An outbreak of gastroenteritis – likely caused by Campylobacter – has sent at least 20 people to hospital in Hawke’s Bay.
Hawke’s Bay District Health Board Medical Officer of Health Dr Nick Jones has said the majority of people presenting with the illness were affected by Campylobacter, a water-borne bacteria. Dr Jones has told media that animal faeces might have contaminated the water supply, possibly into the groundwater itself.
ESR has released a preliminary report on the possible source of the contamination.
The Science Media Centre gathered the following expert reaction.
NEW COMMENTS: Professor Jenny Webster-Brown, director, Waterways Centre for Freshwater Management, University of Canterbury, comments:
“Although Campylobacter is more commonly a food-borne bacteria, there have been previous occurrences of water-borne Campylobacter infection in New Zealand. There was one in Darfield in Canterbury in 2012, for example, when water being taken from the Waimakariri River for the town water supply (after a storm) was inadvertently not chlorinated. However, that outbreak involved far fewer cases than the Havelock outbreak.
“It is rarer to get Campylobacter in groundwater, than in river, stream or lake water, but it can persist in shallow groundwaters (and the Havelock North aquifer at 20m is relatively shallow).
“Campylobacter is one of the more common bacteria causing diarrhoea, as it is found in the digestive system of most warm-blooded animals, including stock (chickens, pigs, cattle etc) and pets. The likely source of the Havelock groundwater contamination will only be able to be identified once ESR has completed its testing.
“Daily water testing for the presence of sewage indicator bacteria (such as E. Coli) is normal for untreated water supplies, and can help identify such pathogenic contamination, but won’t entirely prevent its effects on a community. The nature of the testing is such that it is usually 24 hours before a result can be obtained, as an incubation time is required. This means that contaminated water can be released into a drinking water supply before the results are known.
“The only sure means of avoiding this type of drinking water contamination is to continuously chlorinate or otherwise disinfect the water supply. The only relatively safe, untreated drinking water would be from deep groundwater systems, and they may have other quality problems that require treatment, such as elevated arsenic or hydrogen sulphide concentrations.”
Expert Q&A with Michael Baker, Professor of Public Health, Department of Public Health, University of Otago:
1: What are the main causes of campylobacter contamination in groundwater?
“Infectious disease outbreaks linked to drinking water can occur in a number of ways. By far the most common contributing factors in New Zealand are use of untreated or inadequately treated water supplies.
“There can also be failures of treatment processes, source water that is more heavily contaminated than usual (eg following a flood) and contamination after treatment. The contributing factors operating in Havelock North will obviously need further investigation.”
2: Are there many communities that have untreated drinking water that might be vulnerable to such contamination?
“While most New Zealanders have drinking water supplies that are considered safe, some communities have untreated drinking water that is potentially vulnerable to contamination. About 15% of the population is not covered by registered community supplies so are particularly vulnerable.
“These are mainly small supplies covering just a few homes, schools or workplaces. Amongst the registered drinking water supplies, most (97%) comply with bacteriological standards (relevant for Campylobacter) but compliance is lower for protozoal standards (relevant for Giardia and Cryptosporidium which are the commonest causes of waterborne outbreaks).”
3: Is it possible to protect our drinking sources from contamination without treatment? Or for best public health outcomes should all drinking water be treated?
“Some water supplies are of very high quality, particularly ground water, so do not need routine treatment.”
4: Is there an overall trend of groundwater quality in NZ? Are such contaminations common, or becoming more/less so?
“There are some long-term data on waterborne outbreaks in NZ. There were 42 such outbreaks reported to ESR in 2014 including 131 identified cases. The most commonly identified pathogens were Giardia and Cryptosporidium followed by Campylobacter which accounted for almost 10% (4/42).
“Over the last 5 years in New Zealand (2010-14) there were typically about 50 reported waterborne outbreaks a year. Around 8 a year were caused by Campylobacter. Most were small, with an average of around 8 cases each.”
5: Other comments
“Waterborne outbreaks of this size are fortunately rare. It is vital that this outbreak is fully investigated to establish its source and contributing factors.
“This kind of event also shows the importance of having high quality surveillance systems to detect such outbreaks as early as possible so they can be stopped. Because Campylobacter infection has quite a long incubation period (up to 10 days) the number of cases caused by this outbreak may continue to increase for a few days.
“There may also be additional transmission in households, so infected people need to be careful not to pass the infection on to others.
“Campylobacter infection remains the highest impact food and waterborne disease in New Zealand. The major source is fresh raw chicken meat (60-90% of which is contaminated by Campylobacter).”
Previously gathered comments:
Professor Nigel French, director, Infectious Diseases Research Centre, Massey University, comments:
“Groundwater is much less likely to be contaminated than surface water, but if it is Campylobacter, based on previous experiences, it is most likely to have come from cattle and sheep and run-off of effluent/faeces.
“However, Campylobacter can also be carried by poultry and wild birds. There was a similar outbreak affecting a water supply in Darfield in 2012 (although this was a surface water supply and failure of chlorination and not a groundwater contamination). There have also been some similar, very serious, events internationally – the most infamous is the Walkerton outbreak in Canada in 2000.
“Most communities and most people are supplied by treated drinking water, but there are still a number that use untreated drinking water.
“I think this outbreak demonstrates that even secure groundwater can become contaminated (most likely with animal faeces), and therefore testing and treatment is advised to ensure the best public health outcomes, particularly if there has been a high-risk event, such as heavy rainfall.”
Dr Murray Close, groundwater specialist, Institute of Environmental Science and Research (ESR), responded to Prof French’s reference to the 2000 Walkerton outbreak:
“This outbreak was a combination of pathogenic E. coli and campylobacter and resulted from a combination of a recent source (cattle manure), rupture of the groundwater confining layer, heavy rainfall and a breakdown of the treatment process.
“A key aspect of whether Campylobacter from animal or bird faeces will enter groundwater is the presence of saturated conditions at the ground surface either from heavy rainfall, flooding or heavy irrigation such as flood irrigation.”