The results of a Government study of animals after slaughter are being published today, revealing the worrying fact that nearly 4 million UK pigs, 23% of the current population, are contaminated with the food poisoning bacteria salmonella. During the last year, around 13 million pigs have been slaughtered, and this new evidence claims that 700,000 of those were contaminated with bacteria by the time they reached the butcher.

As a senior ministry of agriculture official admitted: "We always knew that salmonella was around in pigs," but this study was the first of its kind in allowing the agriculture ministry to quantify the extent of the problem.

Findings show that, of pig carcasses in abattoirs, 5.3% were infected with salmonella, comparing unfavourably to results of similar studies, which uncovered only 0.2% of cattle and 0.1% of sheep similarly contaminated.

More to the point, these figures are thought to be as low as a fraction of 1% for Danish pigs. Indeed, the Danes are currently aiming for a target of 0.05% positive sampling for salmonella in pigs at any point down the chain. German and Dutch rates are probably not far higher. The UK pork sector can only look at these figures in wonder.

Campylobacter bacteria, most common in cases of human food poisoning, were discovered in 94.5% of live pigs. Another report to be published today adds evidence that more than 26% of pigs are infected with yersinia, bacteria which poison around 100 people per year.

Around 60% of salmonella strains do not affect humans, but it seems that bacteria are becoming increasing resistant to antibiotics and therefore more difficult to control.

Whether these high infection rates are due to methods of slaughter or lack of farm controls is not clear. Officials admit that it is impossible to wipe out poisoning bacteria on farms, because pigs are kept outside and the environment is clogged with strains of salmonella, campylobacter and yersinia bacteria.

However, it is also possible that occasionally inefficient slaughtering methods are to blame. If pigs are slaughtered properly, bacteria in their gut cannot contaminate meat, as the guts are not split. Occasionally, accidents happen and a gut splits. Power hoses are used to clean the area involved and it is very difficult to contain the spillage totally. Knives, not used according to the correct procedures, can also become infected with bacteria and then pass this on to other meat.

A code of practise to enable the reduction of salmonella is being launched and incorporated into the farm assurance scheme by the ministry and the Meat and Livestock Commission, aiming to target farmers and the pig industry.

In order to reassure the public, the Food Standards Agency commented, "as long as meat is handled, stored and cooked thoroughly, that should kill any bacteria." In order to lower the risk of gastroenteritis, however, the Commission is urging the public to cook pork thoroughly until the juices run clear, and ensure that kitchen hygiene standards are high.

This news could spark consumer concern over pork, which has not previously been linked with salmonella. Should the pork industry bite back by reminding the public that salmonella rates in chicken remain higher than in pork, the news could prompt a renewed debate on bacterial contamination of meat. With BSE back in the news at home and abroad, the scene could well be set for a move away from meat in general.