THE HSE IS to roll-out retrospective contact-tracing on a widescale to try to establish the source of some of the cases currently being classed as community transmission.

Speaking at the HSE’s weekly briefing today, Dr Greg Martin, clinical lead for contact tracing, said public health doctors have, all through the pandemic, been conducting source investigations in complex cases. However the HSE will now “bring that to scale”, starting on 31 March.

“When we identify cases of Covid-19 about 20% of those cases, we’re not sure what the context was in which they were infected, so we call it community transmission,” he said.

“What we’ll be doing as of the 31st of March is those cases will be asked additional questions about where it is they’ve been, settings that they’ve been in, events they have been at. And those questions will go back seven days, instead of what we usually do in terms of contact tracing which is two days.”

He said this additional data will be available to public health departments which will decide which cases require a more detailed investigation. Dr Martin said that investigation may involve people who were at the same setting at the same time being offered a test.

These people, he said, would not be considered close contacts so they would not have to restrict their movements while waiting for a test result. Dr Martin said this approach will help the health service to identify more cases, providing an opportunity to interrupt transmission.

When that is going to be particularly useful is when this epidemic starts to die down and when the efforts of this vaccination programme really start kicking in, when we’d see the numbers really getting into low numbers. We’ve got a mechanism now whereby we can really aggressively chase down every last case so this is part of an end-game strategy.

He said there is also a substantial value in the immediate future as the health service will have data on settings in which there is increased transmission of the virus.

“As restrictions get lifted, that becomes increasingly important because that gives us an evidence base to make public health advice and recommendations.”

Martin said this new type of contact tracing will be part of the existing system, with a separate section on the database where a person is identified as a community transmission case.

“Within the system they [contact tracers] are working on, it’ll automatically be the case that a series of additional questions will be asked,” he said. He said it is not clear how labour-intensive this additional process will be or whether additional staff will be required to account for that.

Dr Martin said if he incidence rate on a given day gets to a high level or is consistently rising, this sort of backwards contract tracing becomes less useful because any setting becomes an area of high risk when transmission levels in the community are high.

“We need to collect data, so we switch this on and off the back of deepening understand of how it works and the information we can get from it, we will have a better sense of when to switch it on and off,” he said.

Last Friday the HSE also started doing follow-up calls four days after people received their positive results to reiterate some of the public health advice and ask people if they are managing to isolate.