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Background It has been suggested that the transiently increased infection risk following childcare enrolment is compensated by decreased infection risk later in childhood and adolescence. We investigated how childcare enrolment affected rates of antimicrobial-treated infections during childhood and adolescence. Methods In a register-based cohort study of all children born in Denmark 1997–2014 with available exposure information (n = 1 007 448), we assessed the association between childcare enrolment before age 6 years and infection risks up to age 20 years, using antimicrobial exposure as proxy for infections. Nationwide childcare and prescription data were used. We estimated infection rates and the cumulative number of infections using adjusted Poisson regression models. Results We observed 4 599 993 independent episodes of infection (antimicrobial exposure) during follow-up. Childcare enrolment transiently increased infection rates; the younger the child, the greater the increase. The resulting increased cumulative number of infections associated with earlier age at childcare enrolment was not compensated by lower infection risk later in childhood or adolescence. Accordingly, children enrolled in childcare before age 12 months had experienced 0.5–0.7 more infections at age 6 years (in total 4.5–5.1 infections) than peers enrolled at age 3 years, differences that persisted throughout adolescence. The type of childcare had little impact on infection risks. Conclusions Early age at childcare enrolment is associated with a modest increase in the cumulative number of antimicrobial-treated infections at all ages through adolescence. Emphasis should be given to disrupting infectious disease transmission in childcare facilities through prevention strategies with particular focus on the youngest children.

Epstein–Barr virus infection, and perhaps almost exclusively delayed Epstein–Barr virus infection, seems to be a prerequisite for the development of multiple sclerosis. Siblings provide protection against infectious mononucleosis by occasionally preventing delayed primary Epstein–Barr virus infection, with its associated high risk of infectious mononucleosis. Each additional sibling provides further protection according to the age difference between the index child and the sibling. The closer the siblings are in age, the higher the protection, with younger siblings being more protective against infectious mononucleosis than older siblings. If the hypothesis that delayed Epstein–Barr virus infection is necessary for the development of multiple sclerosis is true, then the relative risk of multiple sclerosis as a function of sibship constellation should mirror the relative risk of infectious mononucleosis as a function of sibship constellation. Such an indirect hypothesis test is necessitated by the fact that age at primary Epstein–Barr virus infection is unknown for practically all people who have not experienced infectious mononucleosis. In this retrospective cohort study using nationwide registers, we followed all Danes born during the period 1971–2018 (n = 2 576 011) from 1977 to 2018 for hospital contacts with an infectious mononucleosis diagnosis (n = 23 905) or a multiple sclerosis diagnosis (n = 4442), defining two different end points. Relative risks (hazard ratios) of each end point as a function of sibship constellation were obtained from stratified Cox regression analyses. The hazard ratios of interest for infectious mononucleosis and multiple sclerosis could be assumed to be identical (test for homogeneity P = 0.19), implying that having siblings, especially of younger age, may protect a person against multiple sclerosis through early exposure to the Epstein–Barr virus. Maximum protection per sibling was obtained by having a 0–2 years younger sibling, corresponding to a hazard ratio of 0.80, with a 95% confidence interval of 0.76–0.85. The corresponding hazard ratio from having an (0–2 years) older sibling was 0.91 (0.86–0.96). Our results suggest that it may be possible essentially to eradicate multiple sclerosis using an Epstein–Barr virus vaccine administered before the teenage years. Getting there would require both successful replication of our study findings and, if so, elucidation of why early Epstein–Barr virus infection does not usually trigger the immune mechanisms responsible for the association between delayed Epstein–Barr virus infection and multiple sclerosis risk.

OBJECTIVES: There is a gap in knowledge about the effects of smoking on overall infection risk in otherwise healthy populations, possibly leading to underestimation of the dangers of smoking. The present study aimed to examine the association of smoking with the risk of infections in a large cohort of healthy blood donors.METHODS: This cohort study used questionnaire and health register data from 127 831 Danish blood donors. Multivariable Cox proportional hazards analysis was applied to estimate the association of current smoking with the risk of all-cause infection defined as hospital-based treatment for infection or filled prescriptions of antimicrobials stratified for age and adjusted for relevant confounders.RESULTS: Among 18 272 current smokers, 12 272 filled an antimicrobial prescription and 2035 received hospital-based treatment for infections. Among 101 974 non-smokers, 65 117 filled a prescription and 8501 received hospital-based treatment for infections. Smokers had a higher risk of all-cause infection than non-smokers (hazard ratio estimates were 1.27 in males and 1.33 in females for hospital-based treatment and 1.11 in males and up to 1.20 in females for filled prescriptions). Smoking was most strongly associated with an increased incidence of respiratory tract infection, abscesses, skin infection, and prescriptions for these ailments (hazard ratio up to 2.29). Furthermore, smokers' risk of filled prescriptions of broad-spectrum penicillin was increased (hazard ratio up to 1.96).CONCLUSIONS: Current smoking was strongly associated with the risk of hospital-based treatment of infection and filled prescriptions of antimicrobials in a large cohort of healthy individuals. These findings warrant an increased focus on infectious disease risk among smokers.

