Opioid consumption by cancer patients in an Israeli Health Maintenance Organization from 2007-2018.

PURPOSE: Opioids are the cornerstone of therapy for cancer patients with moderate to severe pain. The objective was to characterize opioid purchases by cancer patients in Clalit Health Services (CHS), the largest Health Maintenance Organization in Israel, over the years 2007-2018. METHODS: Data for all CHS cancer patients aged 18 years old and above who purchased an opioid at least once during the 12-year study period were obtained from computerized databases. The amount of opioids was converted into oral morphine equivalents (OME). RESULTS: 108,543 cancer patients who purchased opioids at least once were enrolled. They comprised 30.5% of the CHS purchasers of opioids in the study period. The total number of cancer patients who purchased an opioid at least once increased gradually from 13,057 in 2007 to 20,675 (58% increase) in 2018, while the annual number of CHS cancer patients increased by only 39%. The annual OME per capita increased from 753 mg in 2007 to 1,432 mg in 2018 (91% increase). In 2007 8.1% of the cancer patients purchased opioids and 9.2% in 2018. Two thirds of all cancer patients purchased opioids for three months or less, 11.9% continued for more than one year, and 5.8% for more than two years. CONCLUSIONS: There is a clinically non-significant increase in the rate of cancer patients purchasing opioids. About two thirds of the cancer patients purchased opioids for only three months, and 94% for up to two years. Under-treatment of cancer pain should still be of concern. While patients are prescribed higher doses, under-prescription may still be a problem..

Arterial and Venous Thromboembolism in ALK-Rearrangement-Positive Non-small Cell Lung Cancer: A Population-Based Cohort Study.

INTRODUCTION: There is scarce data regarding the incidence of venous thromboembolism (VTE) and arterial thromboembolism (ATE) in the molecular subtypes of non-small cell lung cancer (NSCLC). We aimed to investigate the association between Anaplastic Lymphoma Kinase (ALK)-positive NSCLC and thromboembolic events. METHODS: A retrospective population-based cohort study of the Clalit Health Services database, included patients with NSCLC diagnosed between 2012 and 2019. Patients exposed to ALK-tyrosine-kinase inhibitors (TKIs) were defined as ALK-positive. The outcome was VTE (at any site) or ATE (stroke or myocardial infarction) 6 months prior to the diagnosis of cancer, until 5 years post-diagnosis. The cumulative incidence of VTE and ATE and hazard-ratios (HR) with 95% CIs were calculated (at 6- 12- 24 and 60-months), using death as a competing risk. Cox proportional hazards multivariate regression was performed, with the Fine and Gray correction for competing risks. RESULTS: The study included 4762 patients, of which 155 (3.2%) were ALK-positive. The overall 5-year VTE incidence was 15.7% (95% CI, 14.7-16.6%). ALK-positive patients had a higher VTE risk compared to ALK-negative patients (HR 1.87 [95% CI, 1.31-2.68]) and a 12-month VTE incidence of 17.7% (13.9-22.7%) compared to 9.9% (9.1-10.9%) in ALK-negative patients. The overall 5-year ATE incidence was 7.6% [6.8-8.6%]. ALK positivity was not associated with ATE incidence (HR 1.24 [0.62-2.47]). CONCLUSIONS: In this study, we observed a higher VTE risk, but not ATE risk, in patients with ALK-rearranged NSCLC relative to those without ALK rearrangement. Prospective studies are warranted to evaluate thromboprophylaxis in ALK-positive NSCLC.

Psoriasis and hidradenitis suppurativa: A large-scale population-based study.

BACKGROUND: The coexistence of psoriasis and hidradenitis suppurativa (HS) has been described, but the association between these conditions is yet to be firmly established. OBJECTIVE: To study the association between psoriasis and HS by using a large-scale real-life computerized database. METHODS: A cross-sectional study was conducted to compare the prevalence of HS among patients with psoriasis with that among age-, sex- and ethnicity-matched control subjects. RESULTS: A total of 68,836 patients with psoriasis and 68,836 controls were included in the study. The prevalence of HS was increased in patients with psoriasis versus in those in the control group (0.3% vs 0.2%, respectively; odds ratio, 1.8; 95% confidence interval, 1.5-2.3; P < .001). In a multivariate analysis adjusting for smoking, obesity, and other comorbidities, psoriasis was still associated with HS (odds ratio, 1.8; 95% confidence interval, 1.4-2.2; P < .001). Patients with coexistent psoriasis and HS were significantly younger (39.0 ± 15.7 vs 42.6 ± 21.2 years [P = .015]) and had a higher prevalence of obesity (35.1% vs 25.3% [P = .001]) and smoking (58.5% vs 37.3% [P < .001]) compared with patients with psoriasis alone. LIMITATIONS: Retrospective data collection. CONCLUSIONS: A positive association was observed between HS and psoriasis. Further longitudinal observational studies are necessary to establish these findings in other study populations.

