Infections in patients with mantle cell lymphoma.

Advancements in treatments have significantly improved the prognosis for mantle cell lymphoma (MCL), and there is a growing population of survivors with an increased susceptibility to infections. We assessed the incidence of infections by clinical characteristics and treatment both before and after MCL diagnosis in Sweden. Patients with a diagnosis of MCL ≥ 18 years between 2007 and 2019 were included, along with up to 10 matched comparators. Infectious disease diagnosis and anti-infective drug dispensation were identified by the National Patient and the Prescribed Drug Registers, respectively. Patients and comparators were followed from the diagnosis/matching date until death, emigration, or June 30, 2020. Overall, 1559 patients and 15,571 comparators were followed for a median duration of 2.9 and 5 years, respectively. The infection rate among patients was twofold higher, RRadj = 2.14 (2.01-2.27), contrasted to the comparator group. There was a notable rise in infection rates already 4 years before MCL diagnosis, which reached a fourfold increase in the first year after diagnosis and persisted significantly increased for an additional 8 years. Among patients, 69% (n = 1080) experienced at least one infection during the first year of follow-up. Influenza, pneumonia, other bacterial infections, urinary tract infections, and acute upper respiratory infections were the most frequent. Notably, MCL remained to be the primary leading cause of death among patients (57%, n = 467/817). Infections as the main cause of death were rare (2.6%, n = 21). Our study highlights the importance of thoroughly assessing infectious morbidity when appraising new treatments. Further investigations are warranted to explore strategies for reducing infectious disease burden.

Stable use of radiotherapy in lymphoma patients over time - A comprehensive national overview of radiotherapy use in Sweden with focus on older patients.

Background and purpose: The role of radiotherapy (RT) in lymphoma is constantly refined with the advent of novel treatments. However, RT is still an effective treatment and tolerability is high. Therefore, we aimed to describe the use of RT in primary treatment of lymphoma over calendar time, with a specific focus on older patients (age ≥ 70 years) with non-Hodgkin lymphoma (NHL) subtypes. Materials & Methods: All adult patients diagnosed with lymphoma from 2007 to 2018 in Sweden were included and followed for survival until end of 2020. Patient characteristics and relative survival (RS) were described for patients with NHL by subtype and RT use. Results: In the cohort of lymphoma patients aged ≥ 70 years (n = 12,698) 11 % received RT as part of primary treatment. No decline in use of RT over calendar period was seen. Use of RT as monotherapy was associated with stage I-II disease and older age among patients with stage III-IV disease. Patients with indolent lymphomas aged ≥ 70 years who were selected for treatment with RT as monotherapy with a dose of ≥ 20 Gy had 2-year RS rate of 100 % which remained similar at five years. For patients with DLBCL, RT as monotherapy with a dose of ≥ 20 Gy was mostly administered to patients aged ≥ 85 years with a 2-year RS rate of 68 %. Conclusion: The use of RT in first-line lymphoma treatment was stable over calendar time. RT monotherapy is associated with encouraging outcomes among patients with NHL aged ≥ 70 years who were selected to receive this.

Impact of the COVID-19 pandemic on lymphoma incidence and short-term survival - a Swedish Lymphoma Register Study.

BACKGROUND & PURPOSE: The COVID-19 pandemic posed a large challenge for healthcare systems across the world. Comprehensive data on the impact of the COVID-19 pandemic on incidence and mortality in lymphoma are lacking. PATIENTS/METHODS: Using data from the Swedish lymphoma register, we compare incidence and 1-year survival of lymphoma patients in Sweden before (2017-2019) and during the pandemic (2020 and 2021). RESULTS: Fewer patients were diagnosed with lymphomas during March-June 2020, but the annual incidence rates for 2020 and 2021 were similar to those of 2017-2019. A larger proportion of patients presented with stage IV disease during 2021. There were no differences in other base-line characteristics nor application of active treatment in pre-pandemic and pandemic years. One-year overall survival was not inferior among lymphoma patients during the pandemic years compared to pre-pandemic years i.e., 2017-2019. INTERPRETATION: The COVID-19 pandemic had limited impact on the incidence and mortality of lymphoma in Sweden.

