While I wait with the rest of you hitting refresh on the CDC website waiting on an update on the numbers ill and the cause of the “E. coli Outbreak with Unknown Food Source,” I am reminded by how many times I have been asked why it takes so long to figure these outbreaks out. To borrow from the Beatles, it is a “long and winding road.”

In all CDC announcements of a foodborne outbreak is this caveat: As mentioned above, the true number of sick people in an outbreak is likely higher than the number reported, and the outbreak may not be limited to the states with known illnesses. This is because some of the recent illnesses have not yet be reported to PulseNet as it usually takes 3 to 4 weeks to determine if a sick person is part of an outbreak. In addition, some people recover without medical care and are not tested for E. coli. State and local public health officials are interviewing people about the foods they ate in the week before they got sick.

See below for an illustration. First, you need contaminated food being consumed and then that person being ill enough to seek medical attention from a health care provider. Incubation periods (time between ingestion and symptom onset) can be hours to months depending on the pathogen. You also have to account for the tainted product itself – highly tainted or sporadically? Self-stable, Frozen or perishable? The point being, are you seeing a large quick spike in sick people, or a handful over weeks, months or years? If something does not appear out of the ordinary it can be overlooked.

So, if someone is sick enough to seek medical attention, does that provider take a stool or blood culture (as opposed to a PCR test) to determine the likely pathogen and that test result may take days to return. If the provider does order a test and it comes back positive for a reportable pathogen (some are and some are not reportable – more on that another day), then the provider should report the illnesses to the local and state health authorities and the culture – if available – is sent to the state health department lab for further genetic testing. This process may take days or even weeks.

Assuming that the provider reported the illness and sent the culture to the lab, now comes the “Epi” work. Public health investigators attempt to contact the ill person or the person’s family to determine what the person did and/or consumed during the incubation period for the identified bacteria, virus or other pathogen. Remember, depending on the pathogen, the incubation could be a few hours (like Norovirus) or months (like Listeria). Also, complicating things are how broadly was the offending product sent – locally, across the country or internationally, and, how many people are sick. The unfortunate fact is that the broader the product went and the more people sickened – quickly – the better the chance of determining the tainted product.

Now, assuming that a food product is identified, then the traceback and recall begins.

Like I said, a “long and winding road.”