Contact tracing report into Covid 19 Delta outbreak: ‘Stretched with no more than 75 cases a day’

Contact-tracing during the first two months of the Delta outbreak was only above par when daily case numbers dropped after the first two weeks, and before they rose again in mid-October.

Fewer than half of the close-plus contacts in that period were isolating within four days of exposure to the virus, while only a third were isolating within 96 hours of their first symptoms, according to an interim report quietly released today by the Ministry of Health.

The gold standard for both of these metrics is at least 80 per cent, which calls into question director-general of health Ashley Bloomfield’s repeated statements that the system was ready and wasn’t quickly overwhelmed.

The report also highlights how important it is for people to get tested when they feel sick, and how some of the metrics can be impacted by people having to wait up to 12 hours in line at testing stations – which was not uncommon in those first weeks.

The report covers the period from the start of the outbreak up until October 17, which is before daily case numbers really started to climb, and a few days before they first reached triple figures.

The five key contact-tracing metrics only started reaching their performance targets by week three, after daily case numbers in the first wave had already peaked at around 80 and had started dropping again.

By the time the case numbers climbed back up to 75 cases a day in mid-October, all five metrics were again performing below par.

“The system’s components obviously need to be strengthened if it’s going to provide the level of support that we will need, particularly if cases go as high as they could potentially go [over summer],” epidemiologist Professor Michael Baker told the Herald.

“The system was being stretched with no more than 75 cases a day. If the system gets overwhelmed and drops away in terms of performance, then that will mean more cases in the community unaware they’re infected, and more of their contacts not being identified and told to quarantine.”

The number of close contacts over this period was almost 40,000, but the report only measured performance for close-plus contacts – typically those who shared a house or a workplace with a case.

Half of the 2406 household contacts in this period tested positive.

For the five key metrics:

• 48 per cent of close-plus contacts were isolated within 96 hours of being exposed to the virus; the standard is at least 80 per cent. It fell to as low as 30 per cent in the fourth week of the outbreak.

• 29 per cent were tested within 48 hours of their first symptoms; the standard is at least 80 per cent.

• Two-thirds of positive case results were processed within 24 hours of the sample arriving at the lab; the standard is at least 80 per cent. It was as low as 50 per cent in week two, when testing numbers were as high as they have ever been.

• 72 per cent of contacts were isolated within 48 hours of a case being identified; the standard is at least 80 per cent. This hovered around 60 per cent for those first two crucial weeks, and dropped below 80 per cent by mid-October.

• 81 per cent of contacts were isolated within 24 hours of them being identified, above the standard of at least 80 per cent. This has consistently been at least 75 per cent.

Other metrics are reliant on members of the public getting tested, or how quickly labs can process samples:

• 34 per cent were isolated within 96 hours of their first symptoms; the standard is at least 80 per cent.

• 72 per cent were isolated within 72 hours of being tested, just below the standard of at least 80 per cent.

• No data was provided for the average time taken between a test and being notified of a positive result, because this is “not consistently recorded” in the national database. There have been, however, anecdotal reports of it taking several days for some cases.

The public health teams were much closer to meeting their targets, including how quickly it takes to interview a contact after they test positive, and then to have all their contacts isolated.

Otago University Professor and specialist public health physician Philip Hill said the system, as it was, appeared to be unfit for a large outbreak of any Covid-19 strain, including previous variants of the virus before Delta.

Baker said the poor overall system performance indicated people not getting tested when they first felt sick.

But others also tried to get tested, but become disheartened by the massive queues at testing stations in those first days of the outbreak, he said.

“There is a lag, particularly people who were told to go home and to come back tomorrow.”

He said it was important to see the report covering the next period, when daily case numbers rose to more than 200 a day and the Government moved away from elimination and into the traffic light system.

Before the outbreak, the ministry claimed to have surge capacity to contact-trace 6000 contacts a day for 1000 cases.

But the outbreak exposed this estimate as fanciful after the system came under severe strain – hundreds of workers were urgently trained while 600 call centre jobs were urgently advertised – when the daily case numbers only peaking at just over 80.

Contact-tracing performance has also been questioned in light of the large proportion of contacts – more than 20 per cent and up to 33 per cent since mid-October – still waiting to be contacted to check their testing and isolation status.

The ministry has been reluctant to boost contact tracing capacity, and even specify and test what the capacity is, for several months leading up to the outbreak – despite repeated recommendations to do so from several independent expert reports in the last 15 months.

The Government is preparing for the Covid challenges over summer by increasing testing capacity to 60,000 a day by early next year, and boosting contact tracing capacity.

That boost has not been specified, and Bloomfield has repeatedly been vague in answering questions about the system capacity.

Sir Brian Roche, who chairs the continuous improvement advisory group for the Covid response, told the health select committee this morning that contact tracing capacity had increased, but whether it is enough remains to be seen.

“In a way, you don’t know what’s going to happen until it happens,” he said.

The ministry is meant to be able to monitor contact-tracing performance in real time, with regularly published updates on its website.

But despite Official Information Act requests and intervention from the Ombudsman, no data has been released regarding the current outbreak until today – and it was done with no fanfare.


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