Integrated genomic surveillance enables tracing of person-to-person SARS-CoV-2 transmission chains during community transmission and reveals extensive onward transmission of travel-imported infections, Germany, June to July 2021

Background: Tracking person-to-person SARS-CoV-2 transmission in the population is important to under-stand the epidemiology of community transmission and may contribute to the containment of SARS-CoV-2. Neither contact tracing nor genomic surveillance alone, however, are typically sufficient to achieve this objective. Aim: We demonstrate the successful appli-cation of the integrated genomic surveillance (IGS) system of the German city of Dusseldorf for tracing SARS-CoV-2 transmission chains in the population as well as detecting and investigating travel-associated SARS-CoV-2 infection clusters. Methods: Genomic sur-veillance, phylogenetic analysis, and structured case interviews were integrated to elucidate two geneti-cally defined clusters of SARS-CoV-2 isolates detected by IGS in Dusseldorf in July 2021. Results: Cluster 1 (n = 67 Dusseldorf cases) and Cluster 2 (n = 36) were detected in a surveillance dataset of 518 high-quality SARS-CoV-2 genomes from Dusseldorf (53% of total cases, sampled mid-June to July 2021). Cluster 1 could be traced back to a complex pattern of transmission in nightlife venues following a putative importation by a SARS-CoV-2-infected return traveller (IP) in late June;28 SARS-CoV-2 cases could be epidemiologically directly linked to IP. Supported by viral genome data from Spain, Cluster 2 was shown to represent multi-ple independent introduction events of a viral strain circulating in Catalonia and other European coun-tries, followed by diffuse community transmission in Dusseldorf.

SARS-CoV-2 seroprevalence and determinants of infection in young adults: a population-based seroepidemiological study.

OBJECTIVES: Most SARS-CoV-2 seroprevalence studies have focussed on adults and high-risk populations, and little is known about young adults. The objective of the present study was to provide evidence on the SARS-CoV-2 seroprevalence among young adults in Germany and to explore determinants associated with seropositivity in general and, specifically, with previously undetected infections. STUDY DESIGN: This was a population-based SARS-CoV-2 seroprevalence study. METHODS: In November 2020, a population-based study on SARS-CoV-2 seroprevalence in young adults (aged 18-30 years) was conducted in a large German city. Serum samples were obtained to analyse the SARS-CoV-2 antibody status using the Elecsys Anti-SARS-CoV-2 immunoassay. Descriptive statistics and odds ratios (ORs) of seropositivity and of previously undetected infections in relation to different determinants were calculated. RESULTS: Among 2186 participants, SARS-CoV-2 antibodies were detected in 72 individuals, equalling a test performance-adjusted seroprevalence of 3.1% (95% confidence interval [CI]: 2.4-4.0). Based on reported COVID-19 cases to the public health authority, a moderate underascertainment rate of 1.7 was calculated. Seropositivity was higher among individuals who sought COVID-19-related information from social media (OR: 1.83, 95% CI: 1.2-3.1), and undetected COVID-19 infections were more prevalent among men and those not adhering to social distancing. CONCLUSIONS: The results show a substantial underascertainment of SARS-CoV-2 infections among young adults and indicate that seroprevalence is likely to be much higher than the reported COVID-19 prevalence based on confirmed COVID-19 cases in Germany. Preventive efforts should consider the heterogeneity of risk profiles among the young adult population.

Underascertainment of COVID-19 cases among first responders: a seroepidemiological study.

BACKGROUND: Providing frontline support places first responders at a high risk for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection. AIMS: This study was aimed to determine the anti-SARS-CoV-2 seroprevalence in a cohort of first responders (i.e. firefighters/paramedics), to detect the underascertainment rate and to assess risk factors associated with seropositivity. METHODS: We conducted a serological survey among 745 first responders in Germany during 27 November and 4 December 2020 to determine the anti-SARS-CoV-2 seroprevalence using Elecsys® Anti-SARS-CoV-2 immunoassay (Roche Diagnostics, Mannheim, Germany). As part of the examination, participants were asked to provide information on coronavirus disease 2019 (COVID-19)-like-symptoms, information on sociodemographic characteristics and workplace risk factors for a SARS-CoV-2 infection and any prior COVID-19 infection. Descriptive statistics and logistic regression analysis were performed and seroprevalence estimates were adjusted for test sensitivity and specificity. RESULTS: The test-adjusted seroprevalence was 4% (95% CI 3.1-6.2) and the underascertainment rate was 2.3. Of those tested SARS-CoV-2 antibody positive, 41% were aware that they had been infected in the past. Seropositivity was elevated among paramedics who worked in the emergency rescue team providing first level of pre-hospital emergency care (6% [95% CI 3.4-8.6]) and those directly exposed to a COVID-19 case (5% [95% CI 3.5-8.1]). Overall, the seroprevalence and the underascertainment rate were higher among first responders than among the general population. CONCLUSIONS: The high seroprevalence and underascertainment rate highlight the need to mitigate potential transmission within and between first responders and patients. Workplace control measures such as increased and regular COVID-19-testing and the prompt vaccination of all personnel are necessary.