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Flow-chart showing how contact tracing should work. The communication of data to local health protection teams is not working well in all areas at the moment.

Coronavirus statistical update: localised test and trace still proving problematic

Despite the deficiencies in data provision shown up by the Leicester outbreak, and government promises to remedy the situation, reports are still indicating that the NHS Test & Trace system is not working as well as it needs to on the ground. Research and graphics by Russell Hall, text by Nick Terdre.

The recent surge in cases of coronavirus in Leicester reached alarming proportions before the national health authorities acknowledged it as an outbreak of infections rather than an artefact of increased testing, making it the first town to be subjected to a local lockdown, which has since been partially eased.

The mayor of Leicester has now published a detailed account of how events unfolded, and the difficulties met by the council in coordinating action on the ground as higher level authorities refused to provide the necessary data.

It was only this week, on 21 July, that the health secretary Matt Hancock promised better data provision to local authorities, telling the House of Commons, “…we are publishing more data, and sharing more data with local bodies.” He added that, “From last month, local directors of public health have had postcode-level data about outbreaks in their area.”

However, if this is happening, it is not happening everywhere. And rather than make use of local resources, the government’s primary resource for contact tracing  remains the call centres run by private operators such as US company Sitel, which operates the North Lanarkshire call centre where there has been a recent outbreak of coronavirus.

On 16 July, Lisa McNally, the director of Public Health at Sandwell in the Midlands, told the BBC’s World At One news programme that in her area “four out of 10 people who test positive are then not being contacted or reached by the Test and Trace system.”

Contact details refused

When they asked for contact details, or access to the database used by the contact tracing system, she said, the request was refused with no reason given. Her team appear to be eminently qualified for local contact-tracing, consisting of local people with good local knowledge, including in their number speakers of the many different languages used in the area. “I’m not saying we could get 100% but I’m sure we could close that 40% gap to some degree,” she said.

When asked about prime minister Boris Johnson’s claim that the Test and Trace system is world-leading, McNally replied, “I can’t imagine our Test and Trace system is world-leading at the moment, unless the rest of the world have some pretty awful Test and Trace systems.”

According to Sage (the Scientific Advisory Group for Emergencies), at least 80% of contacts need to be reached and told to self-isolate for Test and Trace to be effective. Those who are not reached are likely to be circulating normally and, if they are themselves infected, passing the virus on.

In various areas the contact rate is well below 80%. According to the public health director of Blackburn with Darwen in Lancashire, as reported by the BBC on 19 July, contact tracers were only reaching 50% of contacts.

On 22 July The Guardian reported that “in areas with the highest infection rates in England, the proportion of close contacts of infected people being reached is far below 80%”: only 47% in Luton, 65% in Leicester.

Socio-economic disparities

The previous day the paper said it had found significant disparities in the effectiveness of contact tracing in affluent and deprived areas. In Blackpool, a deprived town, 37% of identified contacts of an infected person were not reached by call-handlers, compared with only 9% in the better-off Cheshire East.

The five local authorities with the lowest contact-tracing rate – Blackburn with Darwen, Blackpool, Knowsley, Rochdale and Oldham – all have among the highest proportion of most deprived neighbourhoods in England, it said.

Source: Table 5, NHS Test and Trace bulletin, week 7.

The latest Test and Trace results, up to 15 July, show that since the system started up on 28 May, 38,877 cases of infection had been transferred to the contact-tracing system, of whom 77.1% (29,962) were reached and asked to provide details of recent close contacts. Of the 202,781 contacts identified, 169,546 – 83.6% – were reached and asked to self-isolate. So the 80% minimum stipulated by Sage has been achieved overall.

Source: Table 9, NHS Test and Trace bulletin, week 7.

However, constant improvement is not being achieved. In neither of the two latest weeks was 80% achieved.

This week’s Test and Trace bulletin provides an interesting breakdown of the relative efficiency of contact tracing for complex and non complex cases – complex cases are those in outbreaks associated with particular settings such as a hospital, care home or prison, for which the tracing is done by a Public Health England local health team, and non complex cases which are handled by call centres.

From figure 9, it can be seen that the success rate for tracing the contacts through call centres is modest – over the seven weeks that Test and Trace has been operating, only 54.5% of all cases referred, or 70.7% of all cases reporting contacts, were reached. By contrast, the local teams have rates little short of 100%. The aggregate result of 83.6% of all contacts reached is very dependent, then, on the success of the local teams.

Source: Figure 9, NHS Test and Trace bulletin, week 7.

The above graph shows how the number of people identified as close contacts has fallen since Test and Trace came into operation. Initially composed mainly of complex case contacts (blue line), the numbers of complex and  non complex case contacts are now very similar.

Time improvements

Speed in reaching contacts is also of the essence: Sage says any delay beyond 48-72 hours in a contact self-isolating would result in a significant increase in the infection rate.

The latest data shows that overall, of close contacts who were reached and advised to self-isolate, 82.9% were contacted within 48 hours and a further 9.8% within 48-72 hours, making a total of 92.7%.

Chart showing the number and type of tests carried out, the seven-day rolling average and the overall testing capacity. The tests used to identify cases of infection are Pillar 1 and 2.

New target

Meanwhile health secretary Hancock also told the Commons that he was setting a new target of half a million antigen tests a day (these indicate whether a person is infected) by the end of October. Although he failed to specify, the Department of Health and Social Care told HOT he was referring to capacity. So a large increase is envisaged, as antigen testing capacity currently stands at just under 200,000 a day.

It is far from being fully utilised, however. The number of tests processed fluctuates, but the figure for 24 July – 114,388 – is not atypical.


Posted 13:16 Friday, Jul 24, 2020 In: Covid-19

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