Foodborne campylobacteriosis is the most common notifiable infectious intestinal disease in New Zealand. The Source Assigned Campylobacteriosis in New Zealand Study (SACNZS) was designed to give up-to-date information on how New Zealanders become infected with the Campylobacter bacterium and how we may best move forward.
The year-long study was commissioned by New Zealand Food Safety, approved by the Health and Disabilities Ethics Committee and carried out in 2018-19.
The SACNZ studied people living in Auckland and Manawatu and Whanganui. The study also considered the source of the bacteria so that we could better understand the pathways whereby people get infected.
There are a number of possible sources of Campylobacter and they fit in to a wider framework comprising:
The study used a case-control comparison approach, with researchers interviewing people who had been diagnosed as being infected with the bacteria as well as people who had not had symptoms of the illness.
A total of 666 people who had become ill (cases) were interviewed. These interviews were compared with similar interviews from 600 control subjects.
The study also used new scientific methods to look at the bacteria in-depth and determine their DNA sequence.
Using the samples of bacteria from people who were ill, scientists were able to identify the sequence of all the DNA in these bacteria.
Similarly, they took faeces from animals such as poultry, cattle and sheep in processing plants which were likely to be potential sources of the bacteria. By comparing the DNA, they were able to assess where the Campylobacter infection was likely to have originated.
It was estimated that the sources of the bacteria in the clinical cases of illness were as follows:
A correlation between the source of the bacteria and whether they were found in either rural or urban cases was strongly evident. The proportion of poultry source-assigned cases increased as the location of the cases became more urban. Poultry was likely to have been the source of around 90% of illnesses in urban-dwelling people, while poultry was the likely source in less than 75% of rural-dwelling people.
Poultry is the most commonly consumed meat type in New Zealand and more than 80% of people involved in the study as cases or controls had consumed poultry within the previous seven days. Specific risk factors associated with consumption of poultry were consumption of undercooked poultry, and consumption of poultry outside the home.
The findings of the study identified a number of significant risk factors for contracting campylobacteriosis. They were:
Taking into account the source attribution and specific risk factors for human campylobacteriosis, the study demonstrated that poultry meat remains the dominant pathway for exposure and infection in New Zealand, especially for urban dwellers.
To find out more about the study findings and what New Zealand Food Safety is doing to reduce the number of cases of campylobacteriosis related to food click: