“I’ve never been so sick in my life” was a phrase heard often in PHF Science’s investigation into yersiniosis, an illness that can cause diarrhoea, vomiting and stabbing abdominal pain so severe it was described as a “knock you off your feet type of pain”.
The PHF Science study confirmed that fresh, unprocessed pork meat was an important source of the bacterium that causes yersiniosis, strengthening a concurrent New Zealand Food Safety (NZFS) survey to assess its prevalence at processing plants. While the link between fresh pork and yersiniosis wasn't surprising, robust scientific evidence was needed to strengthen collaboration with the pork industry to understand rising infection rates.
Yersiniosis is the second most-notified bacterial gastrointestinal disease in Aotearoa New Zealand, with infection rates tripling between 2010 and 2021 (see PHF Science’s Notifiable Diseases Dashboard and select Yersiniosis for New Zealand rates).
“New Zealand has very high rates compared to those reported for many other countries, including the US and Europe,” says Dr Lucia Rivas, PHF Science’s yersiniosis research lead.
Interviews from study participants with yersiniosis showed that infections lasted 18 days on average but with some lasting as long as two months. The burden on New Zealand’s healthcare system and the economic impact are significant. One-quarter of the people interviewed reported to hospital, with one in six admitted. Some were hospitalised as long as ten days. One parent reported taking up to a month off work to care for their young child suffering diarrhoea.
PHF Science secured funding from the Health Research Council to determine the risk factors and sources of yersinosis, then partnered with public health services in Canterbury and Wellington, who made the research possible.
“We had been concerned for some time about the high rates of yersiniosis in our region,” says Dr Cheryl Brunton, medical officer of health with the National Public Health Service – Waitaha. “In-depth evidence-gathering like this study is invaluable in helping to confirm sources of infection and develop future public health action.”
PHF Science staff were seconded to public health services, giving them the authority to run phone interviews with yersiniosis patients about what they’d been exposed to, prior to getting sick. People who hadn’t been ill were also surveyed. This identified fresh pork as the biggest risk factor for yersiniosis.
PHF Science’s detective work then extended to supermarkets, with researchers collecting food samples to test. When the bacterium that causes yersiniosis was found, whole genome sequencing identified genetic matches that linked the bacteria found in food to patients’ infections.
“By linking yersiniosis cases with the consumption of pork and by enabling genetic comparisons between samples from different origins, PHF Science’s findings have helped NZFS confirm that pigs and pork play a leading part in the epidemiology of this complex pathogen, and supported our ongoing work with pork industry,” says New Zealand Food Safety deputy director-general Vincent Arbuckle.
The research also identified some good news about antibiotic use. Current treatment guidelines were being followed by most doctors, and there are low levels of antibiotic resistance here.
“People are being given the antibiotic that they should be given, and we don't have any major concerns on the antimicrobial resistance front at this stage,” says Dr Rivas, although ongoing surveillance is critical.
Rates of yersiniosis aren’t evenly distributed, and PHF Science’s work identified New Zealand’s Asian populations as being at particularly high risk. The study also investigated lower reporting rates and higher hospitalisation rates among Māori by interviewing general practitioners and Māori health experts about the experience Māori have when they present at a general practitioners’ office with gastroenteritis. From these findings, several recommendations were made to help reduce health inequities.
PHF Science, in partnership with kaupapa Māori health provider Te Toi Ora ki Whāingaroa, is now undertaking hapū focus groups in Waikato.
“Communities are being asked, ‘If you get gastro, what happens, can you access a doctor?’,” says Dr Rivas.
The Te Niwha-funded project will compile a community narrative about the barriers Māori communities face when confronted with gastroenteritis.
This PHF Science study shows the power of collecting valuable information from those experiencing yersiniosis to enable the identification of a food source.
Innovative solutions are needed to more quickly collect risk factor information from more people experiencing gastroenteritis to support the important work of New Zealand’s public health services. This information would accelerate outbreak investigations as well as help find new ways to prevent future illness.