Summer may bring daily sunshine but also daily gloom in the form of rising food hygiene problems, said Xu Le, director of the Digestive Internal Medicine Department of Beijing Hospital.

"A total of 90 cent of the people who received treatment for diarrhoea fell sick because they ate contaminated food," he said.

The doctor explained that high temperatures in summer were suitable for the fast reproduction of bacteria.

At the same time, the recovery ability of people's intestines is lower and they are therefore more vulnerable.

The doctor said people pay particular attention to several circumstances.

One of them is eating contaminated food stored in a refrigerator as bacteria can still exist at low temperatures.

Xu suggested people should firstly cover food with hygienic packing plastic when storing them. Then leftovers should be heated again before eating.

Another problem is that bacteria in seafood may cause an acute response of the stomach and intestines.

Xu advised people to choose reputable restaurants where seafood is not likely to be contaminated. Otherwise they should make sure the seafood is well cooked following hygienic procedures.

Tap water cannot be drunk directly in China. It may contain an excessive amount of coliform, which will lead to diarrhoea, fevers and vomiting.

The same is true of spring or river water and water at resorts as these may also have been contaminated.

The doctor said the water needs to be heated to boiling point before drinking.

In addition to various bacteria and viruses, food poisoning can also be caused by poisonous elements in plants, animals, medicines and pesticides.

Some fruits and vegetables in China may have an excessive amount of pesticides in them.

People should wash them properly and may need to peel fruit or soak them in water for a day before eating.

Xu advised people to reduce consumption of raw vegetables during summer, such as those for salads.

Rarely cooked Sijidou, a type of Chinese green bean, and potato with buds contain poisonous elements that might lead to food poisoning.

Xu's department has received patients with liver or kidney failure because they ate fish gallbladder raw, thinking it was good for their eyesight.

In some very serious food poisoning cases, Xu's department might apply physical stimulus or medicines to make the patients vomit. Sometimes they need to use a stomach pump to clean out the digestive tract.

The effects of treatment will usually be felt within four hours of the time when the food is eaten.