Secondary malignancies among mantle cell lymphoma patients.

PURPOSE: With modern treatments, mantle cell lymphoma (MCL) patients more frequently experience long-lasting remission resulting in a growing population of long-term survivors. Follow-up care includes identification and management of treatment-related late-effects, such as secondary malignancies (SM). We conducted a population-based study to describe the burden of SM in MCL patients. METHODS: All patients with a primary diagnosis of MCL, aged ≥ 18 years and diagnosed between 2000 and 2017 in Sweden were included along with up to 10 individually matched population comparators. Follow-up was from twelve months after diagnosis/matching until death, emigration, or December 2019, whichever occurred first. Rates of SM among patients and comparators were estimated using the Anderson-Gill method (accounting for repeated events) and presented as hazard ratios (HR) with 95% confidence intervals (CI) adjusted for age at diagnosis, calendar year, sex, and the number of previous events. RESULTS: Overall, 1 452 patients and 13 992 comparators were followed for 6.6 years on average. Among patients, 230 (16%) developed at least one SM, and 264 SM were observed. Relative to comparators, patients had a higher rate of SM, HRadj= 1.6 (95%CI:1.4-1.8), and higher rates were observed across all primary treatment groups: the Nordic-MCL2 protocol, R-CHOP, R-bendamustine, ibrutinib, lenalidomide, and R-CHOP/Cytarabine. Compared to Nordic-MCL2, treatment with R-bendamustine was independently associated with an increased risk of SM, HRadj= 2.0 (95%CI:1.3-3.2). Risk groups among patients were those with a higher age at diagnosis (p < 0.001), males (p = 0.006), and having a family history of lymphoma (p = 0.009). Patients had preferably higher risk of melanoma, other neoplasms of the skin and other hematopoietic and lymphoid malignancies. CONCLUSIONS: MCL survivors have an increased risk of SM, particularly if treated with R-bendamustine. The intensive treatments needed for long-term remissions are a concern, and transition to treatment protocols with sustained efficacy but with a lower risk of SM is needed.

Genomic, transcriptomic and epigenomic sequencing data of the B-cell leukemia cell line REH.

OBJECTIVES: The aim of this data paper is to describe a collection of 33 genomic, transcriptomic and epigenomic sequencing datasets of the B-cell acute lymphoblastic leukemia (ALL) cell line REH. REH is one of the most frequently used cell lines for functional studies of pediatric ALL, and these data provide a multi-faceted characterization of its molecular features. The datasets described herein, generated with short- and long-read sequencing technologies, can both provide insights into the complex aberrant karyotype of REH, and be used as reference datasets for sequencing data quality assessment or for methods development. DATA DESCRIPTION: This paper describes 33 datasets corresponding to 867 gigabases of raw sequencing data generated from the REH cell line. These datasets include five different approaches for whole genome sequencing (WGS) on four sequencing platforms, two RNA sequencing (RNA-seq) techniques on two different sequencing platforms, DNA methylation sequencing, and single-cell ATAC-sequencing.

Nationwide Assessment of Patient Trajectories in Mantle Cell Lymphoma: The Swedish MCLcomplete Project.

