Thea Kølsen Fischer

Nordsjællands Hospital · Department of Research

Background Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and its associated disease coronavirus disease 2019 (COVID-19), is a worldwide emergency. Demographic, comorbidity and laboratory determinants of death and of ICU admission were explored in all Danish hospitalised patients. Methods National health registries were used to ident...

SARS-CoV-2 infection causes COVID-19. Most infected children have asymptomatic or mild clinical manifestations. A few develop serious illness, and the case fatality rate is lower than in adults. The most frequent symptoms are fever and cough. Studies indicate that children might be less susceptible to infection than adults as summarised in this rev...

Respiratory syncytial virus (RSV) is a common cause of acute lower respiratory tract infections (ALRI) and hospitalisations among young children and is globally responsible for many deaths in young children, especially in infants below 6 months of age. Furthermore, RSV is a common cause of severe respiratory disease and hospitalisation among the el...

Background: Households are high-risk settings for the transmission of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Severity of Coronavirus disease 2019 (COVID-19) is likely associated with the infectious dose of SARS-CoV-2 exposure. We therefore aimed to assess the association between SARS-CoV-2 exposure within households and COVI...

Authors of the March WHO report into how COVID-19 emerged warn that further delay makes crucial inquiry biologically difficult

Background: Respiratory syncytial virus (RSV) is a major cause of lower respiratory tract infections in older adults that can result in hospitalisations and death. Estimating RSV-associated hospitalisation is critical for planning RSV-related healthcare needs for the ageing population across Europe. Methods: We gathered national RSV-associated hosp...

Background Viral shedding and neutralizing antibody (NAb) dynamics among patients hospitalized with severe coronavirus disease 2019 (COVID-19) and immune correlates of protection have been key questions throughout the pandemic. We investigated the duration of reverse transcriptase-polymerase chain reaction (RT-PCR) positivity, infectious viral shed...

Work in wastewater treatment plants (WWTPs) can be associated with exposure to airborne microorganisms and endotoxin from the working environment. The aim of this study was to obtain knowledge about whether serum levels of the markers of systemic inflammation, C-reactive protein (CRP) and serum amyloid A (SAA), are associated with personal exposure...

Hospitalisation at Home (HaH) is a new model providing hospital-level care at home as a substitute for traditional care. Biometric monitoring and digital communication are crucial, but little is known about user perspectives. We aim to explore how in-patients with severe COVID-19 infection and clinicians engage with and experience communication and...

Identifying at-risk groups and evaluating preventive interventions in at-risk groups is imperative for the ongoing pandemic as well as for the control of future epidemics. Although DCS staff have a much higher risk of being infected within their own household than at their workplace, most are fearful of being infected with COVID-19 or bringing COVI...

Background SARS-CoV-2 infection is associated with persistent symptoms (long-COVID). We assessed the burden of long-COVID among non-hospitalized PCR-confirmed adults. Methods In the fall of 2020, a cross-sectional survey was performed in the adult Danish general population. This included a self-administered point-of-care test for SARS-CoV-2 antibo...

Background: According to the World Health Organization, the global burden of nosocomial infections is poorly characterized as surveillance systems are lacking. Nosocomial infections occur at higher rates in low- and lower-middle-income countries (LMICs) than in high-income countries (HICs). Current global RSV burden estimates are largely based on...

Background Respiratory syncytial virus (RSV) is a major cause of hospitalisation in infants. The burden of RSV infection in healthy term infants has not yet been established. Accurate health-care burden data in healthy infants are necessary to determine RSV immunisation policy when RSV immunisation becomes available. Methods We performed a multice...

Objective Model-based cost-effectiveness analyses on maternal vaccine (MV) and monoclonal antibody (mAb) interventions against respiratory syncytial virus (RSV) use context-specific data and produce varied results. Through model comparison, we aim to characterise RSV cost-effectiveness models and examine drivers for their outputs. Methods We compa...

Objectives: This pilot study tested the use of an exercise offer to hospital employees during working hours and changes in work and health parameters. Methods: Employees (n = 214) from a medical department on a Danish hospital were invited to 30 minutes exercise training twice weekly for 12 weeks. Outcomes included health and work-related parame...

SARS-CoV-2 variants of concern have continuously evolved and may erode vaccine induced immunity. In this observational cohort study, we determine the risk of breakthrough infection in a fully vaccinated cohort. SARS-CoV-2 anti-spike IgG levels were measured before first SARS-CoV-2 vaccination and at day 21–28, 90 and 180, as well as after booster v...

