What is the source of salmonellosis, particularly in immunocompromised, elderly, or individuals with a history of gastrointestinal illness?

Sources of Salmonellosis

Salmonellosis is primarily acquired through contaminated food products, with poultry and eggs being the most common sources, followed by contaminated produce, unpasteurized dairy products, and direct or indirect animal contact. 1, 2, 3

Primary Food Sources

Animal-Derived Products

• Poultry and poultry products represent the leading source of human Salmonella infection, followed by beef, pork, and fish 3
• Eggs are a major vehicle for transmission, particularly when consumed raw or undercooked 1
• Unpasteurized dairy products pose significant risk and should be specifically assessed in outbreak investigations 1
• All food animals are susceptible to Salmonella infection and can become asymptomatic carriers, serving as ongoing sources of contamination even after recovery from clinical disease 4

Plant-Derived Products

• Fresh produce has emerged as an increasingly important source of salmonellosis outbreaks in recent years, representing a shift from the traditional focus on meat and poultry 2
• Contamination occurs through multiple pathways: irrigation with contaminated water, direct contact with animal manure, or indirect environmental contamination 2
• Salmonella can attach to or internalize within vegetables and fruits, making surface decontamination insufficient 2

Transmission Mechanisms

Direct and Indirect Animal Contact

• Direct contact with infected animals in homes, farms, veterinary clinics, and zoological gardens represents an important non-foodborne transmission route 5
• Both clinically ill and apparently healthy animals can shed Salmonella for prolonged periods, complicating control efforts 5
• Environmental contamination in animal housing areas can lead to indirect transmission through contaminated surfaces, food, and water 5

Food Handler Contamination

• Asymptomatic food handlers colonized with Salmonella can transmit infection without exhibiting symptoms, as demonstrated in outbreak investigations where food service workers tested positive despite denying illness 6, 7
• Bare-handed contact with ready-to-eat foods facilitates transmission from colonized handlers to consumers 6
• Contamination can occur during food preparation, transport, or service, even when handlers are not directly involved in cooking 6

High-Risk Populations

Vulnerable Groups at Increased Risk

• Immunocompromised individuals (HIV infection, chronic immunosuppression) face higher risk of invasive disease and severe outcomes 1, 8
• Elderly patients are at increased risk for severe disease and complications 8
• Individuals with chronic liver disease, cirrhosis, hemoglobinopathies, or recent malaria have predisposition to more severe disease and invasive infection 1
• Neonates and infants require special consideration due to higher risk of bacteremia and systemic complications 9, 8
• Individuals with history of gastrointestinal illness may have altered gut flora that increases susceptibility 1

Critical Risk Assessment Questions

When evaluating potential salmonellosis sources, clinicians should systematically assess:

• Recent consumption of high-risk foods: poultry, eggs, unpasteurized dairy, and fresh produce 1
• Travel history to endemic areas for enteric fever, particularly developing countries 1
• Contact with others experiencing similar symptoms, suggesting common source exposure 1
• Institutional living situations (long-term care facilities, dormitories) where person-to-person transmission can occur 1
• Attendance at large gatherings or events where food was served, particularly buffet-style service 6, 1
• Direct or indirect animal contact in professional, private, or public settings 5
• Occupational exposure to laboratory specimens containing Salmonella 1

Common Pitfalls in Source Identification

• Do not overlook asymptomatic carriers among food handlers, as they can transmit infection without clinical illness 7
• Multiple serotypes can be involved in a single outbreak, which may complicate source identification but can help define outbreak scope when properly characterized 6
• Environmental contamination of produce can occur at multiple points from farm to table, not just at the point of consumption 2
• Wild and domesticated animals can contaminate water sources used for irrigation, creating indirect pathways for produce contamination 2