Booster vaccination with SARS-CoV-2 mRNA vaccines and myocarditis in adolescents and young adults: a Nordic cohort study.

BACKGROUND AND AIMS: The SARS-CoV-2 mRNA vaccines are associated with an increased risk of myocarditis. This association appears to be strongest in male adolescents and younger males and after the second dose. The aim was to evaluate the risk of myocarditis following SARS-CoV-2 mRNA booster vaccination in 12-to-39-year-olds. METHODS: A multinational cohort study was conducted using nationwide register data in Denmark, Finland, Norway, and Sweden and comprising all 8.9 million individuals residing in each of the four countries. Participants were followed for an inpatient diagnosis of myocarditis. In each of the four countries, Poisson regression was used to estimate adjusted incidence rate ratios (IRRs) of myocarditis comparing vaccination schedules, with associated 95% confidence intervals (CIs). Country-specific results were combined in meta-analyses. RESULTS: A total of 8.9 million residents were followed for 12 271 861 person-years and 1533 cases of myocarditis were identified. In 12-to-39-year-old males, the 28-day acute risk period following the third dose of BNT162b2 or mRNA-1273 was associated with an increased incidence rate of myocarditis compared to the post-acute risk period 28 days or more after the second dose [IRR 2.08 (95% CI 1.31-3.33) and 8.89 (2.26-35.03), respectively]. For females, the corresponding IRR was only estimable for BNT162b2, 3.99 (0.41-38.64). The corresponding absolute risks following the third dose of BNT162b2 and mRNA-1273 in males were 0.86 (95% CI 0.53-1.32) and 1.95 (0.53-4.99) myocarditis events within 28 days per 100 000 individuals vaccinated, respectively. In females, the corresponding absolute risks following the third dose of BNT162b2 were 0.15 (0.04-0.39) events per 100 000 individuals vaccinated. No deaths occurred within 30 days of vaccine-related cases. CONCLUSIONS: The results suggest that a booster dose is associated with increased myocarditis risk in adolescents and young adults. However, the absolute risk of myocarditis following booster vaccination is low.

Hoarding of insulin and oral antidiabetics in the first phase of the COVID-19 pandemic: Regulatory actions taken to avoid shortage.

OBJECTIVE: To report on hoarding of prescribed medicines, with focus on insulins, in the early phase of the COVID-19 pandemic and on regulatory actions taken to avoid shortage. MATERIALS AND METHODS: The National Prescribed Drug Register which utilizes the Anatomic Therapeutic Chemical (ATC) Classification System and covers the total Swedish population was used. We calculated the number of packages of insulins (ATC code A10A), oral anti-diabetics (A10B), and all medicines across all ATC codes combined (A-S) dispensed per week in 2019 and 2020. Correspondingly, the number of packages of glucose test strips dispensed was calculated using the data source Concise held by the Swedish eHealth Agency. RESULTS: Prompt increases in numbers of dispensed packages were observed in March, peaking at week 11/2020. The absolute numbers of packages dispensed in week 11/2019 and week 11/2020 were: insulin, 49,694 and 95,767, an increase by +92.7%; oral antidiabetics, 55,478 and 82,684, +47.1%; glucose test strips, 18,119 and 23,476, +29:6%; and all medicines across all ATC codes combined, 1,988,456 and 2,659,421, +33.7%. Voluntary restriction of dispensing and a rapid change to applicable regulation were implemented within 2 weeks. A steep decline occurred, which became more pronounced after temporary regulation came in force from April 1, then leveling out during the following months. CONCLUSION: A signal of insulin hoarding was detected early in the COVID-19 pandemic. A temporary regulation, reducing dispensing to a maximum supply of 3 months was rapidly implemented. A shortage of vitally important prescribed medicines was avoided.

Antipsychotic drugs and risk of acute pancreatitis: A nationwide case-control study.

