Soft Cheese (Hansard, 22 February 1989)

§ Mr. Kenneth Clarke

The chief medical officer at my Department issued general advice to the public about listeria in food on 10 February 1989. He also gave specific advice to pregnant women and to some patients, who are particularly vulnerable because of their illness or treatment, to avoid eating certain cheeses.

His advice said that public attention had recently been drawn to findings of the presence of listeria monocytogenes in a number of different food products. It must be remembered that listeria is widely distributed in the environment and some exposure to this organism is 669W unavoidable. Indeed at any one time a number of us, perhaps as many as 1 in 20, carry this bacteria in our gut without any ill-effects.

The disease, listeriosis, caused by infection with this organism is fortunately still quite rare. Last year 287 cases were reported, although it is certain that there were some other unreported cases. When it occurs it can give rise to a mild 'flu-like illness, although more serious cases may develop meningitis and septicaemia. Of considerable concern is the fact that in pregnant women it may also infect the developing baby and lead to miscarriage, stillbirth or severe illness in the newborn baby.

Unlike most of the bacteria causing food-related illness that we have been used to dealing with in the past, listeria has the unusual property of being able to multiply at the sort of temperatures which may be found in refrigerators. Fortunately in most foods where it is present, it occurs at very low levels and is killed by adequate cooking.

However, for some soft cheeses, the situation is different because the method of preparation and the time they may be kept before eating allows listeria to multiply. High numbers of listeria have been found in several varieties of soft cheeses, and a number of cases of listeriosis—both in this country and abroad—have been associated with eating heavily contaminated soft cheese.

Because of this, having taken the best possible expert advice, the chief medical officer advises that pregnant women should avoid eating certain types of soft cheeses. It is not possible to specify precisely the cheeses in which listeria is likely to grow, but on the basis of current information these are likely to be soft ripened cheeses such as the brie, camembert, and blue vein types. On the other hand, hard cheeses such as the cheddar and cheshire types, processed cheeses, cottage cheeses and cheese spreads have not given cause for concern.

The levels of listeria that have been found in other foods such as cooked-chilled meals and ready-to-eat poultry have usually been very low. Given the particular risks to the developing foetus the chief medical officer feels that it would be prudent for pregnant women to re-heat these types of food until they are piping hot rather than to eat them cold. Otherwise all that is necessary is for pregnant women to follow the normal, general hygiene precautions summarised here and to take care that they maintain a well-balanced diet during pregnancy.

Other people who appear to be at special risk and should therefore follow this advice are those with underlying illness which results in impaired resistance to infection, such as patients who have had transplants, those on particular drugs which depress the immune system, and those with leukaemia or cancers of the lymphatic tissues.

The chief medical officer also said that although the wider public have become worried about reports of listeria contamination of a variety of foods, including salads and some cooked-chilled ready-to-eat foods on sale, the evidence so far is that the amount of listeria in these foods is generally very low. Provided that the good hygiene practices recommended are followed there is no need to change the type of food regularly eaten and enjoyed.

The general advice to the public is that listeria monocytogenes is widely distributed in the environment, for example, it has been found in vegetation, water, soil and the faeces of man and animals and therefore some exposure to this organism is unavoidable. For the average healthy member of the public the risk of becoming ill with listeriosis from eating food is very small indeed. 670W Nevertheless there are a number of simple precautions which the public can take which will reduce their exposures to listeria and other pathogenic bacteria:

(i) Keep foods for as short a time as possible, follow the storage instructions carefully and observe the "best-by" and "eat-by" dates on the label;
(ii) do not eat under-cooked poultry or meat products. Make sure you re-heat cooked-chilled meals thoroughly and according to the instructions on the label. Wash salads, fruit and vegetables that will be eaten raw;
(iii) Make sure your refrigerator is working properly and is keeping the food in it really cold;
(iv) Store cooked foods in the refrigerator away from raw foods and cheeses;
(v) When re-heating food make sure it is heated until piping hot all the way through and do not re-heat more than once;
(vi) When using a microwave oven to cook or re-heat food observe the standing times recommended by the oven manufacturer to ensure that the food attains an even temperature before it is eaten;
(vii) Throw away left-over re-heated food. Cooked food which is not to be eaten straight away should be cooled as rapidly as possible and then stored in the refrigerator.