My last piece concerned itself with the importance of continuing to fund research on foodborne pathogens and I pointed out how little we still know about Campylobacter, despite its apparently unassailable position at the top of the food poisoning league table. Helpfully, two recent reports have now shown just how badly that research is needed.
I’m referring to the 2011 annual report on zoonoses (diseases transmitted from animals to humans) in the EU and the latest release of data from the US FoodNet system for surveillance of foodborne pathogens. These show that the incidence of Campylobacter infections across Europe and in the United States continues to rise. Meanwhile, in Europe at least, the incidence of Salmonella infection is falling, and this is widely attributed to successful interventions in the food supply chain, most notably the vaccination of poultry flocks.
There is something of a paradox here. On the face of it, Salmonella should be a much more effective foodborne pathogen than Campylobacter. It is present in many foods, is able to multiply in food and is also relatively resistant to heat and other environmental stresses. By contrast, Campylobacter is found mainly in fresh poultry, raw milk and a few other unprocessed foods, doesn’t multiply in food, is killed quickly by mild heat and doesn’t survive in frozen foods. Yet we seem unable to halt its progress as a growing cause of disease.
The latest figures suggest that measures to reduce the incidence of Campylobacter in poultry have yet to have much of an effect on the number of cases in humans, although it is still early days. Is this because most poultry is still contaminated, or is there another major source that has yet to be discovered? Conventional microbiological methods for detecting Campylobacter in foods are notoriously difficult to perform consistently and results have been known to vary considerably between laboratories. But newer PCR-based techniques should help to overcome that problem. Perhaps it would be a good use of resources to screen a wider range of foods for genetic markers of Campylobacter, just in case we have been missing something important.