Covid 19 Delta outbreak: Editorial - Is surveillance testing the key to containment?

Registered nurses await their next clients at the Turuki Healthcare Covid testing station in Mangere. Photo / Michael Craig

EDITORIAL:

There have been some fortunate episodes in New Zealand's Delta outbreak, despite it ultimately defeating our attempt to eliminate Covid.

Positive cases in Wellington, Coromandel and Christchurch did not result in rampant transmission of the virus due to fortuitous combinations of contact tracing, localised precautions, vaccination efforts and, likely, some sheer luck.

Another location looking increasingly likely to join the good luck club is Stratford. A week after half a dozen positive cases were found in the small Taranaki township, the number of current cases remains at six.

When the Stratford infections were announced, it was reported the cases were from one family who had refused to get tested.

"We have been working with them over a day or so and eventually managed to persuade them to have a test," Taranaki medical officer of health Dr Jonathan Jarman said.

He said the family had not been using the Covid tracer app so health workers traced their steps manually to busy locations such as a supermarket, pharmacy and hardware store.

One of the striking features of the Stratford case is the way it was discovered. Wastewater sampling had detected Covid in the town infrastructure and follow-up testing confirmed it. Publicity around the likelihood of the virus being in the community resulted in a family being identified as showing symptoms.

Last updated in August, the Ministry of Health's surveillance strategy still talks of "elimination" of the virus but it's number one objective is identifying cases. The key methods cited are: "Collect, analyse and report on data from border testing, community testing, case investigation and management, case and testing rates in other countries, contact tracing and management and background scanning for trends and emerging disease."

The strategy mentions wastewater testing as part of "background scanning", which also includes checking people arriving at hospitals and the FluTracker survey.

But should we be conducting sweeps to proactively seek the virus? Should we be surveillance testing vulnerable communities to detect infection at the earliest possible opportunity?

The Ministry of Health's strategy currently contends that general testing of asymptomatic people in the community is recommended only for border workers, managed isolation and quarantine workers, and for contact tracing.

National Party leader Judith Collins says there should be saliva surveillance testing in the community and rapid antigen testing at the Auckland border. Auckland University Professor of Medicine Des Gorman last month also called for community surveillance testing at supermarkets.

Unfortunately, rapid antigen testing, while less intrusive than nasal swabs, requires a higher quantity of the virus to be present in the sample than other Covid‑19 testing methods. As a result, antigen tests are less sensitive at detecting cases, especially in asymptomatic people or people who are early in their infectious period.

That leaves us with the obtrusive nasal swab being the most effective tool.

In situations where we have cause to believe the virus could be moving through households and communities undetected, there may be a case for increased surveillance testing.

But it remains a blunt and intrusive weapon, best kept holstered for when needs must.