Mantle cell lymphoma (MCL) is a B-cell malignancy currently considered incurable. Although some patients obtain prolonged remission after first-line chemoimmunotherapy, many will need several treatment lines. Here, we present a nationwide assessment of treatment strategies, time to progression and survival in MCL. All patients diagnosed with MCL 2006-2018 were identified in the Swedish Lymphoma Register. Information on all lines of therapy was extracted from the medical records. Overall and progression-free survival (OS and PFS) were assessed through August 2021. In total, 1367 patients were included (median age, 71 years) and median follow-up was 6.8 years. Two hundred and one (15%) were managed initially with watch-and-wait, but 1235 (90%) eventually received treatment. The most frequently used first-line regimens were rituximab-bendamustine (BR) (n = 368; 30%) and Nordic MCL2 (n = 342; 28%). During follow-up, 630 patients (46%) experienced relapse/progression and 546 (40%) received second-line treatment. The most frequently used second-line regimen was BR (n = 185; 34%) but otherwise a wide variety of second-line treatments were used. Further, 382 and 228 patients experienced a second or third relapse/progression, respectively. Median PFS after first (PFS-1), second (PFS-2), third (PFS-3), and fourth (PFS-4) treatment lines was 29.4, 8.9, 4.3, and 2.7 months. Patients with early progression, defined as a PFS-1 <24 months, had an inferior median OS of 13 versus 37 months in patients with later relapse. For patients treated with frontline BR, however, time to relapse had no impact on later outcome. By use of nationwide population-based data, we provide important benchmarks for future studies of all treatment lines in MCL.

Survival by First-line Treatment Type and Timing of Progression Among Follicular Lymphoma Patients: A National Population-based Study in Sweden.

In follicular lymphoma (FL), progression of disease ≤24 months (POD24) has emerged as an important prognostic marker for overall survival (OS). We aimed to investigate survival more broadly by timing of progression and treatment in a national population-based setting. We identified 948 stage II-IV indolent FL patients in the Swedish Lymphoma Register diagnosed 2007-2014 who received first-line systemic therapy, followed through 2020. Hazard ratios (HRs) with 95% confidence intervals (CIs) were estimated by first POD at any time during follow-up using Cox regression. OS was predicted by POD using an illness-death model. During a median follow-up of 6.1 years (IQR: 3.5-8.4), 414 patients experienced POD (44%), of which 270 (65%) occurred ≤24 months. POD was represented by a transformation in 15% of cases. Compared to progression-free patients, POD increased all-cause mortality across treatments, but less so among patients treated with rituximab(R)-single (HR = 4.54, 95% CI: 2.76-7.47) than R-chemotherapy (HR = 8.17, 95% CI: 6.09-10.94). The effect of POD was similar following R-CHOP (HR = 8.97, 95% CI: 6.14-13.10) and BR (HR = 10.29, 95% CI: 5.60-18.91). The negative impact of POD on survival remained for progressions up to 5 years after R-chemotherapy, but was restricted to 2 years after R-single. After R-chemotherapy, the 5-year OS conditional on POD occurring at 12, 24, and 60 months was 34%, 46%, and 57% respectively, versus 78%, 82%, and 83% if progression-free. To conclude, POD before but also beyond 24 months is associated with worse survival, illustrating the need for individualized management for optimal care of FL patients.

Late effects in patients with mantle cell lymphoma treated with or without autologous stem cell transplantation.

Studies on late effects in patients with mantle cell lymphoma (MCL) are becoming increasingly important as survival is improving, and novel targeted drugs are being introduced. However, knowledge about late effects is limited. The aim of this population-based study was to describe the magnitude and panorama of late effects among patients treated with or without high-dose chemotherapy with autologous stem cell transplantation (HD-ASCT). The study cohort included all patients with MCL, recorded in the Swedish Lymphoma Register, aged 18 to 69 years, diagnosed between 2000 and 2014 (N = 620; treated with HD-ASCT, n = 247) and 1:10 matched healthy comparators. Patients and comparators were followed up via the National Patient Register and Cause of Death Register, from 12 months after diagnosis or matching to December 2017. Incidence rate ratios of the numbers of outpatient visits, hospitalizations, and bed days were estimated using negative binomial regression models. In relation to the matched comparators, the rate of specialist and hospital visits was significantly higher among patients with MCL. Patients with MCL had especially high relative risks of infectious, respiratory, and blood disorders. Within this observation period, no difference in the rate of these complications, including secondary neoplasms, was observed between patients treated with and without HD-ASCT. Most of the patients died from their lymphoma and not from another cause or treatment complication. Taken together, our results imply that most of the posttreatment health care needs are related to the lymphoma disease itself, thus, indicating the need for more efficient treatment options.

