Part 1 and Part 2 of this series examined the historical context of the debate surrounding dairy product food safety, and the mechanisms by which pasteurized or raw dairy products may become contaminated with foodborne pathogens. Part 3 compared foodborne illnesses and disease outbreaks linked to raw and pasteurized dairy products. In this section, the potential risks and benefits that consumers must weigh when buying dairy products for themselves or their children are compared.
Recommendations to move this debate forward in a direction that promotes dairy food safety regardless of processing method will be published in a final summary of this series.
Making a Decision at the Dairy Case, Farmers’ Market, or on the Farm
As described in Part 1, there is considerable variation from state-to-state in the way raw dairy products are regulated in the US. Only a few states allow retail stores or farmers’ markets to sell raw milk, while others restrict sales to on-farm purchases, or ban raw milk altogether (Oliver et al, 2009). The FDA allows cheeses made with raw milk to be sold interstate so long as they have been aged for 60 days.
For consumers who live in states where both pasteurized and raw milk are sold legally for human consumption, there are three broad considerations to weigh when making a choice between the products:
I. Food Quality: including taste, nutrients and other health benefits
II. Food Safety: potential for contamination with dangerous pathogens or toxins
III. Value: including cost to purchase, as well as values such as environmental stewardship, support for community farms
I. Quality and Health
The websites that promote raw (unpasteurized) milk products often claim that there are substantial losses in nutrients due to the heat treatment used during pasteurization. In contrast, public health agencies such as the FDA and CDC cite nutritional analyses showing that the losses in nutritional content after pasteurization are negligible for the key nutrients that milk provides in the human diet. A comparison of the nutrition labels on raw and pasteurized milk purchased at a retail store shows very little difference between commercial raw, organic milk and organic or conventional pasteurized milk products.
A. Raw whole milk, organic, unhomogenized.
B. Pasteurized whole milk, organic, unhomogenized.
C. Pasteurized whole milk, conventional, homogenized, fortified with vitamin D
The Table below shows the differences on the labels (highlighted in yellow). Comparison of nutrition labels from three commercial raw and pasteurized milk products.
b. Health Benefits
Overall, the medical benefits of dairy products (raw or pasteurized) beyond basic nutrition are unclear. The “raw milk pros” review published previously showed results from epidemiological studies in Europe that suggested consumption of raw milk products in childhood may help prevent some allergic conditions (e.g., asthma, hay fever, eczema). Both raw and pasteurized dairy producers have also made claims about beneficial or “probiotic” bacteria, and their effects on digestive health and immunity. The science behind probiotics in dairy products such as yogurts and kefirs is an active area of research (Sanders 2009).
Although dairy products may provide health benefits beyond nutrition, consumers should be wary of product claims that appear to be implausible, or "too good to be true." For example, WAPF promotes raw milk consumption for its curative effects on conditions ranging from autism to allergies to tooth decay to lactose intolerance and heart disease. It seems implausible that one food product could provide so many different and unrelated health benefits, which suggests that the claims may be primarily a marketing strategy not founded in sound medical research.
The sensory qualities of milk, cheeses and other dairy products include taste, texture, and aroma. These qualities are mostly subjective, and depend on personal preference. For example, traditional Mexican-style soft cheeses such as queso fresco made with raw milk have a distinctive flavor; however, these raw cheeses have also been associated with a number of outbreaks and illnesses. An interesting intervention to address an ongoing problem with Salmonella in queso fresco cheeses occurred in Yakima County, Washington. Several agencies worked together with the Hispanic community to develop a pasteurized milk queso fresco recipe with a taste and texture as desirable as the raw cheese product (Bell et al, 1999). The educational effort, termed “The Abuela Project” (“abuela” is “grandma” in Spanish) successfully reduced the incidence of Salmonella in that community.
II. Food Safety
In Part 3, CDC data on milk-related outbreaks from 1973-2005 was analyzed. To examine more recent food safety trends, data from surveillance records and the literature from 2000-2007, was analyzed and summarized in the attached tables. This period also coincides with the time that WAPF has been most active in promoting raw milk sales.