Abstract Background People experiencing homelessness (PEH) and associated shelter workers may be at higher risk of infection with “Severe acute respiratory syndrome coronavirus 2” (SARS-CoV-2). The aim of this study was to determine the prevalence of SARS-CoV-2 among PEH and shelter workers in Denmark. Design and methods In November 2020, we conduc...

Background: Knowledge on age-specific hospitalizations associated with RSV infection is limited due to limited testing, especially in older children and adults in whom RSV infections are not expected to be severe. Burden estimates based on RSV coding of hospital admissions are known to underestimate the burden of RSV. We aimed to provide robust an...

Aim Infant respiratory syncytial virus infection (RSV) has been associated with asthma later in life. We explored the risk of recurrent wheeze or asthma in children with infant RSV-associated hospitalization compared to other respiratory infections. Methods We performed a retrospective cohort study using Danish national hospital discharge register...

Introduction: Knowledge of the seroprevalence and duration of antibodies against SARS-CoV-2 was needed in the early phases of the COVID-19 pandemic and is still necessary for policy makers and healthcare professionals. This information allows us to better understand the risk of reinfection in previously infected individuals. Methods: We investig...

Background Estimates of the severity of the SARS-CoV-2 omicron variant (B.1.1.529) are crucial to assess the public health impact associated with its rapid global dissemination. We estimated the risk of SARS-CoV-2-related hospitalisations after infection with omicron compared with the delta variant (B.1.617.2) in Denmark, a country with high mRNA v...

Background: Since the widespread adoption of palivizumab prophylaxis in Europe, there have been a number of clinical practice guidelines (CPGs) published for the prevention of respiratory syncytial virus (RSV) infection in children. The aim of this systematic review was to identify CPGs for the prevention of RSV infection across Europe. Methods:...

Introduction: We aimed to evaluate post-COVID-19 fatigue, change in functional capacity and health-related quality of life (HRQoL) eight months after discharge from hospital due to COVID-19. Methods: A total of 83 patients (35 women) admitted to the Copenhagen University Hospital - North Zealand Hospital, Denmark, for COVID-19 during the period...

Objectives To identify individual characteristics associated with serological COVID-19 vaccine responsiveness and durability of vaccine-induced antibodies. Methods Adults without history of SARS-CoV-2 infection from the Danish population scheduled for SARS-CoV-2 vaccination were enrolled in this parallel group, phase IV study. SARS-CoV-2 Spike IgG...

Abstract Background COVID-19 is thought to be more prevalent among ethnic minorities and individuals with low socioeconomic status. We aimed to investigate the prevalence of SARS-CoV-2 antibodies during the COVID-19 pandemic among citizens 15 years or older in Denmark living in social housing (SH) areas. Methods We conducted a study between January...

Background The purpose of this study was to assess whether influenza vaccination has an impact on the risk of coronavirus disease 2019 (COVID-19). Methods A cohort of 46 112 healthcare workers were tested for antibodies against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and filled in a survey on COVID-19 symptoms, hospitalization...

To date, including 318,522 participants, this is the largest population-based study with broad national participation where tests and questionnaires have been sent to participants’ homes. We found that more emphasis from national and local authorities toward the risk of infection should be placed on age of tested individuals, type of occupation, as...

Background Despite availability of pre-exposure prophylaxis (PrEP), the incidence of HIV-1 in Europe remained stable the past decade. Reduction of new HIV-1 infections requires more knowledge about the profiles of high-risk transmitters and late presenters (LP). Aim We aimed to investigate risk factors associated with HIV-1 transmission clusters a...

We report a rapid increase in enterovirus D68 (EV-D68) infections, with 139 cases reported from eight European countries between 31 July and 14 October 2021. This upsurge is in line with the seasonality of EV-D68 and was presumably stimulated by the widespread reopening after COVID-19 lockdown. Most cases were identified in September, but more are...

Most individuals seroconvert after infection with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), but negative serology is observed in 1 to 9%. We found that asymptomatic or mild infection as well as a BMI above 30 were associated with being seronegative. Since the presence of antibodies against SARS-CoV-2 reduces the risk of reinfect...

Background: Universal mass vaccination (UMV) against rotavirus has been implemented in many but not all European countries. This study investigated the impact of UMV on rotavirus incidence trends by comparing European countries with UMV: Belgium, England/Wales and Germany versus countries without UMV: Denmark and the Netherlands. Methods: For th...

