Why the Numbers Went Down
According to the CDC, the new estimates are more precise than the 1999 numbers since they were derived from a greater volume of data and used better definitions of food-borne illness.
The new data include surveys of more than 48,000 people, five times as many people as were included in the 1999 report.
The new numbers also rely heavily on estimates of food poisoning caused by so-called unspecified agents. These were cases of gastrointestinal illness that couldn’t be tied to a known pathogen but that seemed to have all the hallmarks of a food-borne illness: cases of vomiting or diarrhea that lasted more than a day but were not associated with cough or sore throat.
“We took the number of cases of acute gastroenteritis illnesses and subtracted the ones we knew about, that is the number caused by known pathogens, and arrived at an estimate of unspecified agents,” says Elaine Scallan, PhD, an assistant professor at the Colorado School of Public Health in Aurora, Colo., who was the lead author of both of the new studies.
Additionally, the new numbers discount cases of food poisoning acquired during international travel, whereas the 1999 numbers included travel-related illnesses.
While the new estimates are more refined, experts say they could still be viewed as conservative.
“Not everybody who becomes ill sees their doctor, and even when they do, not everybody has tests done to determine what’s causing the illness,” says Braden. “That is taken into account in the estimates. However, one could look at the methods for these estimates and determine that our methods were quite conservative and in reality, for a number of these pathogens it could be more than we’ve estimated.”