Association between neonatal inflammatory markers and risk of infections before age 2 years.

ICD-10 codes for infections and ATC codes for antimicrobials.

It has been proposed that children with acute lymphoblastic leukemia (ALL) are born with a dysregulated immune function that together with postnatal environmental exposures causes childhood ALL. Despite its importance for the understanding of ALL etiology, this hypothesis has been inadequately explored. In a population-based case–control study, we measured the concentrations of 10 cytokines and other inflammatory markers on neonatal dried blood spots from 178 children who at ages 1 to 9 years were diagnosed with B-cell precursor ALL and 178 matched controls. Through linkage with Danish nationwide registers, we also assessed whether neonatal inflammatory markers were associated with previously demonstrated risk factors for childhood ALL. Children who developed B-cell precursor ALL had significantly lower neonatal concentrations of IL8, soluble IL6 receptor (sIL6R) α, TGFβ1, monocyte chemotactic protein (MCP)-1, and C-reactive protein (CRP) and higher concentrations of IL6, IL17, and IL18 compared with matched controls. Concentrations of IL10 were below the detection level for both patients and controls. Birth order (IL18 and CRP), gestational age (sIL6Rα, TGFβ1, and CRP), and sex (sIL6Rα, IL8, and CRP), but not maternal age, infections during pregnancy, birth weight nor mode of delivery were significantly associated with the neonatal concentrations of inflammatory markers. Our findings support the hypothesis that children who later develop B-cell precursor ALL are born with a dysregulated immune function.Significance: Children who develop acute lymphoblastic leukemia are immunologically distinct at birth and could potentially react abnormally to infections in early childhood. Cancer Res; 78(18); 5458–63. ©2018 AACR.

In this review we present contemporary understanding of aetiological heterogeneity in Hodgkin lymphoma, discuss how this may influence tumour phenotype and whether it does or may impact treatment outcomes. Many new treatments are being tested in this era. We especially discuss T-cell therapy and immune checkpoint blockade, because these two modern treatments are expected to have differential efficacy by the presence/absence of Epstein-Barr virus in the malignant Hodgkin-Reed-Sternberg cells. Survival after Hodgkin lymphoma is excellent in many patient strata with first-line treatment, but less so for patients with refractory or relapsing disease. On the other hand, this good prognosis also means that very large trials are needed to demonstrate superior efficacy of new treatment regimes. And our understanding of aetiological heterogeneity in Hodgkin lymphoma and how it affects prognosis is hampered for the same reason. We discuss the potential for fine-tuning risk stratification and treatment based on information that is little used today.

BACKGROUND: The healthy donor effect (HDE) is a selection bias caused by the health criteria blood donors must meet. It obscures investigations of beneficial/adverse health effects of blood donation and complicates the generalizability of findings from blood donor cohorts. To further characterize the HDE we investigated how self-reported health and lifestyle are associated with becoming a blood donor, lapsing, and donation intensity. Furthermore, we examined differences in mortality based on donor status.STUDY DESIGN AND METHODS: The Danish National Health Survey was linked to the Scandinavian Donations and Transfusions (SCANDAT) database and Danish register data. Logistic- and normal regression was used to compare baseline characteristics and participation. Poisson regression was used to investigate future donation choices. Donation intensity was explored by the Anderson-Gill model and Poisson regression. Mortality was investigated using Poisson regression.RESULTS: Blood donors were more likely to participate in the surveys, OR = 2.45 95% confidence interval (2.40-2.49) than non-donors. Among survey participants, better self-reported health and healthier lifestyle were associated with being or becoming a blood donor, donor retention, and to some extent donation intensity, for example, current smoking conveyed lower likelihood of becoming a donor, OR = 0.70 (0.66-0.75). We observed lower mortality for donors and survey participants, respectively, compared with non-participating non-donors.CONCLUSION: We provide evidence that blood donation is associated with increased likelihood to participate in health surveys, possibly a manifestation of the HDE. Furthermore, becoming a blood donor, donor retention, and donation intensity was associated with better self-reported health and healthier lifestyles.

