Cases of giardiasis in England have reached their highest level since 2016 after infections climbed by 11 per cent in a single year, the UK Health Security Agency has warned.
Confirmed cases across England rose from 5,450 in 2024 to 6,069 in 2025. London recorded the highest regional total with 1,568 cases, followed by the North West, where health authorities confirmed 1,029 cases.
Infections peaked during the autumn, with 599 people falling ill in October alone. Health chiefs are investigating potential reasons for the unprecedented increase, pointing to a combination of more effective testing, increased international travel since the pandemic, and climate changes.
The UK Health Security Agency, the government body responsible for public health protection and infectious disease monitoring across England, stated that the microscopic parasite feeds on gut cells. Symptoms include diarrhoea, abdominal cramps, flatulence, weight loss and fatigue.
Symptoms and transmission of giardiasis
Although giardiasis is found worldwide, it is most prevalent in developing countries and remains one of the most common foodborne illnesses caught by backpackers. Infections are most frequently reported among travellers returning from Southern Asia, South-East Asia, Africa and South America, though the parasite is also caught within the UK.
The infection spreads through direct contact with infected individuals or animals, or by swallowing contaminated food or water. Health officials note that about half of those who contract the parasite experience no symptoms.
For those who develop symptoms, treatment with antibiotics generally clears the infection easily, with symptoms usually stopping within about a week. However, symptoms can sometimes last longer, and untreated cases carry a rare risk of causing malnutrition and stunted growth in children, as well as serious complications in elderly patients and people with weakened immune systems.
The rise in cases follows the tragic death of two children who were pupils at Millstead Primary School in 2024, when the school was dealing with a giardia outbreak. Michelle Beard, the headteacher at Millstead Primary School, said the community was "devastated" by the deaths of the children, though UKHSA officials stated it was unlikely the deaths were linked to the outbreak.
Prevention and travel advice from health chiefs
Nicola Love, Senior Food Safety Surveillance Lead at UKHSA, said: "We are seeing a rise in giardiasis in the UK. Symptoms can last from weeks to several months and if left untreated, it can cause serious complications, especially in young children, the elderly and those with weakened immune systems."
"There are some simple precautions everyone can take to reduce their risk, whether you are planning an autumn getaway somewhere warm or staying in the UK," Love added. "Good hygiene can help prevent giardiasis and other common gastro illnesses."
Love advised: "Wash your hands with soap and water after using the toilet, after changing nappies, and before preparing food. Encourage children to wash their hands regularly too."
To limit the spread of the bug, the health official provided specific advice for anyone suffering from symptoms. "If you have a giardia infection, continue to hydrate yourself and see your GP, do not go swimming until two weeks after your diarrhoea has stopped," Love said.
She added: "Parents should contact their GP or NHS 111 if they or their children are ill with dehydration, or if diarrhoea worsens or lasts longer than three days." NHS 111 is the national non-emergency telephone service providing health advice across Britain.
For international travellers, UKHSA recommends drinking bottled water rather than tap water and avoiding raw items, such as salad vegetables washed in tap water. Travellers are also advised to take care when swimming where water may be contaminated, including in rivers, lakes and the sea.