INTRODUCTION: Use of antipsychotic drugs, especially second-generation agents, has been suggested to cause acute pancreatitis in multiple case reports; however, such an association has not been corroborated by larger studies. This study examined the association of antipsychotic drugs with risk of acute pancreatitis. METHODS: Nationwide case-control study, based on data from several Swedish registers and including all 52,006 cases of acute pancreatitis diagnosed in Sweden between 2006 and 2019 (with up to 10 controls per case; n = 518,081). Conditional logistic regression models were used to calculate odds ratios (ORs) in current and past users of first-generation and second-generation antipsychotic drugs (dispensed prescription <91 and ≥91 days of the index date, respectively) compared with never users of such drugs. RESULTS: In the crude model, first-generation and second-generation antipsychotic drugs were associated with increased risk of acute pancreatitis, with slightly higher ORs for past use (1.58 [95% confidence interval 1.48-1.69] and 1.39 [1.29-1.49], respectively) than for current use (1.34 [1.21-1.48] and 1.24 [1.15-1.34], respectively). The ORs were largely attenuated in the multivariable model-which included, among others, alcohol abuse and the Charlson comorbidity index-up to the point where only a statistically significant association remained for past use of first-generation agents (OR 1.18 [1.10-1.26]). CONCLUSION: There was no clear association between use of antipsychotic drugs and risk of acute pancreatitis in this very large case-control study, indicating that previous case report data are most likely explained by confounding.

Federated analyses of multiple data sources in drug safety studies.

PURPOSE: Studies of rare side effects of new drugs with limited exposure may require pooling of multiple data sources. Federated Analyses (FA) allow real-time, interactive, centralized statistical processing of individual-level data from different data sets without transfer of sensitive personal data. METHODS: We review IT-architecture, legal considerations, and statistical methods in FA, based on a Swedish Medical Products Agency methodological development project. RESULTS: In a review of all post-authorisation safety studies assessed by the EMA during 2019, 74% (20/27 studies) reported issues with lack of precision in spite of mean study periods of 9.3 years. FA could potentially improve precision in such studies. Depending on the statistical model, the federated approach can generate identical results to a standard analysis. FA may be particularly attractive for repeated collaborative projects where data is regularly updated. There are also important limitations. Detailed agreements between involved parties are strongly recommended to anticipate potential issues and conflicts, document a shared understanding of the project, and fully comply with legal obligations regarding ethics and data protection. FA do not remove the data harmonisation step, which remains essential and often cumbersome. Reliable support for technical integration with the local server architecture and security solutions is required. Common statistical methods are available, but adaptations may be required. CONCLUSIONS: Federated Analyses require competent and active involvement of all collaborating parties but have the potential to facilitate collaboration across institutional and national borders and improve the precision of postmarketing drug safety studies.

Risk of suicide and self-harm in university students entering different university programs - a national register-based cohort study in Sweden.

PURPOSE: It is not known whether the elevated suicide risk in certain occupations, such as health care professionals, is partly attributable to a selection of individuals with prior vulnerability. We aimed to determine the risk of suicide and self-harm already in students entering different university programs. METHODS: We used national registers to identify 621,218 Swedish residents aged 18-39 years with registration for a university program 1993-2013. Outcomes were suicide and self-harm within three years. We applied logistic regression analyses to calculate odds ratios (OR) and 95% confidence intervals (CI) of risk of suicide and self-harm, with the Education program category as a reference. Results were adjusted for sex, age, time period and for history of hospitalization due to mental disorder or self-harm, as a measure of previous vulnerability. In the second step, we stratified results by sex. RESULTS: There was a higher risk of suicide (OR 2.4) in female nursing students and natural science students (OR 4.2) and of self-harm in female and male Nursing/Health care students (OR range 1.2 -1.7). Subcategorization into nursing students only strengthened the association with self-harm for both sexes. Prior vulnerability did not fully explain the increased risk. CONCLUSION: The elevated risk of suicide in nursing and health care occupations partly has its onset in vulnerability factors present before or emerging during university studies. Increased efforts in identifying and treating mental disorders and preventing self-harm in university students could be an important step in preventing future suicides.

