Drink at your own perceived risk

2 05 2012

by Helen Shen

How dangerous is unpasteurized milk? Many health-conscious consumers want to know. The answer depends on how you look at the numbers.

In March, CDC scientists published a study in the journal Emerging Infectious Diseases that tried to quantify this risk by analyzing milk-related disease outbreaks from 1993 to 2006.

The research was widely covered in the mainstream news media, including in a story I wrote for the San Jose Mercury News. The study also attracted a fair amount of online outrage from many raw milk enthusiasts, who treated it as a piece of biased government propaganda.

The CDC media press release, several news stories, and the research paper itself highlighted two main points: first, that 75 percent of raw milk outbreaks occurred in states where raw milk was legal at the time (in an interview with me, first author Adam Langer called this “the most important result of the study”); and second, that raw milk is 150 times more dangerous than pasteurized milk.

Plenty of aspects of the raw milk debate are unscientific. Food choices are personal, cultural, and political. Twelve states allow retail sales of raw milk. Twenty states ban raw milk sales outright. The remaining states allow only limited raw milk sales, such as on-farm transactions.

Unfortunately, emphasizing those particular research findings may have hindered a truly scientific discussion about raw milk risks.

Photo credit: cyclonebill, Wikimedia Commons

Proving the obvious

Let’s think about the first conclusion. Between 1993 and 2006, raw milk caused more outbreaks in states where the unpasteurized product was legal. Is that like saying car accidents happen more often on roads that permit cars?

Langer told me, “It is not necessarily surprising. We do occasionally have to do scientific studies in order to prove what one would think would be obvious. But it is important evidence to show that laws that restrict the sale of unpasteurized dairy products are very important public health tools to reduce the number of outbreaks that are caused by these products.”

Basically, the study suggests that in states that ban raw milk sales, few people consume and get sick from black market raw milk, says Michele Jay-Russell, a food safety expert at UC Davis and a former scientist with the California Department of Public Health.

Hm. That’s probably good news, but it doesn’t offer any real information about how risky raw milk actually might be. That’s where the second point could help.

Outbreaks versus individuals

The authors concluded that raw milk carries 150 times greater risk than pasteurized milk of causing disease outbreaks. (A disease outbreak is a cluster of illnesses thought to originate from the same source. It could involve 2, 200, or 2,000 people.)

Here’s some of the math: Only about 1 percent of the population is thought to consume raw milk. Assuming they consume milk in roughly the same quantities as other milk drinkers, and assuming the two types of milk were equally safe, you’d expect about 1 percent of outbreaks to be related to raw milk. Instead, the CDC found 60 percent of outbreaks—150 times more than expected—were linked to raw milk.But what happens if, instead of using outbreaks, you look at those individuals involved in milk-related outbreaks? Those numbers tell a slightly different story.

In total, raw milk outbreaks sickened 1571 people. Pasteurized milk sickened 2842. So, while raw milk was implicated in 60 percent of outbreaks, it accounted for only 35 percent of all outbreak-sickened individuals. Thirty-five percent is still 55 times more than you’d expect to see from the small fraction of milk drinkers who consume unpasteurized dairy. That’s cause for concern, but it’s a much smaller effect than if you measure risk by outbreaks.

The average reader doesn’t think in terms of disease clusters, but is interested in individual risk. Health agencies, on the other hand, get concerned and become involved when outbreaks occur, says Jay-Russell.

“If you’re part of an outbreak, or if you’re the only one that got sick, it’s all the same ‘badness’ for you personally. From a public health resource standpoint, having these dozens of outbreaks, every one of those requires stopping work on other public health issues,” she said.

Milking a goat
Photo credit: Teunie from nl, Wikimedia Commons

The authors didn’t communicate the reasons for their choice—non-intuitive for the general public—for calculating outbreak statistics in their paper. Nor did they include the relative risk statistics for individuals. Doing so could have helped their case.

But because the omitted statistics would have produced a weaker result, the authors invited criticisms of manipulating the numbers to their advantage.

In a press release entitled “CDC Cherry Picks Data to Make Case Against Raw Milk,” the pro-milk non-profit Weston A. Price Foundation said, “Perhaps most troubling is the authors’ decision to focus on outbreaks rather than illnesses… In addressing the risk posed for individuals who consume a food, the logical data to examine is the number of illnesses, not the number of outbreaks.”

Distracting from the data

Jay-Russell says she’s more concerned that young people and children are disproportionately sickened by raw milk—a finding that received relatively less attention. The CDC study found that 60 percent of individuals sickened by raw milk outbreaks were younger than 20. That number contrasts with 23 percent for pasteurized milk outbreaks.

Even though a small fraction of the population drinks raw milk, the majority of those sickened in raw milk outbreaks are young. This effect is partly explained by the fact that raw milk is touted by its fans as a health food—not just acceptable for children, but especially beneficial to their growth and well-being.

In my next blog post, I’ll examine some of these health claims.

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Got raw milk?

20 10 2011

By Tanya Lewis

You drink it. You put it on your cereal. You dunk cookies in it.

MILK!

Life's first beverage. (Photo by Tanya Lewis)

This magical substance is the first beverage most of us consume, when our wimpy newborn bodies can’t handle much else. But it’s not just a beverage, it’s a hyper-nutritious, calcium-packed nectar, produced by the mammary glands of female mammals to nourish their young.

Yeah, okay, so what’s the story with milk? Well, when I first arrived in Santa Cruz a little over a month ago, milk seemed to be the talk of the town. After all, it turns out, California is the leading producer of milk in the nation. It produced 38 billion pounds of milk in 2006. In fact, California dairy farms produce over 21% of the nation’s total milk supply.

