This page links to a report by ESR detailing the results of sampling of shellfish on reefs off Waitara, of effluent from the Waitara outfall, and of water from the Waitara River.
The study was commissioned by the New Plymouth District Council at the request of the Taranaki District Health Board, through the Taranaki Regional Council, as part of efforts to ensure comprehensive information is available ahead of a hearing on a renewal of the Waitara Wastewater Treatment Plant consents.
Samples were taken on 10 August and 24 August, and tested for a range of viruses. The detailed results are available below. Of four samples taken from shellfish on the Tuaranga and Airedale reefs, human norovirus virus was found in low concentrations in three and moderate concentrations in one. A further eight samples were taken from the nearby Epiha Reef and on water in the Waitara River. On these, human norovirus was not found.
The following points should be noted:
It's usual to find viruses in shellfish throughout New Zealand
While shellfish aren't routinely tested for viruses (see below), there have been a number of long-term studies involving samples taken from a variety of locations around New Zealand. They all show that you can expect the possibility of viruses and bacteria in the coastal environment off any town in New Zealand.
Sampling in the Bay of Islands, for example, detected widespread viruses, with no correlation with sewage outfalls or overflow events, other than for major discharge events. In another study of 28 sites throughout New Zealand, half of all shellfish samples contained viruses and every site except two showed viruses at some time.
And a joint agency report last year noted that a 12-month survey of Tauranga Harbour and Waihi Estuary routinely found regular contamination, with regular contamination at the two sites closest to the urban centres - but not necessarily closest to identified sewage discharge points.
This report endorsed NZ Food Safety Authority advice not to collect shellfish near urban centres because of the impacts of stormwater and sewage-related contamination. The advice in the box below is from the NZFSA Foodsmart website. Click on the logos to go to the website.
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What about areas that don’t have warning signs?Areas without warning signs are not always safe for gathering shellfish. You should avoid collecting and eating shellfish from areas where:
Do not collect shellfish after heavy rain as storms may flush sewage overflow or farm run-off downstream which contaminates the water. After the water has run clear for a few days shellfish should be safe to collect again.
Source: http://www.foodsmart.govt.nz/food-safety/hunting-collecting-fishing/seafood-gatherers/ |
This is not the discovery of a new risk
As noted above, there is the possibility that viruses are present in shellfish near any coastal community. What is new is that we now have actual numbers from analysis.
Virus numbers and concentrations are relatively low
The ESR report notes the low level of viruses in the outfall effluent, and generally low in the shellfish from two reefs, apart from moderate levels in one sample. Virus concentrations are in the lowest two of four categories used by ESR. However, the limited number of samples taken at Waitara should be noted. Virus numbers will vary. The New Plymouth District Council is continuing its investigation to improve our information.
Little risk to swimmers
The detection of viruses in shellfish does not change the risk profile for swimmers. Shellfish concentrate virus levels several hundreds of times over; it is recognised that the risk to swimmers is much lower than to gatherers of shellfish from the same waters.
If the virus is in the shellfish, it's in the community
If human entero-viruses are in shellfish, it's because they are already present in the local community. They can be spread in a number of ways, for example when people exchange coins or handshakes, eat ice cream or potato salad, cough and sneeze, or meet with neighbours and friends. Eating raw or under-cooked shellfish is only one of many ways you might be exposed to viruses. The Waitara shellfish survey will help identify how significant this particular exposure pathway is.
The norovirus could have got to the shellfish via a number of paths
Potential routes include either intermittent or ongoing discharges, from boats, the outfall, leaking or overflowing septic tanks, or leaking or overflowing sewer systems, or stormwater discharges. Because viruses can survive for months in the sea and in shellfish, they can be transported for many kilometres from the source.
Waitara hasn't had an outbreak of shellfish-related disease
The Taranaki District Health Board, has noted that there have been a number of documented outbreaks of shellfish/waterborne virus disease episodes in New Zealand but there have been no such known outbreaks in Waitara.
Shellfish aren't routinely tested for viruses
The Waitara survey was carried out to ensure that information is comprehensive and current. Virus testing is relatively rare in New Zealand because it is costly, time-consuming and technically difficult. There are no routine ongoing virus testing programmes of seawaters/shellfish reefs in NZ that the TRC is aware of. However, New Plymouth District Council will continue further investigations off Waitara.
Links:
ESR Report: Summary and interpretation of virology results for Waitara River sampling programme (24 KB)
Media release on Waitara shellfish advisory
Advice to seafood gatherers (Foodsmart/NZFSA)
Reference material:
Microbiological Quality of Shellfish in Estuarine Areas - Joint Agency Research Report 2009 (Bay of Plenty Regional Council, NZ Food Safety Authority, Tauranga City Council, Bay of Plenty District Health Board Public Health Service, Western Bay of Plenty District Council, ESR, Bay of Plenty District Health Board)
Envirolink Project No. 162 NLRC 20. Report: NLRC Shellfish safety following sewage spills (Dr Gail E Greening, ESR)