Objectives: Antibodies to severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) are a key factor against COVID-19. We examined longitudinal changes in seroprevalence in healthcare workers (HCW) in Copenhagen and the protective effect of antibodies against SARS-CoV-2. Methods: In this prospective study, screening for antibodies against SAR...

Background: Non-polio enteroviruses (EVs) and human parechoviruses (PeVs) cause a wide range of human infections. Limited data on their true disease burden exist as standardized European-wide surveillance is lacking. Aims: Our aim is to estimate the disease burden of EV and PeV infections in Europe via establishment of standardized surveillance...

Human respiratory syncytial virus (RSV) is a major cause of lower respiratory tract infection in young children globally, but little is known about within-host RSV diversity. Here, we characterised within-host RSV populations using deep-sequencing data from 319 nasopharyngeal swabs collected during 2017–2020. RSV-B had lower consensus diversity tha...

Background National data on the spread of SARS-CoV-2 infection and knowledge on associated risk factors are important for understanding the course of the pandemic. Testing Denmark is a national large-scale epidemiological surveillance study of SARS-CoV-2 in the Danish population. Methods Between September and October 2020, approximately 1.3 million...

Background: The SARS-CoV-2 pandemic spread across Europe from February 2020. While robust SARS-CoV-2 serological assays were quickly developed, only limited information on applied serological testing is available. We describe the extent and nature of SARS-CoV-2 serological testing used in Europe and assess the links between epidemiology, mitigatio...

Poliovirus is known to most people in the world as the cause of polio, a devastating paralytic disease from the past. Success in polio eradication has understandably translated into stricter containment plans for poliovirus, coordinated by WHO. In this Personal View, we discuss the impact of recent biosafety level 3+ guidelines for handling potenti...

In 2018, an upsurge in echovirus 30 (E30) infections was reported in Europe. We conducted a large-scale epidemiologic and evolutionary study of 1,329 E30 strains collected in 22 countries in Europe during 2016-2018. Most E30 cases affected persons 0-4 years of age (29%) and 25-34 years of age (27%). Sequences were divided into 6 genetic clades (G1-...

Background COVID-19 is suggested to be more prevalent among ethnic minorities and individuals with low socioeconomic status. We aimed to investigate the prevalence of SARS-CoV-2 antibodies during the COVID-19 pandemic among citizens 15 years or older in Denmark living in social housing (SH) areas . Methods As part of Testing Denmark, a nationwide s...

Background People experiencing homelessness (PEH) and associated shelter workers may be at higher risk of infection with 'Severe acute respiratory syndrome coronavirus 2' (SARS-CoV-2). The aim of this study was to determine the prevalence of SARS-CoV-2 among PEH and shelter workers in Denmark. Design and methods In November 2020, we conducted a nat...

Background Prevention of illness due to infection by influenza viruses is important for children with rheumatic diseases. Biological disease modifying antirheumatic drugs have become increasingly important in the treatment of juvenile idiopathic arthritis, and combinations of immunosuppressive drugs are used for the treatment of systemic disorders,...

The COVID‐19 pandemic caused by the novel coronavirus SARS‐CoV‐2 continues to have a major impact on healthcare and social systems throughout the world. As the clinical and epidemiological features of COVID‐19 have many parallels with influenza, it is important to ensure optimal management of both respiratory diseases as we anticipate their continu...

Background: Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and its associated disease coronavirus disease 2019 (COVID-19), is a worldwide emergency. Demographic, clinical and laboratory factors associated with mortality in Danish patients hospitalised with COVID-19 is limited. Methods: National health registries were used to identify...

Introduction: Coronavirus disease 2019 (COVID-19) is an ongoing pandemic associated with significant morbidity and mortality worldwide. Limited data are available describing the clinical presentation and outcomes of hospitalised COVID-19 patients in Europe. Methods: This was a single-centre retrospective chart review of all patients with COVID-19 a...

Background Health-care workers are thought to be highly exposed to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection. We aimed to investigate the prevalence of antibodies against SARS-CoV-2 in health-care workers and the proportion of seroconverted health-care workers with previous symptoms of COVID-19. Methods In this observa...

Picornaviruses (family Picornaviridae) are small, nonenveloped, positive-sense, single-stranded RNA viruses. The members of this family are currently classified into 47 genera and 110 species. Of picornaviruses, entero- and parechoviruses are associated with aseptic meningitis. They are transmitted via fecal-oral and respiratory routes, and occasio...

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Background: The long-term clinical course of patients with an enterovirus central nervous system infection (ECI) is poorly understood. Methods: We performed a nationwide population-based cohort study of all Danish patients with an ECI diagnosed during 1997-2016 (n=1745 patients) and a comparison cohort from the general population individually ma...