Using provisional or opportunistic data, three nationwide studies (The Netherlands, the USA and Denmark) have identified a reduction in preterm or extremely preterm births during periods of COVID-19 restrictions. However, none of the studies accounted for perinatal deaths. To determine whether the reduction in extremely preterm births, observed in Denmark during the COVID-19 lockdown, could be the result of an increase in perinatal deaths and to assess the impact of extended COVID-19 restrictions, we performed a nationwide Danish register-based prevalence proportion study. We examined all singleton pregnancies delivered in Denmark during the COVID-19 strict lockdown calendar periods (March 12–April 14, 2015-2020, N = 31,164 births) and the extended calendar periods of COVID-19 restrictions (February 27–September 30, 2015-2020, N = 214,862 births). The extremely preterm birth rate was reduced (OR 0.27, 95% CI 0.07 to 0.86) during the strict lockdown period in 2020, while perinatal mortality was not significantly different. During the extended period of restrictions in 2020, the extremely preterm birth rate was marginally reduced, and a significant reduction in the stillbirth rate (OR 0.69, 0.50 to 0.95) was observed. No changes in early neonatal mortality rates were found.Conclusion: Stillbirth and extremely preterm birth rates were reduced in Denmark during the period of COVID-19 restrictions and lockdown, respectively, suggesting that aspects of these containment and control measures confer an element of protection. The present observational study does not allow for causal inference; however, the results support the design of studies to ascertain whether behavioural or social changes for pregnant women may improve pregnancy outcomes. What is Known:• The aetiologies of preterm birth and stillbirth are multifaceted and linked to a wide range of socio-demographic, medical, obstetric, foetal, psychosocial and environmental factors.• The COVID-19 lockdown saw a reduction in extremely preterm births in Denmark and other high-income countries. An urgent question is whether this reduction can be explained by increased perinatal mortality. What is New:• The reduction in extremely preterm births during the Danish COVID-19 lockdown was not a consequence of increased perinatal mortality, which remained unchanged during this period.• The stillbirth rate was reduced throughout the extended period of COVID-19 restrictions.

Childhood acute lymphoblastic leukaemia (ALL) is suggested to result from a dysregulated immune response to infections in children with a preleukaemic state. Childcare in early life supposedly may protect against childhood ALL by facilitating sufficient exposure to infections to stimulate and ensure normal maturation of the immune system. We assessed the association between childcare attendance before age two years and risk of childhood ALL in a register-based cohort study, including all children aged 2-14 years born in Denmark during 1991-2014 with available childcare information recorded in the Danish Childcare Database (n=1,116,185). Cox regression was used to estimate hazard ratios (HRs) comparing children enrolled in childcare and children not enrolled before age two years. Further, we assessed the association according to age at enrolment, type of childcare facility and specific ALL subtypes. During 10,460,811 person-years of follow-up, 460 children developed ALL at ages 2-14 years. Of these, 57 (12.4%) never attended childcare before age two years compared with 10.6% in the total cohort. Compared with homecare, childcare attendance before age two years was associated with a statistically non-significantly, marginally decreased risk of childhood ALL with adjusted HR = 0.87 (95% confidence interval (CI): 0.65-1.16). Risk estimates did neither vary statistically significantly by age at enrolment nor by type of childcare facility and also not between childhood ALL subtypes, including frequently prenatally initiated ALL subtypes. Results from this large, nationwide register-based study provided no evidence that childcare attendance in the first years of life protects against childhood ALL.

PURPOSE: In pharmacoepidemiology, correctly defining the exposure period of pharmacological treatment is a challenging step when information on the time in treatment is missing or incomplete.METHODS: In this review, we describe several methods for defining exposure to pharmacological treatments using secondary data sources that lack such information.RESULTS AND CONCLUSION: Several methods for assessing the duration of redeemed prescriptions and combining them into temporal sequences are available. We present a set of considerations to make researchers aware of the potentials and pitfalls of these methods that may aid in minimizing biases in research using these methods. Additionally, we highlight that, to date, there is no one-size-fits-all solution. Thus, the choice of method should be based on their area of applicability combined with a careful mapping to the research scenario under investigation.

BACKGROUND: Blood donors report better health-related quality of life (HRQL) than non-donors. Likewise, donors reporting good health are less likely to stop donating and have a higher donation frequency. This is evidence of the healthy donor effect (HDE). This study is the first to investigate the impact of HRQL and depressive symptoms on subsequent donor career.STUDY DESIGN AND METHODS: Prospective cohort study includes 102,065 participants from the Danish Blood Donor Study applying the 12-item short-form health survey (SF-12) measuring a mental (MCS) and a physical component score (PCS) and the Major Depression Inventory (MDI). Poisson and Cox regression models were used to assess the effect of SF-12 and MDI scores on donation frequency and donor cessation. Higher MCS/PCS scores indicate good HRQL, while higher MDI score indicates higher experience of depressive symptoms.RESULTS: For both sexes, MCS was positively correlated with donation frequency for up to 5 years, and similarly for PCS among women. A negative correlation between MDI score and donation frequency in the year following assessment was observed only among men. No correlation was observed among women. An increase in both MCS and PCS was associated with a lower risk of donation cessation in both sexes, while an increase in MDI score was only associated with an increased risk of donation cessation in men.CONCLUSION: MCS, PCS, and MDI score affect donor career. Thus, adjusting for donation frequency may reduce HDE-bias in donor health research. However, because of the small effect sizes, other ways of quantifying HDE may be beneficial.

