Experts are scrambling to find the source of an explosive diarrhoea outbreak in the US.An outbreak of the parasite cyclospora throughout the States has already left 20 people in hospital.According to the US Centre for Disease Control, 145 people ranging from five to 86 years old have been struck by the stomach-churning illness between May and June 16.Doctors believe the cause of the outbreak may be food – but are uncertain of the exact source.The cyclospora causes cyclosporiasis, a food poisoning which leads to diarrhoea, nausea, vomiting, severe cramping and fatigue.Infection is caused by consuming food or water contaminated with faeces, often outside the US.However, none of the current patients had recently travelled abroad.A previous US outbreak in 2018 was linked to McDonald’s salads.Infection is caused by consuming food or water contaminated with faeces (file photo) | GETTYThe illness also does not transmit from human to human.The CDC said: “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.”Experts fear there are more cases which have yet to be reported.New York has the highest number of cases, between 31 and 80, with a significant number of cases in Texas and Illinois.A previous outbreak of cyclospora was caused by raspberries from South America | GETTYThere are also reported cases in Alaska, Colorado, Louisiana, Tennessee, Florida, Georgia, Virginia, North Carolina, Ohio, Pennsylvania, Wisconsin, Washington DC and Massachusetts.Symptoms usually appear a week after infection and mainly affect the intestines.Someone who has contracted the parasite may not have symptoms emerge at all.Cyclosporiasis infections should go away on their own – but last for a month or longer if untreated.Cyclosporiasis infections are usually linked to food consumed outside the US | CDCTreatment is a course of antibiotics, known as trimethoprim-sulfamethoxazole, otherwise known as Septrin and Bactrim.Vegetables consumed in subtropical or tropical areas outside the US are one of the main vectors of transmission.An outbreak in 2019 was connected to food such as coriander, sweet peas, mesclun lettuce, basil and raspberries imported from Mexico.While in 2016, the UK faced an outbreak linked to Britons travelling to Mexico.At the time, the Government warned against consuming fresh uncooked berries, unpeeled fruit and salad items in the country.