Children under 10 years old are most likely to contract campylobacter disease from drinking raw milk, research shows.
They account for 29% of the raw milk-related cases notified in the Mid Central Health Board area from 2012 to 2017.
The study collected data on all cases of campylobacter notified to Mid Central Health in that period. It then dug deeper into raw milk campylobacteriosis cases, comparing the demographics of the cases to other campylobacter cases where raw milk was not drunk.
Raw milk was linked to almost 8% of the notified cases.
There was a peak in cases among children from both rural and urban homes.
Among the raw milk cases 17% were rural children and 8% were urban children. Two-thirds of raw milk cases were urban.
Campylobacter is far from the worst bacteria that can be contracted through raw milk consumption. However, it is the most commonly contracted, typically resulting in stomach cramps, diarrhoea and vomiting.
The findings indicate raw milk cases are more likely to be associated with outbreaks of campylobacter than non-raw milk cases .
As a medium raw milk provides an ideal culture for the likes of campylobacter bacteria as a good food source, in an environment naturally close to the livestock source.
Previous Primary Industries Ministry studies have found almost two-thirds of dairy farmers drink raw milk but there are also a number of associated factors that could influence the rate of disease among rural children.
“There has not been a lot of work done but it appears milk consumption may decline with age so children might be drinking more. Children may also be more susceptible to raw milk associated disease organisms in general,” Massey University masters researcher Genevieve Davys said.
The seasonal potential for cows to shed campylobacter bacteria cells in greater numbers at certain times of year can also come into play.
“It could be they are shedding more bacteria at a time when milk production is starting to increase after calving, often when contact with cattle is starting to increase on a daily basis.”
There is also some evidence exposure to campylobacter can deliver a level of resistance that fades after weeks or months.
In rural families who drink milk from the farm dairy during the season then switch to pasteurised purchased milk over the dry period that resistance might fade, leaving them more at risk in a higher danger period when they start using farm milk again.
“So you have a bit of a double header there, with increased bacteria shedding and a lift in consumption of the farm-sourced milk.”
Davys said the survey held some surprises about the reasons people choose to drink raw milk.
Overseas work has shown a desire to support local farmers, a belief in better animal welfare and for perceived health reasons.
However, in the study there was no strong consensus among raw milk cases about their motivation for choosing the product. The most common motivation reported was for health reasons but it was only in about a third of the cases. Other popular reasons were taste and convenience.
Davys said it would have been interesting to also better understand what the behaviour change was, if any, in people who drank raw milk and became sick.
While not intending to take the work any further herself, Davys said there were some interesting areas researchers might want to examine in the future.
They include a better understanding of the spatial link between raw milk supply points and disease outbreaks. Further exploration of data from the sequence typing of the campylobacter organisms isolated could determine if there is a statistical difference between the types seen in raw milk cases compared to general campylobacteriosis cases.
In terms of advice gleaned from the work, Davys said she would not choose to drink raw milk knowing the types of infections that can come from it, of which campylobacter is only one.
“So you need to be aware, if you do choose it there is a higher risk of becoming sick and children are most at risk.”
