At least 14 people have fallen ill with a parasite after visiting Gaston Farm, the national health authority has said.
Specialists from Public Health England (PHE) are urging people to be vigilant with their hygiene in an effort to stop it spreading.
PHE received reports of people becoming ill after visiting the Slindon farm between March 17 to April 11.
The initial symptoms of cryptosporidium – which is caused by a parasite – can take up to two weeks to emerge so experts are urging people to remain on their guard if they or their family have visited the farm during this period.
The farm shut as a precautionary measure earlier this week. Click here to read the story.
Dr Kevin Carroll, a consultant with PHE South East’s health protection team said: “Cryptosporidium causes vomiting and diarrhoea in those affected.
“Cryptosporidium is highly infectious so as with all gastrointestinal illness it is important to be scrupulously clean around your home.
“It is vital to wash hands thoroughly using liquid soap and warm running water after using the toilet, before and after handling food and after contact with any animals and pets.”
The gastroenteritis illness is caused by a tiny organism, which in this outbreak is most likely to have resulted from contact with animals shedding the organism in their faeces.
The infection can also be easily passed from person to person so it is also important to maintain good hand hygiene around the home, when petting animals and in the preparation of food.
PHE is encouraging people to seek medical advice from their GP or NHS 111 if they or a family member becomes unwell.
Dr Carroll added: “Clean toilet seats, toilet bowls, flush handles, taps and wash hand basins after use.
“Make sure all members of your household wash their hands thoroughly with soap and hot water after going to the toilet and after handling soiled clothing or bedding. Make sure that everyone has their own towel and that they do not use anybody else’s.
“Wash all soiled clothes and linen on as hot a machine wash as possible.
“Particular care needs to be taken when preparing food to avoid further infection and should ensure all meat is thoroughly cooked and fruit and salad items are washed before eating.
“Anyone suffering from diarrhoea symptoms is being advised not to attend school or childcare settings for 48 hours after recovery.
“And if you have been diagnosed with cryptosporidium you must not swim until at least two weeks after the symptoms have ended.”
Earlier this week Gaston Farm made the decision to close while the problem was dealt with.
They said on Facebook at the time: “Our main priority has always been to make sure that the farm is safe for everyone who comes here to visit, and we would prefer to take the precautionary measure of closing the farm completely, to ensure that we are doing all that we can to protect our visitors, staff and our animals, while the situation remains unclear.
“We hope we have your support with our decision and our thoughts are with those affected.
PHE and West Sussex County Council have circulated information to schools advising on symptoms and actions to take to prevent further infection.
The farm is assisting PHE and remains closed to visitors.
If the public visit farms they should ensure they always wash their hands with soap and hot water (not hand gels) after petting animals.