A false-positive test result that caused a measles scare in Waikato likely picked up a child’s own vaccination, health authorities say. Illustration / Paul Slater
A false-positive test result that caused a measles scare in Waikato likely picked up a child’s own vaccination, health authorities say. Illustration / Paul Slater
A “false-positive” test result that caused a measles scare in Waikato likely detected a child’s vaccination rather than the fast-spreading virus, health authorities say.
But Te Whatu Ora has justified alerting the public to a “confirmed” measles case - and a second suspected case - on Sunday, saying it doesn’t wait for thorough testing before warning the community of possible infections.
On Monday, officials announced further testing showed that neither of the cases – both young children – were infected.
Asked to explain, Te Whatu Ora said initial PCR testing – a lab process also used to confirm Covid-19 infections – initially returned a positive result from one of the children.
Dr Susan Jack, the National Public Health Service’s national clinical director for protection, said a positive PCR result could be due to picking up a “wild-type” measles virus - a strain that naturally occurs in the environment.
The other possibility was that it reflected that person having been vaccinated – and the only way to tell was through a further kind of testing called genotyping.
“The result of this genotyping testing showed that the positive PCR result was consistent with the child having been vaccinated,” Jack said.
“This means it is not a measles case and there is no risk of measles transmission.”
Jack said that until genotyping results were available, anyone with a positive PCR result for measles was managed as a measles case.
About a third of people with measles, which affected adults as well as children and babies, could be sick enough to need hospital care – and one in 1000 could die. Photo / Rob Dixon, RNZ
The Herald asked whether Te Whatu Ora should have carried out this further testing before notifying the public.
Jack said public health teams had to take any suspected case of measles “very seriously”.
“Once the initial testing results were made available the National Public Health Service responded rapidly and took appropriate actions to ensure close contacts were identified and people in the local community were notified of their potential increase in risk,” she said.
“The fact that further testing indicates the child does not have infectious measles after all, does not diminish the importance and the effectiveness of the actions undertaken by our public health officials.”
About one-third of people with measles, which affected adults as well as children and babies, could be sick enough to need hospital care – and one in 1000 could die.
Among the unvaccinated, just one case of measles could spread to 16 to 18 others, she said, and New Zealand’s overall vaccination rates were too low to prevent outbreaks.
“This means we need to respond very rapidly to every measles case to prevent a widespread outbreak,” she said.
“We do not wait until genotyping results are available.”
Jamie Morton is a specialist in science and environmental reporting. He joined the Herald in 2011 and writes about everything from conservation and climate change to natural hazards and new technology.
