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Swabbing your throat before your nose could help catch Omicron earlier, but New Zealand's test kits weren't designed with that in mind. Photo: Jonathan Milne

Marc Daalder is a senior political reporter based in Wellington who covers Covid-19, climate change, energy, technology and violent extremism. Twitter: @marcdaalder.

Experts are divided on whether swabbing your throat before your nose might improve your chances of detecting Omicron with an at-home test, Marc Daalder reports

More than 4 percent of the country is now considered an active case, but there are fears rapid tests are missing the early stages of infection, further fuelling the spread of the virus.

Social media is awash with anecdotes of people with Covid-19 symptoms testing negative again and again on rapid antigen tests (RATs). Some experts think it could be user error - people may be swabbing themselves wrong and making the process more painful than it needs to be besides.

Eric Levi is an ear, nose and throat surgeon based in Melbourne whose instructional videos on self-swabbing have gone viral.

"A lot of us are just swabbing the front part of the nose, which is the dry, skin, hairy part of the nose, when what we want is actually the deeper part of the nose that has the mucus," he told Newsroom. "That was one of the big triggers for me coming up with that video, to say, look, if you swab it properly and you go low and you go slow, it is not painful. If you rest it there and twirl it for 15 seconds, you are probably likely to catch a good sample."

But others are looking at the Omicron variant's tendency to make itself known in the mouth and throat before it hits the nose. In the United States, where Omicron ran rampant in December and January, New Zealand microbiologist Anne Wyllie spotted a tendency for saliva PCR tests her non-profit ran to come back positive while nasal swabs returned negative results.

"This is what we saw in December in New York is that people could be screaming hot positive on their saliva PCR test but negative for days by both nasal antigen tests and nasal PCR tests," she told Newsroom. "It was a crazy thing to be witnessing, especially when the US was, much like New Zealand at the moment, relying so heavily on antigen tests."

University of Auckland microbiologist Siouxsie Wiles said early studies indicated that Omicron shows up in saliva in the mouth before mucus in the nose - the inverse of some previous variants.

"We know that the tissue tropism has changed from lab studies that have been done. There's been a few things looking at what kind of cells they like and that has clearly changed a bit," she told Newsroom.

"There was this really important study from South Africa that took paired samples from people - a saliva sample and a nasal sample - and then ran them both through PCR. They did this for people who had Delta and they did this for people who had Omicron."

All of the nasal samples for the Delta cases came back positive, compared to just 71 percent of the saliva samples. For Omicron, it was the opposite, with 86 percent of nasal samples returning a positive result but all of the saliva samples testing positive.

Wyllie and three other researchers found similar results in their own study of a small number of people who tested positive for Omicron with a saliva PCR test and who then undertook regular rapid test monitoring.

All seven of those who took a rapid test the same day (Day 0) as their saliva sample got a false negative. The next day, eight of the now-confirmed cases took RATs, all of which came back negative. Just two of eight tests carried out on Day 2 of the infection returned positive results. From Day 3, almost all of the RATs lit up positive.

Neither of these studies has yet been peer reviewed, but they flag a trend that's also backed up by a lot of anecdotes from all around the world, including increasingly in New Zealand. Symptomatic people who swab their throat and then their nose for a RAT are getting positive results when their nasal tests alone report a false negative.

Two of Newsroom's own journalists have found this to be the case as well. National affairs editor Sam Sachdeva tested negative on a nasal RAT, then got a faint positive on a throat and nasal swab. A second combined test the next morning returned a very strong positive result - much stronger than the solely nasal one he ran later that afternoon.

Political editor Jo Moir got a negative result on a nasal swab on Tuesday evening (and had a negative RAT the previous morning as well). Just 12 hours later, a throat and nasal swab returned a clear positive.

Both were symptomatic when they got their false negative results.

Wyllie told Newsroom that New Zealand was seeing a continuation of the trend from overseas.

"We went through this sort of thing in December, January, ourselves over here where, indeed, people started hacking the tests, doing their throat swabs and getting the positives."

It's worth noting here that the RATs authorised for use in New Zealand were only designed with nasal samples in mind. They also have only been authorised for use with nasal samples by the Government, putting officials and experts into a tough position about what to do.

"If the Government hasn't approved the nasal swab for throat swabs, we in medicine can't really ask people to do a test in a way it wasn't designed for," Levi said.

"What do you do in the interest of public health, in the end? There were a number of people in the end who did speak out, in the US at least. Saying: 'If this is going to give you a positive earlier, yes they're not labelled this way or tested this way, but if you're going to find out earlier and not think you're negative and go on and infect other people, at what stage do you say, hey, you should consider trying this so we can at least slow the spread a bit?'

"That or at least have really clear messaging that, if you've been exposed, if you have typical symptoms, even if you are testing negative, treat yourself as positive, continue to isolate and test again a couple of days later."

She added that there were a few key things to keep in mind if you want to try the throat swab.

"If people are looking to hack these tests, the recommendations are to make sure you haven't eaten or drunk anything for half an hour beforehand to make sure that you're not going to get a weird pH effect. I hacked the test a couple of times myself and what I looked at was the NHS guidance for the UK. They show you don't need to go all the way back, down the throat or into the hole at the back, just even swabbing to each of the sides and then swab around a couple of times and then swab the nose is sufficient."

Jo Pugh, the Ministry of Health's acting group manager for testing and supply, told Newsroom in a statement that nasal swabs are good enough.

"Our current advice for RATs is to follow the manufacturer’s instructions and that nasal swabs are sufficient for their current purpose," she said. "The more testing technologies and innovations we have the better to fight against Covid-19 but we have to make sure they are safe and effective as part of the overall testing regime in a New Zealand setting."

Director-General of Health Ashley Bloomfield was asked about the issue on Thursday and suggested it would be okay to swab your throat.

"The main thing is that people follow the instructions of the manufacturer for that specific test, but if people are swabbing both throat and nose, there's nothing necessarily wrong or bad about doing that," he said. "I would encourage people to follow the instructions but certainly swabbing the nose is most important."

Levi said there also might be a safety issue. Some test kits come with short swabs designed only for the nose.

"When you have a short swab, you won't be able to reach the back of the throat easily. You might end up swallowing it as well," he said.

"None of these tests are natural activities that we do, right? As long as there is good education technique and the right test, you're going to be okay. But I think that is the key, the education part and the right test for the right anatomy."

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