As before, the type of milk was divided into three categories:
• Pasteurized milk/cheese
• Raw milk/cheese
• Mexican-style fresh queso fresco cheese (see photo and description in Figure 1c, Part 3 )
The analysis summarized in the Table focused on the four pathogens most often implicated in dairy-related foodborne disease outbreaks: Campylobacter, E. coli O157:H7, Listeria monocytogenes, and Salmonella. The limitations and caveats relating to this type of analysis using surveillance data were described previously in Part 3. Most importantly, we know that many outbreaks and illnesses are not reported to health departments (Mead et al, 1999), thus these numbers are an underestimation of the true burden of illness. But, despite these limitations, the statistics provide a useful snapshot of differences between these three categories of milk products.
Summary of Findings for Four Major Pathogens Involved in Dairy-Related Outbreaks in the US, 2000-2007 are summarized in the table below.
• Raw dairy products caused 42 (75%) of 56 dairy-related outbreaks during this 8-year period due to the four major pathogens, which is almost 5 times more outbreaks compared with pasteurized dairy products and about 8 times more outbreaks compared with queso fresco cheeses.
• Outbreaks cause a burden on the public health system because each one must be investigated to determine the cause and prevent future illnesses. Furthermore, outbreaks often involve recalls, which hurt the industry through loss of product, and loss of consumer confidence in milk.
• Both pasteurized and raw milk outbreaks have resulted in farm closures including Whittier Farms in Massachusetts in 2007 (pasteurized milk, listeriosis) and, more recently, Simsbury Town Farm Dairy in Connecticut (raw milk, E. coli O157:H7).
• Pasteurized dairy products caused 2,181 (65%) of 3,371 milkborne outbreak-related illnesses for these four major pathogens, which was approximately 2 times as many illnesses compared with raw dairy products and queso fresco cheeses during this recent 8 year period.
• 84% of these pasteurized milk-related illnesses were due to campylobacteriosis from milk produced and distributed at prison facilities (not sold to the general public).
• These illnesses cause suffering and costs to individuals and their families, as well as increased stress on the health care system.
Campylobacter: Raw dairy products caused 34 (94%) of the Campylobacter outbreaks compared with only 2 from pasteurized milk and none due to queso fresco from 2000-2007 (Table). The two large campylobacteriosis outbreaks due to pasteurized milk involving 1,844 illnesses were both associated with prison dairies, which suggests that prisoners may be at increased risk of Campylobacter infections if there is post-pasteurization contamination during processing at on-site dairies. The disproportionate number of Campylobacter outbreaks from raw milk is not a new trend. Indeed, since first identified as a human pathogen in the late 70’s, Campylobacter has repeatedly been linked to raw milk outbreaks. In a review of Campylobacter outbreaks in 10 different countries from 1978 to 2002, Miller and Mandrell (2005) identified only 5 outbreaks traced to pasteurized or heat-treat milk compared with 68 outbreaks from consumption of raw dairy products. Unfortunately, WAPF often uses conspiratorial arguments to discount the problem with Campylobacter in raw milk, rather than helping raw dairy producers address the ongoing contamination events with this foodborne pathogen in their products, or downplay the importance of the illnesses. Campylobacter infections usually result in full recovery, but about 1 in 1,000 patients may develop Gillain Barre syndrome (GBS) and become permanently paralyzed. As an example, there was a tragic case of GBS in a previously healthy woman who drank raw milk purchased through an unlicensed herdshare program in 2008; leftover raw milk still in her refrigerator tested positive for Campylobacter.
