Enhanced surveillance of COVID-19 in Scotland: population-based seroprevalence surveillance for SARS-CoV-2 during the first wave of the epidemic.

OBJECTIVES: The impact of the COVID-19 pandemic in Scotland has been amongst the most severe in Europe. Serological surveillance is critical to determine the overall extent of infection across populations and to inform the public health response. This study aimed to estimate the proportion of people who have antibodies to SARS-CoV-2 ('seroprevalence') in the general population of Scotland and to see if this changes over time. STUDY DESIGN/METHODS: Between International Organization for Standardization (ISO) week 17 (i.e. week commencing 20th April) and ISO week 25 (week commencing 15 June), 4751 residual blood samples were obtained from regional biochemistry laboratories in six participating regional health authority areas covering approximately 75% of the Scottish population. Samples were tested for the presence of anti-SARS-CoV-2 IgG antibodies using the LIAISON®SARS-CoV-2 S1/S2 IgG assay (DiaSorin, Italy). Seroprevalence rates were adjusted for the sensitivity and specificity of the assay using Bayesian methods. RESULTS: The combined adjusted seroprevalence across the study period was 4.3% (95% confidence interval: 4.2%-4.5%). The proportion varied each week between 1.9% and 6.8% with no difference in antibody positivity by age, sex or geographical area. CONCLUSIONS: At the end of the first wave of the COVID-19 pandemic, only a small fraction of the Scottish population had antibodies to SARS-CoV-2. Control of COVID-19 requires the ability to detect asymptomatic and mild infections that would otherwise remain undetected through existing surveillance systems. This is important to determine the true number of infections within the general population which, in turn, can help to understand transmission, inform control measures and provide a denominator for the estimation of severity measures such as the proportion of infected people who have been hospitalised and/or have died.

National population prevalence of antibodies to SARS-CoV-2 in Scotland during the first and second waves of the COVID-19 pandemic.

OBJECTIVES: Studies that measure the prevalence of antibodies to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) ('seroprevalence') are essential to understand population exposure to SARS-CoV-2 among symptomatic and asymptomatic individuals. We aimed to measure seroprevalence in the Scottish population over the course of the COVID-19 pandemic - from before the first recorded case in Scotland through to the second pandemic wave. STUDY DESIGN: The study design of this study is serial cross sectional. METHODS: We tested 41,477 residual samples retrieved from primary and antenatal care settings across Scotland for SARS-CoV-2 antibodies over a 12-month period from December 2019-December 2020 (before rollout of COVID-19 vaccination). Five-weekly rolling seroprevalence estimates were adjusted for the sensitivity and specificity of the assays and weighted to reference populations. Temporal trends in seroprevalence estimates and weekly SARS-CoV-2 notifications were compared. RESULTS: Five-weekly rolling seroprevalence rates were 0% until the end of March, when they increased contemporaneously with the first pandemic wave. Seroprevalence rates remained stable through the summer (range: 3%-5%) during a period of social restrictions, after which they increased concurrently with the second wave, reaching 9.6% (95% confidence interval [CI]: 8.4%-10.8%) in the week beginning 28th December in 2020. Seroprevalence rates were lower in rural vs. urban areas (adjusted odds ratio [AOR]: 0.70, 95% CI: 0.61-0.79) and among individuals aged 20-39 years and 60 years and older (AOR: 0.74, 95% CI: 0.64-0.86; AOR: 0.80, 95% CI: 0.69-0.91, respectively) relative to those aged 0-19 years. CONCLUSIONS: After two waves of the COVID-19 pandemic, less than one in ten individuals in the Scottish population had antibodies to SARS-CoV-2. Seroprevalence may underestimate the true population exposure as a result of waning antibodies among individuals who were infected early in the first wave.

The incidence and prevalence of HIV infection among childbearing women living in Edinburgh city, 1982-1995.

OBJECTIVE: To track the complete course of the HIV epidemic among women from the city of Edinburgh who delivered babies during 1982-1995. METHODS: The performance of the modified Serodia HIV test on dried blood spots from archived neonatal metabolic screening cards stored for up to 11 years was evaluated by testing 221 cards from neonates whose mothers' HIV infection status was already known (100 HIV-positive, 121 HIV-negative). Unlinked anonymous HIV testing of cards from neonates born during 1982-1989 was then performed and the resulting prevalence data were combined with existing data from 1990-1995. Maximum and minimum limits of HIV incidence among women during the 36-month period prior to delivery were calculated using data held on a clinical database of HIV-infected pregnant women that had been generated under strict conditions of confidentiality; these data included the date of the woman's first HIV-positive and, if available, last HIV-negative specimen. RESULTS: The evaluation revealed a sensitivity of 91%, not clearly related to storage time, and a specificity of 100%. HIV infection first entered Edinburgh's childbearing population during the early 1980s with prevalence peaking at 0.4% in 1986 and then decreasing to 0.1% in 1995; a similar incidence profile was seen during this period. Since 1986, the first full year that HIV testing was available, 78% of all infections were known during the pregnancy, 13% were identified retrospectively, and only 10% (10 cases) remain unaccounted for. For infected cases during 1984-1987, 78% were injecting drug users (IDU) and only 22% acquired their infection sexually; this distribution had reversed by 1992-1995. CONCLUSION: HIV testing of neonatal metabolic screening cards stored for up to 11 years can yield results of sufficient accuracy for epidemiological purposes. There has been a substantial decline in the prevalence and incidence of HIV since the mid-1980s. Although new infections are still occurring, the numbers are small. The decline may largely be explained by the impact of preventive measures on the spread of HIV amongst IDU, and thus from IDU to their sexual partners.