Patients with chronic lymphocytic leukaemia (CLL) have an increased risk of new malignancies. However, limited data have been published about the impact of CLL treatment on this risk. Here we followed a Danish population-based cohort of CLL patients for risks of new malignancies. Patients in the Danish CLL registry (2008–2017) were included. Up to 50 CLL-free matched comparators were identified. First-line treatment was categorized into four groups; bendamustine, chlorambucil, fludarabine or other. Patients were followed from CLL diagnosis for individual types of malignancy. Adjusted hazard ratios (HR) for new malignancies and 95% confidence intervals (95% CI) were calculated. Overall, 4286 CLL patients and 214 150 controls developed 594 and 20 565 new malignancies respectively. Risk of new malignancies was increased for CLL patients. Chemotherapy treatment was registered for 1064 (25%) patients with CLL. Chemotherapy was associated with increased HR (1·51, 95% CI: 1·3–1·8) of any new malignancy. Specifically, fludarabine was associated with an increased risk of myelodysplastic syndrome (MDS) (HR 4·93, 95% CI: 1·2–19·8). Patients with CLL are at increased risk of other haematological and solid malignancies compared to the general population. Chemotherapy exposure is associated with increased risk of second malignancies and fludarabine is associated with increased risk of MDS.

Background The two previous versions of the Scandinavian donations and transfusions (SCANDAT) databases, encompassing data on blood donors, blood components, transfusions, and transfused patients linked to national health registers in Sweden and Denmark up until 2012, have been used to study donor health, disease transmission, the role of donor characteristics, and more. Study Design and Methods Here we describe the creation of the Swedish portion of the third iteration of SCANDAT – SCANDAT3‐S – with follow‐up from 1968 to the end of 2017, resulting in up to 50 years of uninterrupted follow‐up for donors and recipients. The database now also includes non‐transfused non‐donors with a blood typing result, increased temporal resolution for transfusions, and linkages to laboratory and drug prescription data. Results After data cleaning, the database contained 23 579 863 donation records, 21 383 317 transfusion records, and 8 071 066 unique persons with valid identification. In total, the database offers 28 638 436 person‐years of follow‐up for donors, 13 582 350 person‐years of follow‐up for transfusion recipients, and 65 613 639 person‐years of follow‐up for non‐recipient non‐donors, with possibility for future extension. Additionally, the database includes 167 820 412 dispense records for prescribed drugs and 316,338,442 laboratory test results. Since the latest update in 2012, >99.9% of all donations were traceable to a donor with valid identification, and >97% of all transfusions to a recipient with valid identification. Conclusion With extended follow‐up and more clinical detail, the Swedish portion of the third and latest iteration of the SCANDAT database should allow for more comprehensive analysis of donation and transfusion‐related research questions.

Background Patients with hematological malignancies (HM) are known to carry an increased risk of invasive pneumococcal disease (IPD). However, temporal variations in IPD risks following a cancer diagnosis remain poorly characterized. To inform vaccine guidelines and patient management, we assessed the IPD incidence among patients with HM and other malignancies. Methods The study population included all individuals aged ≥15 years during 2000–2016 in Denmark. Variations in incidences of IPD over time and between different types of hematological malignancies and diagnoses were assessed by Poisson regression. Results During 85 002 224 person-years of observation, 13 332 episodes of a first IPD were observed, of which 765 (5.7%) occurred among individuals with HM. Among HM patients, the IPD incidence rate decreased continuously during the study period (rate ratio per year, 0.91; 95% confidence interval, .90–.92). The risk of IPD in patients with HM was up to 39 times higher when compared to the background population and was highest for multiple myeloma, acute lymphoblastic leukemia, and chronic lymphocytic leukemia. Unlike other malignancies, the increased IPD risk did not wane with the time since HM diagnosis. We found a vaccination uptake of only ≤2% in patients with HM and ≤1% for those with other types of malignancies. Conclusions Adults with HM in general and patients with lymphoid malignancies in particular have an increased risk for IPD, compared with patients with other types of cancer and with individuals free of cancer. The pneumococcal vaccination uptake is extremely low in this at risk-population. Efforts to prevent IPD in HM patients are continuously warranted.

BackgroundA large discrepancy between physician-diagnosed and self-reported Hidradenitis suppurativa (HS) exists. Knowledge regarding incidence and remission rates of self-reported HS is missing, but may help bridge the gap in understanding between these two phenotypes.ObjectivesTo determine the incidence and remission rates of self-reported HS, and to what degree these are affected by sex, smoking and BMI.MethodsA prospective cohort of 23 930 Danish blood donors. Information on self-reported HS, symptom-localisation, sex, age, BMI and smoking status was collected at baseline and study termination. Self-reported HS fulfilled clinical obligatory diagnostic criteria. Cox proportional hazards regression analyses were conducted for both incidence and remission rates providing a hazard ratio (HR) of risk for each variable in the regression.ResultsIncidence rate of self-reported HS was 10.8/1000 person-years (95% confidence interval (CI): 9.9–11.7), decreasing as a function of numbers of areas affected. Female BMI points above 25 (HR = 1.11, 95% CI: 1.09–1.13), male BMI points above 25 (HR = 1.07, 95% CI: 1.04–1.11), active smoking (HR = 1.72, 95% CI: 1.15–2.57), male sex (HR = 0.55, 95% CI: 0.45–0.67) and years of age above 25 (HR = 0.97, 95% CI: 0.96–0.97) were all statistically associated with the development of self-reported HS. Remission rate of self-reported HS was 256.7/1000 person-years (95% CI: 223.9–292.6), decreasing as a function of numbers of affected areas. Symptoms in ≥3 areas (HR = 0.54, 95% CI: 0.34–0.85), active smoking (HR = 0.49, 95% CI: 0.32–0.76) and female weight loss (every percentage drop in BMI: HR = 1.07, 95% CI: 1.05–1.11) all significantly affected the remission rate.ConclusionsBoth incidence and remission rates of self-reported HS are high, indicating that many with self-reported HS are unlikely to be diagnosed, as they to a higher degree experience mild transient HS symptoms.

Dry skin or xerosis is a common ailment occurring both as a separate disease entity and as a symptom of other diseases, e.g. it is a cardinal symptom of atopic dermatitis1 . Infections have been described in xerosis associated with dermatitis2 . Whether xerosis without dermatitis is a risk factor for skin infections remains unknown. We therefore tested if individuals with xerosis had a risk of skin infections.

Background The present study aimed to assess whether the widespread concern of inferior cancer survival in adolescents and young adults (AYAs) compared with children and adults holds true in a Nordic setting with important differences in healthcare organisation compared with the United States (e.g. free access to healthcare) and the United Kingdom (e.g. young teenagers are treated in paediatric departments). Methods Five-year relative survival was calculated for 17 diagnostic groups in patients diagnosed in 2000–2013 in three diagnostic age categories: children (0–14 years), AYAs (15–24 years) and adults (25–34 years). Results For 13 out of 17 diagnostic groups examined, there was no difference in survival between AYAs and neighbouring age categories. For acute lymphoblastic leukaemias, astrocytomas, rhabdomyosarcomas and non-rhabdomyosarcoma soft tissue sarcomas we found survival in children to be superior to that in AYAs. For these four diagnostic groups, the rate of survival improvement over three calendar periods (1980–1989, 1990–1999 and 2000–2013) was not particularly low in AYAs compared with neighbouring age categories. Conclusions The present study suggests that in an affluent setting with free access to healthcare, meaningful differences in survival between AYA patients and either childhood or adult patients are a phenomenon of the past for most AYA cancer diagnostic groups.

Emelie C Rotbain,1– 5 Klaus Rostgaard,3,5 Michael A Andersen,2,3 Caspar Da Cunha-Bang,2 Carsten U Niemann,2 Henrik Frederiksen,1,4,6 Henrik Hjalgrim2,3,5,7 1Department of Hematology, Odense University Hospital, Odense, Denmark; 2Department of Hematology, Rigshospitalet, Denmark; 3Department of Epidemiology Research, Statens Serum Institut, Copenhagen, Denmark; 4Department of Clinical Research, University of Southern Denmark, Odense, Denmark; 5Danish Cancer Society Research Center, Hematology Research Group, Copenhagen, Denmark; 6Academy of Geriatric Cancer Research (AGECARE), Odense University Hospital, Odense, Denmark; 7Department of Clinical Medicine, Copenhagen University, Copenhagen, DenmarkCorrespondence: Emelie C RotbainDepartment of Hematology, Odense University Hospital, Kløvervænget 6, Odense, DK-5000, DenmarkTel +45 5369 0201Email erot0006@regionh.dkPurpose: Age-related comorbidity is highly prevalent in chronic lymphocytic leukemia (CLL). The purpose of this study was to provide information on current patterns of healthcare utilization in CLL.Patients and Methods: We used data from Danish nation-wide registers to study healthcare utilization the year before and the year after CLL diagnosis and in relation to first-line treatment. Patients diagnosed with CLL between 1997 and 2018 were included and stratified on number of comorbidities, presence of specific comorbidities, and fitness status, respectively. Healthcare utilization was studied in terms of hospital admissions, in-hospital bed days, out-patient visits, emergency room visits, and prescription drugs. Odds ratios with 95% confidence intervals were calculated using multivariable logistic regression analyses adjusting for age, sex, and calendar year.Results: The study comprised 9170 patients with CLL with a median age of 71 years, of whom 35% had ≥ 1 comorbidity. Healthcare utilization increased markedly upon CLL diagnosis both in patients with and without comorbidities. During the year after CLL diagnosis, 39% were hospitalized, 16% visited an emergency room, 88% visited an out-patient clinic, and 93% received prescription drugs. Both individual comorbidities and the total number of comorbidities were associated with increased healthcare utilization of all types, except for contacts to hematological departments.Conclusion: Our results suggest that CLL diagnosis may unveil incipient diseases and aggravate comorbidities and thereby have considerably wider health implications than those directly related to CLL. These findings may be used by clinicians and decisions makers to guide planning of multidisciplinary care for cancer patients.Keywords: chronic lymphocytic leukemia, hematology, epidemiology, real-world data

