Ministry of Health Believes Waterborne Diseases Under-reported in New Zealand
19 January 2007
Research by one of New Zealand's leading microbiologists has confirmed the Ministry of Health's long-held belief that
the number of reported waterborne diseases is much higher than it appears.
Massey University's Stan Abbott was partly funded by the Ministry to carry out a study over a five year period, looking
at 560 water samples from private dwellings who drank roof-collected water.
Ministry of Health Principal Public Health Engineer Paul Prendergast says they were not surprised that more than half of
the 560 samples exceeded the minimal standards for contamination and 30 per cent showed evidence of heavy faecal
contamination.
"It's widely known that around 400,000 Kiwis rely on roof-collected rainwater systems. While the majority of New
Zealanders get good quality drinking-water, around 16% of people, mainly in small rural communities, get water that is
not safe to drink.
Mr Prendergast says New Zealand has high reported rates of disease that are potentially caused by contaminated water.
Research tells us that rates of sickness are higher in areas where people don't have access to safe drinking-water. It
is well known internationally that diarrhoea is a greatly under-reported disease in the developed world. The level of
reporting varies from place to place, but usually lies between 30 per cent and five per cent of actual cases. This also
applies in New Zealand. Often it is only when the disease progresses to a serious stage that it is reported.
He says Stan Abbott reached his conclusions by directly asking people who had contaminated roof water whether they had
experienced diarrhoea. Studies by ESR reached a similar conclusion, but these applied to a much wider range of sources
of drinking-water, not just to roof water. The notifiable disease data are harder to interpret than are the results of
direct questioning.
"The ESR studies showed that in New Zealand there are an average of 16.8 waterborne outbreaks each year. Luckily so far
these have usually been small, averaging 145 cases per year, although a single outbreak at Cardrona ski field earlier
this year caused well over 213 cases."
"The number of 'routine' cases (not due to outbreaks) of waterborne disease in New Zealand varies between 878 to 2,574
cases per 100,000 head of population", says Mr Prendergast.
The largest outbreak reported in New Zealand affected 3,500 people in Queenstown in 1984.
"The Ministry of Health is working towards ensuring all New Zealanders have access to safe drinking water. There is a
comprehensive work programme underway to achieve this."
Mr Prendergast says there are some simple steps people on roof-collected water supplies can do to minimise the risk of
contracting a water-borne illness.
"Good maintenance of roof-collected water supplies is essential and there is a range of devices such as 'first flush
diverters' to reduce contamination from roofs entering water tanks as well as treatment systems to kill bacteria and
diseases for individual homes. The Ministry of Health has also printed two publications which provides comprehensive
advice," Paul Prendergast says.
Links to these documents are below -
Household Water Supplies - http://www.healthed.govt.nz/uploads/docs/1777.pdf
Water Collection Tanks and Safe Household Water -
http://www.healthed.govt.nz/resources/watercollectiontanksandsafehouseho.aspx
ENDS