Cases of a diarrhea-causing parasite have reached their highest level since 2016, health officials have warned.
Giardiasis is an infection caused by a microscopic parasite that feeds on intestinal cells. The most common symptoms are diarrhea, abdominal cramps, flatulence, weight loss and fatigue.
If left untreated, it can rarely cause malnutrition and stunted growth in children.
The infection can also cause serious complications in the elderly and people with weakened immune systems.
The number of cases in England has risen by 11 per cent in the past year, the UK Health Security Agency (UKHSA) has revealed, from 5,450 in 2024 to 6,069 in 2025.
London has seen the highest number of cases, a total of 1,568, followed by the North West, where 1,029 cases have been confirmed.
Cases peaked in the fall, with 599 people falling ill in October.
Health chiefs continue to investigate possible reasons for the unprecedented rise, but believe it could be due to more effective testing, increased travel since the pandemic and climate changes.
Cases of giardiasis, an infection caused by parasites, have reached their highest level in England since 2016
Although the disease occurs all over the world, it is most common in developing countries and is one of the most common foodborne illnesses that backpackers contract.
Infections are most common in people returning from South Asia, South East Asia, Africa and South America, but the disease can also be contracted in Britain.
Giardia infection spreads through direct contact with infected people or animals, or by swallowing contaminated food or water. After treatment, symptoms should disappear within about a week, but they can sometimes last longer.
The UKHSA says international travelers should take precautions when traveling abroad to reduce the risk of infection.
This includes drinking bottled water instead of tap water, and consuming cooked foods instead of raw produce such as salad vegetables washed in tap water.
Travelers are also advised to be careful when swimming in places where the water may be polluted, for example in rivers, lakes and the sea.
Giardiasis is generally not considered a serious health risk and is easily treated with antibiotics.
However, about half of those who contract the parasite experience no symptoms.
Michelle Beard, the head of Millstead Primary School, said the community was ‘devastated’ by the children’s deaths
The bug can be prevented by washing hands with soap and water, especially after using the toilet and before handling and eating food. Children should be encouraged to wash their hands regularly.
Nicola Love, Senior Food Safety Surveillance Lead at UKHSA, said: ‘We are seeing an increase in giardiasis in the UK.
‘The symptoms can last for weeks to several months and if left untreated they can cause serious complications, especially in young children, the elderly and people with weakened immune systems.
‘There are some simple precautions everyone can take to reduce the risk, whether you’re planning an autumn holiday somewhere warm or staying in Britain.
‘Good hygiene can help prevent giardiasis and other common gastrointestinal diseases.
‘Wash your hands with soap and water after going to the toilet, after changing diapers and before preparing food. Encourage children to wash their hands regularly as well.
‘If you have a Giardia infection, keep yourself hydrated and see your doctor, don’t go swimming until two weeks after your diarrhea has stopped.
‘Parents should contact their GP or NHS 111 if they or their children are ill and dehydrated, or if the diarrhea worsens or lasts for more than three days.’
It comes after the tragic deaths of two children who were pupils at Millstead Primary School in 2024.
The school was dealing with an outbreak of Giardia at the time, although the UKHSA said the deaths were unlikely to be linked to the outbreak.