Inequalities in Income and Education Are Associated With Survival Differences After Out-of-Hospital Cardiac Arrest: Nationwide Observational Study.

BACKGROUND: Despite the acknowledged importance of socioeconomic factors as regards cardiovascular disease onset and survival, the relationship between individual-level socioeconomic factors and survival after out-of-hospital cardiac arrest is not established. Our aim was to investigate whether socioeconomic variables are associated with 30-day survival after out-of-hospital cardiac arrest. METHODS: We linked data from the Swedish Registry for Cardiopulmonary Resuscitation with individual-level data on socioeconomic factors (ie, educational level and disposable income) from Statistics Sweden. Confounding and mediating variables included demographic factors, comorbidity, and Utstein resuscitation variables. Outcome was 30-day survival. Multiple modified Poisson regression was used for the main analyses. RESULTS: A total of 31 373 out-of-hospital cardiac arrests occurring in 2010 to 2017 were included. Crude 30-day survival rates by income quintiles were as follows: Q1 (low), 414/6277 (6.6%); Q2, 339/6276 (5.4%); Q3, 423/6275 (6.7%); Q4, 652/6273 (10.4%); and Q5 (high), 928/6272 (14.8%). In adjusted analysis, the chance of survival by income level followed a gradient-like increase, with a risk ratio of 1.86 (95% CI, 1.65-2.09) in the highest-income quintile versus the lowest. This association remained after adjusting for comorbidity, resuscitation factors, and initial rhythm. A higher educational level was associated with improved 30-day survival, with the risk ratio associated with postsecondary education ≥4 years being 1.51 (95% CI, 1.30-1.74). Survival disparities by income and educational level were observed in both men and women. CONCLUSIONS: In this nationwide observational study using individual-level socioeconomic data, higher income and higher educational level were associated with better 30-day survival after out-of-hospital cardiac arrest in both sexes.

Death of a child and the risk of atrial fibrillation: a nationwide cohort study in Sweden.

AIMS: The role of psychological stress in the aetiology of atrial fibrillation (AF) is unclear. The death of a child is one of the most severe sources of stress. We aimed to investigate whether the death of a child is associated with an increased risk of AF. METHODS AND RESULTS: We studied parents with children born during 1973-2014 included the Swedish Medical Birth Register (n = 3 924 237). Information on death of a child, AF and socioeconomic, lifestyle and health-related covariates was obtained through linkage to nationwide population and health registers. We examined the link between death of a child and AF risk using Poisson regression. Parents who lost a child had a 15% higher risk of AF than unexposed parents [incidence rate ratio (IRR) and 95% confidence intervals (CI): 1.15 (1.10-1.20)]. An increased risk of AF was observed not only if the child died due to cardiovascular causes [IRR (95% CI): 1.35 (1.17-1.56)], but also in case of deaths due to other natural [IRR (95% CI): 1.15 (1.09-1.21)] or unnatural [IRR (95% CI): 1.10 (1.02-1.19)] causes. The risk of AF was highest in the 1st week after the loss [IRR (95% CI): 2.87 (1.44-5.75)] and remained 10-40% elevated on the long term. CONCLUSIONS: Death of a child was associated with a modestly increased risk of AF. Our finding that an increased risk was observed also after loss of a child due to unnatural deaths suggests that stress-related mechanisms may also be implicated in the development of AF.

Association of SARS-CoV-2 Vaccination During Pregnancy With Pregnancy Outcomes.