Increased Prevalence of Systemic Lupus Erythematosus Comorbidity in Patients With Psoriatic Arthritis: A Population-based Case-control Study.

OBJECTIVE: To assess the prevalence of systemic lupus erythematosus (SLE) in a psoriatic arthritis (PsA) cohort and to compare it to the general population using the database of a large healthcare provider. METHODS: We analyzed the database of a PsA cohort (2002-2017), matched for age and sex, with randomly selected controls for demographics, clinical and laboratory manifestations, and dispensed medications. Statistical analysis used t test and chi-square test as appropriate. In the PsA group, incidence density sampling was performed matching PsA patients without SLE as controls to each case of PsA with SLE by age and follow-up time. Univariable and multivariable conditional logistic regression analyses were used to assess factors affecting SLE development. RESULTS: The PsA and control groups consisted of 4836 and 24,180 subjects, respectively, with a median age of 56 ± 15 years, and of whom 53.8% were female. Eighteen patients (0.37%) in the PsA group and 36 patients (0.15%) in the control group were diagnosed with SLE (P = 0.001). SLE patients without PsA had higher anti-dsDNA and anticardiolipin antibodies. The usage of drugs with known potential to induce SLE was higher in the PsA than in the control group. Older age at PsA diagnosis, shorter PsA duration, and statin treatment were associated with SLE in PsA patients. CONCLUSION: A 2.3-fold increase in the prevalence of SLE in PsA relative to the control group was found. Risk factors for SLE development included older age at PsA diagnosis, shorter PsA duration, and statin treatment. The association between PsA and SLE may affect treatment choices and medication development.

The Risk of Pulmonary Embolism in Patients With Pemphigus: A Population-Based Large-Scale Longitudinal Study.

Growing evidence suggests that inflammation may pose an atypical risk factor for pulmonary embolism (PE), as it drives venous thrombosis via several pathways. The increased risk of PE in several autoimmune diseases has lent weight to this concept. However, the relative risk of PE among patients with pemphigus has not yet been established. We aimed to examine the risk of PE in patients with pemphigus. A large-scale population-based longitudinal cohort study was conducted to evaluate the relative risk (RR) of PE among 1,985 patients with pemphigus relative to 9,874 age-, sex-, and ethnicity-matched control subjects. A multivariate Cox regression model was utilized. The incidence of PE was 3.0 (95% CI, 2.2-4.0) and 1.2 (95% CI, 1.0-1.5) per 1,000 person-years among patients with pemphigus and controls, respectively. The period prevalence of PE corresponding to the study period was 2.2% (95% CI, 1.6-2.9%) among cases and 0.9% (95% CI, 0.7-1.1%) among controls. Patients with pemphigus were twice as likely to develop PE as compared to control subjects (adjusted RR, 1.98; 95% confidence interval [CI], 1.29-3.04). The highest PE risk was observed during the 1st year following the diagnosis of pemphigus (adjusted RR, 3.55; 95% CI, 1.78-7.09) and decreased over time. The increased risk was robust to a sensitivity analysis that included only cases managed by pemphigus-related systemic medications (adjusted RR, 1.82; 95% CI, 1.11-2.98). In conclusion, pemphigus is associated with an increased risk of PE, particularly during the 1st year of the disease. An awareness of this risk should be increased, additional precipitating factors for PE should be avoided, and thromboprophylaxis may be evaluated in high-risk patients. Further research is required to establish this risk.

Direct oral anticoagulation and mortality in moderate to high-risk atrial fibrillation.