Patient trajectories after diagnosis of diffuse large B-cell lymphoma-a multistate modelling approach to estimate the chance of lasting remission.

BACKGROUND: Achieving lasting remission for at least 2 years is a good indicator for favourable prognosis long term after Diffuse large B-cell lymphoma (DLBCL). The aim of this study was to provide real-world probabilities, useful in risk communication and clinical decision-making, of the chance for lasting remissions by clinical characteristics. METHODS: DLBCL patients in remission after primary treatment recorded in the Swedish Lymphoma register 2007-2014 (n = 2941) were followed for relapse and death using multistate models to study patient trajectories. Flexible parametric models were used to estimate transition rates. RESULTS: At 2 years, 80.7% (95% CI: 79.0-82.2) of the patients were predicted to remain in remission and 13.2% (95% CI: 11.9-14.6) to have relapsed. The relapse risk peaked at 7 months, and the annual decline of patients in remission stabilised after 2 years. The majority of patients in the second remission transitioned into a new relapse. The probability of a lasting remission was reduced by 20.4% units for patients with IPI 4-5 compared to patients with IPI 0-1, and time in remission was shortened by 3.5 months. CONCLUSION: The long-term prognosis was overall favourable with 80% achieving durable first remissions. However, prognosis varied by clinical subgroups and relapsing patients seldom achieved durable second remissions.

Outcomes of relapsed/refractory diffuse large B-cell lymphoma and influence of chimaeric antigen receptor T trial eligibility criteria in second line-A population-based study of 736 patients.

Several recently published trials investigate novel therapies for relapsed/refractory diffuse large B-cell lymphoma (R/R DLBCL). To estimate the benefit of these therapies in the real-world setting, comprehensive data on patients treated in clinical routine are needed. We report outcomes for 736 R/R DLBCL patients identified among all curatively treated DLBCL patients in Sweden in the period 2007-2014. Survival and associations with disease characteristics, second-line treatment and fulfilment of chimaeric antigen receptor (CAR) T-cell trial criteria were assessed. Median overall survival (OS) was 6.6 months (≤70 years 9.6 months, >70 years 4.9 months). Early relapse (≤12 months) was strongly associated with selection of less intensive treatment and poor survival. Among patients of at most 70 years of age, 63% started intensive second-line treatment and 34% received autologous stem cell transplantation (ASCT). Two-year OS among transplanted patients was 56% (early relapse ≤12 months 40%, late relapse >12 months 66%). A minority of patients 76 years (n = 178/506, 35%) fitted CAR T trial criteria. Median progression-free survival (PFS) for patients with early relapse fitting trial criteria was 4.8 months. In conclusion, most R/R DLBCL manifest early and are often ineligible for or cannot complete intensive regimens resulting in dismal survival. Real-world patients eligible for CAR T trials also did poorly, providing a benchmark for efficacy of novel therapies.

Statin use and survival in 16 098 patients with non-Hodgkin lymphoma or chronic lymphocytic leukaemia treated in the rituximab era.

Statin use has been associated with reduced mortality from several cancers but also suggested, in vitro, to diminish the effectiveness of lymphoma treatments including rituximab. The present study aimed to assess the association of statin use with mortality in patients with non-Hodgkin lymphoma (NHL) and chronic lymphocytic leukaemia (CLL). We identified all incident NHLs and CLLs in Sweden from 2007 to 2013 with subtype information in the Swedish Lymphoma and Cancer Registers. Using Cox regression, we estimated hazard ratios (HRs) and 95% confidence intervals (CIs) for the association of pre- or post-diagnosis statin use (yes/no, intensity) with lymphoma-specific, cardiovascular, or all-cause mortality; and for follicular lymphoma (FL) by initial treatment strategy (active/watch-and-wait). Among 16 098 incident NHL/CLL patients, 20% used statins at diagnosis. Pre- and post-diagnosis statin use, and statin intensity were not consistently associated with any mortality outcome in patients with NHL, overall or for any subtype. For actively treated patients with FL, statin use did not appear to increase lymphoma-specific mortality (vs. non-users, HR [95% CI]after diagnosis 0·87 [0·45-1·67]). For CLL, statin use was associated with all-cause and cardiovascular but not consistently with lymphoma-specific mortality. In conclusion, statin use was not associated with improved lymphoma survival but appears safe to use during lymphoma treatment.