Importance: Data about the safety of vaccines against SARS-CoV-2 during pregnancy are limited. Objective: To examine the risk of adverse pregnancy outcomes after vaccination against SARS-CoV-2 during pregnancy. Design, Setting, and Participants: This registry-based retrospective cohort study included 157 521 singleton pregnancies ending after 22 gestational weeks from January 1, 2021, until January 12, 2022 (Sweden), or January 15, 2022 (Norway). The Pregnancy Register in Sweden and the Medical Birth Registry of Norway were linked to vaccination and other registries for identification of exposure and background characteristics. Exposures: Data on mRNA vaccines-BNT162b2 (Pfizer-BioNTech) and mRNA-1273 (Moderna)-and 1 viral vector vaccine-AZD1222 (AstraZeneca)-were collected from national vaccination registries. Main Outcomes and Measures: The risk of preterm birth and stillbirth was evaluated using Cox regression models, with gestational day as the time metric and vaccination as a time-dependent exposure variable. The risk of small for gestational age, low Apgar score, and neonatal care admission was evaluated using logistic regression. Random-effects meta-analysis was used to combine results between countries. Results: Among the 157 521 singleton births included in the study (103 409 in Sweden and 54 112 in Norway), the mean maternal age at the time of delivery was 31 years, and 28 506 (18%) were vaccinated against SARS-CoV-2 (12.9% with BNT162b2, 4.8% with mRNA-1273, and 0.3% with AZD1222) while pregnant. A total of 0.7%, 8.3%, and 9.1% of individuals delivering were vaccinated during the first, second, and third trimester, respectively. Vaccination against SARS-CoV-2 was not significantly associated with increased risk of preterm birth (6.2 vs 4.9 per 10 000 pregnancy days; adjusted hazard ratio [aHR], 0.98 [95% CI, 0.91 to 1.05]; I2 = 0%; P for heterogeneity = .60), stillbirth (2.1 vs 2.4 per 100 000 pregnancy days; aHR, 0.86 [95% CI, 0.63 to 1.17]), small for gestational age (7.8% vs 8.5%; difference, -0.6% [95% CI, -1.3% to 0.2%]; adjusted OR [aOR], 0.97 [95% CI, 0.90 to 1.04]), low Apgar score (1.5% vs 1.6%; difference, -0.05% [95% CI, -0.3% to 0.1%]; aOR, 0.97 [95% CI, 0.87 to 1.08]), or neonatal care admission (8.5% vs 8.5%; difference, 0.003% [95% CI, -0.9% to 0.9%]; aOR, 0.97 [95% CI, 0.86 to 1.10]). Conclusions and Relevance: In this population-based study conducted in Sweden and Norway, vaccination against SARS-CoV-2 during pregnancy, compared with no SARS-CoV-2 vaccination during pregnancy, was not significantly associated with an increased risk of adverse pregnancy outcomes. The majority of the vaccinations were with mRNA vaccines during the second and third trimesters of pregnancy, which should be considered in interpreting the findings.

Death of an offspring and parental risk of ischemic heart diseases: A population-based cohort study.

BACKGROUND: The death of a child is an extreme life event with potentially long-term health consequences. Knowledge about its association with ischemic heart diseases (IHDs) and acute myocardial infarction (AMI), however, is very limited. We investigated whether the death of an offspring is associated with the risk of IHD and AMI. METHODS AND FINDINGS: We studied parents of live-born children recorded in the Danish (1973 to 2016) and the Swedish (1973 to 2014) Medical Birth Registers (n = 6,711,952; mean age at baseline 31 years, 53% women). We retrieved information on exposure, outcomes, and covariates by linking individual-level information from several nationwide registers. We analyzed the abovementioned associations using Poisson regression. A total of 126,522 (1.9%) parents lost at least 1 child during the study period. Bereaved parents had a higher risk of IHD and AMI than the nonbereaved [incidence rate ratios (IRRs) (95% confidence intervals (CIs)): 1.20 (1.18 to 1.23), P < 0.001 and 1.21 (1.17 to 1.25), P < 0.001, respectively]. The association was present not only in case of losses due to CVD or other natural causes, but also in case of unnatural deaths. The AMI risk was highest in the first week after the loss [IRR (95% CI): 3.67 (2.08 to 6.46), P < 0.001], but a 20% to 40% increased risk was observed throughout the whole follow-up period. Study limitations include the possibility of residual confounding by socioeconomic, lifestyle, or health-related factors and the potentially limited generalizability of our findings outside Scandinavia. CONCLUSIONS: The death of an offspring was associated with an increased risk of IHD and AMI. The finding that the association was present also in case of losses due to unnatural causes, which are less likely to be confounded by cardiovascular risk factors clustering in families, suggests that stress-related mechanisms may also contribute to the observed associations.

