Wednesday, December 17, 2014

Comment on potential hazards of raw milk consumption.

I was recently asked for comment on the tragic death of a youngster in Australia, apparently caused by consumption of raw milk.  I was given only 200 words to get the message across.  Rather than go over all of the arguments again, I have reproduced my comments below:

The recent tragic death of a 3-year old infant and serious illness of four other children in Australia is  yet another example of the risks associated with consumption of raw milk.

Proponents of the consumption of raw milk claim that this is a natural food and has been consumed for hundreds if not thousands of years.  That is true, but ignores the fact that many diseases can be transmitted from animals to humans in the milk.

The hazards of consuming raw milk have been known for a long time. In Ontario around 1900, over 10% of all childhood tuberculosis was thought to be caused by unpasteurised milk. The rate of tuberculosis infection and many other milk-borne diseases in children fell dramatically after enactment of a law in 1938 requiring milk to be pasteurised; this was hailed as a major achievement.

The fact is that between 1998 and 2005, a total of 45 outbreaks resulting in more than 1,000 illnesses, 104 hospitalisations and two deaths due to raw milk or soft raw milk cheese were reported to the US Centres for Disease Control and Prevention. 

There is some evidence that consumption of raw milk early in life can reduce the incidence of allergies.  Bacteria in the raw milk may transiently colonise the intestine, resulting in stimulation of the immune system through infection.  

In addition, when milk is digested, a variety of beneficial ‘bioactive peptides’ are released.  However, it should be noted that pasteurisation does not adversely affect the release of these peptides.

I have said this before and say it again:  Adults who decide for whatever reason to consume raw milk should consider the potential hazards and make an informed decision.  Children, who have no choice in the matter, should not be fed raw milk or soft raw milk cheeses.

The situation is a little different for hard cheeses, such as Parmesan, in which the conditions, or the process, are inhibitory to most pathogens.  Food Standards Australia and New Zealand has made the following determinations:

Extra hard raw milk cheeses pose a low to negligible risk to public health and safety as survival and growth of Campylobactyer jejuni/coli, enterohaemorrhagic Escherichia coli (EHEC), Salmonella spp., Staphylococcus aureus and Listeria monocytogenes is very unlikely.
The selected Swiss-type raw milk cheeses were all assessed as posing a low to negligible risk to public health and safety for the general population as survival and growth of C. jejuni/coli, E. coli (EHEC), Salmonella spp. and S. aureus is very unlikely. 

Note:  The FSANZ document is comprehensive and readers should consult the report for more detail. See:

Thursday, November 13, 2014

The wonder fat?

This press release came to me via the NZIFST FaceBook Group of the same name:

The bad oil on coconut oil.pdf

It has been released by a marketing, PR and communications consultancy consultancy, AMG.

Like many snake oil adverts, this release contains some grains of truth.  However, it also make many unsubstantiated health claims, which is illegal in New Zealand.
I'm not going to comment on the release; suffice it to say that I shall not be buying any of the product.  Have a look and decide for yourself whether this is the sort of oil that you want to use for cooking and treating your family.

Wednesday, October 8, 2014

Food poisoning with a difference

The usual symptoms of food poisoning are vomiting, with or without diarrhoea, and sometimes fever.  Abdominal pain is also a frequent accompaniment.  Yersinia pseudotuberculosis doesn't fit this mould.

Since the beginning of September 2014, there has been a total of 124 confirmed cases and 18 suspected cases of Y. pseudotuberculosis in New Zealand.  I was asked by the Science Media Centre (NZ) to comment on this outbreak, and to provide a general overview of the bacterium, how it is transmitted in the food chain, and what the potential sources of the current outbreak.

Yersinia is a genus containing 11 species of Gram negative rod-shaped bacteria (the Gram stain is a relatively simple microscopy technique used by microbiologists to divide bacteria into convenient groups for study).  Three species of Yersinia cause illness in humans,  the most infamous member being Yersinia pestis, which caused the Black Death. 

The other two human pathogens are Yersinia enterocolitica and Yersinia pseudotuberculosis, the latter being much less commonly seen in infections.

The natural hosts of Y. pseudotuberculosis are rodents and sometimes other mammals.  Infection of humans normally occurs through consumption of foods contaminated with faeces or urine.  The outbreak currently occurring in New Zealand appears to be associated with bagged lettuce and raw carrots.  The full cause of the infections is still being investigated by Ministry of Primary Industry workers.

