R value, Growth Rate and Estimated New Daily Infections
The reproduction number (R) is the average number of secondary infections produced by a single infected person. If R is greater than one the epidemic is growing, if R is less than one the epidemic is shrinking. The higher R is above one, the more people one infectious person might further infect and so the faster the epidemic grows. Please note that R is an indicator that lags by two or three weeks. For more information please visit the UK government website.
The UK Health Security Agency’s (UKHSA) consensus estimate for R in Scotland as at 26 April is between 0.7 and 0.9. The lower and upper limits of the R value have both decreased since the previous publication (Figure 1) .
As at 26 April, the UKHSA’s consensus view was that the incidence of new daily infections in Scotland was between 16 and 302 per 100,000. This equates to between 900 and 16,500 people becoming infected each day in Scotland .
The growth rate reflects how quickly the numbers of infections are changing day by day. It is an approximation of the percentage change in the number of new infections each day. More information can be found on the UK government website.
Covid-19 Infection Survey – Headline Estimates
The Covid-19 Infection Survey is a UK wide study carried out by the Office for National Statistics (ONS) and the University of Oxford. The survey invites private residential households to test whether they have the infection, regardless of whether they have symptoms, using a PCR test. This means the study is unaffected by testing policy changes. Participants are also asked to provide a blood sample to test for antibodies.
In Scotland, the percentage of people living in private residential households testing positive for Covid-19, as estimated by the Covid-19 Infection Survey, continued to decrease in the most recent week (1 to 7 May), as seen in Figure 2. The estimated percentage of people testing positive in Scotland has been decreasing since the end of March. This follows a peak in the week 14 to 20 March 2022 which saw the highest estimate for Scotland since the survey began. The estimated percentage of people testing positive for Covid-19 in the private residential population in the week 1 to 7 May in Scotland is 3.01% (95% credible interval: 2.57% to 3.45%), equating to around 1 in 35 people (95% credible interval: 1 in 40 to 1 in 30).
In the week 1 to 7 May 2022, estimates for the other nations of the UK are as follows and can be seen in Figure 2:
- In England, the percentage of people testing positive continued to decrease: 2.21% (95% credible interval: 2.09% to 2.33%), equating to around 1 in 45 people (95% credible interval: 1 in 50 to 1 in 45).
- In Wales, the percentage of people testing positive continued to decrease: 2.91% (95% credible interval: 2.40% to 3.46%), equating to around 1 in 35 people (95% credible interval: 1 in 40 to 1 in 30).
- In Northern Ireland, the percentage of people testing positive continued to decrease: 1.84% (95% credible interval: 1.34% to 2.39%), equating to around 1 in 55 people (95% credible interval: 1 in 75 to 1 in 40).
In Scotland, the estimated percentage of people testing positive has decreased for all age groups in recent weeks.
Covid-19 Infection Survey – Regional Analysis
The ONS have created sub-regions across the UK for the purposes of providing Covid-19 positivity estimates for the residential populations on a lower level than the four nations. In Scotland, these sub-regions are comprised of Health Boards (for an overview on how these align with local authorities, please see Table 1 in the Technical Annex).
Sub-regional estimates are based on a different model to the headline estimates, and should not be compared to headline positivity estimates. The sub-regional figures may differ from the headline estimates because they are averaged over a longer time period.
There is a higher degree of uncertainty in the sub-regional estimates because of a smaller sample size in each sub-region relative to their respective national sample. This is indicated by wider credible intervals and therefore results should be interpreted with caution.
In the most recent week (1 to 7 May 2022), estimates for the percentage of people testing positive for Covid-19 were similar for all CIS Regions in Scotland and ranged from 3.17% in CIS Region 128 (NHS Ayrshire & Arran, NHS Borders and NHS Dumfries & Galloway) (95% credible interval: 2.65% to 3.81%) to 3.25% in CIS Region 127 (NHS Lanarkshire) (95% credible interval: 2.65% to 3.89%). Overlapping credible intervals indicate that there may not be a true difference between the estimates (Figure 3) . Figure 3 is also available as a dynamic map.
Covid-19 Wastewater Estimates
The Scottish Government has been working with the Scottish Environment Protection Agency (SEPA) to detect and analyse fragments of Covid-19 virus RNA in wastewater. The levels of SARS-CoV-2 in wastewater are monitored at 141 sites around Scotland. In contrast to Covid-19 case records, virus shedding into wastewater is a biological process. This means that wastewater data is unaffected by factors that impact whether testing is done.
