(NewsNation) — As federal health officials try to pinpoint the source of Cyclospora that has caused intestinal distress across the U.S., one internist has some thoughts about why the parasite has spread so quickly.

Dr. Peter Chin-Hong of the University of California, San Francisco, cites three factors explaining why the parasite, which infamously causes explosive diarrhea, became so widespread.

First, he tells “Jesse Weber Live” that given the way food is packaged and distributed, product that has been tainted by the organism can move quickly through retail outlets and restaurants.

The Washington Post reported Thursday that health officials were looking at iceberg lettuce from a California-based supplier to Taco Bell restaurants.

“It probably speaks to how we’re eating food now, in packages from single large distributors, and they go to a specific geographic part of the country simultaneously,” Chin-Hong said.

In the meantime, he said, Cyclospora’s long incubation period makes it harder to trace the source of the outbreak.

Chin-Hong also says cuts at the Centers for Disease Control and Prevention may have contributed to the wave of illnesses.

“We just don’t have the surveillance systems that we used to have,” he said. “We don’t have the personnel that would normally go to these states to help local health departments. So, all of that leads to delay, and when you have delay, you can’t find out the source.”

Produce can become contaminated with Cyclospora, which originates from human feces, through water or soil.