Pediatric use of prescribed melatonin in Sweden 2006-2017: a register based study.

Sleep disturbances are common in the pediatric population and should primarily be treated non-pharmacologically. Most medicines for sleep disturbances are not approved for pediatric use and data on long-term safety is scarce. In Sweden, melatonin is classified as a prescription medicine. The aim of the present study was to characterize the prevalence and incidence of dispensed melatonin prescriptions, long-term treatment, concomitant dispensation of psychotropic medication, and psychiatric comorbidity, in children and adolescents aged 0-17 years living in Sweden during 2006-2017. Data was retrieved by linking the national population-based registers, the Swedish Prescribed Drug register and the National Patient register. In 2017, nearly 2% of the pediatric population 0-17 years was dispensed at least one prescription of melatonin, which was more than a 15-fold increase for girls and a 20-fold increase for boys, when compared to 2006. Among the children in the age group 5-9 who initiated a melatonin treatment in 2009, 15% of girls and 17% of boys were found to be continuously prescribed melatonin 8 years later. Nearly 80% of all children with dispensed melatonin had concomitant dispensations of psychotropic medications. The most common combination was melatonin together with centrally acting sympathomimetic medicines (23% of girls and 43% of boys). About half of the children (47% of girls and 50% of boys) had at least one registered diagnosis of mental or behavioral disorders. The most common diagnosis was attention deficit hyperactive disorder, across all age groups and genders. The continuous increase of use of melatonin in children, often concomitant with other psychotropic medications, together with a high proportion of younger children with prescriptions of melatonin on a long-term basis, suggests the need for further structured follow up studies, in particular of long-term use.

Increased risk of mental health problems after cancer during adolescence: A register-based cohort study.

In this nationwide, register-based study, we estimated the risk of mental health problems in 2822 individuals diagnosed with cancer in adolescence (13-19 years). Mental health problems were assessed by psychiatric diagnoses and/or prescribed psychotropic drugs. Cox proportional hazards models estimated hazard ratio (HR) for a psychiatric diagnosis and prescription of psychotropic drug compared to a matched comparison group (n = 28 220). Estimates were adjusted for calendar period and parent characteristics (eg, history of psychiatric diagnosis, education, country of birth). We found an increased risk of a psychiatric diagnosis during the first 5 years after the cancer diagnosis (females: HR 1.23, 95% CI, 1.06-1.44; males: HR 1.32, 95% CI, 1.11-1.56), and at >5 years after diagnosis (females: HR 1.31, 95% CI, 1.09-1.58, males: HR 1.45, 95% CI, 1.18-1.77). The risk of being prescribed antidepressant (females: HR 1.54, 95% CI, 1.30-1.84, males: HR 2.06, 95% CI, 1.66-2.55), antipsychotic (females: HR 2.28, 95% CI, 1.56-3.34, males: HR 3.07, 95% CI, 2.13-4.42), anxiolytic (females: HR 1.95, 95% CI, 1.64-2.31, males: HR 4.02, 95% CI, 3.34-4.84) and sedative drugs (females: HR 2.24, 95% CI, 1.84-2.72, males: HR 3.91, 95% CI, 3.23-4.73) were higher than for comparisons during the first 5 years after diagnosis. Median age at first psychiatric diagnosis and first prescribed psychotropic drug were 18 years. In conclusion, cancer during adolescence is associated with increased risk of mental health problems that may develop in close proximity to treatment. The findings emphasize the need for comprehensive care during treatment and follow-up.

Colon and rectal cancer risk after bariatric surgery in a multicountry Nordic cohort study.

