An urgent warning has been issued to parents and school staff as increasing numbers of people have reported contracting a nasty virus.
Public Health Wales has confirmed it has been informed of many people reporting gastroenteritis-like illnesses in the area.
Letters have been sent to parents and staff at educational establishments in the Swansea and Carmarthenshire areas, providing crucial advice on how to protect themselves and others in their care during the outbreak.
Local environmental health authorities are currently working to contain the spread of the disease.
An electron micrograph of the Norwalk virus which can cause nonbacterial gastroenteritis. An estimated 181,000 cases of this type of food poisoning occur each year
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Gastroenteritis is a very common condition which mainly causes diarrhea and vomiting, according to the NHS.
The disease can affect people of any age, although it is particularly common in young children.
The disease is usually caused by a bacterial or viral bug.
Public health officials are particularly concerned about its spread in educational and child care settings, where children are in close contact with each other.
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Health authorities have issued strict guidelines to educational establishments, stating that anyone suffering from diarrhea or vomiting should be sent home immediately.
Students and staff can only return to school or daycare after 48 hours without symptoms.
Health authorities have stressed the crucial importance of hand hygiene, especially after using the toilet.
People with symptoms have been advised to avoid preparing food for others.
Norovirus (pictured) is the most common cause of gastroenteritis in adults, while rotavirus is the most common cause in children.
PA/CDC
Authorities are urging anyone experiencing diarrhea or vomiting to contact their GP or local health service to provide a stool sample.
Medical advice should be sought if symptoms begin to worsen or if individuals have concerns about their condition.
Those affected can contact the AWARE team at Public Health Wales on 0300 003 0032 for more information.