Six more states have joined those listed as being impacted by a cyclosporiasis parasite outbreak that's been linked to contaminated lettuce, brining the total to 15. 

Arkansas, Iowa, Missouri, Nebraska, New Hampshire and North Carolina are now on the list, joining Illinois, Indiana, Kansas, Kentucky, Michigan, Ohio, Oklahoma, Pennsylvania and West Virginia, NBC News reported, citing an unnamed source. 

The outbreak, which is caused by a microscopic parasite found in human feces, has caused hundreds of hospitalizations and at least two deaths since early May. 

While the number of states impacted by the disease is increasing, it doesn't indicate the outbreak is spreading, Dr. Stephen Ostroff, a former acting Food and Drug Administration commissioner, told NBC. The new cases may involve people who ate contaminated lettuce weeks ago but were only recently diagnosed and reported to health officials, he said.