Covid 19 coronavirus: Could antibody testing hold clues for virus mystery?

Serology testing may be the key to identifying reasons for community transmission. Photo / acc.af.mil

A public health expert is calling for serology testing to gain a wider picture of New Zealand's total Covid-19 exposure and says it might also help solve the mystery of how a hotel worker contracted the virus.

Genetic sequencing has linked the Rydges Hotel worker to the same strain of virus found in a woman who stayed at the Auckland hotel between July 28 and 31 after returning from the United States.

But the Ministry of Health has said there is no evidence the worker had any direct contact with the traveller.

University of Auckland public health lecturer Simon Thornley told Kathryn Ryan an antibody blood test may indicate whether a third party at the hotel could have been an intermediary passing on the virus somehow.

"It spreads a wider blanket of information. You can tell whether somebody has had Covid in the past and whether that's linked to certain person. Although that's still a question for judgment, it adds more evidence to the scenario," he says.

The blood test would pick up if someone had the virus and had cleared it without knowing.

"The swab test just looks for active virus in the body at one point in time, whereas if the virus has been and gone from the body, the body mounts a response and we make anti-bodies and that's what serological tests are all about.

"These have certainly been shown to be effective in public health contact-tracing settings."

He said a study in Singapore had shown the tests had been useful in gathering information about the chain of transmission, more so than what the current swab tests could offer. Serology testing would add to a body of evidence useful in both contact-tracing and better determining the nature of the illness.

Thornley is advocating for antibody testing across the country as part of a wider approach to tackling the public health crisis, although acknowledges it would put more pressure on already-stretched laboratory staff and resources.

"I believe antibody testing is very important to New Zealand for a number of reasons. First, we assume that everyone is still susceptible in New Zealand. Until we do antibody testing we really don't know.

"It's also been important overseas for dialling back how lethal the virus has been. Initially the World Health Organisation came out with figures that three in 100 of us were going to die. Once the antibody tests were coming back it became more like 2 in 1000 deaths.

"It's still greater than seasonal influenza, which is around 1 in 1000 deaths, but the figure was certainly dialled back the lethality of the virus by a big margin.

"Also, other countries are using it for their contact tracing and case finding. For example, Iceland is testing serology in travellers over the border who test positive on a swab and if they've got serology, there's some pretty good evidence now that they're not infectious and Iceland is treating travellers in that way, allowing a far greater number of travellers than other countries are doing."

He said initial concerns about the efficacy of these tests had been largely addressed by the larger pharmaceutical manufacturers.