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The number of reported Giardia infections in England rose by 11.4% in 2025, compared with the previous year, UK Health Security Agency (UKHSA) data have revealed.
According to updated UKHSA data, published on 26 August 2026, there were 5,450 reported cases of Giardia in 2024, which climbed to 6,069 in 2025.
The data also highlighted that between 2024 and 2025, London saw the highest number of Giardia infections, with 1,568 cases, which is followed by the north-west of England with 1,029 cases. The data showed that there were 604 cases in the most deprived areas of England and 501 cases in the least deprived.
Just under two-thirds (64.2%) of infections were in men, while the 30–39 age group had the most reported cases, the data revealed.
Giardia is caused by infection with the Giardia duodenalis parasite, with symptoms that include diarrhoea, abdominal cramps, bloating, belching, flatulence and weight loss. It can be spread through contaminated drinking water, food and direct person-to-person contact.
The number of cases in England has been rising annually since 2022, the data underscored.
The UKHSA said that it is likely that changes to testing, including the introduction of multiplex gastrointestinal infection polymerase chain reaction testing, have contributed to recent reported increases, but it added that “other potential factors are being investigated including travel, climate and other environmental changes”.
While infection is frequently self-limiting, it can be persistent, and infections can be treated with nitroimidazoles and combinations of antiparasitics, if the infection does not respond to standard treatment.
However, the UKHSA said: “Infections which persist despite standard treatment (refractory infections) are increasingly common in the UK in both asymptomatic and symptomatic individuals, particularly among children seeking asylum and travellers returning from India.”
Further research is needed to understand why treatment sometimes fails, it continued.
On 26 August 2026, 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.”
“Good hygiene can help prevent giardiasis and other common gastro illnesses. 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,” she added.
