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Sasko Lazarov/
source investigation

Wider-scale retrospective contact tracing begins today - here's how it'll work

For the 20% of cases categorised as community transmission, additional questions will be asked about their movements over the previous seven days.

CONTACT TRACING TEAMS will, from today, begin asking additional questions to help identify the source of cases identified as community transmission.

Currently around 20% of cases are categorised as community transmission. This means it is not clear to contact tracers after initial questions where the person picked up the virus.

If a case has been categorised as community transmission, the person will be asked an additional set of questions. These questions will be based on the various events or settings they have been in over the previous seven days.

“There’s additional questions about when you were there, what was the date, what was the time and there’ll be questions about that setting. It’s actually a detailed set of questions that’s asked,” Dr Greg Martin HSE clinical lead for contact tracing said during a briefing today.

This information will be passed on to public health departments and they will then decide whether the case requires a more detailed investigation.

“The purpose of that investigation will be to identify the source, so it might be that we actually find the original index case, but perhaps equally or more importantly we will identify other close contacts who were exposed at the same time,” Martin said.

“Those are the close contacts may be asymptomatic so they might not even know that they’ve been exposed or that they’ve at this point, contracted Covid-19.”

These people will receive a text message offering them a test, but will not be required to restrict their movements while waiting for the results, Dr Martin said, because there is no firm information that this was necessarily the transmission setting. If they test positive, they will then be given the guidance on self-isolation.

“They’ll be offered a test, and that will be a mechanism whereby we will identify additional cases, and where we identify additional cases there’s an opportunity to interrupt transmission because, of course, those people will be given the additional advice to self isolate,” he said.

He said public health departments may conclude that they are unlikely to learn something from one particular setting but others could yield valuable information.

They may say ‘look this was a wedding or a restaurant at a particular time’, so it may be possible for us to reach out to that restaurant and identify the names and contact details of additional people that were there, or in the case of a wedding we can reach out to the wedding organisers and we can identify the names and contact details of the people that were at that setting. At that point in time, they’ve now got a list of other people who may have been exposed.

“Now we don’t know that they were exposed because at that point in time, we don’t really have any evidence that that’s the venue or event where the transmission took place. But the public health professionals, having looked at the possibilities, think that this is worth investigating.”

Public health departments are already doing this kind of source investigation locally, particularly where there are larger outbreaks connected to particular locations or events.

In some cases public health departments have been able to bring down the level of cases categorised as community transmission to 10% using this more detailed process. This will see the process become a more routine part of the contact tracing process to pick up more cases and to provide health officials with additional data on risks associated with certain settings.

“The other really useful thing that comes out of this is we will get a much better sense of where it is; which settings, which circumstances, which kinds of events, there’s increased transmission and increased risk to people at events like that,” Dr Martin said.

“That will give us real data to make informed, evidence-based public health recommendations and guidelines and advice. As the economy gets opened up and as the restrictions get lifted we’re going to be able to give detailed and specific advice based on data that we collected in this way.”

Martin said this approach is most effective when case numbers are low and as numbers go down, “chasing down every live case is going to be an important part of the endgame of our public heath response to this pandemic”.

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