Friday, December 18, 2009

It’s not quite about food safety…

Recently I was asked by a reporter to test magazines found in doctors’ waiting rooms for presence of pathogens. She wanted to do a story about the risks of going to the GP. I wasn’t sure what to expect, but asked her to collect a range of magazines from various waiting rooms. She brought me ten glossy or super glossy magazines covering popular women’s and men’s titles.

Each magazine was opened randomly and two pieces of the right hand page were cut aseptically, using sterile scissors. Each piece was 100mm x 100mm; one piece was cut from the top right, the other from the bottom right. This was to increase the chance of sampling the area most handled by readers.

The pieces of paper were transferred to a sterile bag with sterile diluent and massaged thoroughly by hand and then for two minutes in a machine called a Stomacher. I transferred samples onto agar plates that would enable me to assess general microbial contamination, faecal bacteria and Staphylococcus.

After incubation, I examined the plates, looking for typical bacterial colonies. The levels of contamination on all media were low. The limit of detection in this analysis was 3.7 colony forming units/10 cm2. In the food industry, a count of less than about 100 cfu/cm2 is considered acceptable, though the count on food contact surfaces at the start of food processing should be close to zero. Thus, the analysis I used was sufficiently sensitive to indicate whether the magazines were microbiologically hazardous with respect to Staphylococcus and faecal bacteria.

Staphylococcus is typically found on the skin and can be transferred to food and there produce enterotoxin, which causes food poisoning when we eat the contaminated food. It is unlikely that the low levels of S. aureus detected in this work would lead to significant transfer between readers. No typical colonies of faecal coliforms were detected, suggesting that there were no, or very low numbers of faecal bacteria on the magazines and hence that the likelihood of faecal contamination of the pages was also low.

All of the samples were printed on glossy paper, which doesn’t absorb water, a fact I confirmed by measuring the water activity* of the samples. There was thus no opportunity for bacteria to grow on the pages and in fact, they may have died off reasonably quickly.

One thing I should point out is that it is not possible by any simple analysis to detect viruses, so the work done here doesn’t completely rule out contamination by viruses of upper respiratory tract or gastrointestinal tract origin. Some, such as the Norwalk virus that causes gastroenteritis, can survive on surfaces for long periods.

I conclude from this cursory examination that, with the possible exception of viruses, the pages of the magazines were relatively free of pathogens. Handling the magazines is therefore relatively hazard free. However, as always, it would be advisable to wash or sanitise hands before consuming foods, snacks or sweets after visiting the surgery.

Have a happy and safe Christmas, everyone. Make sure your Christmas fare and BBQs are safe.

* For a description of water activity see:

Wednesday, December 2, 2009

Raw milk and people with influence

It’s happened again! Bill Marler quotes a Washington State Department of Agriculture News Release, reporting that three recent Escherichia coli infections in Washington have been linked to drinking raw, unpasteurised milk. The Washington state departments of Health and Agriculture have put out new warnings about the risks of consuming unpasteurised milk and milk products.

All the patients involved have reported drinking raw milk from the same supplier. Though no E. coli have been found in the most recent batch of product tested, the Washington State Department of Agriculture did find in the dairy the same strain involved in one of the illnesses.
Bill Marler, Doug Powell and I have all written on many occasions about the hazards of consuming raw milk. Doug has emphasized that personal freedom is all very fine, but young children cannot exercise freedom of choice. They are often the ones made ill by bacteria carried in raw milk. If you think that we are a bit over the top on this issue, have a look at the You Tube clip of Barb Kowalcyk talking about her son, Kevin, who contracted haemorrhagic E. coli infection.

A few days ago, Tamati Coffey was shown on TVNZ’s “Breakfast” programme milking a cow and then drinking the milk. No real problem there. The show’s hosts, Pippa Wetzell and Paul Henry then discussed the merits of drinking raw milk. Typically, Paul reckoned he wouldn’t touch the stuff, but I was surprised when Pippa, who recently had a new baby, argued that drinking raw milk is good for you. Many people watch this programme every day and there must be a proportion of those who are mothers of young children. Judging by the daily feedback, viewers hang on every word the presenters utter. I have to admit that I too enjoy the quick repartee of Paul and Pippa, but her throwaway line could easily influence parents to feed raw milk products to their children, with potentially disastrous consequences.

Perhaps television presenters should be a bit more careful when it comes to expressing views on the safety of foods – they are not trained in food safety. As they said in the post-war years when I was a lad “Careless talk costs lives”. It’s just as true today.