A technique recently developed in Princeton and elsewhere apparently uses radio waves to destroy Salmonella in eggs using a novel form of Pasteurisation that doesn’t affect flavour and texture. This technique sounds interesting (but it’s a magazine article with no data so difficult to comment!) however I think it misses the point somewhat.
So what’s the risk from Salmonella in eggs?
It never ceases to amaze me how crap we are at judging relative risk. Everyone is paranoid about Salmonella in eggs but hardly anyone considers the risk of severe food poisoning when reheating rice at home.
Ever since that nice Mrs Currie got stuck in 25 years ago we’ve gone from 12,000 cases of the PT4 serovar then most commonly found in poultry to – essentially – Salmonella-free egg production in the UK. She didn’t deserve the stick – this was a politician who made a real difference. (There was an outbreak associated with imported Spanish eggs in 2011 but most salmonellosis now comes from a range of sources from peanut butter to ham – but not eggs).
Also Salmonella tends to be on eggs (because it’s in the chicken’s intestines and they poop indiscriminately) not in them. Yes, a hen can have a Salmonella infection in an ovary which could infect an egg during its formation but flocks are checked frequently for infection. Before an infected hen is identified the occasional egg might get infected but not all of them will by a long way. In the USA they estimate the risk to be 1 in 20,000 eggs. It’s theoretically possible for a bacterium to penetrate an eggshell – but the odds are so low if you’re that unlucky an asteroid strike will almost certainly kill you long before the egg has finished cooking.
Note from the Bleedin’ Obvious Dept: The surfaces of a carcass are a different matter and so must be thoroughly cooked but Salmonella is easily killed by heat and with the right chemicals. Chefs: all the technical data on killing it is here and here.
In the UK surveillance of Salmonella serovars of public health significance has been in operation 1989 so incidence is very low. Breeding flocks where Salmonella is confirmed are compulsorily slaughtered. While the incidence of Salmonella in poultry has decreased it is still a risk – but in imported meat; a recent survey by EHOs found no Salmonella or Campylobacter on eggshells – despite 20% of hen eggs being contaminated with faecal matter.
So, considering we consume 11 billion eggs in the UK each year – 85% produced by the UK’s 29 million hens – the risk from eggs is negligible. But we’re lucky. Tens of millions of human cases occur worldwide per year resulting in over 100,000 deaths. Over 2,500 different strains have been identified and it’s a hardy little bugger as well.
Here’s the point. Finally.
The reason I think this research is interesting but completely arse-backwards is they’re looking at the wrong part of the production cycle. The real solution here isn’t zapping eggs with RF, it’s better animal husbandry, better surveillance and – critically – banning the use of antibiotics in animal feed. This is what is driving antibiotic resistance in Salmonella and other zoonotic infections – one egg in 20,000 is an acceptable risk if you can treat salmonellosis relatively easily.
The game changes when we have pan-resistant strains in our Caesar dressing.
The FDA recently released a document suggesting it would be really nice if primary producers might think about phasing out antimicrobials in animal feed – but only if they want to – and wouldn’t it be nice if the pharmaceutical and agribusinesses that supply feed thought about it too and everyone works together so they all make a bit less cash in the interests of public health. In the USA resistant infections cost $70bn pa in additional healthcare costs and MRSA infection rates went up tenfold in US children’s hospitals in 1998-2008.
C’mon, guys, this isn’t difficult. Microbiology and infection is evolution in action. The selective pressure you’re putting on our Microbial Overlords to try to outwit them in order to make chicken fatter quicker is manifesting itself in your hospitals – for those who can afford to go to them.
And no gee-whizz RF scheme is going to change that. Especially one that takes 20 minutes when you go through 220 million eggs a day…