OBJECTIVE: Although direct oral anticoagulants (DOAC) are the recommended antithrombotic therapy for patients with non-valvular atrial fibrillation (NVAF), anticoagulation in patients with NVAF is still inadequate. The effect of withholding DOAC therapy on patient survival is unknown. Therefore, our objective was to compare all-cause mortality rates between DOAC-treated patients with NVAF and similar patients receiving no anticoagulation. METHODS: We performed a retrospective cohort study analysing Clalit Health Services' extensive electronic database, regarding all newly diagnosed, anticoagulant-naïve patients with NVAF who were eligible for DOAC therapy from 1 January 2011 to 31 December 2016. Patients who received DOAC therapy were matched by propensity scoring to patients receiving no anticoagulation. The primary outcome was all-cause mortality. Final patient follow-up date was 15 May 2017. RESULTS: 18 901 eligible patients were identified. 8298 received treatment with a DOAC and 10 603 received no anticoagulation therapy. Of those, 5657 patients who received DOAC therapy were matched with 5657 patients who did not receive any anticoagulant. Death occurred in 715 patients in the DOAC-treated group (7.6% per year) and in 2075 patients in the non-anticoagulated patient group (11.1% per year). DOAC therapy was associated with significantly lower risk for all-cause mortality (HR=0.69, 95% CI 0.63 to 0.75, p<0.001). The benefit of DOAC therapy was demonstrated across all subgroups analysed. CONCLUSIONS: In this cohort of newly diagnosed patients with NVAF, DOAC therapy was associated with a significantly lower risk of death compared with no oral anticoagulation. Our findings provide further evidence for the importance of providing DOAC anticoagulation in patients with NVAF.

Effectiveness and Safety of Off-Label Dose-Reduced Direct Oral Anticoagulants in Atrial Fibrillation.

BACKGROUND: Direct oral anticoagulants (DOACs) reduce the risk of stroke and systemic embolism in patients with nonvalvular atrial fibrillation but may result in serious bleeding complications. Off-label dose-reduced use of DOACs to mitigate bleeding is common in routine clinical practice although data about its consequences on patient outcomes are limited. Therefore, our objective was to evaluate the effectiveness and safety of off-label dose-reduced vs per-label standard-dose DOAC treatment. METHODS: The study cohort included newly diagnosed patients with nonvalvular atrial fibrillation that had initiated DOAC therapy between 2011 and 2017 in Clalit Health Services (Tel Aviv, Israel). Effectiveness was defined as the composite outcome of all-cause mortality, stroke, or myocardial infarction. The safety outcome was defined as bleeding events requiring hospitalization. Patients were followed until March 30, 2018 or until occurrence of an outcome event. Hazard ratios (HR) were adjusted for 21 variables, including comorbidities, concomitant medications, and socioeconomic factors, using multivariate regression. RESULTS: A total of 8425 patients met the study criteria; 5140 (61%) patients were treated with DOACs at per-label dosing and 3285 (39%) patients were treated with off-label dose-reduced DOAC. Off-label dose-reduced treatment was associated with a higher rate of the composite effectiveness outcome: adjusted HR 1.57 (95% confidence interval, 1.34-1.83; P < .001) and a higher rate of bleeding: adjusted HR 1.63 (95% confidence interval, 1.14-2.34; P = .008). CONCLUSIONS: Almost 4 of 10 patients were treated with off-label dose-reduced DOAC, which was associated with reduced effectiveness without a safety benefit. Compliance with per-label dosage may significantly improve outcomes of this population.

The relationship between pemphigus and systemic lupus erythematosus: a cross-sectional study, systematic review, and meta-analysis.

The coexistence of pemphigus and systemic lupus erythematosus (SLE) had been reported anecdotally. Anti-desmoglein (Dsg)1 and anti-Dsg3 antibodies were detected concomitantly with antinuclear autoantibodies among blood donors. The aim of the current study was to study the association between pemphigus and SLE in Israeli patients and to synthesize existing data on this association in the current literature. The current study included two sections. Initially, a cross-sectional study was performed to compare pemphigus patients with age-, sex-, and ethnicity-matched control subjects regarding the prevalence of SLE using a real-life large-scale computerized database. Next, a systematic review and meta-analysis of similar observational studies in Medline, Embase, and Web of Science (1823-2017) was conducted. As for the cross-sectional study, a total of 1985 patients with pemphigus and 9874 controls were included in the study. The prevalence of SLE was slightly higher among patients with pemphigus as compared to controls (OR, 1.85; 95% CI, 0.89-3.82). In a sensitivity analysis that included patients who received pemphigus-related treatments, the association between pemphigus and SLE had been substantiated and was statistically significant (OR, 2.10; 95% CI, 1.00-4.48). In the meta-analysis section, three eligible studies, comprising 10,389 pemphigus patients met the eligibility criteria. The overall pooled multivariate OR was 2.50 (95% CI 1.54-4.07, I2 = 44.19%, P = 0.167) across all studies. In conclusion, the meta-analysis provides epidemiologic evidence that these B cell-driven diseases are significantly associated. Further research is required to elucidate the molecular mechanism underlying this association.