E. coli O157:H7: From 2000-2007, there were 5 raw milk-associated outbreaks with 232 illnesses including several HUS cases among children compared with 1 outbreak linked to queso fresco cheese and no outbreaks linked to pasteurized milk (Table). In general, milk-related outbreaks due to E. coli O157:H7 are uncommon, but almost always associated with raw milk products when they occur (Rangel et al, 2005; Hussein et al, 2005). The severity of some of the recent E. coli O157:H7 illnesses associated with raw milk and/or raw colostrum consumption by children should be a cause for concern, yet WAPF and other raw milk advocates frequently dismiss these illnesses despite strong epidemiological and laboratory evidence implicating raw milk. For example, two raw milk dairies that specifically followed WAPF principles were associated with 6 cases of HUS among children in Washington and California in 2005-2006 (CDC 2007; CDC 2008). During the Washington investigation, unsanitary conditions were found at the dairy, and the outbreak strain was isolated from the raw milk (see Figure 1a, Part 3 ). The California investigation revealed very high coliform counts in the raw milk and raw chocolate colostrum, which suggested fecal contamination. Although the outbreak strain was not isolated from raw milk during that investigation, other E. coli O157:H7 strains were found in feces from heifers on the dairy. Notably, the California dairy owner later admitted to buying and bottling raw colostrum from surrounding dairies not licensed to sell Grade A raw milk in order to meet his supply demands (a dangerous practice called “outsourcing”); thus, it is theoretically possible that the outbreak strain was introduced into the implicated raw milk dairy from colostrum that was destined to be consumed by calves and/or pasteurized. In 2008, two more E. coli O157:H7 outbreaks were linked to raw goat’s milk sold illegally in Missouri and raw cow’s milk from a Connecticut dairy, respectively. Three children were hospitalized due to HUS, and the Connecticut dairy ultimately closed down. An injunction was sought in the Missouri case.
Listeria monocytogenes: From 2000-2007, there were 3 queso fresco- and 2 pasteurized milk-related outbreaks involving several deaths, still births, premature deliveries (Table). During that same time period, there were no reported outbreaks linked to raw dairy products except those involving queso fresco or Mexican style cheese. In general, dairy products are considered moderate to high risk for listeriosis infections, second only to deli meats and other ready-to-eat processed meats (Swaminathan and Gerner-Smidt, 2007). Pregnant women and persons with weakened immune systems are at much great risk of serious illness from listeriosis than the general population. Historically, soft Mexican-style cheeses such as queso fresco have been associated with severe listeriosis outbreaks, especially cheeses prepared illegally under unsanitary conditions. Sanitation problems were identified as the key factors in both of the recent listeriosis outbreaks that were published. The North Carolina outbreak in 2000-2001, involved consumption of Mexican-style cheese made from raw milk. The cheese was manufactured illegally, and the “outbreak strain” was found in 4 cheese samples and raw milk taken from the farm that supplied the milk (CDC 2001). The Massachusetts outbreak in 2007, involved pasteurized milk from a local dairy and bottling facility that was likely contaminated with Listeria over an extended period of time; three patients died as a result of their infections, and the dairy ultimately shut down. The Massachusetts outbreak underscores the vulnerability of dairy products to becoming contaminated after pasteurization if stringent hygiene is not maintained throughout processing, bottling, and handling of the milk.
Salmonella: From 2000-2007, there were 4 (329 illnesses) pasteurized-, 3 (163 illnesses) raw-, and 1 (135 illnesses) queso fresco-related outbreaks of salmonellosis (Table). Notably, over one-third (233 of 588 illnesses) of the salmonellosis cases during this period were from multidrug resistant strains (MDR) of Salmonella Newport. These outbreaks from MDR Salmonella Newport were linked to raw cheese served at a picnic in 2001 (multistate), pasteurized milk in California in 2004, and Mexican-style cheese served in homes in Illinois in 2006 (Oliver et al, 2009; CDC 2008b), which suggests that the problem may be important in all three categories of dairy products (e.g., pasteurized milk, raw milk, and queso fresco cheese). Additionally, Olsen et al (2004) described an outbreak of MDR Salmonella Typhimurium linked to milk contaminated post-pasteurization involving 96 illnesses in 2000. The issue of antibiotic resistant Salmonella strains in dairy products (whether raw or pasteurized) is a cause for concern.
