A rapid antigen test. Photo / File
Doctors are urging people with Covid symptoms to keep testing even after multiple negative RAT results - and one specialist says the tests are just 60 to 80 per cent accurate.
The Ministry of Health says there have been reports of symptomatic people testing negative for Covid-19 in their initial test but later returning a positive test.
Dr Daniel McIntosh, of Mount Maunganui's Dee St Medical Centre, said if he was asked a month ago if there was a cold virus going around that wasn't Covid, he would have said yes.
He was testing constantly what he thought was Covid only to get negative results.
There were always viruses that caused cold symptoms, but there had been a "huge" number of Covid notifications recently.
He said the clinic was seeing patients with Covid symptoms testing negative on RATs which might not always pick up Covid because it depended on viral loads.
He said there was a lag between initially getting symptoms and getting a positive test, and he told patients to test again in two days.
"It shouldn't be a concern because you should be isolating if you've got symptoms regardless of if you've got a positive reading or not."
Three Lakes Clinic GP Dr Cate Mills, in Rotorua, said people were becoming "hypersensitive" to symptoms and "more aware of their bodily signals" - which was a good thing.
Mills said people were now more vigilant and testing mild symptoms they wouldn't previously remark on, and "certainly wouldn't go to a doctor about".
This included a bit of sore or tickly throat, voice hoarseness, or any feelings of hotness - symptoms people previously went to work with.
She said Covid cases could be found when people were more in tune with their symptoms and got tested.
She said there did not appear to be another virus in the community causing similar symptoms to Covid.
However, she had seen people who were sick with similar symptoms to Covid and had repeatedly tested negative until they were better.
She said these patients looked "very similar" to the Covid cases she was seeing at the clinic.
She said she has had patients test negative five or six times on a RAT before testing positive.
"We're repeatedly testing people because our feeling at the moment is that it's more likely to be Covid than anything else."
Western Bay of Plenty Public Health Organisation clinical adviser and Mount Medical Centre GP Dr James Peckett said RATs "are not perfect", estimating they are between 60 and 80 per cent accurate on symptomatic people.
RATs looked for proteins, or antigens, that were found on the surface of the Covid virus only during an active infection, he explained.
He said the PCR testing technology amplified even small amounts of viral genetic material which picked up the virus with those infected as well as recovered.
Although less accurate, he said RATs needed to be used more often to relieve pressure on the PCR testing system as these tests were processed in a lab.
He said it was not uncommon for someone with Covid-19 to return a negative test on the first few days of their illness, then test positive on day 3.
He said symptoms must be assumed to be related to a Covid infection, even with a negative test.
A Ministry of Health spokesman said there had been reports of symptomatic people testing negative for Covid-19 in their initial test but later returning a positive test.
The 20-minute rapid antigen test results - although faster than the two to five day PCRs – were less sensitive because they needed more of the virus to trigger a positive result.
This meant a false negative was more likely.
RATs had been distributed around the country and were now the primary form of testing.
The ministry advised anyone with symptoms who tested negative stayed at home until they were well and retest after 24 hours if the symptoms continued or worsened.
The spokesman said while a cold and influenza virus was circulating as it always did, it was believed to be lower than usual at this time of year given the use of masks, social distancing, and restrictions on the size of events.
He said people with cold or flu-like symptoms should get tested, and masks, physical distancing and good hand hygiene were still important.
"The Ministry of Health and ESR continue to only approve tests that meet a very high threshold for quality to reduce the number of false positives and negatives."
ESR is New Zealand's Crown Research Institute that specialises in science relating to people and communities.
Step 1: Take the swab and insert it back into a nostril by 2cm to 3cm. Be sure to insert it backwards and not upwards. Then swirl the swab inside the nostril for 15 seconds. Repeat in the other nostril.
Step 2: Put the swab into the vial of solution and rotate it at least five times. While removing the swab, squeeze the sides of the vial to release the liquid.
Step 3: Using the vial, put three drops into the testing well and wait for the time specified per kit instructions. This could be up to 15 minutes.