INCREASED dependence on convenience foods with fewer preservatives and intensive farming methods are contributing towards a rapid increase in food-borne illness. The infectious agents themselves are also changing, with drug resistant bacteria and viruses becoming more important in the occurrence of "tummy bug".
Trends in food-borne infection were discussed at a medical conference in Dublin yesterday, and made depressing listening. Incidence of illness caused by infected food products was climbing rapidly, according to Dr Patrick Wall, a consultant epidemiologist at the Communicable Disease Surveillance Centre in London. And the figures recorded by the centre "are a gross underestimate of the real situation", he said.
Dr Wall was speaking at the Academy of Medical Laboratory Science annual conference, a two-day event which got underway yesterday at the RDS. It was opened by the Minister of State for Commerce, Science and Technology, Mr Pat Rabbitte.
People come down with gastroenteritis, suffer for a few days and then forget it, leaving the illness and the bug that caused it unrecorded. Those that are reported, however, provide ample evidence that evolving food consumption and production methods are changing the types of bugs involved and the incidence.
There were almost no campylobacter bacteria infections recorded in 1977 by the centre, he said but in 1996 there were over 40,000, making it the commonest cause of diarrhoeal disease.
A three-fold increase in salmonella cases recorded annually by the centre from the early 1980s to 1996 masks changes in a type of salmonella - enteritidis PT4 - which is linked to poultry and poultry products.
The centre recorded 395 cases of this bug in 1981 and 13,614 in 1996. The peak 50 far was 17,257 cases in 1993.
Dr Wall puts the increases down to changes in what we eat and how farmers produce food. "We are all part of the biggest father and mother of an experiment," he said. The goal was to "try to strike a balance between cheap food, and health food" in many cases," for example in the high volume production of poultry.
Another troubling development was the speed with which some bacteria achieved resistance to antibiotics. He cited another salmonella type - typhimurium DT 104 - which was resistant to all the main antibiotics. The case load rose from a few hundred in 1985 to 4,000 recorded by the centre last year he said. About a third of infected patients needed hospitalisation and there were 10 deaths.
This bug was causing "particular concern", he added, and raised questions about antibiotic treatment of animals and poultry. "There is a big question whether antibiotics used in human treatment should be used in animals."
Viruses are also causing more food-related illness, an unwelcome risk added to the existing burden of bacteria and protozoans which can cause infection. Dr Hazel Appleton, a colleague of Dr Wall's at the London centre, said that viral gastroenteritis was seldom recorded 20 years ago but is now thought to cause almost a fifth of cases today.
The two viral agents of concern are the small round structured viruses and hepatitis A, both associated with shellfish. They survive refrigeration, freezing, alcohol and sugar preservation but are destroyed by cooking. Infected food handlers can easily spread the virus during food preparation.