Incidence of relapsed/refractory diffuse large B-cell lymphoma (DLBCL) including CNS relapse in a population-based cohort of 4243 patients in Sweden.

We performed a national population-based study of all patients diagnosed with diffuse large B-cell lymphoma (DLBCL) in Sweden in 2007-2014 to assess treatment intent and risk of relapsed/refractory disease, including central nervous system (CNS) relapse, in the presence of competing risks. Overall, 84% of patients started treatment with curative intent (anthracycline-based) (n = 3550, median age 69 years), whereas 14% did not (n = 594, median age 84 years) (for 2% the intent was uncertain). Patients treated with curative intent had a 5-year OS of 65.3% (95% CI: 63.7-66.9). The median OS among non-curatively treated patients was 2.9 months. The 5-year cumulative incidence of relapsed/refractory disease in curative patients was 23.1% (95% CI: 21.7-24.6, n = 847). The 2-year cumulative incidence of CNS relapse was 3.0% (95% CI: 2.5-3.6, n = 118) overall, and 8.0% (95% CI: 6.0-10.6, n = 48) among patients with high CNS-IPI (4-6), when considering other relapse locations and death as competing events. The incidence of relapsed/refractory DLBCL overall and in the CNS was lower than in previous reports, still one in seven patients was not considered fit enough to start standard immunochemotherapy at diagnosis. These results are important for quantification of groups of DLBCL patients with poor prognosis requiring completely different types of interventions.

Concordance in survival among first-degree relatives diagnosed with indolent lymphoid malignancies including chronic lymphocytic leukemia.

OBJECTIVES: To investigate concordance in survival time among first-degree relatives with lymphoid malignancies. METHODS: By linkage of national Swedish registers, we identified 66 430 patients diagnosed with a lymphoid malignancy 1958-2016 with information on first-degree relationships and follow-up until 2017. Among these, we identified pairs of first-degree relatives with any (N = 3326) or a similar (N = 690) lymphoid malignancy subtype. We defined survival in the first-degree relative as good, expected, or poor based on tertiles of deviance residuals from a multivariable Cox regression model. Next, we used Cox regression to estimate hazard ratios (HR) of death with 95% confidence intervals (CI) among patients, using the survival of their first-degree relative as exposure and adjusting for confounders. RESULTS: There was no concordance in survival among first-degree relatives with any lymphoid malignancy (HRgood  = 1.00 (reference), HRExpected  = 1.02, 95% CI: 0.89-1.17, HRPoor  = 1.12, 95% CI: 0.98-1.27, Ptrend  = .08). Among first-degree relatives with indolent lymphoma, including chronic lymphocytic leukemia, those with a first-degree relative to an expected or poor survival had worse outcome compared to those with a first-degree relative with good survival (HRExpected  = 1.44, 95% CI: 0.82-2.53, HRPoor  = 1.79, 95% CI: 1.07-3.00, Ptrend  = .03). CONCLUSION: Our results support a role of inherited factors in the outcome of indolent lymphoma, including chronic lymphocytic leukemia.

Statin use is associated with improved survival in multiple myeloma: A Swedish population-based study of 4315 patients.