Although no recent review paper was available, the epidemiology of Salmonella in dairy products appears to be changing. It is also worth noting that a major shift in raw milk-associated salmonellosis occurred over the last three decades. Specifically, in the 70’s and 80’s, there were significant problems with Salmonella Dublin infections and deaths linked to a single, large certified raw milk dairy in California (Werner et al, 1979; Richwald et al, 1988). Since that dairy shut down, the salmonellosis problem with raw dairy products has been greatly reduced in the US. Likewise, in the 80’s and 90’s, two of the largest ever documented salmonellosis outbreaks were linked to pasteurized dairy products including milk (contaminated after pasteurization) and ice cream (cross-contaminated with raw eggs) (Ryan et al, 1987; Hennessey et al, 1996). No similar enormous salmonellosis outbreaks have been documented from pasteurized dairy products in 15 years.
Brucellosis and Bovine Tuberculosis: Although not shown in the table, these diseases continue to occur in the US, but are mostly a problem among travelers that consume raw dairy products in countries where the infections are endemic in cattle or goat populations. Illnesses have also been documented following consumption of raw dairy products imported illegally into the US. For example, from 2001-2004, 35 cases of human bovine tuberculosis were linked to fresh cheese (queso fresco) brought to New York City from Mexico (CDC 2005). Similarly, the two most recent reports of brucellosis outbreaks in California were traced to consumption of imported raw cheeses (CDPH 2009).
In addition to food quality and food safety, consumers may also factor cost and other more subjective values into their decision about which type of dairy product they choose to buy. First, there is the actual cost to purchase the product. In general, commercial, Grade A raw milk sold in the US is more expensive than its organic or conventional pasteurized counterparts. For example, the organic, whole raw milk (photo A) cost ~$15/gallon compared with ~$10/gallon (photo B) for the organic, pasteurized whole milk, and ~$6/gallon (photo C) for the conventional, pasteurized milk (each were bought at the same food co-op). These prices are likely to vary depending on regional differences, but overall raw milk is more expensive than pasteurized milk, and organic milk is more expensive than conventional milk.
Second, beyond the purchase price, many consumers consider other values such as how the milk was produced. Consumers may be willing to pay more for organic dairy products (raw or pasteurized) because of the perceived environmental benefits. Similarly, there is a growing desire to support local, smaller farmers in the community, which potentially creates new niches for dairy products.
In summary, consumers must weigh many different factors when choosing the most appropriate dairy product for themselves and their families. The data on outbreaks and illnesses show that there is currently more risk of exposure to foodborne pathogens such as Campylobacter and E. coli O157:H7 from raw milk products compared with pasteurized milk products. Children, pregnant women, and immune-compromised individuals are at higher risk of illness from contaminated raw dairy products and soft cheeses (raw or pasteurized). Both pasteurized and raw dairy products can be dangerous if produced under unsanitary conditions. Consumers should avoid any dairy products sold illegally, especially “black market” raw milk/cheeses, and soft Mexican-style cheeses such as queso fresco sold by unlicensed vendors, or imported illegally into the US.
1. Bell, R. A., V. N. Hillers, and T. A. Thomas. 1999. The Abuela Project: safe cheese workshops to reduce the incidence of Salmonella Typhimurium from consumption of raw milk fresh cheese. Am J Public Health 89:1421-4.
2. CDC. 2001. From the Centers for Disease Control and Prevention. Outbreak of Listeriosis associated with homemade Mexican-style cheese–North Carolina, October 2000-January 2001. Jama 286:664-5.
3. CDC. 2005. Human tuberculosis caused by Mycobacterium bovis – New York City, 2001-2004. MMWR Morb Mortal Wkly Rep 54:605-8.
4. CDC. 2007. Escherichia coli O157:H7 infection associated with drinking raw milk – Washington and Oregon. November – December 2005. MMWR Morb Mortal Wkly Rep 56:165-7.CDC. 2008a. Outbreak of Listeria monocytogenes infections associated with pasteurized milk from a local dairy–Massachusetts, 2007. MMWR Morb Mortal Wkly Rep 57:1097-100.
5. CDC. 2008a. Escherichia coli 0157:H7 infections in children associated with raw milk and raw colostrum from cows–California, 2006. MMWR Morb Mortal Wkly Rep 57:625-8.