Apparently, all the fuss had to do with recent crackdowns on producers of raw milk (or rather, owners of the milk producers, who were, in fact, farm animals).

Raw milk is milk that has not been pasteurized or homogenized. What exactly is pasteurization? You always see it on milk cartons, but how often do you stop to wonder what it actually involves?

Pasteurization, named after the Frenchman Louis Pasteur, is essentially heating up a liquid or food to kill pathogenic bacteria that can be threatening to your health. Sounds like a good idea, right? Well, the FDA thought so, and it’s become pretty much standard practice in the retail dairy business. But not everyone’s happy about it… more on this later.

Here in California, milk production is regulated by the California Department of Food and Agriculture (CDFA). On their website, they have a chart showing California’s bacteriological standards for milk:

Standard

Federal

California

Grade “A” Raw Milk for Pasteurization Bacterial (Standard Plate Count) Limits Not to exceed 100,000 per ml Not to exceed 50,000 per ml
Somatic Cell Count Not to exceed 750,000 per ml Not to exceed 600,000 per ml
Coliform No Standard Not to exceed 750 per ml
Laboratory Pasteurized Count No Standard Not to exceed 750 per ml
Grade “A” Pasteurized Milk Standard Plate Count Maximum 20,000 per ml Maximum 15,000 per ml
Coliform Maximum 10 per ml Maximum 10 per ml

Clearly, California is more anal than the federal government, at least when it comes to bacterial standards.

Back in 2008, the CDFA passed a bill called “AB 1735” which established new standards for coliform bacteria in raw milk sold in California. As of January 2008, the state’s two raw milk bottlers were required to have a final product with no more than 10 coliform bacteria per milliliter (same as pasteurized milk).

What’s a cauliflower coliform anyway? Colforms are a group of bacteria typically found in the environment: in soil, surface water, vegetation and the intestines of warm-blooded animals.  Well, I guess cauliflower could be found in that last one, too. Anyway, coliforms are used as a gauge of sanitary conditions in things like…(surprise) dairy production. They also produce the characteristic “off” taste in sour milk. While most don’t actually cause disease, a small fraction can make you sick, especially if you’re a young child, old person, or have a weakened immune system.

Kiyoshi Shiga (Tanakadate Aikitu Memorial Science Museum)

For example, a strain of E.coli O157:H7 has been implicated in some pretty sordid cases of foodborne illness. They produce a toxin called “Shiga toxin”, named after the Japanese physician and bacteriologist Kiyoshi Shiga, who first described the bacterial origin of dysentery due to Shigella dysenteriae.

(I can think of better things to have named after you than a toxin, but at least he got his own Wikipedia page.)

Shiga toxins work by inhibiting protein synthesis in cells by cleaving off a nucleobase from the RNA of a ribosome. The dysfunctional ribosome stops being able to produce protein. Clearly this not optimal. Shiga toxin-producing E.coli were behind for the recent outbreak in deadly sprouts from Germany.

Another kind of sprouts, of the nonlethal Trader Joe's variety (photo by Tanya Lewis)

But back to milk…

How do coliform get into milk? The most common way is milking cows with wet, grimy udders or using unclean milking equipment. Their presence, while not inherently harmful (unless they’re the toxic variety), has been used as an indicator of sanitation for years. In dairy farms, coliform count is a measure of the fecal bacteria in milk (eww, right?), but coliforms can also signal environmental contamination of drinking water supply systems.

The good news (some would argue) is that pasteurization of dairy products easily kills coliform. Contamination can occur after pasteurization too, though, which is why it’s important to refrigerate milk. For raw milk, California law mandates it be cooled to 50 deg. F after milking begins and maintained at 45 deg. F within two hours after milking.

According to the CDFA, the new standards for coliform count in raw milk can be achieved without pasteurization, “with utilization of sound cleaning and sanitation practices.” They say that on average, about 25% of milk samples from dairy farm inspections fall within the allowable range for colliform bacteria. ** Agreeing with national data collected by USDA’s National Animal Health Monitoring System, and published in the Journal of Dairy Science in 2004 (J. Dairy Sci. 87:2822).

The CDFA lists a few suggestions for minimizing coliform count in raw milk. Here are two of my favorites:

  • Properly managing manure, bedding, housing and pastures to prevent cows from arriving overly dirty at the milking parlor.
  • Use of an appropriate commercially available pre-milking teat sanitizer to further reduce the amount of bacteria contacting milking equipment

    Penny Ice Creamery Pasteurizer, Santa Cruz (photo by Tanya Lewis)

The raw milk bill specifies maximum bacterial counts for a whole range of dairy products, including ice cream, sherbet, and eggnog! I did a bit of “field research” at the Penny Ice Creamery  here in Santa Cruz, and found out their ice cream is a) delicious and b) pasteurized in-shop (see photo).

Well, not everyone’s on board with the raw milk restrictions. Many people consider it their right to drink and distribute raw milk. This isn’t prohibition, after all. Recently, Santa Cruzans (or whatever the right collective noun is) staged a Milk-In at the Downtown Farmers Market. People are serious about their milk, so don’t even try to move their cheese.

On that note, I leave you with some cow pictures:

“Pauline was the pet of President William Howard Taft and is seen here grazing on the south lawn of the White House. She supplied the Taft family with fresh milk daily.” (DC Public Library Commons)

A Canadian Holstein (image from http://www.dairycowdaily.com)

Gladys the Swiss Dairy Cow, as a schoolbus (image from James Lebinski, Wikimedia Commons) More versions of Gladys at wikipedia.org/wiki/Gladys_the_Swiss_Dairy_Cow.