(file image). Photo: 123rf
Authors of a new study are warning that climate change could cause outbreaks of a diarrhoea-causing parasite to become more frequent.
Research from the University of Otago compared clusters of cryptosporidium cases in New Zealand between 1997 and 2015, and found a third coincided with severe weather.
One of the researchers, Professor Simon Hales from the University of Otago's Department of Public Health in Wellington, said heavy rain washes higher levels of the parasite into waterways, which could overwhelm drinking water.
"Cases and outbreaks of cryptosporidiosis, as well as other infectious intestinal diseases, are often caused by contamination of water supplies," he said.
The 2023 Queenstown outbreak, where more than 72 people got sick, was likely caused by water supplies becoming contaminated by human faeces.
Professor Simon Hales. Photo: Supplied/Luke Pilkinton-Ching
The study found 38 "statistically significant" clusters in its analysis, which it said were unlikely to have occurred by chance - and 13 of them aligned with heavy rain events.
In one instance, 55 cases occurred after heavy rain in Kaikōura in March 1999, and in October 2000, 22 cases followed a nationwide weather bomb of high winds, heavy rain and flooding.
Hales said as climate change increases the frequency of heavy rainfall, it could also increase the frequency of outbreaks.
The findings also indicated a link between outbreaks and livestock runoff.
Hales said newborn livestock was a known source of the parasite, and six of the 13 outbreaks occurring in heavy rainfall happened in the spring, during calving and lambing times.
"These outbreaks highlight the need to strengthen source protection for water supplies, and for a strong regulatory framework to prevent water being polluted by runoff from livestock farms," he said.
"Our findings show how important it is to protect our drinking water supply, and the places people swim, from contamination from agricultural runoff and sewage leaks from broken pipes."
