More than a thousand Americans have fallen ill with a condition that can cause “explosive” diarrhea. The culprit, the cyclospora parasite, triggers an unpleasant gastrointestinal infection known as cyclosporiasis. Some states have been more impacted by the parasite than others. As of Thursday, Michigan alone has confirmed nearly 1,000 cases so far, up from the average 50 cases it sees per year. New York on Wednesday confirmed 394 cases, 273 of which were in New York City alone.