Covid-19

How will we know it’s gone?

How will we know when we’ve been successful in stopping Covid-19 within New Zealand? Farah Hancock reports.

As the country moves into its third week of lockdown and the daily number of cases continues to drop, how can we be certain it's safe to move levels and how will we know if fresh outbreaks occur?

The idea of random population sampling has been suggested as a way to determine whether there are cases circulating in the community.

On Monday, Director-General of Health Ashley Bloomfield said a draft surveillance plan has been created and it’s not all about testing a random sample of the population.

“You would need to survey at least 100,000 people just to get any idea of prevalence around the community,” he said.

New Zealand currently has the capacity to process fewer than a tenth of that number of tests in a day. 

The answer might be a work smarter not harder approach which isn't about how many tests are done, but how they’re done and who they are done on. 

It's a topic which has generated plenty of discussion according to University of Otago Professor David Murdoch. 

“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.'.”

While New Zealand’s capacity to test has rapidly scaled up, it’s still reliant on consumables, says Murdoch. 

“With the unprecedented global demand for Covid-19 testing, all supply chains are being stretched to capacity, so securing this supply is high priority."

As we move to surveillance - or monitoring - the current approach to testing is likely to change. 

With winter and flu season looming, people who are sick will get tested. Bloomfield said yesterday there would be “very wide testing of anyone with flu-like illness symptoms.”

Also on the cards is a voluntary contact tracing mobile phone app. This will make tracking contacts and “ring-fencing” them easier.

Outbreaks could become like a game of whack-a-mole, where contacts are identified quickly so they can self-isolate.

“Our intention is to get the case numbers down as low as possible - if not to zero - and then be able to stamp out any cases and outbreaks that do pop up.”

Community testing - one test tube, many samples

As infection rates drop, there’s one approach to testing large groups at once raised by Bloomfield at a press conference.

“Any community testing would be part of broader surveillance and you might use different approaches. For example, one of the approaches being used, I know, in Israel is they swab a group of people, but, instead of testing each swab individually, they will run a batch of 50 swabs through one test, and only then go back and retest if they get a positive test from that.”

The researchers who have worked on this approach say when testing a group of 64 people with only one positive sample, their technique still picked up the positive sample. In practice this would raise a red flag, and from that batch all samples would be individually tested to identify what samples were positive. 

“And that way you cannot use up so much of your laboratory capacity but still do wider testing,” said Bloomfield.

“That would be more part of our ongoing surveillance to support our efforts to keep stamping it out as we go into levels 3 and then down to 2.”

Targeted or smarter testing 

University of Otago’s Professor Murdoch said another approach was targeting who is getting tested.  

“It could be targeting certain groups that are particularly vulnerable or at risk  - healthcare workers, etc, or contacts.”

Already there’s talk of looking at the testing rates of different DHBs, to see if there are gaps across the country. 

People without symptoms could also be tested, although Murdoch raised a caution on that.

“It's actually a little bit of a dangerous area because we don't know the test performance in that setting.”

There's also an option for tests to get smarter according to Bloomfield.

“The other technology which ESR has developed is to be able to actually genome-sequence each of the isolates, or a proportion of the isolates, which will show exactly what the pattern of spread and distribution is in New Zealand, too.”

Environmental monitoring - testing sewage

Another approach is to test sewage for Covid-19. Scientists from ESR have been collecting and freezing sewage from areas where clusters of cases exist. These will be kept as testing methodology is established. 

“By detecting and monitoring Coronavirus in wastewater we could potentially see how effective eradication is, gauge changes in different regions as well as better understand the patterns of community transmission,” says ESR chief scientist Dr Brett Cowan.

The technique of sampling wastewater has been used for polio in some countries, so the idea isn’t new, but Cowan warns it’s not going to be an easy task as the virus levels may be low and tricky to detect. Researchers in the Netherlands claim to have successfully found it according to an article which has been published before peer review.

What are the existing surveillance tools?

A report from March 20 discussing surveillance and outbreak analytics has identified what surveillance tools are currently available and how they could be used to flag outbreaks.

These include surveys such as the New Zealand Health Survey which is a continuous survey with sampling established to ensure various groups are well represented. There is work underway to use the survey to assess the impact of the pandemic.

Numerous reporting tools exist already to track influenza. While these are unlikely to pick up every case, they could be used to track variations over time in regions of the country.

Hospitals also feed information into the imaginatively-named Southern Hemisphere Influenza and Vaccine Effectiveness Research and Surveillance (SHIVERS) database. This gathers cases where a patient has had an overnight hospital stay due to an acute respiratory infection. GPs can report cases through HealthStat, and Healthline, a phone-based system staffed by nurses can also collate cases from symptoms described by callers. 

The crowd-sourced FluTracking website is another tool which has been mentioned. People who are signed up to it receive an email each Monday asking whether they’ve had a fever or a cough in the past seven days. It also asks whether a person has been tested for Covid-19 and whether they have received the 2020 flu vaccine.

Last week 44,279 responses to the weekly survey were collected. 

With a vaccine not likely to be completed for many more months, Prime Minister Jacinda Ardern has repeatedly warned the effort to keep the virus at bay will be a "marathon".
 

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