Giardia cases in England reach highest level in a decade

Cases of the diarrhoea-causing parasite Giardia have risen to their highest level in England since 2016, prompting health officials to urge people to take precautions both at home and when travelling abroad.

New figures published by the UK Health Security Agency (UKHSA) show that 6,069 laboratory-confirmed cases of Giardia were reported in England during 2025, an increase of 11.4% from the 5,450 cases recorded in 2024.

The latest total is the highest reported since 2016 and is now above levels recorded before the COVID-19 pandemic. Cases peaked during the autumn, with 599 reported in October, 580 in September and 574 in November.

Giardia is a gastrointestinal infection caused by the parasite Giardia intestinalis. Diarrhoea is its most common symptom, although people can also experience stomach cramps, bloating, excessive wind and burping, as well as weight loss.

Symptoms can continue for several weeks and, in some cases, for months. Although the infection can usually be treated, health officials warn that untreated Giardia can occasionally lead to more serious complications, particularly among young children, older people and those with weakened immune systems. In rare cases, prolonged infection in children can result in significant weight loss, malnutrition and problems with growth.

London recorded the highest number of cases during 2025, with 1,568 infections reported, followed by the North West with 1,029. The highest infection rate was also recorded in London, at 17.3 cases per 100,000 people.

Adults aged between 30 and 39 accounted for the largest proportion of infections, representing 20% of all laboratory reports. Almost two-thirds of cases, 64.2%, were among men.

The UKHSA said it is continuing to investigate the reasons behind the increase and stressed that changes in testing are likely to have contributed. More laboratories are now using multiplex gastrointestinal PCR testing, which can identify Giardia more effectively than some previous testing methods.

However, officials are also investigating other possible factors, including increased international travel following the pandemic and the potential impact of climate and environmental changes.

Giardia can be contracted in the UK as well as overseas. The parasite spreads through direct contact with infected people or animals and through swallowing contaminated food or water. It can also be transmitted sexually.

People travelling to parts of Southern and South-Eastern Asia, Africa and South America are among those who may face an increased risk. Travellers are being advised to take precautions including drinking bottled rather than potentially unsafe tap water and avoiding raw foods, such as salad vegetables, which may have been washed in contaminated water.

Swimming can also present a risk. The parasite can be present in rivers, lakes and other bodies of water, and infection can occur when contaminated water is accidentally swallowed during swimming or open-water activities.

Good hand hygiene remains one of the simplest ways of reducing transmission. The UKHSA is advising people to wash their hands thoroughly with soap and water after using the toilet, after changing nappies and before preparing or eating food.

People diagnosed with Giardia should remain well hydrated and seek medical advice. They should also avoid swimming until at least two weeks after their diarrhoea has stopped to reduce the risk of passing the infection to others.

Parents are advised to contact their GP or NHS 111 if they or their children show signs of dehydration, if diarrhoea becomes worse or if it continues for longer than three days.

Only one Giardia outbreak was reported to national surveillance during 2025. It occurred in a nursery in December and affected seven people, three of whom had laboratory-confirmed infections. No hospitalisations or deaths were reported in connection with the outbreak.

The UKHSA has cautioned that the rise in reported infections should be interpreted carefully because improved testing is likely to be identifying cases that previously may have gone undetected. Nevertheless, with infections now above pre-pandemic levels, officials are encouraging people to be aware of how the parasite spreads and to take simple precautions to reduce their risk.

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