Nationwide, wastewater Covid-19 levels declined slightly in the last two weeks. The week ending 10 May saw levels of around 84 million gene copies per person per day (Mgc/p/d), a decrease compared to 97 Mgc/p/d two weeks ago (week ending 26 April) and 76 Mgc/p/d observed in the previous week (week ending 3 May) (Figure 4).
Although overall there are decreases in wastewater Covid-19 levels across most of Scotland in the last two weeks, 14 local authorities have increased their levels over the past week. Increases were reported in Angus, City of Edinburgh, Clackmannanshire, Dundee City, East Dunbartonshire, East Lothian, Falkirk, Highland, Inverclyde, Midlothian, Moray, Perth and Kinross, Renfrewshire, and West Lothian. Please note that comparisons for Argyll and Bute, Na h-Eileanan Siar, Orkney, Shetland and Stirling are not possible due to sampling coverage.
Reported Covid-19 Cases
The LFD Universal Offer for asymptomatic testing came to an end on 18 April 2022. In addition, on 1 May 2022 the purpose of COVID-19 testing shifted from population-wide testing to reduce transmission, to targeted testing and surveillance. Reported cases will no longer be representative of all COVID-19 cases in Scotland, and caution is advised when comparing trends in cases over time. For more information, see the Scottish Government Covid-19 Test and Protect Transition Plan.
Please note that due to testing policy changes, reported cases will no longer be representative of all COVID-19 cases in Scotland, and caution is advised when comparing trends in cases over time. By specimen date, there were 158 weekly combined PCR and LFD cases (including reinfections) per 100,000 population in the week to 6 May (Figure 5). This follows a period of sharply decreasing case rates since the most recent peak in March. The regular analyses on case rates in different age groups and among care home residents are no longer included in this report.
The proportion of reinfections among the total weekly cases has increased in the most recent week. By specimen date, there was a total number of 1,159 reinfection cases confirmed by either a PCR or LFD test in the week leading up to 6 May. This represents 13.4% of reported cases, and compares to 12.8% in the week leading up to 29 April . However, this number is likely affected by testing changes and this figure may no longer be comparable over time. The proportion of reinfections have increased rapidly since December 2021 and the emergence of the Omicron variant.
While the LFD Universal Offer for asymptomatic testing came to an end on 18 April 2022 in Scotland, 129,983 LFD tests were reported in the week to 8 May. This is a 29% decrease from the week previously (week to 1 May), when 182,972 LFD tests were reported. This compared to a peak of 865,561 tests being reported in the week to 26 December 2021, while the LFD Universal Offer was still in place.
The Scottish Contact Survey continues to ask whether people use LFD tests and if so how often. Approximately 51% of individuals had taken at least one lateral flow test within the last 7 days for the survey pertaining to the period 28 April to 4 May, decreasing from 68% two weeks prior.
Antimicrobial Resistance and Healthcare Associated Infection Scotland (ARHAI Scotland) provide analyses on hospital onset acquired Covid-19 infections, where patients are likely to have been infected after being admitted to hospital, based on the date when the sample was collected for a first positive Covid-19 test. Cases where the sample was collected before a hospital admission are considered community onset cases, while samples collected on day eight or later are considered nosocomial cases, or cases likely to have been acquired in a hospital setting. For more information, see this ARHAI weekly publication.
According to data from ARHAI Scotland, 97.8% of the 30,262 Covid-19 cases reported in the week ending 17 April 2022 were reported as community onset cases. 237 cases in the same period were reported as nosocomial cases. This is a 27% decrease from the previous week ending 10 April (324 nosocomial cases). This follows a period of increasing numbers of nosocomial cases since the beginning of February (following a peak in late December 2021 and early January 2022). The number of cases in all categories of inpatient diagnosed COVID-19 cases increased during the same time period, including those diagnosed on day one or two, reflecting the high levels of transmission in the community.
In line with recent changes to testing policy and transitions to long term strategies in the four UK nations, cases comparison between countries will no longer be included in the report. For more information see following links for England, Scotland, Wales, and Northern Ireland.
To compare trends in estimated infection levels in private residential households across the UK, please see the previous section on the Covid-19 Infection Survey.
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