Aims To investigate seasonality and association of increased enterovirus and influenza activity in the community with ventricular fibrillation (VF) risk during first ST-elevation myocardial infarction (STEMI). Methods This study comprised all consecutive patients with first STEMI (n = 4,659; aged 18–80 years) admitted to the invasive catheterizati...

Norovirus (NoV) infections occur very frequently yet are rarely diagnosed. In Denmark, NoV infections are not under surveillance. We aimed to collect and describe existing laboratory-based NoV data. National NoV laboratory data were collected for 2011-2018, including information on patient identification number, age and sex, requesting physician, a...

Background: Enteroviruses can cause severe infections, especially in young children. Non-polio enterovirus infections are not notifiable in most countries in the EU and European Economic Area (EEA) region, and surveillance varies substantially between countries. We collected and analysed available enterovirus data across EU and EEA countries to as...

PCR detection has become the gold standard for diagnosis and typing of enterovirus (EVs) and human parechovirus (HPeV) infections. Its effectiveness depends critically on using appropriate sample types and high assay sensitivity since viral loads in cerebrospinal fluid samples from meningitis and sepsis clinical presentation can be extremely low. T...

Background Respiratory syncytial virus (RSV) is a major contributor to lower respiratory tract infections worldwide and several vaccine candidates are currently in development. Following vaccine introduction, reliable RSV surveillance should enable monitoring of vaccination impact. Data on the RSV disease burden in the European Union and European E...

Background: Recurrent wheeze and asthma in childhood are commons causes of chronic respiratory morbidity globally. We aimed to explore the association between respiratory syncytial virus (RSV) infection in early life and subsequent respiratory sequelae up to age 12 years. Methods: We estimated the strength of association by 3 control groups and...

Introduction Sequence-based typing of hepatitis A virus (HAV) is important for outbreak detection, investigation and surveillance. In 2013, sequencing was central to resolving a large European Union (EU)-wide outbreak related to frozen berries. However, as the sequenced HAV genome regions were only partly comparable between countries, results were...

Background: In randomized trials, it has been found that maternal influenza vaccination reduces influenza infections in both women and their infants. However, these trials have been performed in low-resource settings, and evidence from high-resource settings is limited. Methods: Nested within a register-based cohort of all women giving birth in...

Enteric viruses, particularly rotaviruses and noroviruses, are leading causes of gastroenteritis worldwide. Human rotaviruses are ubiquitous and globally almost every child has been infected by 3-5 years of age. Noroviruses affect people of all ages and is the leading cause of foodborne outbreaks. Rota- and noroviruses account for ˜40% and ˜17% of...

This study describes the prevalence of human immuno-deficiency virus (HIV) drug resistance mutations among 1,815 patients in Denmark from 2004 to 2016 and char-acterises transmission clusters. POL sequences were analysed for subtype, drug resistance mutations and phylogenetic relationship. The prevalence of surveillance drug resistance mutations (S...

An upsurge in Echovirus 30 (E30) infections, associated with meningitis/meningoencephalitis, has been observed in Denmark, Germany, the Netherlands, Norway and Sweden in the period April to September 2018, compared with 2015-2017. In total, 658 E30 infections among 4,537 enterovirus infections were detected in 15 countries between January and Septe...

Transmission of HIV-1 resistance mutations among therapy-naïve patients impairs the efficiency of antiretroviral therapy (ART). Therefore, genotypic resistance testing of patients is recommended at baseline, as this both allows for the selection of the correct ART regimen and for surveillance of transmitted drug resistance mutations (TDRM) among th...

We use surveillance data to describe influenza A and B virus circulation over two consecutive seasons with excess all-cause mortality in Europe, especially in people aged 60 years and older. Influenza A(H3N2) virus dominated in 2016/17 and B/Yamagata in 2017/18. The latter season was prolonged with positivity rates above 50% among sentinel detectio...

The World Health Organization recommends inclusion of rotavirus vaccines in national immunization programs (NIPs) worldwide. Nordic countries are usually considered comparable in terms of demographics and health-care services and have comparable rotavirus disease burden. Nevertheless, the countries have reached different decisions regarding rotavir...

We analyzed blood samples from infants born with microcephaly and their mothers in Guinea-Bissau in 2016 for pathogens associated with birth defects. No Zika virus RNA was detected, but Zika virus IgG was highly prevalent. We recommend implementing pathogen screening of infants with congenital defects in Guinea-Bissau