Intestinal Giardiasis: Symptoms, Treatment & UK Online Doctor Guide

Intestinal giardiasis is a type of gastroenteritis caused by a microscopic parasite known as Giardia lamblia (or Giardia duodenalis). Unlike viral or bacterial stomach bugs, this is a parasitic infection that targets the small intestine. In the UK, it is one of the most common parasitic causes of diarrhoea, frequently associated with international travel, though it can also be caught domestically through contaminated water sources or close contact with infected individuals.

The parasite exists in two forms: the active trophozoite that lives in the gut, and the hardy cyst that is shed in faeces. These cysts can survive for weeks in cold water, making lakes, rivers, and even improperly treated swimming pools potential sources of infection. Because the parasite is highly infectious, it only takes a small number of cysts to cause illness in a healthy adult.

The symptoms of giardiasis typically appear between 1 and 2 weeks after exposure, though the incubation period can vary. The hallmark of a Giardia infection is the nature of the bowel movements. Patients often report steatorrhoea—pale, greasy stools that are difficult to flush and have a particularly offensive, sulfur-like odour.

Key symptoms include:

• Profuse, watery or greasy diarrhoea.
• Stomach cramps and abdominal bloating.
• Excessive flatulence (frequently described as 'sulfur burps').
• Nausea and occasional vomiting.
• Fatigue and general malaise.
• Loss of appetite and unintended weight loss.

Importantly, giardiasis does not usually cause a high fever or bloody stools. If you notice blood in your diarrhoea, this may indicate a different bacterial infection or inflammatory condition, and you should seek urgent medical advice.

While often termed a 'travel disease,' giardiasis is prevalent within the UK. According to NHS data, transmission occurs via the faecal-oral route. This means the parasite enters the mouth through contaminated food, water, or hands. Common scenarios for transmission include:

• Drinking untreated water from streams or lakes while hiking.
• Swimming in contaminated pools or hot tubs.
• Close contact in environments like nurseries or care homes.
• Handling infected animals or manure without proper handwashing.
• Sexual contact that involves faecal exposure.

Because the cysts are resistant to standard chlorine levels found in many swimming pools, outbreaks can occasionally occur even in regulated leisure facilities. Following strict hand hygiene is the most effective way to break the cycle of transmission.

In the UK, the National Institute for Health and Care Excellence (NICE) recommends diagnosis through stool sample analysis. A GP will typically request a 'Stool Ova, Cysts and Parasites' (OCP) test. Because Giardia is shed intermittently, it is common for doctors to ask for three separate samples collected over several days to increase the likelihood of detection.

Once confirmed, the primary treatment for giardiasis involves a course of antibiotics that specifically target parasites. The most common prescriptions in the UK are:

• Tinidazole: Often given as a single high dose, which is convenient for most patients.
• Metronidazole: Usually taken for 5 to 7 days. It is crucial to avoid alcohol entirely during this treatment and for 48 hours afterward to avoid a severe reaction.

During recovery, it is vital to stay hydrated. Oral rehydration salts can be helpful, particularly for those with persistent diarrhoea. It is also recommended to avoid lactose (dairy) for a few weeks after the infection clears, as Giardia can cause temporary lactose intolerance by damaging the lining of the small intestine.

If you are experiencing persistent digestive issues, speaking to a GP online can be a fast and effective way to begin your recovery. An online consultation allows you to discuss your symptoms, travel history, and duration of illness from the comfort of your home. This is particularly useful if you are feeling too unwell to visit a physical surgery or if you are worried about spreading the infection to others in a waiting room.

A GP can advise you on how to collect a stool sample and can provide private prescriptions for treatments like metronidazole if the diagnosis is clear. They can also offer guidance on 'exclusion periods'—for example, the UK government advice is typically that children and workers in high-risk sectors (like food handling) should stay away from school or work until they have been symptom-free for 48 hours.

To prevent passing the infection to others in your household, follow these hygiene rules:

• Wash hands thoroughly with soap and warm water after using the toilet and before handling food.
• Do not share towels, flannels, or cutlery.
• Clean toilet seats, flush handles, and taps with disinfectant daily.
• Avoid swimming pools for at least two weeks after your diarrhoea has completely stopped.
• Wash clothes and bedding at a high temperature (60°C).