Free Choice or Safety of the Population?

Governments and regulators are always in a difficult position. Do they allow total freedom of choice, or does their responsibility to the population require them to make restrictive decisions based on the greater good of the people? The government then performs a balancing act, running the risk of being labelled as Big Brother (or at least Nanny Government) or as being irresponsible. For example, should we all be allowed to use any chemical we can obtain to relieve the monotony of our daily lives, or should there be regulations to control the use of mind-altering substances and thus protect us from ourselves? If we allow unfettered use of any substance and thus maintain personal freedom, how do we protect the innocent - those who are too young or too poorly educated to know that these materials may be harmful?

Most people would probably come down on the side of some restrictions for the use of drugs, though some would argue for freedom of choice. The same applies to the sale and consumption of raw milk and raw milk products.

I have discussed raw milk before in this blog. I might have left it at that, but the New Zealand Government, in the form of the New Zealand Food Safety Authority has now called for submissions on a proposal to permit direct imports of Roquefort, a soft raw milk cheese made in France, and extra hard Parmesan-style raw milk cheeses Grana Padano, Pamigiano Reggiano, Romano, Asiago and Montasio. An extensive programme of risk assessment has already been undertaken and the Authority is now consulting with industry groups.

This development may lead some members of the community to believe that Big Brother has been wrong all along and is now backing down. Extra hard cheeses have a low water activity* of about 0.693 that prevents the growth of most bacteria. Soft cheeses, such as Brie, Camembert and Roquefort have much higher water activities and thus may permit the growth of pathogens such as Listeria monocytogenes (see post To Pasteurize or not? - 10th December 2006). The truth is that cheeses made from raw milk are not as safe as those made with pasteurized milk.

European Community (EC) legislation sets microbiological, food safety and process hygiene criteria that reduce the risks in consumption of raw milk cheeses. NZFSA has recommended that if these products are to be directly imported and ultimately manufactured in New Zealand, additional risk mitigation measures should be introduced:

• 100% verification of certificates attesting that the relevant EC standards have been met

• continuing monitoring of products to check for E. coli levels, which can indicate unsafe manufacturing conditions leading to faecal contamination of the cheese.

It is expected that leaflets, posters and point of sale brochures will be required to educate the consumers on the risks of eating cheeses made from unpasteurized milk and that labelling of the products will be mandatory. Yet another acronym has been added to our lexicon: YOPI - Young, Old, Pregnant or Immunocompromised. This group of the population should not consume raw milk products.

*Water activity is a measure of the ability of water to take part in biological and chemical reactions. It is measured as a ratio of the partial vapour pressure of the food to that of pure water. That sounds complicated, (it's not) but it results in a scale of water activity running from 0 to 1. Generally speaking, the lower the water activity, the harder it is for micro-organisms to grow. Water activity in foods can be controlled by salts and sugars. So we can formulate food to have a particular water activity and thus preserve the food.

Yet more on unpasteurized milk

This post was updated on 30th April, 2007.

In the previous post I mentioned the potential for contraction or spread of disease that could result from the consumption of raw milk or products made from unpasteurized milk. In that case the consumers may have contracted salmonellosis from the milk.

This week the Grey Bruce Health Unit in Ontario, Canada, issued a press statement, warning pregnant women to avoid consumption of raw milk and unpasteurized dairy products. The warning was issued to help prevent listeriosis infection in newborn babies. The original release can be found at:
http://www.publichealthgreybruce.on.ca/HOME/NewsEvents/2007/Mar/2006Mar14_Infant-Listeriosis.htm

Non-pregnant humans are highly resistant to the infection, though if they do become infected, the symptoms can be very serious, including meningitis and sepsis (invasion of the blood or tissues by bacteria or their toxins). Pregnant women may contract Listeriosis, but show no serious symptoms beyond mild influenza-like signs. Their foetus, however, may be infected, resulting in abortion or stillbirth. If the infant is infected during delivery, symptoms of meningitis begin 1 to 4 weeks later.

The Grey Bruce Health Unit news release stated that it had received a laboratory-confirmed report of an infant who contracted the disease. The most likely source of infection was said to be the mother’s consumption of raw milk cheese.

The release went on to say that pregnant women are at a 17 times higher risk than the general population of contracting the disease.