The symptoms of Y. pseudotuberculosis infection include fever and right-sided abdominal pain, which makes diagnosis difficult, since these symptoms are also seen in appendicitis.  The patient may have diarrhoea, but this is often absent.  Less frequently, long-lasting joint pain may occur.  Symptoms take 5 to 10 days to develop, so it is often difficult for the patient to remember what foods they had eaten that might have transmitted the infection.

Y. pseudotuberculosis is very well adapted to infecting humans.  The bacterial cells have a number of virulence factors, most encoded on a small transmissible piece of DNA called a plasmid.  The virulence factors enable the bacterial cells to adhere strongly to intestinal cells, and to evade the host’s normal defence mechanisms, while other proteins enable the bacteria to invade host cells.

The best way to avoid infection is probably to throw away bagged pre-prepared lettuce or shredded carrots that have been in your refrigerator for a while, and to prepare these items fresh as required.  Since Yersinia species are not heat resistant, they can be killed by normal cooking.  Be careful to maintain good kitchen hygiene, and avoid cross contamination of cooked foods from raw foods of any kind.

Saturday, September 27, 2014

Don't put Cleaning Chemicals in Food Containers!

It's happened again! According to Doug Powell's Barfblog Daily, a woman was poisoned and nearly died after drinking iced tea containing cleaning chemicals at a suburban Salt Lake City restaurant.

Apparently, a worker at the restaurant put cleaning lye (probably sodium hydroxide) into a sugar bag. A second worker put the material into an iced tea dispenser. The restaurant chain claims that this is the first time in 73 years that this has happened.

Indeed, if the restaurant chain is using any kind of food safety programme, this should never have happened, and as Doug says, "It has never happened before" is no defence. One of the basic principles of Good Catering Practice and HACCP is not to put non-food materials into food containers, and to store cleaning chemicals away from food.

There are many incidences of accidental poisoning occurring because of mis-identification of chemicals. All could have been avoided by using proper containers and labelling them clearly with the contents.

Of course, this principle doesn't just apply to restaurants - it is just as important at home. Ayesha tells me that the kitchen is her preserve, and she knows what is in the glass jars in the pantry. On some occasions when I have had to fend for myself, deciding on the identity of the white powders in the identical unlabelled glass jars has taxed my scientific abilities! Icing sugar and cornflower are subtly different, and custard powder is slightly yellow with a vanilla odour. Salt and castor sugar look the same but taste different. These are trivial examples, but in the high pressure of a restaurant kitchen, unlabelled materials, or worse, mislabelled materials are unlikely to be identified and will find their way into foods, sometimes with serious consequences.

Wednesday, August 6, 2014

Vomiting and Diarrhoea doesn't necessarily mean food poisoning.

If someone reported that they had vomiting and diarrhoea, I would normally suggest that they had contracted food poisoning.  Further questions about recent meals, travel history, etc. would help to clarify the situation.

However, with the current Ebola virus outbreak in West Africa - Sierra Leone, Guinea and Nigeria - and two Americans apparently infected, together with a reported potential case in Sydney, the possibility of a world wide epidemic is not far fetched.  

Ebola viral disease is not new - it first appeared in 1972, just after I qualified as a microbiologist, in the Sudan and Democratic Republic of Congo.  There was then and still is no licenced vaccine and the fatality rate can be as high as 90%.  

Ebola is not transmitted by food.  The reservoir appears to be wild animals and there are documented cases of transmission of the virus to humans through handling or contact with bodily fluids of infected chimpanzees, gorillas, fruit bats, monkeys, forest antelope and porcupines found ill or dead or in the rainforest (WHO, 2014).  Transmission is then human to human, again by contact with bodily fluids through broken skin or mucous membranes.  Contact with environments contaminated with fluids from infected individuals can also result in transmission.

According to staff at the Mayo Clinic, signs and symptoms typically begin abruptly within five to 10 days of infection with Ebola or Marburg virus. Early signs and symptoms include:
Severe headache
Joint and muscle aches

Of course, some other diseases including influenza can produce similar symptoms. However, in the case of Ebola viral disease, symptoms become increasingly severe and may include:
Nausea and vomiting
Diarrhea (may be bloody)
Red eyes
Raised rash
Chest pain and cough
Stomach pain
Severe weight loss
Bleeding, usually from the eyes, and bruising (people near death may bleed from other orifices, such as ears, nose and rectum)
Internal bleeding

There is no need to panic if you or family members have vomiting and diarrhoea, but the application of sensible precautions can help to limit the spread of the virus or any other causative agent.  Air travel is a very rapid way for infections to spread around the world.  If you have been in Central or West Africa within the last few days and start to show the early symptoms listed above, you should immediately contact a doctor and, to be fair to your fellow man, avoid air travel.  If you have been on an aircraft where someone had vomiting and diarrhoea, it might also be a good idea to consult a doctor, even thought the cause is most likely food poisoning.

