Change in food-borne illness control became necessary because of the way food is distributed in the United States, reports Susan Brink of the Times. In the old days of food poisoning, the source usually could be traced back to a local event: potato salad at a family picnic or bad chicken at a church supper. Today, with massive amounts of food going from farms to food processing centers and then mixing with food from other farms before heading to tables in all 50 states, outbreaks are far less likely to be local, and thus, far more difficult to notice.

The change that came out of the 1993 Jack-In-The-Box tragedy is called PulseNet, a partnership between the CDC and state health departments. Stool samples are sent to state public health departments by doctors. The health departments then use DNA analysis to subtype pathogenic bacteria present in the stools. The resulting DNA fingerprints can identify not only species but also strains of such bacteria as E. coli, salmonella, shigella, listeria and Campylobacter.

Then the information gets sent to a central CDC database. This can quickly let public health officials know if cases strewn far and wide across the country carry identical fingerprints.

Epidemiologists also weigh in, fanning out within affected states and using food questionnaires to find out what people had eaten before getting sick (in the current outbreak, identifying pre-washed, bagged spinach).

But this is still not a perfect system, says Bala Swaminathan, acting senior advisor for laboratory science at CDC’s division of food-borne safety.. It typically takes three to four days for a patient’s symptoms to kick in, a day or two before the patient seeks medical care, then up to three days for results from a stool sample to reach the physician. And frustrating slowdowns can come from something as simple as how long it takes for positive results to make their way from a physician’s office to state labs and then into the PulseNet database.

In some states, reporting can happen the same day the physician gets lab results. In others, it can take up to a week. And all this time, Americans — oblivious to any problem — continue to eat the contaminated food.