safety Authority (EFSA) continue to strengthen surveillance systems, set reduction targets for Salmonella in poultry, and promote education for consumers and food handlers on safe food practices.

Key takeaways 🔗

Salmonellosis remains one of the most common and preventable foodborne infections worldwide. It is primarily transmitted through contaminated poultry, eggs, meat, and dairy products. While most cases resolve on their own with supportive care, the infection can be dangerous for vulnerable populations. Prevention hinges on thorough cooking, meticulous hygiene, proper food storage, and avoiding cross-contamination. For food industry professionals and public health authorities, a comprehensive farm-to-fork strategy is essential to reduce the incidence of this persistent pathogen.

What do you think? Given that most Salmonella contamination is invisible – with no change in the taste, smell, or appearance of food – how can we better encourage everyday consumers to adopt strict food safety habits at home? And should food safety education be a compulsory part of school curricula?

References

1. https://www.who.int/news-room/fact-sheets/detail/salmonella-(non-typhoidal)
2. https://www.fsis.usda.gov/food-safety/foodborne-illness-and-disease/illnesses-and-pathogens/salmonella
3. https://www.cdc.gov/salmonella/about/index.html
4. https://www.cdc.gov/salmonella/spread/index.html
5. https://pmc.ncbi.nlm.nih.gov/articles/PMC10506869/
6. https://www.mayoclinic.org/diseases-conditions/salmonella/symptoms-causes/syc-20355329
7. https://www.foodsafety.gov/blog/salmonella-and-food
8. https://pmc.ncbi.nlm.nih.gov/articles/PMC8143179/
9. https://www.efsa.europa.eu/en/topics/topic/salmonella