Salmonella control in the food chain. (Part 1)

Part I: Are you doing enough to control Salmonella?

Salmonella ranks among the world´s biggest threats to health. In the United States alone, it is thought to be responsible for around 378 deaths and an estimated 19,336 hospitalisations each year. And these are just the reported cases. If you´ve ever had to take a few days off work with a nasty case of "food poisoning", but not bothered the doctor to get it treated, there´s a chance you´ve had a close encounter with this unpleasant little bug without becoming one of the statistics yourself. Salmonella ranks second on the food poisoning leader-board in the US where it´s the premier bacterial food-borne disease.

Yet the name Salmonella doesn´t leave us quaking in our boots in the same way as the world´s other major killers, which, according to the latest statistics from the World Health Organization, might include heart disease, cancer, AIDS, or road traffic accidents depending on whereabouts in the world you´re based. It doesn´t generate the same levels of media frenzy as SARS or bird flu, though perhaps it should. It'´s certainly serious enough to merit significant attention from the WHO and the US-based Center for Disease Control. Developing and implementing effective Salmonella monitoring, reporting and control systems has been prioritised in many countries.

Where does it come from?

Salmonella is often associated with poultry products - chicken and eggs, but it would be a mistake to assume that these are the only food sources that can transmit the disease. Birds are a major source, true; strains can also be transmitted through pork and processed pork products, but it´s also been spread through salad vegetables and peanuts. If we can eat it, there´s a good chance that the bacteria can live on it, or at least survive long enough to be carried into an animal (or person)´s digestive tract.

Since its discovery in the late 19^th Century, more than 2,500 different types (serovars) have been discovered. All of these can cause disease in humans, which is most commonly associated with acute gastroenteritis - fever, abdominal pain, diarrhoea and nausea, sometimes with vomiting. More often than not, this clears up within a week of infection without treatment. However, if the pathogen enters the bloodstream, or the disease leads to dehydration, effective antibiotic treatment can be a lifesaver. Children and the elderly are particularly vulnerable, as are people with weakened immune systems.

The health statistics also make for some sobering economic facts. In the US, for instance, the Center for Disease Control recently estimated a total annual cost of US$3 billion associated with Salmonella. Similar calculations from Denmark in 2001took this further, suggesting that spending the equivalent of US$14.1 million implementing a Salmonella control programme actually resulted in a net saving of US$25.5 million to the national economy.

Why should I be worried?

Like other foodborne bugs, Salmonella is developing resistance to the drugs we use to treat it. Much of the blame has fallen with animal production. Preventing or treating diarrhoeal diseases in livestock has played a major part in the development of multi-drug resistant strains. The two most commonly seen serovars in human salmonellosis epidemics, Salmonella enteritidis and S. typhimurium have emerged over the past 30 years in parallel with intensive animal husbandry. Now, we find bacteria, including these two, with worryingly high levels of resistance against the antibiotics we use to treat them. Antibiotic resistance in Salmonella has two major consequences that cause the medical profession so much concern. Firstly, patients taking an antibiotic for unrelated infections, for example a chest infection, are more risk of contracting antibiotic-resistant Salmonella infections. Secondly, treatment for salmonella fails more frequently, causing prolonged or more severe illness, increased hospitalisations and more deaths. A recent US review estimated that antimicrobial resistance in Salmonella may result in 30,000 more infections each year, leading to 300 more hospitalisations and 10 deaths. Salmonella is a big risk to the world´s economies. But it´s a risk that can be reduced. All along the food chain, experts have identified points at which intervention can help reduce the risk of Salmonella infection.

Passing the blame won´t work

Bacteria appear on food all the time, but clearly when a disease-causing one appears, it´s a big problem. The food chain, however, is complex, involving a lot of different inputs and a lot of movement from one place to another. There are a plenty of opportunities for a pathogen like Salmonella to get in - and if it can, it will. Perhaps part of the reason that Salmonella is so common is that it´s always somebody else'´s problem. Consumer can inadvertently contaminate their own food through inadequate basic hygiene and cooking practices, but it the bug was already on the food when it was bought - it´s the supermarket´s problem. The supermarket could be liable, but if that product was already contaminated before it arrived there - it´s the processor´s problem. There are plenty of opportunities for Salmonella to contaminate food during processing (including slaughter), but if the bug was already present - it´s the producer´s problem; and, you´ ve guessed it, if the feed is identified as the cause of the contamination at farm level - the blame is passed all the way back to the feed mill. Obviously the reality isn´t just a simple game of "passing the buck": Salmonella is a serious business, causing severe financial losses and damage to the reputation of all concerned. Can you afford to take that risk?