Foodborne Outbreak–the Process of Epidemiology

Current O157:H7 outbreak map (

Since we’re in the middle of an E. coli O157:H7 outbreak (which unfortunately means I need to toss my freshly-purchased Romaine lettuce), it seems appropriate to write about how the government solves foodborne outbreaks. As discussed in the last post, the USDA is responsible for meat and poultry safety, while the FDA regulates everything else. However, when it comes to solving foodborne outbreaks, a third player takes the lead–the Centers for Disease Control and Prevention (CDC). So, how does this all work?


  1. People get sick, go to the doctor, and the doctor orders a fecal sample (yay).
  2. The hospital finds a specific foodborne pathogen such as E. coli.
  3. The hospital reports this to the state and it gets typed to determine what specific strain (i.e., subtype) it is.
  4. States (hopefully) report confirmed cases to the CDC, which maintains a database.
  5. KEY: State (or federal) health officials note an uptick in cases of foodborne illness from a specific pathogen subtype(s).
  6. Investigation begins


  1. Public health officials begin interviewing patients to find out what foods they ate in the days/weeks before they became ill
  2. Data is analyzed to find out if there is a food or foods eaten by the majority of the patients
  3. If yes, public health officials begin to look for the food handling facility/brand at fault. They may re-interview patients to try to determine this. They may also ask patients for any unopened packages of the brand they suspect is the source.
  4. Lots and lots of laboratory testing of suspected samples
  5. Meanwhile, the FDA/USDA/state public health department will be taking samples from the suspected grower/packer/producer/restaurant to see if they have contamination with the outbreak pathogen.
  6. More laboratory testing of samples
  7. Find source–is it a single facility (ie, restaurant, packing house, etc)? Is it an entire brand? Is it a farm which supplied produce to a multi-farm brand?
  8. If the CDC can successfully link a brand or facility to an outbreak, issue recall. May also ask company to implement additional measures to control source of contamination (i.e., replace equipment, institute new safety protocols)
  9. Outbreak ends (eventually).

Obviously, this process has multiple points where it could break down. For instance, if there’s a small outbreak, a state health official may not notice. Alternatively, the people infected (if it’s a relatively mild foodborne illness) may not go to the doctor. Or the doctor may not order tests (or the right tests). Finally, an outbreak may be hard to trace, since the patients may not remember what they ate recently (do you remember what you ate three days ago?) or may be due to an herb or spice which might go unnoticed. Consequently, it’s not so much surprising outbreaks take a while to solve as that so many do get solved.

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