My personal and professional opinion is that any perceived benefits of drinking raw milk are far outweighed by the risks, both to the individual and to others in the same household. This is supported by scientific evidence: In the last decade the Center for Disease Control and Prevention has documented more than a thousand cases of food-borne illness and two deaths, all caused by unpasteurized dairy products. I have advised my pregnant daughter-in-law to avoid raw milk and raw milk products.

More on unpasteurized milk

The arguments about the desirability or otherwise of drinking unpasteurized milk continue. It seems that its proponents will hear nothing said against the practice; many scientists and doctors provide comment, often supported by case studies, that suggest that there are significant and serious risks associated with drinking unpasteurized milk.

The following report was posted recently on the Food Safety Network mailing list on behalf of Doug Powell of Kansas State University:
Begins
http://www.wdbj7.com/Global/story.asp?S=6170552&nav=S6aK
WDBJ7 News
HARRISBURG, Pa. -- The Pennsylvania Health Department is, according to this story, warning consumers not to drink raw milk from a York County dairy farm after confirming that two people who drank it last month were sickened by salmonella.Health Secretary Calvin Johnson was cited as saying the state Agriculture Department has also obtained three samples from Stump Acres Dairy in New Salem that tested positive for salmonella.
Ends

Of course, the facts that two consumers of the product contracted salmonellosis and that samples taken from the dairy tested positive do not prove that the unpasteurized milk was the source, though detection of the same serotype in patients and the milk would be very strong evidence. However, the correlation between raw milk consumption and illness is hard to ignore.

There are sometimes suggestions that the pasteurization process is too severe. The process was originally designed to eliminate Salmonella, but was later modified to be slightly more rigorous to ensure that Coxiella burnetti (a rickettsia-like organism which is the cause of Q-fever - a febrile disease of man and which sometimes has serious sequellae), was eliminated. There is currently some investigation of the time/temperature relationships in milk pasteurization to see if there is a possibility of making the process less severe.

To pasteurize or not?

Over the past few weeks the issue of milk pasteurization has exercised the people and government of Ontario.

The argument is not a new one: some people believe that the practice of milk pasteurization destroys the nutritional characteristics of the milk and reduces its value as a food. The official line is that the sale (or even giving) of raw milk to the public is illegal, though it is permitted with varying restrictions in 28 states in the USA. Pasteurization of milk has been mandatory in Ontario since 1938. Earlier, around 1900, over 10% of all childhood tuberculosis was thought to be caused by unpasteurized milk. The rate of tuberculosis infection and many other milk-borne diseases in children fell dramatically after the law enactment and was hailed as a major achievement.

To understand the reasons given for pasteurization, we need to go back to the source of milk. Most of our milk supply comes from cows, though goats and sheep are also milked commercially. All of these animals carry bacteria in their intestines and on their skin and feet. They may also carry viruses internally. Some of these micro-organisms can infect humans, occasionally with very serious consequences. Examples are Listeria monocytogenes, Salmonella, Campylobacter, Mycobacterium tuberculosis, Eschericia coli, Brucella and Staphylococcus aureus.

Inside the udder of a healthy animal, the milk is essentially sterile. However, even in a well-run milking shed, it is very difficult to prevent some contamination of the milk from the exterior of the udder. A quick check of the filters will often show a small amount of dirt or fibrous material that has originated either in the gut or on the hide of the cow. Bacteria are too small to be seen with the naked eye, but will be present in the material in the filter and the milk stream. We have to accept that raw milk will contain bacteria and possibly faecal viruses.

All of these micro-oganisms are destroyed by heating the milk to 72C for 15 seconds.

Proponents of raw milk consumption (and the manufacture of cheeses etc. from unpasteurized milk) claim that pasteurization also destroys enzymes in the milk that aid in digestion of the product; the cheeses have less flavour and are inferior compared with their unpasteurized counterparts. I don't intend to get into a debate in this post about nutrition - I am not a nutritionist. So, I will list the effects of just some of these micro-organisms on the human body and leave you, the reader, to do your own nutritional research.

