Freezing isn’t a good preventive control for raw fish sushi

I like sushi, the raw fish kind, but I’m picky about where I eat it, and with each outbreak I’m becoming more apprehensive about consuming it

When I do choose the raw fish-dish, I ask about whether it’s sushi grade and was previously frozen (to take care of the parasitic worms). I stay away from ground tuna or back scrape (which I learned about after a 2012 Salmonella outbreak) since lots of handling and small pieces can increase my risk of foodborne illness. tuna_roll1-300x196

Lydia Zuraw of NPR’s food blog, The Salt writes about a sushi-linked outbreak earlier this year, and points out that freezing isn’t good a Salmonella control measure.

The outbreak in question began in California in March. All told, it sickened 65 people in 11 states. There were 35 cases in California, with another 18 in Arizona and New Mexico. The rest of the cases were scattered across the country, including four in Minnesota.

So if pathogens like Salmonella don’t usually contaminate fish, what went wrong with the sushi tuna in this case? The FDA tells The Salt it doesn’t know for sure. Maybe someone in the processing facility didn’t wash their hands. Maybe the water or equipment used in processing was contaminated. Or maybe a bird or rodent got into the fish on the boat or during the ride to the processing facility. There are many opportunities for contamination to occur between capture and processing.

Ironically, freezing is usually considered a way to make sushi safer, because it kills any parasitic worms living in the raw fish flesh. That’s why last month, New York Citybegan requiring sushi restaurants to freeze their fish before serving it. Many of the city’s top sushi spots have been freezing their raw fish for this very reason for years.

But as this case highlights, freezing doesn’t guarantee your sushi is pathogen-free. While freezing will slow down the growth of Salmonella, cooking or pasteurizing are the only ways to kill the bacteria.

Really? Freezing reduces Campy in chicken

As super professor Schaffner would say, I’d like to see the risk assessment for this.

FunkyChickenHiFood safety experts have suggested that freezing chickens during processing for human consumption could vastly reduce the chances of people catching a food poisoning bug.

Freezing chickens found with campylobacter cells in them could reduce the rate of passing the infection on to humans by up to 90%, according to Dr Frieda Jorgensen, from Public Health England.

In Iceland, chickens found to be infected with campylobacter when they reached an abattoir were not allowed to be sold as fresh or chilled chickens, but instead frozen.

That process does not happen in the UK, Dr Jorgensen said, partly because customers prefer chilled or fresh chicken, rather than frozen produce.

She said: “Freezing does bring about a reduction in the number of (campylobacter) cells. We believe that they can reduce that by 90% if you are undertaking this freezing process.

“And that reducing the number of campylobacter cells on the chicken can matter in terms of the public health risk.” 

Pathogens on farmers’ market and grocery store whole chickens: does location matter?

We eat a lot of chicken. I either stuff a whole chicken with lemons or onions and oven-roast (in the winter) or use indirect heat outside with a 3/4 full beer can stuck into the bird’s, uh, cavity (in the summer). Regardless of where we happen to be shopping (farmers market or a grocery store), I pick one up pretty much every week. I assume that the raw product is covered in Salmonella and Campylobacter so I try not to cross-contaminate and use a digital tip-sensitive thermometer to ensure my chicken has reached a safe temp. I’m doing what I can to reduce risk of illness. Bringing less pathogens into my kitchen would further reduce that risk.BLTYrMoCEAIRhgT

Joshua Scheinberg, Stephanie Doores and friend of barfblog Cathy Cutter published a study in Journal of Food Safety detailing a study they conducted looking at pathogen presence and prevalence on whole chickens purchased from farmers markets or grocery stores as well as produced conventionally or under organic certification. They found (not surprisingly) that there’s a bunch of Campy and Salmonella on chickens, but that there were differences between retail types.