Statin use has been associated with reduced cancer-specific mortality among patients with several cancer types, including multiple myeloma (MM). We aimed to further elucidate the association of statin use and dose intensity with MM survival. Using Swedish population-based national health registers, we identified all incident MM diagnoses occurring January 1, 2007 to December 31, 2013 and their drug dispensations and comorbidities. We assessed statin exposure in 6-month periods pre- and post-diagnosis, treated diagnosis as baseline for calculating survival time, and calculated hazard ratios (HR) and 95% confidence intervals (CI) of exposure-related MM-specific and all-cause mortality using Cox regression. We assessed statin exposure during the entire follow-up and risk of MM-specific mortality in a nested case-control analysis. We classified dose intensity according to American College of Cardiology/American Heart Association recommendations. We ascertained 4315 MM cases during follow-up. Statin use was associated with reduced MM-specific mortality (pre-diagnosis use multivariate-adjusted HR, 95% CI: 0.83, 0.71-0.96; 6 months post-diagnosis: 0.73, 0.60-0.89; entire follow-up: 0.65, 0.52-0.80) and (more weakly) with all-cause mortality. Intensity analyses suggested a dose-response; MM-specific mortality decreased with increasing statin intensity in all time windows (eg, 6 months post-diagnosis: low [0.76 (0.56-1.03)], medium [0.73 (0.58-0.92)], high [0.33 (0.08-1.32)] intensity). However, relatively few patients received high intensity treatment, and the trend was statistically significant only for unadjusted pre-diagnosis use. In this large population-based MM cohort, statin use was associated with improved MM-specific survival in both sexes. Randomized prospective studies are warranted to evaluate statins as adjuvant treatment in MM.

Outcome and determinants of failure to complete primary R-CHOP treatment for reasons other than non-response among patients with diffuse large B-cell lymphoma.

Patients with diffuse large B-cell lymphoma (DLBCL) who fail to complete planned treatment with R-CHOP due to toxicity are sparsely described. We investigated the extent of failure to complete treatment (six cycles or more, or three cycles + RT for patients with stage I disease) with R-CHOP for reasons unrelated to non-response, the determinants of such failure and the outcome among these patients. Three thousand one hundred and forty nine adult DLBCL patients who started primary treatment with R-CHOP were identified through the Swedish lymphoma register 2007-2014. Of these, 147 (5%) stopped prematurely after 1-3 cycles of R-CHOP for reasons unrelated to non-response, 168 (5%) after 4-5 cycles and 2639 patients (84%) completed planned treatment. Additionally, 195 (6%) patients did not complete treatment due to non-response or death before treatment end. In a multivariable logistic regression model, age > 75 years, poor performance status, extranodal disease and Charlson Comorbidity Index ≥1 were significantly associated with failure to complete planned R-CHOP treatment for other reasons than non-response. Non-completion of treatment strongly correlated with survival. Five-year overall survival for patients who received 1-3 cycles was 26% (95% CI: 19%-33%), 49% (95% CI: 41%-57%) for 4-5 cycles and 76% (74%-77%) for patients who completed treatment. Failure to complete planned R-CHOP treatment is an important clinical issue associated with inferior survival. Old age and poor performance status most strongly predict such failure. These results indicate a need for improved treatment tailoring for patients with certain baseline demographics to improve tolerability and chance for treatment completion.

Trends in the prevalence, incidence and survival of non-Hodgkin lymphoma subtypes during the 21st century - a Swedish lymphoma register study.

Non-Hodgkin lymphoma (NHL) prognosis has improved in recent years, yet the number of patients living with the diagnosis, i.e. the prevalence, has seldom been reported. The prevalence provides a measure of the burden of disease, useful for healthcare planning and to optimise resource allocation. We provide a systematic presentation of temporal trends in absolute numbers of prevalent patients by NHL subtypes, linking them to trends in incidence, survival and mortality. Patients diagnosed 2000-2016 were identified in the national Swedish lymphoma register. Incidence and mortality rates, relative survival and prevalence were estimated for NHL overall and for major clinical and morphological subtypes. Poisson regression was used to test for temporal trends. Increasing incidence and improved survival have led to a 47% increase in the five-year prevalence of NHL overall in 2016 compared to 2004. An increasing prevalence was observed for all investigated subtypes during the study period, but most notably for diffuse large B cell lymphomas among aggressive subtypes (66%), and marginal zone lymphomas among indolent subtypes (135%). This dramatic increase in NHL prevalence underscores the need to develop and evaluate alternative follow-up schemes to use resources efficiently and still ensure optimal care of lymphoma survivors.

