Contact tracing struggles to keep pace

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Covid-19

Embroiled in controversy over the government’s continued failure to increase capacity, will contact tracing really be ready for a surge of cases in the months to come? Marc Daalder reports

Analysis: The government insists contact tracing will last through any possible summer surge in cases, but all signs currently available point to a system that is already under immense stress.

Almost a third of close contacts have yet to receive a test, although they are expected to get one immediately after being notified. This is partly a symptom of a failure to notify 31 percent of close contacts in the first place – only 69 percent received a call from contact tracers.

These statistics highlight a tight system to manage the current workload. The government says capacity is being increased, but is unable to say how many contacts per day the system is currently able to trace.

Optimistic assumptions

It is a change from the recent past. On October 6, a spokesperson for the Department of Health said the system could handle 1,000 new cases daily or 6,000 new contacts each day.

Right now we have just under 6,500 contacts in total in the last 14 days and the tracers are still struggling to keep up.

Public health director Caroline McElnay later blurted out what appears to be a more accurate figure. “I think the last one I heard yesterday was that around 170 to 180 cases a day would start to really put pressure on the system as a whole,” she said on Oct. 14.

The government then began to make changes to contact tracing. At the start of the outbreak, authorities broadened the definition of close contact to include people who might previously have been classified as casual contact. This has seen the number of contacts skyrocket to over 40,000 at one point.

Authorities have now refined the definition based on the fact that relatively few of these contacts have tested positive. Now, many people who would previously have been classified as close contacts are also allowed to go to work and school without any testing or isolation requirements, unless they develop symptoms. Public health officials no longer try to find the origins of each case.

Looking back, the Department of Health now says McElnay’s estimate in mid-October was too much optimistic.

The system was originally designed only to handle 180 to 270 daily cases during national shutdowns, a spokesperson told Newsroom. This is well below the 1,000 daily cases that the ministry was responsible for handling in April 2020. But even this lower threshold was exceeded in October.

The government’s belief that it will be able to handle the workload ahead rests on heroically optimistic assumptions.

“The very high levels of case complexity seen in October impacted estimates of the number of manageable cases per day, given the emphasis on following up even casual contacts at this stage of the outbreak. Taking this approach, at that time, meant that it was estimated that public health units had the capacity to manage between 100 and 120 cases per day with the capacity to increase up to 150 cases per day for periods of time. limited periods, ”the spokesperson said.

At this point, the system was unable to manage only 2322 contacts.

Current capacity unknown

So what is the current capacity of the system?

The government is unable to say it. Asked two weeks ago, a spokesperson for the Department of Health said the system was dealing with the then current caseload of 154 cases per day. Efforts were underway to increase capacity to an additional 150 cases per day.

As of Monday, the seven-day average number of cases was 186 daily cases.

The total number of contacts is now 6,473 and nearly two thousand have yet to return a test result of any kind. Since the publication, a spokesperson for the Ministry of Health clarified that only 2.5% of contacts are late for a test.

Last week, Dr Ashley Bloomfield told Newsroom he was convinced contact tracing would last over the summer, although cases are expected to spread to most other countries.

“I am confident in our contact tracing ability, recognizing again that the way we use it has changed to be very focused on these very close and close contacts.”

When asked in a written parliamentary question from National MP Chris Bishop if the contact tracing system was overwhelmed, Covid-19 Response Minister Chris Hipkins covered his response.

“Contact tracing capacity depends on the complexity of the cases, and at this stage of the epidemic the complexity of the cases is high,” he replied. “Currently, all public health units across the country have stopped the non-essential status quo and are completing a case investigation to respond to a high number of cases. “

Contact tracing is crucial

So the system continues to struggle, with officials and ministers claiming that October’s difficulties were due to the “great complexity of the cases” and that the current challenges have the same cause.

As with past statements of confidence in the contact tracing system, the government’s belief that it will be able to handle the workload ahead rests on heroically optimistic assumptions.

Projections from August to October that the system could process 1,000 cases per day were based on the fact that each case only had six contacts – less than a quarter of reality. October’s estimate of capacity for nearly 200 daily cases was based on the fact that most cases were easy to trace, not complex. Bloomfield’s summer promises also appear to be rooted in the expectation that the complexity of cases diminishes.

There is, however, no reason to believe it. In fact, with cases likely to appear in many more places, each spawning a small outbreak that will be most likely to take hold in the unvaccinated and disengaged, the complexity of contact tracing could in fact. to augment over the next few months.

Time and time again, the government has promised that it cannot continue to trace contacts. In May 2020, then Health Minister David Clark said the centralized research facility at the Department of Health could handle 10,000 contact calls per day. Now the system is grappling with far fewer contacts to manage.

This is a crucial issue as contact tracing could play a major role in limiting the spread of Covid-19. Associate Health Minister Ayesha Verrall said contact tracing is expected to offer a 10% benefit by reducing transmission under the traffic light system.

Modeling Te Pūnaha Matatini based on the Continuing Level 3 restrictions in Auckland revealed that contact tracing could play an even bigger role. The researchers simulated two worst-case scenarios – one with very high transmission rates where contact tracing capacity was capped at 1,000 cases per day, and another with very high transmission rates where the tracing capacity evolved ad infinitum with the number of cases.

In the first scenario, 6,629 weekly cases were expected by the end of the year. In the latter case, that number fell to just 2332. So the number of cases could be up to three times as high if contact tracing slows down or stops at 1,000 cases daily – and of course, the capacity. current is well below the threshold of 1,000 cases per day.

Contact tracing will be the key to containing Covid-19 in the months to come, but the government appears to be following the same overconfident path it has taken in the past.

This article has been updated following a response from the Department of Health.

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