What Are Contributing Factors?

Contributing factors are preventable causes of outbreaks.

Contributing factors are food preparation practices, behaviors, and environmental conditions that lead to pathogens getting into food or growing in food; these pathogens in food can cause outbreaks.

Finding contributing factors in foodborne illness outbreaks can help stop them and prevent them in the future.

The 30 contributing factors fall into 3 types.


Pathogens and other hazards get into food.

For example, a sick food worker handling food with their bare hands.


Pathogens already in food grow.

For example, food held in a refrigerator that is too warm.


Pathogens survive a process to kill or reduce them.

For example, food not cooked long enough or to a hot enough temperature.

The most common contributing factors for outbreaks in restaurants come from sick workers and food handling practices

Man holding his stomach in pain.

Sick workers can contaminate ready-to eat-food

  • with bare hands
  • while wearing gloves
  • through a method other than hand contact (such as a cutting board or utensil they contaminated)
Graphic image of a clock.

Improper food handling practices can lead to pathogens growing

(such as food not cooked to a hot enough temperature).

Environmental health and food safety programs can take action to identify contributing factors for all foodborne illness outbreaks.

Take CDC’s free, interactive training on conducting environmental assessments to improve their ability to identify contributing factors.

Badge design with EATS training on it.

Conduct an environmental assessment as soon as they learn of a potential outbreak, which may require multiple visits to the outbreak establishment.

Image of restaurant with a check mark on it.

Use their knowledge about the pathogen linked to the outbreak to guide their environmental assessment.


Environmental assessments during outbreak investigations help identify how pathogens are spread in the environment to cause foodborne illness.

Environmental assessment activities include

  • interviewing kitchen managers and food workers,
  • observing how restaurants prepare food (for example, food temperatures),
  • reviewing or collecting records (for example, records of food cooking temperatures, traceback records), and
  • sampling for pathogens in the restaurant kitchen.

What else can food programs do?

State and local food regulatory programs can

book cover with FDA on it.

Use the FDA Food Code as the model for regulation of restaurants and retail food establishments.

Data reported to CDC’s National Environmental Assessment Reporting System showed that

Investigators were more likely to identify an outbreak’s contributing factors if

  • the germ linked to the outbreak was known,
  • investigators scheduled their assessment visit to the establishment within a day of learning about the outbreak,
  • investigators made multiple visits to the outbreak establishment to complete their assessment,
  • the outbreak establishment prepared all meals on-site, and
  • the outbreak establishment served more than 150 meals daily.

Factors that Contribute to Outbreaks of Foodborne Illness (summary of Brown LG, Hoover ER, Selman CA, Coleman EW, Rogers HS. Outbreak characteristics associated with identification of contributing factors to foodborne illness outbreaks. Epidemiol Infect. 2017;145(11):2254-62)

Want More Information?

Summaries of our food safety studies on policies and practices to reduce foodborne illness in restaurants, banquet facilities, schools, and other institutions

Findings using NEARS data

FDA Food Code