Obesity is a risk factor for colorectal cancer. Yet, some research indicates that weight-reducing bariatric surgery also increases colorectal cancer risk. Our study was undertaken because current evidence examining bariatric surgery and risk of colorectal cancer is limited and inconsistent. This population-based cohort study included adults with a documented obesity diagnosis in Denmark, Finland, Iceland, Norway or Sweden in 1980-2015. The incidence of colorectal cancer in participants with obesity who had and had not undergone bariatric surgery was compared to the incidence in the corresponding background population by calculating standardized incidence ratios (SIR) with 95% confidence intervals (CI). Additionally, operated and nonoperated participants with obesity were compared using multivariable Cox regression, providing hazard ratios (HR) with 95% CIs adjusted for confounders. Among 502,772 cohort participants with an obesity diagnosis, 49,931(9.9%) underwent bariatric surgery. The overall SIR of colon cancer was increased after bariatric surgery (SIR 1.56; 95% CI 1.28-1.88), with higher SIRs ≥10 years postsurgery. The overall HR of colon cancer in operated compared to nonoperated participants was 1.13 (95% CI 0.92-1.39) and 1.55 (95% CI 1.04-2.31) 10-14 years after bariatric surgery. Bariatric surgery did not significantly increase the risk of rectal cancer (SIR 1.14, 95% CI 0.83-1.52; HR 1.08, 95% CI 0.79-1.49), but the risk estimates increased with longer follow-up periods. Our study suggests that bariatric surgery is associated with an increased risk of colon cancer, while the support for an increased risk of rectal cancer was weaker.

Severity of depression, anxious distress and the risk of type 2 diabetes - a population-based cohort study in Sweden.

BACKGROUND: Previous studies assessing the relationship between depression and diabetes mellitus did not consider the severity of depression. In the present study we assessed the risk of developing type 2 diabetes mellitus (T2DM) among people with various severity of depression. METHODS: This prospective longitudinal cohort study included 9,936 individuals residing in Stockholm County, Sweden who responded to the baseline questionnaire in 1998-2000. The participants were followed from 1 year after the baseline up to 2015 for the occurrence of T2DM, using the National Patient Register, Swedish Prescribed Drug Registers, and Cause of Death Register. Depression and anxious distress were assessed using psychiatric rating scales and defined according to the Diagnostic and Statistical Manual of Mental Disorders (DSM-5). RESULTS: Depression was associated with a statistically significant increased risk of T2DM after adjusting for potential confounders (OR 1.48, CI 1.10, 1.99). The strongest association was observed for severe depression (OR 1.72, CI 1.15, 2.59). Further, those with depression, regardless of severity, and with concurrent moderate/severe anxious distress had an increased risk of T2DM (OR 1.73, CI 1.13, 2.63) compared to those with neither depression nor anxious distress. CONCLUSIONS: The study adds evidence that depression is associated with a higher risk for developing T2DM, and the association is stronger among people with severe depression.

Correction to: Severity of depression, anxious distress and the risk of type 2 diabetes - a population-based cohort study in Sweden.

It was highlighted that the original article [1] contained an error in the flow chart in Fig. 1.

The Swedish dental health register - validation study of remaining and intact teeth.

BACKGROUND: Sweden has a long tradition of nationwide registers enabling population-based research of high quality and validity. We aimed to describe the content and validity of reported number of remaining and intact teeth in the Swedish Dental Health Register and report some descriptive data on dental health care utilization. METHODS: The Swedish Dental Health Register was initiated in July 1st 2008 and contains individual data on dental health care to the whole adult population of Sweden. The dental care given freely to children and young adults is not included. Descriptive data on remaining, intact teeth and dental health care utilization is presented by proportion of the population stratified by sex and age. We conducted a validation study, by manual review of randomly sampled 1500 dental health visits records, to assess reported number of teeth to the register with what was actually recorded in the dental health care record (gold standard), analyzed by positive predictive value (PPV) and Bland-Altman plots. RESULTS: Of the Swedish adult population 2014, 2.6 million (69%) men and 2.9 million (76%) women had at least one visit to a dentist during a two-year period 2013 to 2014. More than half of the population up to age 64 have all remaining teeth (28 teeth or more). Of the 1500 requested dental records 1131 (75%) were received. The positive predictive value for patients reported to the register as having at least 1 tooth up to 31 intact teeth was 91.5% (95% confidence interval 89.0-93.5, 567 manually reviewed to be correct out of 620 reported). CONCLUSIONS: For patients coded as having less than 32 intact teeth but not being edentulous the reported number of remaining and intact teeth is to a very high degree correct. However, the correctness for those coded as edentulous or having 32 remaining intact teeth is low and varies substantially by age.

