Public Health England (PHE) have released a report by a Rapid Investigation Team looking at the descriptive epidemiology of COVID-19 in Leicester during June 2020.
Prof Jose Vazquez-Boland, Chair of Infectious Diseases, Edinburgh Medical School, University of Edinburgh, said:
What does the report suggest about the situation in Leicester?
“While not ruling out that the excess of new diagnoses (of subclinical cases) may reflect the existence of an outbreak in Leicester, the report concludes that the evidence is limited and suggests that the observed rise in cases may to some extent be ‘artefactual’.
“Arguments in support are: (i) no parallel rise in hospital admissions, which remain stabilised at between 6 and 10 since the drop in cases after the epidemic surge in early April; (ii) no parallel rise in reported deaths; (iii) no explanatory outbreaks in care homes, hospitals or other sensitive settings; (iv) the rise in new cases is linear which is not characteristic of an unconstrained growth of an epidemic.
“The report specifically suggests that the surge in (subclinical) cases could be related to the increase in pillar 2 testing capacity and its use for a wider range of purposes i.e. outbreak investigation and screening in the community. This is as opposed to pillar 1 testing, which is reserved for hospital diagnosis, at-risk people and essential critical workers, where the number of cases has dropped after the epidemic peak and remains steady.
“There are several caveats with this interpretation.
“First, what is being detected could be an incipient outbreak at early stages with the epidemic curve still in lag phase with a slow, apparently non-exponential rise in subclinical cases in the community. The new infections in Leicester are being detected mainly among young and middle-aged people, relatively resistant to developing overt symptoms, and not in 65+ old people more likely to develop severe illness and require hospitalisation. This can explain the lack of parallel rise in pillar 1 diagnoses, hospital admissions and reported deaths (in addition to the control measures put in place to protect these at-risk people). Moreover, severe cases typically emerge at more advanced stages once ‘silent’ transmission has occurred in the community.
“Second, whether the rise in new cases is attributable to the wider availability of testing could be tested by comparing the rates per 10,000 population between Leicester and other areas after normalisation by the total number of tests performed in each area.
“Third, if the rise in positive tests were in part attributable to the increased availability of testing and wider application to the general public, similar trends would have been detected elsewhere.
“Otherwise, it would mean that there is something specific to pillar 2 testing of the samples from Leicester. The report does not provide information about where exactly the samples have been processed, specifically whether such samples have been all processed in a specific ‘lighthouse’ laboratory different from that used for the samples from other areas. This is an important point that needs clarification.
Has the investigation been carried out well?
“This is a preliminary investigation by a rapid investigation team that reports descriptive information. Further, more detailed analyses should shed additional light and clarify the situation.”
Prof Paul Hunter, Professor in Medicine, UEA, said:
“This is an initial report of the increase in number of cases in the Leicester city in recent weeks which reports the descriptive epidemiology of the outbreak. The report is clear, contains much useful information and PHE should be commended for making this report available to the public at this stage. There are several important observations that come from this report.
“1. There has indeed been a rapid increase in cases in Leicester diagnosed by laboratory confirmed tests up to the 23rd June. The large majority of these tests have been in pillar 2 testing which represent “Mass swab testing for critical key workers in the NHS, social care and other sector”. There has been no obvious increase in positive results taken under pillar 1 testing “swab testing for those with a medical need and, where possible, the most critical key workers”. This is important. Most pillar 2 tests are done by “commercial partners”, the results of which are not currently included in the 4 National totals in the UK COVID-19 dashboard and not in the counts per local authorities that can be downloaded from the dashboard. This means that the data currently made public at local level cannot be used to estimate local risk.
“2. From table 1.3 and figure 1.5 it appears that the incidence may have already plateaued and declined slightly in the last week.
“3. From table 1.4 it would appear that Bradford also has a particularly high incidence in June.
“4. From figure 1.6 the infection was spreading primarily in people in their 20s, 30s and 40s and given that they were primarily pillar 2 samples it is likely that many were not severely ill (from table 1.5 the average age was about 9 years younger in Leicester compared to nearby areas (40.5 vs 49.8 years).
“5. Data on ethnicity was available on only about a half of cases and where available was in the Asian or Asian/British population.
“6. The large majority of cases were in wards in the North East of the city.
“7. As yet the investigative team have not discovered any events that may have caused this spike in cases.
“In conclusion it is not totally clear what has generated this cluster of cases. It is possible (though in my view unlikely) that, as raised in the conclusions, the increase reflects increased uptake of pillar 2 testing. The most likely explanation is that the infection was spreading in people aged 20 to 50 and this generated greater demand for testing. However there is some evidence that the infection may now be spreading into older and younger age groups. As yet there is no apparent impact on hospitalisations or deaths, though it is too early to be certain that these will not increase over the next one to two weeks as the infection increases in older age groups.
“The detection of this cluster raises significant concerns about the local availability of results, especially from tests done in commercial laboratories the numbers of which were not made public at the local authority level on the UK government’s COVID-19 Dashboard. As of today the UK statistics authority has started to make some of that data available, but only for upper tier authorities. Hopefully data availability will further improve in coming days.
“This local cluster also raises issues about the timing of additional interventions. If there is a localised increase in case numbers it is likely to be at least two weeks before the impact is observed in the population and probably longer if data are presented only at the level of the local authority. By which time the size of the outbreak could have increased substantially. In order to detect clusters and possible common factors early enough to intervene at a time when the outbreak may be controlled, local authority public health departments need to be informed of cases from both government and commercial laboratories as a matter of priority, along with enough information to enable them to pinpoint where infections are occurring. It is these local authority public health departments that know their areas and they have to take the lead on controlling localised clusters in their districts. They can only do this effectively if they have timely and full access to information on cases occurring in their patch.”
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