Listeria monocytogenes rarely affects healthy adults; those at high risk include pregnant women, newborn infants, the elderly, and those with weak immune systems. The Centers for Disease Control and Prevention (CDC) estimate that 2,500 people become seriously ill each year in the United States and among these, 500 will die. According to research, pregnant women account for 27% of these cases. CDC claims that pregnant women are 20 times more likely to become infected than non-pregnant healthy adults. Babies may be stillborn or infected at birth. Refrigeration will not stop this micro-oganism from growing, though its growth rate will slow.

Salmonella causes abdominal cramps, diarrhoea, vomiting, headache and elevated temperature when the bacterial cells invade the mucosal cells of the gut. The acute symptoms usually last for only one to two days, though some patients show a much longer illness. Chronic consequences may include arthritic symptoms developing some 3-4 weeks later. Obviously, during the diarrhoeal phase, contamination of the environment and thus other family members can occur.

Campylobacter jejuni is now regarded as the leading cause of gastrointestinal illness in many countries. See earlier posting "So what is this Campylobacter thing?"

Mycobacterium tuberculosis is probably a human-specialised form of M. bovis, which was probably passed to humans from cattle when milk consumption began. There is archaeological evidence that this occurred between 4000 and 8000 years ago and then spread through the migrations of Indo-Europeans throughout the world ( www-micro.msb.le.ac.uk). The normal transfer route is through droplets released during coughing, but tuberculosis can also be transmitted in foods, including unpasteurized milk. If M. tuberculosis reaches the lungs and sets up infection, lung damage results in the longer term if an inflamatory response occurs.

Escherichia coli are found in the gut of man and animals. Microbiologists have always known that some strains of these micro organisms can cause diseases, such as "Travellers' diarrhoea". However, we now know that many strains can cause disease, some life-threatening. There also seems to be an increase in the distribution of these pathogenic strains in farmed animals, as we see from the number of recently reported cases of E.coli O157:H7 in 5 states in USA.

E. coli O157:H7 infection often causes severe bloody diarrhea and abdominal cramps that may last for 5 to 10 days. In some people, particularly young children and the elderly, the infection can also cause hemolytic uremic syndrome (HUS), in which the red blood cells are destroyed and the debris causes kidneys failure. About 8% of patients may develop HUS. Sometimes the patients recover after a long illness, but a significant number of children have required kidney transplants.

Brucella species are passed between animals in many countries, but can also affect humans. Unpasteurized cheeses, often called "Village Cheeses" sold in the Mediterranean Basin, Central America, Eastern Europe, Asia, Africa, the Caribbean and the Middle East may be the source of infection for travellers. The disease may produce flu-like symptoms - fever, sweating, headache, back pain, and physical weakness. However, severe infections of the central nervous systems or heart lining may occur. Brucellosis may also manifest as "undulant fever", a recurrent fever accompanied by joint pain and fatigue.

Staphylococcus aureus produces a heat-stable toxin when it grows in foods. The toxin usually causes vomiting and the effect may become apparent within 30 minutes of consuming the affected food. Diarrhoea may also be present. The symptoms do not usually last for more than 1-3 days and are not life threatening (though those suffering the symptoms may wish that it could be all over!)

Campylobacter

So what is this Campylobacter thing?

Campylobacters are spiral-shaped bacteria (see picture above). They can infect both humans and animals, including birds. About 99% of the Campylobacter infections of humans are caused by just one species - Campylobacter jejuni. The micro-organisms appear to grow well in birds, which have a slightly higher body temperature than humans. Though chickens are often carriers, they show no symptoms of infection, so it's not possible to tell that the bird is infected without doing microbiological testing. C. jejuni does not grow below about 30C, so the presence of high numbers on chicken are unlikely to be the result of temperature abuse.

In humans the disease usually takes the form of abdominal pain and diarrhoea, which may contain blood, fever (typical of the body response to an infection), and vomitting may also occur. The symptoms usually last for about a week and usually no special medical intervention is required, but sometimes the patient requires hospitalization. There are some potential long-term consequences of infection - arthritis or Guillain-Barré Syndrome may follow infection. This is an auto-immune disease caused by the body's own defence system being triggered to attack the nerves. The incidence of Guillain-Barré Syndrome is estimated to be about 1 per 1000 cases.

Human infection is probably caused mainly by handling raw poultry, though the organisms may also be carried by farm animals and can be found in water supplies that have been contaminated by farm run-off. Though consumption of undercooked poultry has been suggested as a cause, in my opinion cross contamination in the kitchen (see "Should I eat the chicken?") is more likely.

