Pre-packaged salad mix is now believed to be the cause of the cyclospora parasite stomach bug that has been baffling health officials.

The outbreak has caused 370 people in 15 states to fall ill, NBC reported.

"The evidence points to a salad mix containing iceberg and romaine lettuce, as well as carrots and red cabbage as the source of the outbreak reported in Iowa and Nebraska," Steven Mandernach, chief of the Food and Consumer Safety Bureau of the Iowa Department of Inspections and Appeals, said.

The brand and producer of the infected salad greens have not yet been released, but Iowa officials have reassured the public the contaminated salad is no longer on grocery store shelves.

It is not yet known if the infections in the other 13 states is from the same source.

A total of 143 people were infected in Iowa alone, a common source of packaged salad greens was a common factor between 80 percent of them.

People consumed most of the infected product before it was identified, so the infected greens are believed to be out of stock as of now,

Cyclospora is a parasite that usually causes: watery diarrhea, explosive bowel movement, weight loss, decreased appetite, stomach pain, nausea, gas, and fatigue, the Centers for Disease Control and Prevention (CDC) reported.

"Cyclospora is spread by people ingesting something - such as food or water - that was contaminated with feces (stool). Cyclospora needs time (days to weeks) after being passed in a bowel movement to become infectious for another person. Therefore, it is unlikely that Cyclospora is passed directly from one person to another," the CDC stated.

The parasite is usually treated with a mix of two different antibiotics.

Iowa authorities warned produce consumers to give fresh fruits and vegetables a thorough washing before eating them, USA Today reported.

"We're not just talking about running them under some water and giving them a little pat," Barbara Chadwick, clinical services manager for the Linn County Health Department, said. "It's about soaking them and giving them a good scrubbing."