Validating inflammatory bowel disease (IBD) in the Swedish National Patient Register and the Swedish Quality Register for IBD (SWIBREG).

BACKGROUND: Both the Swedish National Patient Register (NPR) and the Swedish Quality Register for inflammatory bowel disease (IBD, SWIBREG) are important sources of research data and information. However, the validity of a diagnosis of IBD in these registers is unknown. METHODS: Medical charts of 129 randomly selected patients from the NPR and 165 patients registered both in SWIBREG and the NPR were reviewed. Patients were classified according to standardized criteria for ulcerative colitis (UC), Crohn's disease (CD), or IBD unclassified (IBD-U). Positive predictive values (PPVs) for UC, CD, IBD-U (only SWIBREG), or having any form of IBD were then calculated. RESULTS: For cases with ≥2 diagnoses of IBD in the NPR (hospitalizations or non-primary care outpatient visits), the PPV was 93% (95% CI: 87-97) for any IBD, 79% (66-88) for UC and 72% (60-82) for CD. In UC patients with ≥2 UC diagnoses but never a CD diagnosis, the PPV increased to 90% (77-97). The PPV for CD in patients with ≥2 CD diagnoses but never a UC diagnosis was 81% (67-91)). Combining data from SWIBREG (≥1 record) and the NPR (≥1 record), the PPV was 99% for any IBD (97-100), 96% (89-99) for UC, and 90% (82-96) for CD. CONCLUSION: The validity of the UC, CD, and IBD diagnoses is high in the NPR but even higher when cases were identified both in SWIBREG and the NPR. These results underline the need for a well-functioning Swedish Quality Register for IBD as a complement to the NPR.

Methodological choices affect cancer incidence rates: a cohort study.

BACKGROUND: Incidence rates are fundamental to epidemiology, but their magnitude and interpretation depend on methodological choices. We aimed to examine the extent to which the definition of the study population affects cancer incidence rates. METHODS: All primary cancer diagnoses in Sweden between 1958 and 2010 were identified from the national Cancer Register. Age-standardized and age-specific incidence rates of 29 cancer subtypes between 2000 and 2010 were calculated using four definitions of the study population: persons resident in Sweden 1) based on general population statistics; 2) with no previous subtype-specific cancer diagnosis; 3) with no previous cancer diagnosis except non-melanoma skin cancer; and 4) with no previous cancer diagnosis of any type. We calculated absolute and relative differences between methods. RESULTS: Age-standardized incidence rates calculated using general population statistics ranged from 6% lower (prostate cancer, incidence rate difference: -13.5/100,000 person-years) to 8% higher (breast cancer in women, incidence rate difference: 10.5/100,000 person-years) than incidence rates based on individuals with no previous subtype-specific cancer diagnosis. Age-standardized incidence rates in persons with no previous cancer of any type were up to 10% lower (bladder cancer in women) than rates in those with no previous subtype-specific cancer diagnosis; however, absolute differences were <5/100,000 person-years for all cancer subtypes. CONCLUSIONS: For some cancer subtypes incidence rates vary depending on the definition of the study population. For these subtypes, standardized incidence ratios calculated using general population statistics could be misleading. Moreover, etiological arguments should be used to inform methodological choices during study design.