The bacterium is easy to destroy by cooking. It cannot tolerate drying and can be killed by oxygen, so microbiologists have to take special precautions to handle and culture it - we grow Campylobacter in special containers where we can reduce the amount of oxygen present, replacing oxygen with carbon dioxide.

Should I eat the chicken?

A recent publication in New Zealand caused a lot of interest by claiming that sale of raw chicken should be banned, in favour of frozen chicken. The basis for the claim was that chicken meat is routinely contaminated with Campylobacter. The freezing process would kill the Campylobacter and render the meat safe.

Was this claim justified?

First we need to understand something about chicken farming, chicken processing and, not least, Campylobacter.

Let's start with Campylobacter. Campylobacter is a bacterium commonly found in animals and the environment. It can get into food via many different contamination vectors (carriers), including untreated water, birds, insects and animals. It is often found in the farm environment, which may be contaminated by animals.

The number of Campylobacter we need to eat to become infected is very low; various estimates put the "infecting dose" at between 6 and 800 cells. This means that even low levels of contamination in food can cause a disease if the food is consumed. Even contact with infected animals, for example in petting zoos, can put sufficient bacteria onto the fingers to give an infecting dose if they are put into the mouth (a problem with little children) or used to prepare food without first washing them carefully.

"But surely" you are asking "we cook chicken before we eat it". Well, yes we do. Assuming that we cook it properly, the Campylobacter cells will be killed and the chicken is safe to eat. But supposing that we handle the raw chicken and then prepare a salad; or we use the same chopping board to prepare the raw meat and then cut the salad on the same board, using the same knife? If we don't wash and sanitize the knife and board, we can "cross contaminate" the food from the chicken, via the knife and board.

The suggestion that raw chicken should be banned, and only frozen chicken sold now has some attraction. "Freezing kills Campylobacter, so that will make the chicken safe and we won't get cross contamination, right?" Well, it goes some way to reducing the contamination. But, as with most things to do with bacteria, it's not black and white. Again, estimates vary; freezing may destroy tens of millions of Campylobacter, but equally may have little effect. FAO/WHO data suggest a hundred-fold reduction if the product is frozen and held for a minimum of 3 weeks. A reduction of a hundred-fold sounds a lot, but in microbiological terms this might still leave millions of bacteria on the product. And as we have seen, this is plenty to give an infecting dose.

So, to go back to the title of this posting, should we eat the chicken? My personal opinion is a qualified "Yes". The caveat is that we must make sure to handle the raw chicken safely, preventing cross contamination of utensils, surfaces and other foods in the kitchen. Cook the meat properly and prevent recontamination.

The New Zealand Food Safety Authority (NZFSA) says that two of the most important ways of keeping food safe are to follow the 4Cs rule – Clean, Cook, Cover and Chill the food. Also follow the 20+20 hand wash rule before and after handling poultry and preparing food - wash your hands, using plenty of soap and warm water for at least 20 seconds, paying careful attention to finger nails and the webs between fingers. Rinse well and dry them for a further 20 seconds, using a clean dry hand towel or disposable paper towel. It has been shown that wet hands can transfer microbial contamination to utensils, refrigerator door handles, taps and other potential cross contamination points, so the drying is just as important as the washing.

Odd Spot: On 3 December 1988, Edwina Currie, the outspoken junior health minister in the UK Thatcher government was quoted as telling ITN, "Most of the egg production in this country sadly is now infected with salmonella." Sales of eggs plummeted 60 per cent overnight. The loss of revenue forced farmers to slaughter four million hens and 400 million unsaleable eggs had to be destroyed. The government had to provide a multi million pound rescue package for the poultry industry and the unfortunate Ms. Currie resigned on the 17th December. Undoubtedly, there was some substance to her claims. Vaccination of hens to protect against salmonella has now greatly reduced the levels of egg contamination to the present 0.3% reported by the latest FSA survey and since 1997 the incidence of salmonellosis in UK has fallen by a factor of about 4x. However, there is still a concern that eggs on sale in UK may contain Salmonella Enteritidis organisms, perhaps as a result of importation of eggs produced by unvaccinated hens.

Perhaps Edwina was right. Only time will tell if the advocates of frozen chicken are right too.