What are foodborne illness outbreaks?

Foodborne Illness Outbreaks

Foodborne illness outbreaks are defined as the occurrence of two or more cases of a similar illness resulting from the ingestion of a common food. 1 These outbreaks represent a significant public health threat, with approximately 800 foodborne illness outbreaks occurring annually in the United States, resulting in approximately 15,000 illnesses, 800 hospitalizations, and 20 deaths. 2

Common Causes and Settings

Etiologic Agents

• Viruses (45%): Norovirus is the leading cause of foodborne disease outbreaks in the United States 1
• Bacteria (45%): Including Salmonella, Campylobacter, and E. coli 3
• Chemical and toxic agents (5%) 3
• Parasites (1%) 3

Most Common Settings

1. Healthcare facilities (35.4%)

   • Nursing homes and hospitals are the most commonly reported settings 1
   • Outbreaks can be prolonged, sometimes lasting months 1
   • Illness can be more severe in hospitalized patients, with associated deaths reported 1

2. Restaurants and catered events (31.1%)

   • Handling of ready-to-eat foods by infected food employees is a common contributing factor 1
   • Only a small dose of virus is needed to cause infection 1
   • Example: 500 cases of gastroenteritis reported from a single foodhandler who vomited at work 1

3. Vacation settings including cruise ships (20.5%)

   • Virus can be introduced by passengers or crew infected before embarkation 1
   • Environmental persistence can lead to repeated outbreaks in subsequent sailings 1

4. Schools and communities (13.0%)

   • Includes schools, child care centers, colleges, prisons, and military encampments 1
   • Outbreaks in universities have led to campus closures 1

Contributing Factors

Foodborne illness outbreaks result from three main categories of contributing factors:

1. Contamination (81-86% of outbreaks) 2

   • Food contaminated by an animal or environmental source before preparation (increasing trend: 22.2% to 32.3%) 2
   • Contamination from infectious food workers through barehand contact (decreasing trend: 20.5% to 8.9%) 2
   • Cross-contamination between foods 2

2. Proliferation (35-40% of outbreaks) 2

   • Allowing foods to remain out of temperature control during preparation (decreasing trend: 15.2% to 9.9%) 2
   • Improper cooling of food (fluctuating trend: 9.4%, 8.8%, 10.9%) 2

3. Survival (22-26% of outbreaks) 2

   • Inadequate time and temperature control during cooking/thermal processing 2

Commonly Implicated Foods

The food commodities most frequently implicated in outbreaks are:

• Poultry (18.9%) 3
• Fish (18.6%) 3
• Beef (11.9%) 3
• Leafy vegetables - especially in norovirus outbreaks 3
• Raw foods (e.g., leafy vegetables, fruits, shellfish) are identified most commonly 1

Pathogen-Food Combinations

The most common pathogen-food combinations in outbreaks:

• Scombroid toxin/histamine and fish (317 outbreaks) 3
• Ciguatoxin and fish (172 outbreaks) 3
• Salmonella and poultry (145 outbreaks) 3
• Norovirus and leafy vegetables (141 outbreaks) 3

The pathogen-food combinations causing the most illnesses:

• Norovirus and leafy vegetables (4,011 illnesses) 3
• Clostridium perfringens and poultry (3,452 illnesses) 3
• Salmonella and vine-stalk vegetables (3,216 illnesses) 3
• Clostridium perfringens and beef (2,963 illnesses) 3

Transmission Mechanisms

Food can become contaminated with pathogens at any point during:

• Production
• Processing
• Distribution
• Preparation 1

Common mechanisms include:

• Infected food handlers contaminating ready-to-eat foods 1
• Fecal contamination of food products at the source (e.g., oysters from contaminated waters) 1
• Contamination during processing 1
• Secondary person-to-person transmission following initial food exposure 1

Emerging Trends and Considerations

• Novel data streams: Social media, web-based product reviews, and public-generated notices are emerging as early warning systems for foodborne illness outbreaks 4

• Viral pathogens: Beyond norovirus, other viruses like hepatitis A and E, rotavirus, astrovirus, adenovirus, and sapovirus are associated with foodborne illness outbreaks 5

• Potential emerging threats: Aichi virus, Nipah virus, tick-borne encephalitis virus, avian influenza viruses, and coronaviruses may have potential for foodborne transmission 5

• COVID-19 impact: The pandemic led to a decrease in viral outbreaks, likely due to nonpharmaceutical interventions like increased glove use and enhanced cleaning protocols 2

Prevention Strategies

Effective prevention of foodborne illness outbreaks requires:

• Following science-based food safety guidelines such as the FDA Food Code 2
• Implementing Hazard Analysis and Critical Control Points (HACCP) plans 2
• Proper time and temperature controls during cooking and storage 2
• Written policies for ill worker management 2
• Improved hand hygiene and surface disinfection 1
• Strict control measures in healthcare settings (isolation of symptomatic patients, exclusion of affected staff) 1

Foodborne illness outbreaks remain a persistent public health challenge requiring vigilance and coordinated response across the entire food production and preparation chain.