Background incidence rates of hospitalisations and emergency department visits for thromboembolic and coagulation disorders in Ontario, Canada for COVID-19 vaccine safety assessment: a population-based retrospective observational study.

OBJECTIVE: The objective of this study was to estimate background rates of selected thromboembolic and coagulation disorders in Ontario, Canada. DESIGN: Population-based retrospective observational study using linked health administrative databases. Records of hospitalisations and emergency department visits were searched to identify cases using International Statistical Classification of Diseases and Related Health Problems, 10th Revision, Canada diagnostic codes. PARTICIPANTS: All Ontario residents. PRIMARY OUTCOME MEASURES: Incidence rates of ischaemic stroke, intracerebral haemorrhage, subarachnoid haemorrhage, deep vein thrombosis, pulmonary embolism, idiopathic thrombocytopaenia, disseminated intravascular coagulation and cerebral venous thrombosis during five prepandemic years (2015-2019) and 2020. RESULTS: The average annual population was 14 million with 51% female. The mean annual rates per 100 000 population during 2015-2019 were 127.1 (95% CI 126.2 to 127.9) for ischaemic stroke, 22.0 (95% CI 21.6 to 22.3) for intracerebral haemorrhage, 9.4 (95% CI 9.2 to 9.7) for subarachnoid haemorrhage, 86.8 (95% CI 86.1 to 87.5) for deep vein thrombosis, 63.7 (95% CI 63.1 to 64.3) for pulmonary embolism, 6.1 (95% CI 5.9 to 6.3) for idiopathic thrombocytopaenia, 1.6 (95% CI 1.5 to 1.7) for disseminated intravascular coagulation, and 1.5 (95% CI 1.4 to 1.6) for cerebral venous thrombosis. Rates were lower in 2020 than during the prepandemic years for ischaemic stroke, deep vein thrombosis and idiopathic thrombocytopaenia. Rates were generally consistent over time, except for pulmonary embolism, which increased from 57.1 to 68.5 per 100 000 between 2015 and 2019. Rates were higher for females than males for subarachnoid haemorrhage, pulmonary embolism and cerebral venous thrombosis, and vice versa for ischaemic stroke and intracerebral haemorrhage. Rates increased with age for most of these conditions, but idiopathic thrombocytopaenia demonstrated a bimodal distribution with incidence peaks at 0-19 years and ≥60 years. CONCLUSIONS: Our estimated background rates help contextualise observed events of these potential adverse events of special interest and to detect potential safety signals related to COVID-19 vaccines.

Association of Low-Value Testing With Subsequent Health Care Use and Clinical Outcomes Among Low-risk Primary Care Outpatients Undergoing an Annual Health Examination.

Importance: The association of low-value testing with downstream care and clinical outcomes among primary care outpatients is unknown to date. Objective: To assess the association of low-value testing with subsequent care among low-risk primary care outpatients undergoing an annual health examination (AHE). Design, Setting, and Participants: This population-based retrospective cohort study used administrative health care claims from Ontario, Canada, for primary care outpatients undergoing an AHE between April 1, 2012, and March 31, 2016, to identify individuals who could be placed into one (or more) of the following 3 cohorts: adult patients (18 years or older) at low risk for cardiovascular and pulmonary disease, adult patients at low risk for cardiovascular disease, and female patients (aged 13-20 years or older than 69 years) at low risk for cervical cancer. The dates of analysis were June 3 to September 12, 2019. Exposures: Low-value screening tests were defined per cohort as (1) a chest radiograph within 7 days, (2) an electrocardiogram (ECG) within 30 days, or (3) a Papanicolaou test within 7 days after an AHE. Main Outcomes and Measures: Subsequent specialist visits, diagnostic tests, and procedures within 90 days after a low-value test (if the patient had a chest radiograph, ECG, or Papanicolaou test) or end of the exposure observation window (if not tested). Results: Included in the chest radiograph, ECG, and Papanicolaou test cohorts of propensity score-matched pairs were 43 532 patients (mean [SD] age, 47.5 [14.4] years; 38.5% female), 245 686 patients (mean [SD] age, 49.9 [13.7] years; 51.1% female), and 29 194 patients (mean [SD] age, 45.5 [27.1] years; 100% female), respectively. At 90 days, chest radiographs in low-risk patients were associated with an additional 0.87 (95% CI, 0.69-1.05) and 1.96 (95% CI, 1.71-2.22) patients having an outpatient pulmonology visit or an abdominal or thoracic computed tomography scan per 100 patients, respectively, and ECGs in low-risk patients were associated with an additional 1.92 (95% CI, 1.82-2.02), 5.49 (95% CI, 5.33-5.65), and 4.46 (95% CI, 4.31-4.61) patients having an outpatient cardiologist visit, a transthoracic echocardiogram, or a cardiac stress test per 100 patients, respectively. At 180 days, Papanicolaou testing in low-risk patients was associated with an additional 1.31 (95% CI, 0.84-1.78), 52.8 (95% CI, 51.9-53.6), and 0.84 (95% CI, 0.66-1.01) patients having an outpatient gynecology visit, a follow-up Papanicolaou test, or colposcopy per 100 patients, respectively. Conclusions and Relevance: Observed associations in this population-based cohort study suggest that testing in low-risk patients as part of an AHE increases the likelihood of subsequent specialist visits, diagnostic tests, and procedures.

Low rates of influenza immunization in young children under Ontario's universal influenza immunization program.

OBJECTIVES: To determine physician-administered influenza vaccine coverage for children aged 6 to 23 months in a jurisdiction with a universal influenza immunization program during 2002-2009 and to describe predictors of vaccination. METHODS: By using hospital records, we identified all infants born alive in Ontario hospitals from April 2002 through March 2008. Immunization status was ascertained by linkage to physician billing data. Children were categorized as fully, partially, or not immunized depending on the number and timing of vaccines administered. Generalized linear mixed models determined the association between immunization status and infant, physician, and maternal characteristics. RESULTS: Influenza immunization was low for the first influenza season of the study period (1% fully immunized during the 2002-2003 season), increased for the following 3 seasons (7% to 9%), but then declined (4% to 6% fully immunized during the 2006-2007 to 2008-2009 seasons). Children with chronic conditions or low birth weight were more likely to be immunized. Maternal influenza immunization (adjusted odds ratio 4.31; 95% confidence interval 4.21-4.40), having a pediatrician as the primary care practitioner (adjusted odds ratio 1.85; 95% confidence interval 1.68-2.04), high visit rates, and better continuity of care were all significantly associated with full immunization, whereas measures of social disadvantage were associated with nonimmunization. Low birth weight infants discharged from neonatal care in the winter were more likely to be immunized. CONCLUSIONS: Influenza vaccine coverage among children aged 6 to 23 months in Ontario is low, despite a universal vaccination program and high primary care visit rates. Interventions to improve coverage should target both physicians and families.