When people get sick from food, investigators want to know two things: how it happened and why. The "how" are the contributing factors — the practices and conditions that led to the outbreak. The "why" are the root causes behind them. Knowing both lets environmental health investigators recommend fixes that prevent the next outbreak.
Image from CDC's page on contributing factors.
Three types
| Type | What happens | Example |
|---|---|---|
| Contamination | Germs or other hazards get into food | A sick food worker handles food with bare hands |
| Proliferation | Germs already in food multiply | Food held at the wrong temperature for a long time lets harmful bacteria grow |
| Survival | Germs survive a step meant to kill or reduce them | Food isn't cooked long enough or hot enough |
Image from CDC's page on contributing factors.
What goes wrong in restaurants
The most common contributing factors in restaurant outbreaks involve sick food workers and food preparation practices.
Sick workers. Employees who come to work with symptoms such as vomiting or diarrhea can contaminate ready-to-eat food:
- with their bare hands;
- even while wearing gloves;
- in other ways, such as letting food touch a contaminated cutting board or utensil.
Preparation. Undercooking food, and other poor practices, can let germs grow — for example, not washing hands between handling raw meat and ready-to-eat food like salad.
Handling raw meat, then ready-to-eat food, without washing hands in between. Image from CDC's page on contributing factors.
How investigators find the factors
The environmental assessment part of an outbreak investigation identifies contributing factors and root causes. It includes:
- interviewing kitchen managers and food workers;
- watching how food is prepared;
- reviewing or collecting records, such as cooking temperatures and traceback records;
- sampling the kitchen for germs.
Investigators carry out environmental assessments to find contributing factors. Image from CDC's page on contributing factors.
What programs can do
Environmental health and food safety programs can:
- take CDC's free interactive training on environmental assessments, the Environmental Assessment Training Series;
- start an environmental assessment as soon as they learn of a possible outbreak;
- let epidemiologic and laboratory data guide the assessment;
- report contributing factors to CDC's National Environmental Assessment Reporting System (NEARS).
State and local food regulators can join NEARS, both to inform their own programs and national food safety work, and use the FDA Food Code as the model for regulating restaurants and retail food businesses.
CDC's full list defines 30 contributing factors, and NEARS data point to five situations in which investigators were more likely to identify them.
Sources
Based on "Contributing Factors," Restaurant Food Safety, Centers for Disease Control and Prevention; a work of the United States government in the public domain.
Licence: CC0 1.0 (public domain) · Adapted from www.cdc.gov
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