Cyclospora infection (cyclosporiasis): symptoms, diagnosis and travel advice

Cyclospora cayetanensis is a protozoan that lives inside the cells lining the small bowel. The NHS describes it as an infection that causes diarrhoea and notes that it is not naturally found in the UK. The parasite is passed in the stool of an infected person in a form that cannot yet infect anyone else. It needs time outside the body, in warm conditions, before it becomes infectious.

That detail matters for how the illness spreads and why it is linked to travel. CDC laboratory material says freshly passed oocysts are not infective and mature over days to weeks in the environment, which is one reason direct person-to-person spread is unlikely. Contaminated water used on crops, or on produce that is eaten raw, is the usual route.

The NHS lists Central and South America, south and south-east Asia, the Middle East and Africa as places where the parasite is common. Infection follows eating food that has not been properly cleaned or cooked, or drinking unsafe water. The CDC adds that outbreaks in the United States have been linked to various kinds of fresh produce, so the risk is not limited to tropical destinations, although it remains relatively uncommon there.

Fresh herbs, salad leaves and soft fruit that cannot be peeled are typical of foods that are eaten raw and may have been irrigated or washed with contaminated water. Cooking helps: the CDC advises cooking produce to an internal temperature of at least 70 degrees Celsius where cooking is practical.

• Drink bottled, boiled or otherwise treated water when local supplies are doubtful.

• Avoid ice made from tap water and be cautious with raw vegetables and unwashed fruit.

• Eat fruit you have peeled yourself, and prefer food that is cooked and served hot.

• Wash hands with soap and water before eating and after using the toilet.

The NHS lists diarrhoea, loss of appetite with weight loss, stomach cramps, bloating, tiredness, nausea, muscle aches and a raised temperature. Some people who are infected have no symptoms at all. Illness usually begins around a week after exposure.

What sets cyclosporiasis apart from many other travel infections is its tendency to relapse. According to the CDC, without treatment the illness can last from a few days to more than a month, and symptoms may ease and then come back one or more times. CDC laboratory notes describe untreated infections lasting for many weeks in some people. Someone who felt better on the flight home and then relapsed a fortnight later is a typical story.

A GP who suspects a parasite, particularly after recent travel, can send stool samples. The CDC points out that routine stool tests do not detect Cyclospora and that a specific test must be requested. Because the parasite is shed intermittently, more than one sample on different days may be needed, and the CDC laboratory guidance mentions samples taken a few days apart.

Laboratories use special stains, ultraviolet microscopy (the oocysts glow under UV light) or molecular tests such as PCR. You do not need to know which method is used, but it helps to tell the clinician where you travelled, what you ate and when symptoms began, so that the right tests are chosen.

The NHS says most people recover without treatment and that keeping well hydrated is essential. Antibiotics are prescribed for severe or persistent symptoms and especially for people with a weakened immune system. The CDC adds that people with healthy immune systems may recover on their own but that recovery tends to take longer than with antibiotic treatment. The choice of medicine and its dose are matters for the prescriber, and nothing here replaces that decision.

Oral rehydration solutions from a pharmacy are useful when diarrhoea is watery and you are losing fluid. Anti-diarrhoea tablets are not suitable for everyone, so ask a pharmacist before using them, especially if there is blood in the stool or a fever.

The NHS advises seeking medical help if diarrhoea lasts more than 3 days, becomes severe, contains blood, comes with a fever or signs of dehydration, or if you have a weakened immune system. Signs of dehydration include a dry mouth, dark urine passed infrequently, dizziness on standing and unusual drowsiness. Contact NHS 111 or your GP for advice the same day, and use 999 or A&E for collapse, confusion or severe unrelenting pain.

People with HIV, those taking immunosuppressive treatment and people after transplant can have longer and more severe illness, so they should not wait to see whether it settles.

There is no vaccine. Prevention rests on food and water hygiene when travelling and on hand washing. Because the NHS states that person-to-person spread does not occur, household members are not usually at risk from a returning traveller in the way they would be with infections such as giardiasis, although good toilet hygiene is sensible whatever the cause of the diarrhoea.

Having had the infection does not reliably protect you from a second episode, so the same precautions apply on later trips.