Is there an association between dipeptidyl peptidase-4 inhibitors and autoimmune disease? A population-based study.

The association of dipeptidyl peptidase-4 inhibitors (DPP4is) with autoimmune diseases is controversial. While these agents were proposed as a novel therapeutic approach for several inflammatory diseases by blocking T cell proliferation and cytokine production, they were found to trigger inflammatroy bowel disease, inflammatory arthritis and bullous pemphigoid. Our objective is to examine the association between DPP4i and autoimmune diseases. This study was conducted as a cross-sectional study utilizing the database of Clalit Health Services. The prevalence of 15 autoimmune-/immune-mediated diseases was compared between patients on DPP4i treatment and age-, sex-, and ethnicity-matched controls. Univariate analysis was performed using chi-square and the Student t test and multivariate analysis was performed using a logistic regression model. The study included 283 patients treated with DPP4i agents and 5660 age-, sex-, and ethnicity-matched diabetic control subjects. The prevalence of Crohn's disease (1.1 vs. 0.3%; odds ratios (OR), 3.56; 95% CI, 1.04-12.21, P = 0.031), psoriasis (2.5 vs. 1.2%; OR, 2.12; 95% CI, 0.99-4.66; P = 0.050), and Hashimoto's thyroiditis (16.6 vs. 12.6%; OR, 1.38; 95% CI, 1.00-1.91; P = 0.049) was significantly higher in patients on DPP4i treatment than in controls. The prevalence of the remaining autoimmune diseases did not differ significantly between DPP4i-treated patients and their matched control subjects. In conclusion, this population-based study demonstrates an association of DPP4i intake with three autoimmune and inflammatory diseases noted to be part of a distinct autoimmune cluster that includes multiple sclerosis, psoriasis, thyroiditis, bullous pemphigoid, and inflammatory bowel disease. Experimental studies are required to define the role of DPP4i in this autoimmune cluster.

Autoimmune Thyroid Diseases and Thyroid Cancer in Pemphigus: A Big Data Analysis.

There is a little consensus regarding the association of pemphigus with autoimmune thyroid diseases. While this association had been confirmed by some observational studies, others had refuted it. We aimed to study the association between pemphigus and Hashimoto's thyroiditis, Grave's disease, and thyroid cancer using a large-scale real-life computerized database. A cross-sectional study was performed to compare pemphigus patients with age-, sex-, and ethnicity-matched control subjects regarding the prevalence of overt thyroid diseases. Chi-square and t-tests were used for univariate analysis, and a logistic regression model was used for multivariate analysis. The study was performed using the computerized database of Clalit Healthcare Services ensuring 4.5 million individuals. A total of 1,985 pemphigus patients and 9,874 controls were included in the study. The prevalence of Hashimoto's thyroiditis (12.9 vs. 11.9%; P = 0.228), Graves's disease (0.7 vs. 0.7%; P = 0.986), and thyroid cancer (0.7 vs. 0.5%; P = 0.305) were comparable among patients with pemphigus and control subjects. In sex-stratified analysis, pemphigus associated significantly with Hashimoto's thyroiditis among male patients (OR, 1.36; 95% CI, 1.04-1.79). In multivariate analysis adjusting for potential confounding factors, no independent associations between the conditions were revealed. Study findings were robust to sensitivity analysis that included only patients under pemphigus-specific treatments. In conclusion, Hashimoto's thyroiditis was found to be associated with pemphigus only among male patients, but not among all patients. Physicians treating patients with pemphigus might be aware of this possible association. This study does not provide a clue for an association of pemphigus with Grave's disease or thyroid cancer.

COPD and lung cancer in patients with pemphigus- a population based study.

BACKGROUND: Recent evidence indicates that autoimmunity may contribute to the pathogenesis of chronic obstructive pulmonary disease (COPD). COPD was observed at higher frequency in patients with several autoimmune diseases. The association between pemphigus and COPD has not been evaluated in the past. OBJECTIVES: To study the association between pemphigus and COPD using a large-scale real-life computerized database. METHODS: A cross-sectional study was conducted comparing pemphigus patients with age-, sex- and ethnicity-matched control subjects regarding the prevalence of COPD and lung cancer. Chi-square and t-tests were used for bivariate analysis, and logistic regression model was used for multivariate analysis. The study was performed utilizing the computerized database of Clalit Health Services ensuring 4.4 million subjects. RESULTS: A total of 1985 pemphigus patients and 9874 controls were included in the study. The prevalence of COPD was greater in patients with pemphigus as compared to the control group (13.4% vs. 10.1%, respectively; P < 0.001). In a multivariate analysis adjusting for smoking and other confounding factors, pemphigus was significantly associated with COPD (OR, 1.312-1. 5) but not with lung cancer. Study findings were robust to sensitivity analysis that included patients under pemphigus-specific treatments. CONCLUSIONS: A significant association was found between COPD and pemphigus. Physicians treating patients with pemphigus might be aware of this possible association. This observation may further support the hypothesis that COPD has an autoimmune component.

