From 2014 through 2022, data collected from foodborne illness outbreak investigations across the United States have revealed consistent patterns in the factors contributing to these outbreaks. The Centers for Disease Control and Prevention (CDC), along with state and local health departments, compiled and analyzed thousands of outbreak reports. These reports help identify not only what foods were involved, but also the behaviors, practices, and environmental conditions that made people sick.
Understanding these contributing factors allows for more targeted prevention strategies. It also provides critical insight into where food safety systems are most vulnerable, whether in restaurants, food production facilities, or even at home.
The Top Contributors to Outbreaks
According to outbreak data from the National Outbreak Reporting System (NORS), the most frequently cited contributing factors during this period were related to food handling and preparation. These included:
- Improper food holding temperatures
- Inadequate cooking
- Cross contamination
- Contaminated raw ingredients
- Food prepared by infected food handlers
Time and Temperature Abuse Emerged as a Leading Issue
Many outbreaks involved food held too long at unsafe temperatures, allowing bacteria such as Clostridium perfringens or Salmonella to multiply. Cold foods not held below 41 degrees Fahrenheit or hot foods not kept above 135 degrees were especially problematic in buffet settings and catered events.
Infected or Ill Food Workers
Food prepared by workers who were ill or had poor hygiene was another major contributing factor. Norovirus, a leading cause of outbreaks, is commonly spread by sick employees who handle food with unwashed hands. Between 2014 and 2022, hundreds of outbreaks were linked to ill food handlers, particularly in restaurant and institutional settings.
Despite guidelines requiring food workers to stay home when sick, economic pressures, lack of paid sick leave, and poor enforcement contributed to this persistent issue. Public health advocates have emphasized the need for stronger worker protections and training to reduce illness-related transmission.
Contaminated Raw Ingredients
Another major factor identified was the use of contaminated raw ingredients. Leafy greens, raw sprouts, and undercooked poultry were common culprits. These ingredients often carried pathogens such as E. coli, Listeria monocytogenes, and Salmonella before reaching kitchens or restaurants.
The widespread nature of some outbreaks suggested contamination had occurred early in the supply chain, often at farms or during processing. Investigations showed that poor agricultural water quality, inadequate sanitation, and animal intrusion contributed to contamination before distribution.
Cross Contamination in Kitchens
Cross contamination, especially from raw animal products to ready-to-eat foods, was also frequently reported. This often occurred due to shared cutting boards, improper glove use, and failure to clean and sanitize surfaces and utensils.
In both home and commercial kitchens, storing raw meat above fresh produce or using the same equipment for raw and cooked foods led to numerous preventable outbreaks. This finding highlights the importance of food safety education at every level, from foodservice professionals to home cooks.
Complex Foods and Food Sources
The period between 2014 and 2022 also saw an increase in outbreaks linked to “complex foods,” dishes made up of multiple ingredients prepared in stages. Examples include deli sandwiches, salads, and mixed pasta dishes. These foods are difficult to trace and may involve multiple contributing factors, including mishandling at several points during preparation.
Imported foods also contributed to outbreaks during this time. With a globalized food supply, contaminated products from other countries introduced new risks. Spices, frozen fruits, and seafood items from overseas were among the imported items involved in outbreaks.
Environmental and Behavioral Issues
Environmental assessments conducted during outbreak investigations revealed recurring issues such as broken refrigeration units, pest infestations, and poor facility sanitation. These contributed to foodborne illness by creating conditions where pathogens could survive and multiply.
Behavioral factors such as inadequate food safety training and poor supervision also played a role. Outbreaks were more likely in establishments without a certified food protection manager or in those with high employee turnover.
Moving Forward: Prevention and Policy
The lessons learned from 2014 to 2022 have led to improvements in food safety policy and practice. The implementation of the Food Safety Modernization Act (FSMA) focused on preventing contamination during production and processing. Local health departments have also begun to emphasize risk-based inspections and employee training.
Technology is playing a growing role in outbreak prevention. Digital food safety monitoring, smart refrigeration systems, and real-time temperature logging help reduce risks in commercial kitchens. Increasingly, traceability tools such as blockchain and QR codes are helping identify sources of outbreaks faster.
While foodborne illness remains a major public health concern, the analysis of contributing factors over this nine-year period provides valuable insight. Continued vigilance, education, and investment in food safety infrastructure are essential to reducing the frequency and severity of outbreaks in the future.
