Hundreds of people in the US so far have recently developed a specific type of food poisoning that's causing watery and occasionally explosive diarrhea.Not only is it bad timing with 4th of July celebrations around the corner, but experts are currently at a loss when it comes to the reasons why.As of right now, there's no one known source of infection – but it appears to be coming from within the US, not overseas.The cases don't appear to be linked.This specific infection is called cyclosporiasis food poisoning, and it's caused by Cyclospora parasites.Cyclosporiasis is caused by eating food or drinking water contaminated by feces containing the parasite. Historically, people would acquire it outside the United States.However, of the 190 cases reported to public health authorities between the start of May and the middle of June, 145 involve someone who hasn't traveled beyond US borders in the last couple of weeks.The infection can't be passed directly from person to person, which means the evidence points to contaminated food or water from inside the country, according to the US Centers for Disease Control and Prevention (CDC)."There is currently no evidence of a single, multistate Cyclospora outbreak linking all cases," the CDC said.Cyclosporiasis cases by state. (CDC)While this doesn't happen often, it's not unheard of. You might remember an outbreak from 2018 linked to salads sold by McDonald's.The 145 cases with US origins are spread across 17 states, with New York reporting the most: between 31 and 80, as per the latest figures. While the reports of disease are clustered towards the east coast, there are some as far west as Texas, Colorado, and Alaska.According to the CDC, the real number of cases is likely to be higher still, as these illnesses won't always be reported."Sick people ranged in age from 5 to 86 years, with a median age of 42, and 61 percent were female," says the latest CDC report, dated July 1. "Of 145 people with information available, 20 were hospitalized. No deaths have been reported.""Local, state, and federal (CDC, FDA) public health authorities are investigating several clusters of cases in more than one state. Investigations to identify potential sources are ongoing."