Researchers in New Zealand have compared cases of raw milk-associated campylobacteriosis with those who did not report drinking this product before illness.

Campylobacteriosis is the most common notifiable disease in New Zealand. While risk is strongly associated with eating undercooked poultry, other risk factors include rainwater-sourced drinking water, contact with animals and consumption of raw dairy products such as unpasteurized milk.

A rising demand for untreated or raw milk have also raised concerns that this exposure may become a more important source of disease in the future, according to researchers.

Previously collected data from notified infections of raw milk-associated campylobacteriosis were compared with cases who did not report raw milk consumption in a study published in the journal Epidemiology and Infection

Raw milk vs non-raw milk infections
Raw milk cases differed from non-raw milk cases in age and occupation demographics, with raw milk ones more likely to be younger and categorized as children or students for occupation. Raw milk cases were more likely to be associated with outbreaks than non-raw milk cases.

Study-suggested motivations for raw milk consumption such as health reasons, natural product, produced on farm, inexpensive or to support locals were not strongly supported by cases.

In New Zealand, raw milk can be legally purchased directly from registered farms and is consumed by farm residents and employees. There has been a recent consultation around legislation in the country.

Data was collected by MidCentral District Health Board and Massey University’s Molecular Epidemiology and Public Health Laboratory during 2012 to 2017. The study area was the North Island of New Zealand.

The number of notified campylobacteriosis cases was 1,408. Ninety-three people reported raw milk consumption and completed the raw milk questionnaire. An additional 12 cases said they had raw milk but did not fill in the questionnaire and were identified using data from EpiSurv, New Zealand’s national notifiable disease surveillance database.

The median age was 26 (range zero to 75) for raw milk cases and 39 (zero to 97) for non-raw milk cases. A peak amongst children aged 5 years old or less was seen for both groups. A second peak was apparent for raw milk cases in their early to mid-20s.

Drivers of consumption
Twelve raw milk and 33 non-raw milk cases were associated with an outbreak. The percentage of outbreak cases was significantly greater for raw milk compared to non-raw milk cases. Around 13 percent of all cases were hospitalized, with no difference between exposures.

Results from 93 raw milk questionnaires were available. “Health reasons” was the category with most support as 31 percent agreed. “Support for local producers” was not a driver of consumption with only 2 percent of cases agreeing. Other themes motivating consumption identified from interviews included taste, convenience, product received as a gift and desire to try raw milk. Of these, taste and convenience were most frequently reported.

Results indicated that rural children appeared to be at an increased risk of raw milk-associated campylobacteriosis compared to non-raw milk-associated disease. It is unknown whether this was due to more exposure to raw milk, increased susceptibility among this group or a combination of these factors.

A seasonal pattern was apparent in raw milk-associated campylobacteriosis, with a peak in the spring. This may be due to increased access to raw milk and seasonal increases in the shedding of Campylobacter in dairy cattle, according to researchers.

How to produce safe raw milk
Meanwhile, another paper in the same journal describes safety practices for safe raw milk production.

The German Vorzugsmilch (VZM) is a federally regulated program for raw milk production established in the 1930s. The Raw Milk Institute (RAWMI) is a non-profit organization in California founded in 2011 that has developed a voluntary program in North America.

For the German system, results from monthly pathogen tests are compared to those from other milk sources. Overall results indicate that raw milk can be produced hygienically and safely in various systems. In 2018, around 1,100 tons of raw milk was sold by 13 VZM farms in Germany and most farmers combine the labeling of raw milk with organic labeling.

There are 18 listed RAWMI farms, of which 14 are active, with an average annual production of 6,900 tons of milk.

Consumers are seeking out raw milk due to health reasons, for taste, freshness, closeness to the producer and to support local agriculture. Good farm biosecurity, animal management, hygienic milking techniques, distribution systems, quick cooling and a good cold chain involving consumer handling can assure safety, according to the study. Bacteria in raw milk can come from udder, teat canal, skin, manure, environment, milking equipment, pipelines, tanks and bottles.

In Canada, the sale of raw milk for direct consumption is prohibited. Herd shares are also banned but still exist. They are arrangement between farmers and shareholders in the herd, wher the shareholder can get raw milk and other products from the farmer proportionate to the shareholder’s interest in the herd. Ten producers have been part of a program by the British Columbia Herdshare Association. They are hoping their record of microbial safety can help lift the ban on herd shares.

The Raw Milk Producers Association (RMPA) was created in the United Kingdom in 2019. The group has held workshops with the authors of the paper and FSA inspectors.

Most outbreaks linked to raw milk are associated with dairy farms that have not received training in hazard reduction and hygienic milking procedures, said researchers.

“In addition, raw milk-associated outbreaks are subject to a detection bias, because it is easier to trace an outbreak back to a niche commodity actively sought by few consumers such as raw dairy products than to commodities consumed by a large portion of the population such as pasteurized dairy products. This also leads to a reporting bias, since an investigation that leads to the detection of the source of the risk is much more likely to be reported and published.”