What Are Contributing Factors?

Contributing factors are preventable causes of outbreaks.

Contributing factors are the practices and factors that lead to outbreaks. In an outbreak, contributing factors are the “how” and root causes are the “why.”

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

Watch our short training video on contributing factors, From Inspector to Investigator: Finding the Factors that Lead to Foodborne Outbreaks

Contributing factors fall into 3 types.

Graphic of a sick male food worker handling food with their bare hands illustrates contamination contributing factor.

Pathogens and other hazards get into food.

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

Graphic of sliced deli meats on a counter with spots illustrating germs and potential proliferation contributing factor.

Pathogens already in food grow.

For example, food held at the wrong temperature for a long time can allow harmful bacteria to grow.

Graphic of a grill with a hamburger and buns cooking and a thermometer illustrates potential survival contributing factor.

Pathogens survive a process to kill or reduce them.

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

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

Graphic of a hand touching raw chicken and then the same hand is touching fresh salad.

Sick food workers can contaminate ready-to-eat food when they come into work while experiencing symptoms, such as vomiting or diarrhea. Food workers who are infectious can contaminate food:

  • with bare hands
  • while wearing gloves
  • in other ways, such as letting food touch a contaminated cutting board or utensil

Improper food preparation practices are another common contributing factor for restaurant outbreaks. Not cooking food to a hot enough temperature and other improper food preparation practices can lead to pathogens growing.

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

They can

The environmental assessment component of outbreak investigations helps identify contributing factors.

Environmental assessment activities include

  • interviewing kitchen managers and food workers,
  • observing how food is prepared,
  • 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

  • Join NEARS to provide critical information for their program and to inform national food safety efforts.
  • Use the FDA Food Code as the model for regulation of restaurants and retail food establishments.

Data reported to NEARS showed that

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

  • They knew the pathogen linked to the outbreak,
  • They scheduled their assessment visit to the establishment within a day of learning about the outbreak,
  • They 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.

Read more: 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)