28 Jan 2022

Warning labs can only cope with peak PCR test demand for up to a fortnight

7:35 pm on 28 January 2022

Covid-19 testing laboratories can only cope with peak demand for nasal PCR Covid tests for a couple of weeks before the system will be overloaded.

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Photo: supplied

Tens of thousands of cases of Omicron are expected each day as the outbreak ramps up, peaking at up to 80,000 daily.

Dr Juliet Elvy is a consultant clinical microbiologist with Asia Pacific Health Group - the country's largest provider of Covid-19 testing.

She told Nine to Noon labs can go onto surge staffing and get people working in shifts for about two weeks, but it is only a short term solution.

Ministry of Health figures indicate that New Zealand labs are currently running about 20,000 tests per day, she said.

She said the baseline capacity for PCR tests is for 60,000 tests across the country each day, but she said that includes a pooling strategy used by laboratories.

Dr Elvy said laboratories use different pooling ratios but five samples is a common one.

"So this is taking five tests from five different people and instead of testing them all individually, they're pooled into one test tube and just run once as a combined test."

If the pooled test returns a negative result then it is possible to say each of those five people have a negative result, she said.

When the pooled test returns a positive result, then each of the five samples must be tested again individually to identify which of the cases returned the positive result, she said.

But Dr Elvy said once there are a lot of cases and a high positivity rate pooling samples is not viable because too many of the pooled samples need to be retested.

"Ironically whilst we're in the thick of it our actual capacity will drop because we're obviously heavily relying on the pooling strategy to meet that 60,000 tests a day."

Dr Elvy said without pooling samples laboratories are reporting they would be able to do about 30,000 PCR tests per day nationwide with a surge capacity of up to 80,000 tests per day.

But she warned that higher surge capacity level of testing could only be sustained for a week or two.

"That's where we're really you know pulling out all the stops, getting people in to help with the testing that normally wouldn't be part of our molecular teams and putting on multiple shifts etc."

Change in thinking over when to get tested needed

Dr Elvy said laboratories will not be involved in assessing rapid antigen tests (RAT) which are designed to be done at home or a health care facility.

She said laboratories will need to work closely with the Health Ministry to ensure the right people are getting PCR tests.

"What we need to consider is what groups should have ring-fenced access to the more accurate PCR tests."

She said one example could be critical workers who have tested positive using a RAT test, which can be less accurate than a PCR test.

"We just want to confirm that's a true positive with the PCR before we stand them off work, for example."

She said there will be a list of those who qualify for a PCR "to make sure laboratories are in line with what we envisage is the best usage of what will be quite a precious resource".

Dr Elvy said it would be great to test everybody who wanted to be tested for Covid-19 but that is not realistic due to availability of both PCR and RAT tests.

She said that is going to mean a shift in thinking and pulling back on blanket testing.

"So even with the rapid antigen tests we also need to be careful about their usage because we don't want to be using them on a sort of 'nice to know' basis, we need to be using them in a context that actually leads to a specific action or outcome for that individual getting the test."

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