by Jacek Dylag, Unsplash

Learning from the world’s largest recorded campylobacter outbreak

EIT: Havelock North experienced one of the largest recorded campylobacter outbreaks in August 2016 due to contamination of the town’s untreated, reticulated bore water supply, following a heavy rainfall event.

Campylobacter is a gastroenteritis infection which usually spreads to humans through the consumption of contaminated food.

‘The Havelock North outbreak is really significant. If we look at studies of other outbreaks worldwide, cases are usually in the hundreds, the closest was Finland with about 2,000 cases. At the time of the Havelock North outbreak, about 5,000 cases were reported, but after further research cases were estimated at nearly 8,000,’ explains Research Programme Manager and Senior Academic from the Eastern Institute of Technology (EIT), Dr Anita Jagroop-Dearing.

A year after the event, the Health Research Council of New Zealand invested almost $450,000 in a research programme of six studies to investigate the outbreak and develop recommendations to minimise both the likelihood and impact of future outbreaks.

Hawkes Bay District Health Board (HBDHB) led the programme of research along with the University of Otago’s Department of Public Health in Wellington. Investigators included doctors and scientists from the Institute of Environmental Science Research, HBDHB and Massey University. Jagroop-Dearing collaborated with the study leads and managed the programme of research.

The focus of this article is the first study, where EIT’s Anita Jagroop-Dearing was a co-author, and Brent Gilpin from Environmental Science Laboratory, the principal author. The aim of the study was to summarise what happened, to determine the extent of the outbreak and explain why it occurred. The goal was to identify current levels of preparedness in case of a repeat outbreak, and to prevent a large-scale outbreak like this from happening again. An important aspect of this research included tracing, isolating and identifying the campylobacter bacteria using a technique called Whole Genome Sequencing (WGS).

In the first phase of the research, environmental and geographical data was collated to produce an accurate picture of what led to the flooding that culminated in the outbreak.

‘It was a perfect storm,’ explains Jagroop-Dearing as she describes the physical factors impacting on the outbreak.

Heavy rainfall that continued over two days, resulted in flooding, effecting the town’s low-lying underground water bores and nearby sheep paddocks. It was later confirmed that the town’s reticulated water supply was contaminated by sheep faeces harbouring campylobacter. The first cases were identified at an aged residential care facility. As school absenteeism increased, an outbreak was officially declared. The water supply was sampled for campylobacter before being chlorinated.

In the second phase of the research, epidemiological investigations were undertaken to determine the total number of infections during the outbreak. This was achieved in two ways. Campylobacter is a notifiable disease, so data could be accessed retrospectively from the national notifiable disease database. These cases included probable and confirmed cases within the outbreak period.

Additionally, probable case data was collected during the outbreak via a cross-sectional study of Havelock North residents. This was used to estimate the proportion of households and residents effected by the outbreak. The survey was conducted by telephone, and 660 households were included.

The final phase of the research was a microbiological investigation where samples collected from three different sources during the outbreak were assessed. These included human faecal samples, water specimens from across the network, and faecal samples from sheep in paddocks close to the water bores. Campylobacter bacteria was isolated from all the samples using a novel real-time Whole Genome Sequencing technique (WGS).


Results from the epidemiological research showed 225 confirmed and 728 probable cases. Of the 953 campylobacteriosis cases notified by clinicians, 763 lived within the Havelock North reticulated water zone.

The highest rates were observed in those over 60 years of age. Four deaths occurred in confirmed cases in those over 70 years of age.

‘The risk of a Havelock North resident becoming a notified case was nearly 30 times greater than for residents of other Hawke’s Bay towns.

‘Usually, campylobacter infections are higher in children under five, in males and in those between 20 and 29. The demographic data was of statistical significance here considering the disproportionately higher case numbers for the those over 60. This can be attributed to underlying susceptibility in this age group, and the use of active case finding targeted to older residents,’ says Jagroop-Dearing.

The household telephone survey estimated that just over one third of residents and over a half of households developed symptoms of gastroenteritis. Based on this, it was estimated that 5,540 infections had occurred in the approximately 14,118 Havelock North residents. Extending this to include those living outside of Havelock North, the research indicated 7,570 illnesses linked to the outbreak.

Results from the microbiological research indicated that all four reticulated water samples and one of the bore water samples were positive for campylobacter jejuni. The same species of campylobacter was also isolated from the sheep faecal samples. Over 90% of the isolates had the same genotype.

‘WGS was valuable as a supplement to the epidemiologic investigation because it could separate outbreak-linked and unlinked cases, confirm the suspected exposure period, identify the likely source and mechanism of contamination, and define the geographical scope of the outbreak.

‘It is the same technique used to trace, or identify new strains of, COVID-19. The use of it in relation to the Havelock North outbreak confirms that you can identify cases in real time, and it was crucial to defining the source of the outbreak,’ explains Jagroop-Dearing.

The combined results of the research demonstrated the extent of the outbreak and detailed how it occurred. The estimated total of between 6,260 and 8,320 cases was the largest ever reported Campylobacter outbreak worldwide.

The research drew attention to system failures which can have significant repercussions during extreme environmental events. A governmental inquiry into the outbreak recommended a significant reorganisation of drinking water management in New Zealand. Specifically, that all drinking water supplies, including groundwater, should be treated, and routinely tested to reduce the risk of contamination within the supply network.

The research won best presentation when Jagroop-Dearing presented in May 2020 at the World Academy of Scientific and Engineering Conference in London. The results of this study have been published, with the five remaining studies at various stages of publication.

  • Research was undertaken in collaboration with study leads from Hawkes Bay DHB - Bridget Wilson, Tim Frendin, Colin Hutchinson; Environmental Science Research - Brent Gilpin, Tiffany Walker, Jill Sherwood, Claire Newbern, Menhaz Adnan; Massey University - Jonathan Marshall; Hawkes Bay DHB - Nicholas Jones (Programme Director); Otago University - Michael Baker (Programme Director); and Eastern Institute of Technology - Dr Anita Jagroop-Dearing (Research Programme Manager/Collaborator).

  • 'A large scale waterborne Campylobacteriosis outbreak, Havelock North, New Zealand,' by Brent J. Gilpin, Tiffany Walker, Shevaun Paine, Anita Jagroop, Rachel Eyre, Michael G. Baker, Nicholas Jones et. al. in Journal of Infection, 81 (2020), p390-395, published online 28 June 2020.

  • Dr Anita Jagroop-Dearing migrated to New Zealand after more than 20 years of medical research and academic success as a Senior Scientist at the major teaching hospital, University College London Hospital (Royal Free Campus, London) in the U.K. Her research interests are in the field of Medical Health and Wellbeing. Anita currently works as a Senior Academic at EIT, where she is the Chair of the Health Research Committee. She is the International Postgraduate Programme Coordinator in Health Science, and a Senior Lecturer. She also sits on the EIT Strategic Research Committee and holds a range of professional memberships.
    Anita is a member of Research Futures: Health and Wellbeing Working Group across Te Pūkenga network. Contact Dr Anita Jagroop-Dearing.

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