Point prevalence of SARS-CoV-2 infection in Sweden at six time points during 2020.

BACKGROUND: In order to estimate the prevalence and understand the spread of SARS-CoV-2 in Sweden, the Public Health Agency of Sweden, with support from the Swedish Armed Forces, conducted a series of point prevalence surveys between March and December 2020. METHODS: Sampling material and instructions on how to perform self-sampling of the upper respiratory tract were delivered to the homes of the participants. Samples were analysed by real-time PCR, and the participants completed questionnaires regarding symptoms. FINDINGS: The first survey in the Stockholm region in March 2020 included 707 participants and showed a SARS-CoV-2 prevalence of 2.5%. The following five surveys, performed on a national level, with between 2461 and 2983 participants, showed SARS-CoV-2 prevalences of 0.9% (April), 0.3% (May), 0.0% (August), 0.0% (September), and 0.7% (December). All positive cases who responded to questionnaires reported experiencing symptoms that occurred from 2 weeks before the date of sampling up to and including the date of sampling. INTERPRETATION: None of the individuals shown to be PCR-positive were asymptomatic at the time of sampling or in the 14 days prior to sampling. This is in contrast to many other surveys in which a substantial proportion of positive cases have been reported to be asymptomatic. Our surveys demonstrate a decreasing ratio between notified cases and the observed prevalence throughout the year, in line with increasing testing capacity and the consecutive inclusion of all symptomatic individuals in the case definition for testing.

Point prevalence of SARS-CoV-2 infection in Sweden at six time points during 2020 (preprint)

Background: To estimate the prevalence and understand the dissemination of SARS-CoV-2 in Sweden, the Public Health Agency of Sweden, with support from the Swedish Armed Forces, conducted a series of point prevalence surveys between March and December 2020. Methods: Sampling material and instructions on how to perform self-sampling of the upper respiratory tract were delivered to the homes of the participants. Samples were analysed by real-time PCR, and the participants completed questionnaires regarding symptoms. Findings: The first survey in the Stockholm region in March, including 707 participants, showed a SARS-CoV-2 prevalence of 2.5%. The following five surveys, performed on a national level, with between 2,461 and 2,983 participants, showed SARS-CoV-2 prevalences of 0.9% (April), 0.3% (May), 0.0% (August), 0.0% (September), and 0.7% (December).All positive cases responding to the questionnaires regarding experienced symptoms had experienced symptoms two weeks before sampling up until the day of sampling. Interpretation None of the individuals shown to be PCR-positive were asymptomatic at the time of sampling, including 14 days prior to sampling. This is in contrast to many other surveys, where a substantial proportion of positive cases are reported to be asymptomatic.In line with an increasing testing capacity and consecutive inclusion of all symptomatic individuals in the case definition for testing, our surveys demonstrate a decreasing ratio between notified cases and shown prevalence throughout the year.

Civil-Military Collaboration to Facilitate Rapid Deployment of a Mobile Laboratory in Early Response to COVID-19: A High-Readiness Exercise.

Rapid and adaptable diagnostic capabilities are of great importance in the face of emerging infectious diseases. In an outbreak, timely establishment of diagnostic routines is crucial to identifying cases and preventing the spread of the disease, especially when faced with high-consequence pathogens. In this article, we describe a multiagency exercise including the rapid deployment and diagnostic adaptation of the Swedish Armed Forces mobile laboratory (biological field analysis laboratory) in the context of COVID-19. This deployment was initiated as a high-readiness exercise at the end of January 2020, when the global development of the outbreak was still uncertain. Through collaboration with the Public Health Agency of Sweden and a civilian hospital, a real-time reverse transcriptase polymerase chain reaction method specific to SARS-CoV-2 was made available and adapted to the mobile laboratory, and the team established and evaluated a functional and efficient diagnostic asset along with a logistical support chain. We also organized and evaluated mobile testing teams, and the method was later used in large-scale, national, cross-sectional COVID-19 surveys in several regions of Sweden. In this article, we focus on the challenges of overbridging the civil-military interface in this context and identifying lessons learned and added values to the response during the early pandemic. We propose that the experiences from this exercise and governmental agency collaboration are valuable in preparation for future outbreaks.

Evaluation of 11 SARS-CoV-2 antibody tests by using samples from patients with defined IgG antibody titers.

We evaluated the performance of 11 SARS-CoV-2 antibody tests using a reference set of heat-inactivated samples from 278 unexposed persons and 258 COVID-19 patients, some of whom contributed serial samples. The reference set included samples with a variation in SARS-CoV-2 IgG antibody titers, as determined by an in-house immunofluorescence assay (IFA). The five evaluated rapid diagnostic tests had a specificity of 99.0% and a sensitivity that ranged from 56.3 to 81.6% and decreased with low IFA IgG titers. The specificity was > 99% for five out of six platform-based tests, and when assessed using samples collected ≥ 22 days after symptom onset, two assays had a sensitivity of > 96%. These two assays also detected samples with low IFA titers more frequently than the other assays. In conclusion, the evaluated antibody tests showed a heterogeneity in their performances and only a few tests performed well with samples having low IFA IgG titers, an important aspect for diagnostics and epidemiological investigations.

Massive and rapid COVID-19 testing is feasible by extraction-free SARS-CoV-2 RT-PCR.

Coronavirus disease 2019 (COVID-19), caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), is commonly diagnosed by reverse transcription polymerase chain reaction (RT-PCR) to detect viral RNA in patient samples, but RNA extraction constitutes a major bottleneck in current testing. Methodological simplification could increase diagnostic availability and efficiency, benefitting patient care and infection control. Here, we describe methods circumventing RNA extraction in COVID-19 testing by performing RT-PCR directly on heat-inactivated or lysed samples. Our data, including benchmarking using 597 clinical patient samples and a standardised diagnostic system, demonstrate that direct RT-PCR is viable option to extraction-based tests. Using controlled amounts of active SARS-CoV-2, we confirm effectiveness of heat inactivation by plaque assay and evaluate various generic buffers as transport medium for direct RT-PCR. Significant savings in time and cost are achieved through RNA-extraction-free protocols that are directly compatible with established PCR-based testing pipelines. This could aid expansion of COVID-19 testing.