From the article:

Chicken obtained from farmers’ markets were positive for Salmonella spp., at a prevalence rate of 28%, which was not significantly different than the prevalence of 20% found in organically processed chicken. Salmonella spp. prevalence in both farmers’ market and organic chicken however, were found to be significantly higher than that of conventional chicken. Campylobacter spp. contamination rate was found to be high in farmers’ market whole chicken, with a positive prevalence of 90%. The prevalence of Campylobacter spp. in farmers’ market chicken was significantly higher than both conventionally and organically processed chicken, while organic chicken exhibited the lowest prevalence of 28%. Within the 90 Campylobacter spp.-positive farmers’ market whole chickens, 67% were found to harbor enumerable Campylobacter spp. populations compared with 52 and 22% of conventional and organic chicken enumerable populations, respectively.

Scheinberg et al. also looked at whether pathogens recovered from farmers’ markets chickens differed whether they were frozen or fresh – as campy is pretty delicate and has been shown to be affected by freezing.

Also from the article:

To evaluate whether freezing may be beneficial for farmers’ market vendors in reducing potential pathogen load on raw whole chicken, both fresh and frozen chicken were purchased from farmers’ markets. All chicken obtained from supermarkets were purchased as fresh. In this study, Campylobacter spp. and Salmonella spp. prevalence between farmers’ market, fresh and frozen chicken were not significantly different from one another, suggesting that freezing may not reduce either pathogen to nondetectable levels. Significant differ- ences were found between the number of chickens contain- ing enumerable Campylobacter spp. concentrations above 1.0 log10 cfu/mL in frozen versus fresh chicken. This obser- vation may suggest that freezing raw chicken may not reduce Campylobacter spp. to undetectable levels; yet the lower storage temperatures may reduce higher populations of Campylobacter spp. present on the raw chicken.

This data helps farmers’ market folks make risk management decisions: While freezing isn’t going to eliminate the pathogen, it is an added step that a vendor can take to reduce how much campy makes it in to kitchens. The location doesn’t matter as much as the practices of the vendor.

The article, A microbial comparison of poultry products obtained from farmers’ markets and supermarkets in Pennsylvania can be found as an early view article at the Journal of Food Safety website.

Scotland seeks to address Campylobacter in poultry meat through super freezing

Those who work with Campylobacter say that it’s delicate and doesn’t respond well to stress, like freezing. Those who have had campylobacterosis say that it makes your intestines delicate and your gastrointestinal tract doesn’t respond well to stress, like eating. I’m one of them. In 2009 a campy infection gave me the worst November I can remember which led to me retiring a salad spinner after collecting a stool sample (it’s all detailed here).

Folks in the UK are dealing with their own Campylobacter crisis and are looking to super freezing (which sounds a bit like double secret probation) to address the situation according to The Scotsman,

Food safety experts plan to “superfreeze” chickens to halt the rise of campylobacter food poisoning. The Food Standards Agency is currently looking into a procedure which involves exposing the surface of slaughtered chickens to extreme cold, known as rapid surface chilling.

The FSA aims to reduce the proportion of birds in the highest category of contamination at UK poultry houses from 27 per cent to 10 per cent by 2015.

Dr Jacqui McElhiney, policy adviser on food-borne disease at the FSA in Scotland, said: “This process acts to temporarily cool only the very outer surface of the chicken carcass without freezing the meat itself. It involves exposing the surface of poultry carcasses to very low temperatures for a very short time, which reduces the numbers of campylobacter bacteria on the surface, as they are sensitive to an extreme cold shock treatment of this type.”

Although it performed well during trials, the “superfreezing” procedure has yet to be approved by the European Union and its legality is still to be determined, said McElhiney.
Professor Hugh Pennington, emeritus professor of bacteriology at Aberdeen University, said: “I think it’s about the only thing on the table to get rid of campylobacter contamination. The bacteria don’t like being messed around with the cold. Anything that shows any promise of eradicating campylobacter is a good thing to get the number of infections down.”

Since freezing poultry seems to matter (resulting in significant reductions) I guess super freezing will really matter – and preserve quality. Reducing the Campylobacter loads entering a kitchen, whether it’s just 1-log or up to 3-logs, is a good thing and puts less of an emphasis on relying on consumers to be a critical control point in the home.