Background Although the vast majority of individuals succumbing to infection with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) are elderly, infection fatality rate (IFR) estimates for the age group ≥70 years are still scarce. To this end, we assessed SARS-CoV-2 seroprevalence among retired blood donors and combined it with national coronavirus disease 2019 (COVID-19) survey data to provide reliable population-based IFR estimates for this age group. Methods We identified 60 926 retired blood donors aged ≥70 years in the rosters of 3 regionwide Danish blood banks and invited them to fill in a questionnaire on COVID-19–related symptoms and behaviors. Among 24 861 (40.8%) responders, we invited a random sample of 3200 individuals for blood testing. Overall, 1201 (37.5%) individuals were tested for SARS-CoV-2 antibodies (Wantai) and compared with 1110 active blood donors aged 17–69 years. Seroprevalence 95% confidence intervals (CIs) were adjusted for assay sensitivity and specificity. Results Among retired (aged ≥70 years) and active (aged 17–69 years) blood donors, adjusted seroprevalences were 1.4% (95% CI, .3–2.5%) and 2.5% (95% CI, 1.3–3.8%), respectively. Using available population data on COVID-19–related fatalities, IFRs for patients aged ≥70 years and for 17–69 years were estimated at 5.4% (95% CI, 2.7–6.4%) and .083% (95% CI, .054–.18%), respectively. Only 52.4% of SARS-CoV-2–seropositive retired blood donors reported having been sick since the start of the pandemic. Conclusions COVID-19 IFR in the age group >69 years is estimated to be 65 times the IFR for people aged 18–69 years.

Background: Investigations of migraine among childhood cancer survivors have predominantly relied on self-reported information and hospital discharge diagnoses. Alone, both approaches are liable to bias. We used Danish nationwide registers to obtain data on both prescriptions of acute migraine medications (antimigraines) and hospital discharge diagnoses of migraine to assess the relative risk of migraine across a wider spectrum of migraine presentations than previously studied. Methods: We followed a Danish population-based cohort of 7771 individuals with childhood cancer diagnosed in the period from Jan 1st, 1978 to Dec 31st, 2017, for risk of prescription antimigraine initiation and for risk of hospitalization due to migraine. Rates of hospitalization were assessed for the entire follow-up period whereas rates of antimigraine initiations were assessed in the period from Jan 1st, 1997, to Dec 31st, 2017. Relative to the general population without childhood cancer, standardized incidence ratios (SIRs) were calculated for each outcome. Results: Individuals exposed to childhood cancer were at increased risk of antimigraine initiation (SIR of 1.24, 95% CI: 1.11–1.38) and of migraine hospitalization (SIR of 2.44, 95% CI: 1.87–3.12) from the day of their cancer diagnosis and up to 40 years after. Conclusions: Individuals diagnosed with childhood cancer have a higher risk of migraine of varying presentations, in addition to migraine resulting in hospitalization as previously reported. This potentially preventable problem warrants clinical attention.

Background and aims Allergic rhinitis (AR), allergic conjunctivitis (AC), and asthma are characterized by activation of the immune system. The aim of this study was to explore the long-term association between AR, AC, asthma, and specific immunoglobulin E (IgE) and blood platelet and leukocyte differential counts. Material and methods In the Danish Blood Donor Study, 14,440 participants from Central Denmark Region had platelet and leukocyte differential counts available and completed a questionnaire regarding AR, AC, and asthma. Of these participants, 8485 were tested for IgE to inhalation allergens. Results The prevalence of AR, AC, asthma, and IgE sensitization was 19%, 15%, 9%, and 29%, respectively. AR, AC, asthma, wheeze, and IgE sensitization was associated with increased blood eosinophil concentration even in IgE sensitized participants who did not report any allergy or asthma. The strongest associations were observed for participants with current disease. We found no differences in eosinophil concentration between months without symptoms and months with symptoms of AR and asthma. Conclusion AR, AC, asthma, wheezing, and IgE sensitization to inhalation allergens are associated with increased eosinophil concentration. This may reflect a persistent inflammation even in periods without symptomatic disease.

