A reader from the part of Kent made famous by Dickens asks whether it is still safe to eat shellfish. He and his girlfriend enjoy oysters and mussels but recently there have been reports of health problems being suffered by French and British consumers. The reader asks whether he is dicing with death by having moules marinière and, if his girlfriend chooses them when he might have preferred steak, should he also order mussels so that they can die together?

Mussels and oysters are a temptation that, in principle, should be resisted until there is an R in the month. One of Oscar Wilde's best-known quips was “I can resist everything except temptation”. Perhaps this didn't apply only to his sexual inclinations but also to his enjoyment of shellfish, as it is known that he once suffered from mussel poisoning in Paris. In Dickens's time oysters were a cheap source of food for the poor. Few delicacies provide more zinc, iodine, iron and copper, and they are rich in protein without having too much fat or carbohydrate.

Although oysters don't suffer diseases that affect people, they can carry, concentrate and transmit the bacteria and viruses that flourish in polluted rivers and seas. They can also harbour polluting chemicals, including mercury.

An oyster takes in gallons of water a day and filters it through its gills. Small hairs sweep food particles, chemicals, bacteria and some viruses into its gut and, from there, it takes about five hours for most to be expelled. Typhoid, however, can remain in the oyster for much longer than that. Oysters are most active during warm months, so they filter even more gallons of water. Unfortunately, this is also the season when oyster beds are most likely to be contaminated. This problem also affect clams, scallops and mussels, as well as crustaceans such as lobsters, crabs, crayfish, shrimps and prawns.

The type of organism that is most likely to be carried by any type of shellfish varies. Salmonella is often found, for example, in molluscs, cholera is carried by oysters and shrimps; and hepatitis A and the Norwalk virus seems to favour clams and oysters. After hot weather, algae cause a sheen, “the red tide”, on the surface of the water. The dinoflagellates that produce this cause the toxin that can result in paralytic shellfish poisoning (PSP). Recently, the Food Standards Agency found that some fresh mussels sold on September 4 to 6 last year had unacceptably high levels of this toxin.

Although food poisoning delivers an unpleasant attack of diarrhoea and vomiting, it usually takes no longer to recover from than from a hangover. Even PSP is likely to cause no more trouble than general malaise, coupled with a tingling sensation around the mouth and tongue, together with some breathlessness. The symptoms are worrying but usually not dangerous - although there are occasional fatal cases. A small number of people suffer a dangerous intolerance to shellfish.

Fortunately, doctors are well aware of the dangers and keep a close check on levels of PSP. I would recommend that our reader and his girlfriend continue to enjoy their mussels and oysters.