Extensive interviews with Nebraskans and Iowans sickened by a parasite so far have failed to turn up the source of the infections.
At least 37 people in the two states have been sickened in the past few weeks by cyclospora infections, which can cause watery diarrhea, fatigue, a lack of appetite, nausea, abdominal cramping, low-grade fever and weight loss. Eleven of the 15 Nebraskans who have been sickened live in Douglas County, officials said.
It's possible that the Cyclospora cayetanensis parasite hitched a ride on fresh fruits or vegetables. Past outbreaks of cyclospora illness in the U.S. were linked to various types of imported fresh produce, such as raspberries, basil, snow peas and mesclun lettuce.
That's the most likely scenario, “but we aren't ruling anything out,” said Dr. Anne O'Keefe, senior epidemiologist with the Douglas County Health Department.
The source of the parasite, she said, may be “one field, maybe one farm,” with contamination.
“Probably the way it gets contaminated is the produce field is irrigated or somehow contaminated with water that has been contaminated with sewage,” O'Keefe said.
It usually takes a week after exposure to develop the illness, she said, but it can take up to two weeks.
All fresh produce should be washed thoroughly, O'Keefe said, but washing doesn't guarantee that the parasite will be removed.
Investigators in Douglas County have asked the ill people when their symptoms started, what foods they have eaten in recent weeks, where they bought the food and what restaurants they have visited, O'Keefe said.
“Then we try to compare all the interviews and try to find common things,” she said.
It's difficult for people to remember everything they have eaten in a two-week span, O'Keefe said. Some people have allowed investigators to review their food purchases by handing over grocery store discount cards, she said.
Iowa officials said that most people first became ill in mid- to late June, and at least one person has been hospitalized. One of the ill Douglas County residents was hospitalized, O'Keefe said. The county's first cases were reported Wednesday, she said.
Physicians in Nebraska and Iowa are being asked to test specifically for the parasite. The cyclospora illness can be treated with a common antibiotic if it's properly identified.
O'Keefe said people in her office have been taking part in regular conference calls with Nebraska and Iowa public health officials and officials from the U.S. Centers for Disease Control and Prevention.
All the Nebraska cases identified through testing are in the eastern part of the state, Nebraska officials said. Most of the Iowa cases are in central and eastern Iowa, but a case was reported in Mills County in southwest Iowa and two cases were reported in O'Brien County in northwest Iowa.
The ages of the sickened Douglas County residents ranged from 26 to 89.