As with all cases of vomiting and diarrhoea, take great care with personal hygiene and ensure that those people looking after you do the same.  The chances are that you don't have Ebola, but this outbreak looks to be the most widespread so far. 

WHO (2014)  Fact sheet N°103. Updated April 2014.Retrieved from:

Wednesday, March 12, 2014

Unsafe Hospital Food? There is a greater concern

A couple of days ago, I came across a reference to a report that claimed 85% of raw chicken delivered to the University Hospital in Geneva tested positive for strains of Escherichia coli resistant to extended-spectrum beta lactam antibiotics. These antibiotics belong to the penicillin family. The original study was published in  Infection Control and Hospital Epidemiology, the journal of the Society for Healthcare Epidemiology of America.  (Unfortunately, when I tried it, the link was broken).
Apparently, there were workers in the hospital kitchen who tested positive to carriage of the ESBL E. coli, however, the frequency was no greater than in the general population.

The finding of the high rate of contamination with ESBL resistant bacteria in the raw chickens is a concern, not because patients were at risk, but because it indicates that the poultry flocks had probably been exposed to antibiotics that are still used in therapy.  Proper procedures in the kitchens should ensure that the contaminating bacteria are destroyed and that cross contamination from raw meat to cooked or fresh foods is controlled.

The use of antibiotics in animal husbandry is leading to increased incidence of antibiotic resistant bacteria.  See my previous posts on antibiotics:    
et seq.

When I gave my inaugural lecture as Professor of Food Microbiology, I reviewed the developments in microbiology that led to the discovery and development of penicillin.  Before the advent of this antibiotic, a simple scratch with a rose thorn could be a death sentence if the scratch became infected.  It would be a catastrophe if we returned to those days because we had squandered our slim advantage over the pathogenic bacteria for short term financial gains by the animal rearing industries.

Sunday, March 2, 2014

To flush or not to flush ...

This post was originally published on 7th February, 2011.  I accidentally deleted it while trying to answer a question from a reader.  Here it is again.

No, this one isn't about faecal bacteria, at least not directly.

Our major TV news broadcaster was guilty over the weekend of a dreadful beat-up on the use of gas mixtures to extend the shelf life of fresh meat.  Under the banner of "How safe is your meat?", the channel made a big deal of the use of gas mixtures containing carbon dioxide to inhibit bacteria on the meat.  They implied that suppliers were trying to pass off old meat as "fresh" and that the process was used to make the meat look redder and thus deceive the consumer into thinking that the meat was fresher.  A further implication of the banner was that gas flushed meat is unsafe.  Must have been a slow news day.

Meat technologists and microbiologists have known for many years that gas mixtures containing carbon dioxide inhibit bacteria, such asPseudomonaswhich are responsible for the development of slime and odours on meat stored under refrigerated conditions.  The gas also inhibits many pathogens, which may potentially cause disease.  

Consumers interviewed in supermarkets said that the meat should be labeled to indicate that it had been gas flushed.  Of course, one supermarket chain said they would do this if customers wanted it, while another tried to take the high ground and claim that they would never gas flush meat.

This is all playing on the ignorance of many consumers about food technology and food safety.  Certainly the meat keeps longer when gas flushed. Why does meat normally have such a short shelf life?  Because some bacteria can grow under refrigeration conditions and turn the meat slimy or produce odours that consumers find objectionable.

Should we ignore and reject the many years of research on food preservation?  Should we perhaps go back to taking meat home wrapped in paper and cooking it the same day?  That's "natural".  Should we reject vacuum packaging - it's not natural, but in fact works in a very similar way to gas flushing.  Consumers have demanded longer shelf life in all sorts of foods - meat, strawberries, smoked mussels, cakes and pastries.  In response, food technologists have developed ways to deliver such foods and these techniques involve preservative chemicals, vacuum packaging, pasteurisation and gas flushing (modified atmospheres).  If we are prepared to go back to foods with a shelf life of just a few days, we can reject gas flushing and other technologies.

If consumers are really concerned about gas flushing, they can recognise flushed packs by the fact that the film is sealed to the tray, or in some cases, such as gas flushed bakery goods, the package looks like a pillow.

Me?  Well, I'll happily buy carbon dioxide flushed meat - it keeps longer and in some cases looks better.