ImportanceUsing provisional or opportunistic data, three nationwide studies (The Netherlands, USA, and Denmark) have identified a reduction in preterm or extremely preterm births during periods of COVID-19 restrictions. However, these findings have been challenged as none of the studies accounted for perinatal deaths.ObjectiveTo determine whether the reduction in extremely preterm births, observed in Denmark during the COVID-19 lockdown, could be a result of an increase in number of perinatal deaths; and to assess the impact of extended COVID-19 restrictions on the prevalence of preterm birth and perinatal death.DesignThe study is a nationwide Danish register-based prevalence proportion study using detailed data to capture all births (induced abortions were excluded) throughout Denmark. We assessed the prevalence of stillbirth, preterm birth, and early neonatal death.SettingPopulation-based studyParticipantsAll singleton pregnancies delivered in Denmark, between February 27, and September 30, 2015-2020. COVID-19 lockdown was studied in 31,164 births and the extended period of COVID-19 restrictions in 214,862 births.ExposureCOVID-19 restrictions broadly (February 27, – September 30, 2020) or COVID-19 lockdown specifically (March 12, – April 14, 2020).Main OutcomePrevalence of preterm births, stillbirths and early neonatal deaths across the periods under study.ResultsThe extremely preterm birth rate was reduced (OR 0.27, 95% CI 0.07 to 0.86) during the strict lockdown period, while perinatal mortality was not significantly different. During the extended period of restrictions, the extremely preterm birth rate was marginally reduced, and a significant reduction in the stillbirth rate (OR 0.69, 0.50 to 0.95) was observed. No changes in early neonatal mortality rates were found.Conclusion and RelevanceStillbirth and extremely preterm birth rates were reduced in Denmark during the period of COVID-19 restrictions and lockdown, respectively, suggesting that aspects of these containment and control measures confer an element of protection. The present observational study does not allow for causal inference; however, the results support design of studies to ascertain whether behavioural or social changes for pregnant women may improve pregnancy outcomes.FundingNoneKey pointsQuestionCan changes in stillbirth and early neonatal mortality rates during the COVID-19 lockdown explain the reduction in extremely preterm birth seen in Denmark?FindingsIn this nationwide register-based study that included data pertaining to 245,999 pregnancies, the statistically significant reduction in extremely preterm birth during the COVID-19 lockdown was confirmed. The stillbirth and early neonatal mortality rates were unchanged during lockdown, while the stillbirth rate was reduced over the extended period of COVID-19 restrictions.MeaningThe reduction in extremely preterm births seen during the COVID-19 lockdown in Denmark is not a result of increased stillbirth or early neonatal death.

The peculiar bimodal age distribution of Hodgkin lymphoma (HL), together with other epidemiological findings, inspired the so-called “late infection hypothesis” in the 1970s. Under this model, HL in young adults is caused by delayed infection with a relatively common agent, with HL risk increasing with age at infection. We time-dependently tallied prescriptions filled, for a broad spectrum of antimicrobials, at age 0 to 9 years for all Danish HL patients diagnosed in 1997 to 2015 at age 10 to 25 years (n = 296) and up to 10 controls for each of these, individually matched for sex and birthdate (n = 2688). Antimicrobial use was taken as a proxy for general infectious disease pressure. Analyses were also stratified by the 2 main histological subtypes: nodular sclerosis HL (NSHL) (n = 206) and mixed cellularity HL (MCHL) (n = 47). We compared antimicrobial use at ages 0 to 9 years between cases and comparators using stratified Cox regressions with repeated follow-up for a next prescription, to produce hazard ratios (HRs) of antimicrobial use according to (future) HL status. Reverse causation was mitigated by disregarding risk time

Background Allergic rhinitis (AR), allergic conjunctivitis (AC), and asthma composing multiple phenotypes and improved understanding of these phenotypes and their respective risk factors are needed. Objectives The objective of this study was to define the prevalence of AR, AC, and asthma and their association with allergen-specific immunoglobulin E (sIgE) sensitization in a large cohort of blood donors and identify risk factors. Methods From the nationwide population-based Danish Blood Donor Study, 52,976 participants completed an electronic questionnaire including AR, AC, asthma, allergic predisposition, and childhood residence. Of these, 25,257 were additionally tested for sIgE to inhalation allergens (Phadiatop). Results The prevalence of sIgE sensitization, AR, AC, and asthma was 30%, 19%, 15%, and 9%, respectively. The youngest birth cohorts had the highest prevalence of sIgE sensitization and symptoms of asthma, AR, and AC, and for asthma, they apparently experienced symptoms at an earlier age. The sIgE sensitization was positively associated with male sex. The sIgE seroprevalence was higher in participants with both AR and AC (ARC) than in participants with either AR or AC. Allergic predisposition and sIgE sensitization increased the risk of the diseases, while farm upbringing was associated with reduced prevalence of ARC, however, only in sIgE sensitized participants. Conclusion Birth year, childhood residence, sIgE sensitization, and allergic predisposition were associated with asthma, AR, and AC prevalence. Individuals with self-reported ARC represent a primarily sIgE-positive phenotype, while those with either AR or AC represent more diverse phenotypes. Background: Allergic rhinitis (AR), allergic conjunctivitis (AC), and asthma composing multiple phenotypes and improved understanding of these phenotypes and their respective risk factors are needed. Objectives: The objective of this study was to define the prevalence of AR, AC, and asthma and their association with allergen-specific immunoglobulin E (sIgE) sensitization in a large cohort of blood donors and identify risk factors. Methods: From the nationwide population-based Danish Blood Donor Study, 52,976 participants completed an electronic questionnaire including AR, AC, asthma, allergic predisposition, and childhood residence. Of these, 25,257 were additionally tested for sIgE to inhalation allergens (Phadiatop). Results: The prevalence of sIgE sensitization, AR, AC, and asthma was 30%, 19%, 15%, and 9%, respectively. The youngest birth cohorts had the highest prevalence of sIgE sensitization and symptoms of asthma, AR, and AC, and for asthma, they apparently experienced symptoms at an earlier age. The sIgE sensitization was positively associated with male sex. The sIgE seroprevalence was higher in participants with both AR and AC (ARC) than in participants with either AR or AC. Allergic predisposition and sIgE sensitization increased the risk of the diseases, while farm upbringing was associated with reduced prevalence of ARC, however, only in sIgE sensitized participants. Conclusion: Birth year, childhood residence, sIgE sensitization, and allergic predisposition were associated with asthma, AR, and AC prevalence. Individuals with self-reported ARC represent a primarily sIgE-positive phenotype, while those with either AR or AC represent more diverse phenotypes.

