Colorized scanning electron micrograph of an apoptotic cell (green) heavily infected with SARS-COV-2 virus particles (orange), isolated from a patient sample. Image captured at the NIAID Integrated Research Facility (IRF) in Fort Detrick, Maryland. Credit: NIAID

Testing for SARS-CoV-2 in NZ – Expert Reaction

Testing for COVID-19: what’s the most effective method? What do we still need to learn? Do we have enough supplies?

The Science Media Centre held an online media briefing this week with University of Otago, Christchurch Professor David Murdoch on the ins and outs of testing for the SARS-CoV-2 virus.

The SMC asked experts to comment on the role of testing amidst the pandemic, and we have included an abbreviated version of our conversation with Professor Murdoch as well.

Dr Amanda Kvalsvig, Senior Research Fellow, Department of Public Health, University of Otago, Wellington, comments:

“In just a few weeks, COVID-19 surveillance has had to sprint from a standing start to a point where thousands of tests are being conducted every day. The information we get from testing is vital. Each positive test is an opportunity to stop onward spread of the virus by isolating the case and tracing their contacts. And by putting together test results around the country, we can track the progress of the pandemic and direct action to where it’s needed.

“But COVID-19 surveillance is about much more than counting cases. To make a safe decision about when to exit lockdown, we need to know not just who is being counted, but who isn’t. We need a pandemic response that uses common-sense approaches, e.g., ensuring that community-based assessment centres (CBACs) are accessible for anyone who needs them. We also need a cohesive and innovative 21st century approach to tracking COVID-19. This means developing a system that collates multiple available data sources to pick up signals about illness in communities, physical distancing, and other indicators of outbreak risk. This information must be used sensitively and appropriately to guide critical decisions for public health.”

Conflict of interest statement: All views expressed are in my university capacity only, and have no connection with my current advisory role with the Ministry of Health.

Professor David Murdoch, Dean and Head of Campus, University of Otago, Christchurch, comments:

“Never before has diagnostic testing been so much in the global spotlight. Never before have we had so many non-experts, from both within and outside the scientific community, giving advice about diagnostic testing, nor instructions from national leaders to ‘test, test, test.’

“So, here are some basics of COVID-19 testing in the current New Zealand context.”

What tests are being used to test for COVID-19 in New Zealand?

“The widely deployed tests to diagnose COVID-19 are based on a method called the polymerase chain reaction (PCR) and they detect the genetic material of the virus – in this case the virus’ RNA. These tests simply detect the presence or absence of the virus in clinical samples. As the virus is found in highest concentrations in the very back of the nose and throat, swabs from these areas are the preferred samples to test. These PCR tests are accurate and the equipment used has the potential to test large numbers of samples at the same time. The test itself takes a few hours to perform, but with additional time to transport samples to the laboratory and with reporting and quality checking requirements, results are usually available within 24 hours of sample collection.”

Are we testing enough at the moment?

“Currently, New Zealand is among the highest testing nations globally on a per capita basis. Importantly, with testing across the country having been ramped up and with broad indications for testing, the proportion of tests that are positive are low (<2%) and we are starting to see a reduction in numbers of new cases each day. Collectively, this is encouraging. We also need to ensure that the testing is reaching all communities in the country.

“There has also been a considerable focus on the country’s testing capacity. New Zealand now has PCR testing available in at least seven labs throughout the country. The biggest concern now is not necessarily the number of labs doing the testing (arguably we have enough now), it is the supply of consumables for the tests that is the major concern. With the unprecedented global demand for COVID-19 testing, all supply chains are being stretched to capacity, so securing this supply is high priority.”

What other types of tests are available?

“Two other types of tests are also in various stages of development – antigen detection tests and antibody detection tests. Antigen detection tests (often referred to as rapid tests), like PCR, directly detect the virus in clinical samples. Whereas PCR detects the virus’ RNA, antigen detection tests detect other parts of the virus. The main advantages with antigen tests are their ability to produce a result very quickly and the potential to be used at point of care in devices similar to many pregnancy tests. Unfortunately, the experience with this type of test for other respiratory viruses (like influenza) has not been great because they have produced a high proportion of false negative results. This does not mean that these type of tests won’t work for COVID-19, but it does mean that they first need to be properly evaluated to show that they perform well.

“The other type of test in development are antibody detection (serological) tests. Rather than detecting the virus itself, these tests measure the body’s response to the virus. A person infected with the COVID-19 virus will respond by producing antibodies to the virus, and these can be measured in the blood. Unfortunately, these antibodies are only detectable sometime after the person has been infected (often weeks later), so they are not useful for diagnosing acute infections. However, they may have a role in determining which people in the population have had COVID-19 at some time in the past, including identifying people who may not have realised that they had the infection. Reliable serological tests can also be difficult to develop and even the best serological tests for some infections have a high proportion of false positives and false negatives.

“Among the many commercial antigen and serological tests being offered at the moment, a considerable proportion have either not been adequately evaluated yet and/or are being promoted for the wrong purpose. All tests need to be carefully scrutinised and supported by good evidence before used in a clinical context.”

What is surveillance testing?

“With the aim of eliminating COVID-19 from New Zealand, the focus to date has been on the rapid identification of cases of COVID-19 in the country. Testing will also be critical to ensure that elimination has been achieved and maintained. Other testing strategies will likely be introduced at some stage and could include further broadening of the case definition, targeting certain at risk groups and, potentially, the testing of specific groups of people without symptoms.”

Hidden heroes

“This is also the time for a big shout out to medical laboratory staff and to the medical laboratory science profession. Laboratory staff are so often the hidden heroes, yet have such a vital role in the response to this pandemic.”

No conflict of interest.