The epidemiology of psoriatic arthritis in Israel - a population-based study.

BACKGROUND: There is limited information on the epidemiology of psoriatic arthritis (PsA) in general and in Middle Eastern populations in particular. The aims of this study were to estimate the prevalence and incidence rates of PsA and their temporal trends in the general population in Israel. METHODS: In this study, a cohort of adult patients with PsA was derived from the database of Clalit Health Services (CHS), Israel's largest health fund, with over 4.4 million members. The crude and age- and sex-standardized prevalence and incidence rates of PsA from 2006 to 2015 in the general population were calculated. The variation in PsA prevalence was assessed in relation to several demographic factors. RESULTS: Among the 2,931,199 individuals aged 18 years and older registered in the CHS database in 2015, 4490 patients had a diagnosis of PsA (322 incident cases), resulting in overall crude prevalence and incidence rates of 0.153% (95% CI 0.149%, 0.158%) and 10.9 (95% CI 9.8, 12.3) per 100,000 population, respectively. The reported prevalence of PsA in Israel has doubled between 2006 and 2015 (from 0.073% to 0.153%). In contrast, the global incidence rate remained stable, with a gradual increase in incidence among individuals aged 51 to 70 years. PsA is associated with Jewish ethnicity, high socioeconomic status, and higher body mass index. CONCLUSIONS: The prevalence and incidence of PsA in Israel are within the range of previous estimates from Southern European populations. An increase in the reported prevalence of PsA was observed over the past decade in the general population in Israel.

Pemphigus and hematologic malignancies: A population-based study of 11,859 patients.

BACKGROUND: The association of nonparaneoplastic pemphigus with comorbid hematologic malignancies has yet to be established. OBJECTIVE: To estimate the association between pemphigus and the common types of hematologic malignancies. METHODS: A cross-sectional study was conducted comparing pemphigus patients with age-, sex- and ethnicity-matched control subjects regarding the prevalence of 6 comorbid hematologic malignancies. The study was performed using the computerized database of Clalit Health Services ensuring the availability of 4.5 million patients. RESULTS: The study included 1985 pemphigus patients and 9874 control subjects. The prevalence of chronic leukemia (0.9% vs 0.4%, odds ratio [OR] 2.1, 95% confidence interval [CI] 1.2-3.6), multiple myeloma (0.8% vs 0.4%, OR 2.2, 95% CI 1.2-3.9), and non-Hodgkin lymphoma (1.8% vs 1.2%, OR 1.5, 95% CI 1.0-2.2) was greater in patients with pemphigus than in controls. The association with chronic leukemia remained significant following the adjustment for immunosuppressive therapy (adjusted OR 2.0, 95% CI 1.1-3.7). No significant associations were observed between pemphigus and acute leukemia, Hodgkin lymphoma, myelodysplastic syndrome, and polycythemia vera. LIMITATIONS: Lack of immunopathologic validation of the diagnosis of pemphigus. CONCLUSION: A significant association was observed between pemphigus and chronic leukemia, multiple myeloma, and non-Hodgkin lymphoma. Further research is warranted to establish this observation in other cohorts.

Endocrine Comorbidities in Patients with Psoriatic Arthritis: A Population-based Case-controlled Study.