6. CDC. 2008b. Outbreak of multidrug-resistant Salmonella enterica serotype Newport infections associated with consumption of unpasteurized Mexican-style aged cheese – Illinois, March 2006 – April 2007. MMWR Morb Mortal Wkly Rep 57:432-5.
7. CDPH. 2009. Epidemiologic summary of human brucellosis in California. Available from: http://www.cdph.ca.gov/data/statistics/Documents/brucellosis-episummary.pdf
8. Hennessy, T. W., C. W. Hedberg, L. Slutsker, K. E. White, J. M. Besser-Wiek, M. E. Moen, J. Feldman, W. W. Coleman, L. M. Edmonson, K. L. MacDonald, and M. T. Osterholm. 1996. A national outbreak of Salmonella enteritidis infections from ice cream. The Investigation Team. N Engl J Med 334:1281-6.
9. Hussein, H. S. and T. Sakuma. 2005. Prevalence of shiga toxin-producing Escherichia coli in dairy cattle and their products. J Dairy Sci 88:450-465.
10. MacDonald, P. D., R. E. Whitwam, J. D. Boggs, J. N. MacCormack, K. L. Anderson, J. W. Reardon, J. R. Saah, L. M. Graves, S. B. Hunter, and J. Sobel. 2005. Outbreak of listeriosis among Mexican immigrants as a result of consumption of illicitly produced Mexican-style cheese. Clin Infect Dis 40:677-82.
11. Mead, P. S., L. Slutsker, V. Dietz, L. McCaig, J. S. Bresee, C. Shapiro, P. M. Griffin, and R. V. Tauxe. 1999. Food-Related Illness and Death in the United States. Emerg Infect Dis 5:607-25.
12. Miller, W. G. and R. E. Mandrell. 2005. Prevalence of Campyobacter in the food and water supply: incidence, outbreaks, isolation and detection. In: Campylobacter: Molecular and Cell Biology. Ketley, J. M. and M. E. Konkel, eds. Norfolk, UK: Horizon Biosciences, pp. 101-63.
13. Oliver, S. P., K. J. Boor, S. C. Murphy, and S. E. Murinda. 2009. Food safety hazards associated with consumption of raw milk. Foodborne Pathog Dis 6:793-806.
14. Olsen, S. J., M. Ying, M. F. Davis, M. Deasy, B. Holland, L. Iampietro, C. M. Baysinger, F. Sassano, L. D. Polk, B. Gormley, M. J. Hung, K. Pilot, M. Orsini, S. Van Duyne, S. Rankin, C. Genese, E. A. Bresnitz, J. Smucker, M. Moll, and J. Sobel. 2004. Multidrug-resistant Salmonella Typhimurium infection from milk contaminated after pasteurization. Emerg Infect Dis 10:932-5.
15. Rangel, J. M., P. H. Sparling, C. Crowe, P. M. Griffin, and D. L. Swerdlow. 2005. Epidemiology of Escherichia coli O157:H7 outbreaks, United States, 1982-2002. Emerg Infect Dis 11:603-9.
16. Richwald, G. A., S. Greenland, B. J. Johnson, J. M. Friedland, E. J. C. Goldstein, and D. T. Plichta. 1988. Assessment of the excess risk of Salmonella Dublin infection associated with the use of certified raw milk. Public Health Rep 103:489-93.
17. Ryan, C. A., M. K. Nickels, N. T. Hargrett-Bean, M. E. Potter, T. Endo, L. Mayer, C. W. Langkop, C. Gibson, R. C. McDonald, R. T. Kenney, and et al. 1987. Massive outbreak of antimicrobial-resistant salmonellosis traced to pasteurized milk. JAMA 258:3269-74.
18. Sanders, M. E. 2009. The Pros of Probiotics. California Dairy Dispatch. Published by the California Dairy Research Foundation. Available from: http://www.cdrf.org/content.asp?contentID=539.
19. Swaminathan, B., and P. Gerner-Smidt. 2007. The epidemiology of human listeriosis. Microbes Infect 9:1236-43.
20. Werner, S. B., G. L. Humphrey, and K. I. Kamei. 1979. Association between raw milk and human Salmonella Dublin infection. BMJ 2:238-41.