Mortality from infancy to adolescence in singleton children conceived from assisted reproductive techniques versus naturally conceived singletons in Sweden.

OBJECTIVE: To assess infant (<1 year) and childhood (1-18 years) mortality in singletons conceived through assisted reproductive techniques (ART) versus naturally conceived singletons. DESIGN: Nationwide prospective study. SETTING: Sweden. PATIENT(S): All singleton liveborn infants born from 1983 to 2012 in Sweden identified using the Medical Birth Register (N = 2,847,108), of whom 43,506 were conceived through ART treatments including in vitro fertilization with and without intracytoplasmic sperm injection. INTERVENTION(S): None. MAIN OUTCOME MEASURES(S): Infant (<1 year) and childhood (1-18 years) mortality. RESULT(S): Data on ART treatment and covariates were retrieved from population-based registers using the unique personal identity number assigned to all permanent residents in Sweden. Cox proportional hazards models estimated the hazard ratios (HRs) with 95% confidence intervals (CIs) as measures of association between ART treatments and death. The analyses were adjusted for maternal characteristics, infertility, child sex, and birth cohort and were restricted to individuals with complete information on covariates for fully adjusted analysis. Compared with naturally conceived singletons, higher infant mortality risks were seen in infants conceived through ART (adjusted HR 1.45; 95% CI, 1.19-1.77), especially after transfer of cryopreserved embryos (adjusted HR 2.30; 95% CI, 1.46-3.64). Early neonatal mortality risk (deaths during the first week) was increased in children born after transfer of blastocysts (HR 2.40; 95% CI, 1.05-5.48). No increased mortality risk was observed between the ages of 1 and 18 years. CONCLUSION(S): Singletons conceived through ART had an increased risk of infant mortality from birth up to 1 year of life, predominantly in the early neonatal period and in pregnancies after transfer of frozen and thawed embryos.

Season of birth, childhood asthma and allergy in a nationwide cohort-Mediation through lower respiratory infections.

BACKGROUND: Previous studies have suggested an association between season of birth and risk of childhood asthma and allergic disease. The association may be modified by birth year and region, or mediated by respiratory tract infections. OBJECTIVE: We aimed to estimate the association between season of birth and risk of childhood asthma/wheeze or allergic rhinoconjunctivitis in a population-based setting, and the mediating effect of lower respiratory infections. METHODS: Two population-based cohorts were identified from the nationwide Swedish Medical Birth, Patient and Prescribed Drug Registers. The association between birth month/season and asthma/wheeze incidence was analysed using Cox proportional regression in the younger cohort born 2005-2010 (n = 582 494) and asthma/allergic rhinoconjunctivitis prevalence during the 7th year of life using log-binomial models in the older cohort born 2001-2004 (n = 367 583). Interactions were formally tested. Mediation analyses to address the effect of lower respiratory infections were performed in the older cohort using the R package "medflex." RESULTS: Children born during fall and winter had an increased risk of asthma/wheeze after 2 years of age in the younger cohort: hazard ratio 1.24 (95% confidence interval, CI 1.17, 1.33) for winter and risk of prevalent asthma during their 7th year of life in the older cohort; prevalence ratio (PR) 1.12 (95% CI 1.08, 1.16) for winter. These estimates were partly mediated by lower respiratory infections; the indirect effect for winter compared with summer was PR 1.03 (95% CI 1.03, 1.04). The association was similar for allergic rhinoconjunctivitis in the 7th year of life, but not mediated by respiratory infections. CONCLUSION: We found that the association between season of birth and risk of childhood asthma/wheeze, but not allergic rhinoconjunctivitis, is partly mediated through lower respiratory infections. CLINICAL RELEVANCE: This has important implications for patient care, such as asthma management programmes to notify timing of seasonality for viral respiratory tract infections.