Kiwi science: how to trace a gastro outbreak

The pathogen campylobacter was singled out as the cause of the Havelock North gastro outbreak, which affected around 5500 people and prompted protests and a public inquiry. Photo / File

Scientists have suggested a better way to reveal the source of outbreaks like that which hit a third of Havelock North's population in 2016.

The pathogen campylobacter, which causes the gastrointestinal infection campylobacteriosis, is the most frequently notified enteric disease in New Zealand, and remains a burden upon the public health system.

It was singled out as the cause of the Havelock North gastro outbreak, which affected around 5500 people and prompted a public inquiry.

While infection rates had dramatically dropped over recent years, partly thanks to guidance from statistical models, New Zealand's figures were still high by international standards.

Massey University PhD student Jing Liao said before control measures could be put in place, it was crucial to understand the source of infection – whether that was contaminated water, under-cooked animal food products, or food products tainted with animal faeces.

The highest risk factors, she explained, could be revealed by modelling potential sources and pathways of infection.

A notable example was models which, a decade ago, turned up high rates of campylobacteriosis cases attributable to poultry.

That allowed authorities and the poultry industry to intervene with measures such as improving slaughter and processing.

Today, scientists used a range of complex genetic models to help distinguish between different animal sources of human infection.

But it had remained unclear whether these were any more effective than simpler models – or whether any of the models could be improved to include risk factor information on individual human cases.

"Simpler non-genetic models can help to test model assumptions that underpin the more complex genetic models, but they may not perform well under certain conditions."

A new comparison of genetic and "non-genetic" models, led by Liao, found the simpler one proved just as efficient at pin-pointing the source of common human strains of campylobacter, but didn't perform as well for rare strains.

However, she said, if the majority of infections were caused by highly observed strains, the simpler model might be fit for purpose, and also had the advantage of being quicker to implement.

Liao's study also threw up some interesting differences between people living in her focus area, Manawatu.

Those living in largely rural areas were much more likely to get campylobacteriosis from mammals, while poultry was the main source of infection in urban areas.

Liao said the research was promising, but there are more areas to explore.

She was interested in widening models to incorporate other factors like age, occupation, and contact with animals.

"Another direction is in expanding the role of water," she said.

"Characterising the source of campylobacter found in water has important implications for both water quality and public health."