OBJECTIVE: To investigate endocrine comorbidities in patients with psoriatic arthritis (PsA). METHODS: A retrospective, cross-sectional study was performed with the database of Clalit Health Services, the largest healthcare provider in Israel, between 2002 and 2014. Patients with PsA were identified and matched by age and sex to healthy controls. The following morbidities were analyzed: hypo/hyperthyroidism, hypo/hyperparathyroidism, hyperprolactinemia, Cushing disease, Addison disease, diabetes insipidus, diabetes mellitus (DM), pituitary adenoma, acromegaly, and osteoporosis. Descriptive statistics were applied. The associations between PsA and endocrine comorbidities were analyzed by univariable and multivariable analysis. RESULTS: The study included 3161 patients with PsA, 53.4% women, mean age 58.4 ± 15.4 years, and 31,610 controls. Comparative analyses yielded higher proportion of hypothyroidism (12.7% vs 8.6%, p < 0.0001), Cushing disease (0.3% vs 0.1%, p < 0.0001), osteoporosis (13.2% vs 9.1%, p < 0.0001), and DM (27.9% vs 20.7%, p < 0.0001) in the PsA group compared with the control group. In the multivariable regression analysis, the following diseases were more frequent in the PsA group: hypothyroidism (OR 1.61, 95% CI 1.47-1.81), DM (OR 1.35, 95% CI 1.18-1.42), Cushing disease (OR 3.96, 95% CI 1.67-9.43), and osteoporosis (OR 1.56, 95% CI 1.37-1.78). CONCLUSION: PsA is associated with a high frequency of hypothyroidism, osteoporosis, DM, and Cushing disease. Awareness of these comorbidities may help physicians provide the optimal medical care to patients with PsA.

Gastrointestinal comorbidities in patients with psoriatic arthritis.

Comorbidities associated with psoriatic arthritis (PsA) include cardiovascular diseases, diabetes mellitus, and obesity. This study evaluated the association between PsA and common gastrointestinal (GI) diseases. A retrospective study was performed in Israel's largest health care provider database between 2002 and 2013. 3161 PsA patients were matched for age and sex with 31610 randomly selected patients. We searched these patients' records for the presence of peptic ulcer disease (PUD), reflux esophagitis, Crohn's disease, ulcerative colitis, irritable bowel syndrome (IBS) and celiac disease. T-test was used to compare continuous variables and a Chi-square test was used for categorical variables. Multivariate logistic regression models were used to assess the association between PsA and GI comorbidities. PsA was associated with Crohn's disease (OR 2.4, 95 %CI: 1.75-3.32, p < 0.0001), ulcerative colitis (OR 2.1, 95 %CI: 1.33-3.26, p = 0.001), reflux esophagitis (OR 1.6, 95 %CI: 1.44-1.78, p < 0.0001), PUD (OR 1.5, 95 %CI: 1.31-1.63, p < 0.0001) and IBS (OR 1.4, 95 %CI: 1.01-1.86, p = 0.045). After controlling for known risk factors, the association remained significant between PsA and Crohn's disease (OR 2.2, 95 %CI: 1.59-3.03, p < 0.0001), ulcerative colitis (OR 1.9, 95 %CI: 1.21-3.00, p = 0.005), reflux esophagitis (OR 1.5, 95 %CI: 1.31-1.63, p < 0.0001), and PUD (OR 1.3, 95 %CI: 1.12-1.47, p < 0.0001). No significant association was found between PsA and celiac disease. In the current study PsA was associated with gastrointestinal morbidities including Crohn's disease, ulcerative colitis, PUD and IBS. Physicians treating patients with PsA should be aware of these associations.

Seasonality of asthma: a retrospective population study.

OBJECTIVES: Seasonal variations in asthma are widely recognized, with the highest incidence during September. This retrospective population study aimed to investigate whether this holds true in a large group of asthmatic children in primary care and to assess the impact of age, gender, urban/rural living, and population sector. METHODS: The key study outcomes were the diagnosis of asthma exacerbations and asthma medication prescriptions, recorded by family physicians during 2005 to 2009. These were analyzed by "week of diagnosis" in Clalit Health Services' electronic medical record database. Regression models were built to assess relative strength of secular trends, seasonality, and age-group in explaining the incidence of asthma exacerbations. RESULTS: A total of 919,873 children aged 2 to 15 years were identified. Of these, 82,234 (8.9%) were asthmatic, 61.6% boys and 38.4% girls; 49.1% aged 2 to 5 years, 24.1% 6 to 9 years, and 26.8% 10 to 15 years. We observed a 2.01-fold increase in pediatric asthma exacerbations and 2.28-fold increase in prescriptions of asthma bronchodilator medications during September (weeks 37-39 vs weeks 34-36) compared with August. The association between the opening of school and the incidence of asthma-related visits to the primary care physician was greatest in children aged 2 to 5 years (odds ratio, 2.15) and 6 to 11 years (1.90-fold). Adolescents (age 12-15 years) had a lesser peak (1.81-fold). In late fall there was a second rise, lasting with fluctuations throughout winter, with a trough in summer. CONCLUSIONS: Returning to school after summer is strongly associated with an increased risk for asthma exacerbations and unscheduled visits to the primary care physician.