Comorbid conditions are highly prevalent in chronic lymphocytic leukemia (CLL), nevertheless, detailed information on the association of specific comorbidities with CLL prognosis is missing. Using Danish, nation-wide registers, we followed consecutive patients from CLL-diagnosis in 1997–2018, until death or end of follow-up. Sub-grouping of comorbidities was defined using a modified Charlson comorbidity index. Patients were matched on sex, date of birth (±1 month), and region of residency with up to ten comparators from the general population. In total, 9170 patients with CLL were included in the study, with a median of 5.0 years of follow-up. All comorbid conditions studied were individually associated with increased mortality, and many also with increased cause-specific mortality, related or unrelated to CLL. Comorbidity correlated with increased mortality from infections and cardiovascular disease. CLL patients, particularly older, had a significant loss of lifetime compared with the general population. This study highlights a large subgroup of comorbid CLL patients with an unmet treatment-need and missing efficacy and safety data on treatment, who are under-prioritized in clinical trials. Also, studies assessing interventions that may provide better tolerability of treatment in older or comorbid patients, with cancer in general, and CLL in particular, are warranted.

To explore the impact of COVID-19 lockdown on premature birth rates in Denmark, a nationwide register-based prevalence proportion study was conducted on all 31 180 live singleton infants born in Denmark between 12 March and 14 April during 2015–2020.The distribution of gestational ages (GAs) was significantly different (p=0.004) during the lockdown period compared with the previous 5 years and was driven by a significantly lower rate of extremely premature children during the lockdown compared with the corresponding mean rate for the same dates in the previous years (OR 0.09, 95% CI 0.01 to 0.40, pThe reasons for this decrease are unclear. However, the lockdown has provided a unique opportunity to examine possible factors related to prematurity. Identification of possible causal mechanisms might stimulate changes in clinical practice.

Objectives To explore the impact of COVID-19 lockdown on premature birth rates in Denmark Design Nationwide register-based prevalence proportion study. Participants 31,180 live singleton infants born in Denmark between March 12, and April 14, from 2015 to 2020 Main outcome measures The Main outcome measure was the odds ratio of premature birth, per preterm category, during the lockdown period compared with the calendar match period in the five previous years. Results A total of 31 180 newborns were included in the study period, of these 58 were born extremely premature (gestational age below 28 weeks). The distribution of gestational ages was significantly different (p = 0.004) during the lockdown period compared to the previous five years. The extremely premature birth rate during the lockdown was significantly lower than the corresponding mean rate for the same dates in the previous years (odds ratio 0.09 [95 % CI 0.01 - 0.04], p < 0.001). No significant difference between the lockdown and previous years was found for other gestational age categories. Conclusions The birth rate of extremely premature infants decreased significantly (~90 % reduction) during the Danish nationwide lockdown from a stable rate in the preceding five years. The reasons for this decrease are unclear. Identification of possible causal mechanisms might stimulate changes in clinical practice. Ideally, some cases of extreme prematurity are preventable which may decrease infant morbidity and mortality.

Introduction: There are conflicting results whether elevated hematocrit is associated with an increased risk of thromboembolic events in individuals without polycythemia vera. To assess the risk of vascular events in relation to hemoglobin concentration, we conducted a large population-based cohort study based on Scandinavian health registers. Materials and methods: We included 1,538,019 Swedish and Danish blood donors between 1987 and 2012. Hazard ratios (HRs) of arterial and venous thrombosis were estimated using Cox regression. Additionally, we fitted person-stratified models where each donor was compared only to him-/herself. Results: The risk of myocardial infarction and ischemic stroke increased with higher hemoglobin concentration in both men and women. The HRs for myocardial infarction and ischemic stroke in men with hemoglobin concentration ≥ 17.5 g/dL were 3.52 (95% confidence interval [CI], 2.85–4.36) and 2.36 (95% CI, 1.63–3.43), respectively, compared to the reference group. The corresponding HRs for women with hemoglobin concentration ≥ 16.0 g/dL were 3.22 (2.12–4.89) and 2.35 (1.37–4.02) for myocardial infarction and ischemic stroke, respectively. The risk of venous thrombosis was highest in men with subnormal hemoglobin concentration (