Sandra Thygesen

Pertussis is associated with encephalopathy and seizures in infants. However, the risk of childhood epilepsy following pertussis is unknown. To examine whether pertussis is associated with the long-term risk of epilepsy. We used individually linked data from population-based medical registries covering all Danish hospitals to identify a cohort of all patients with pertussis born between 1978 and 2011, followed up through 2011. We used the Civil Registration System to identify 10 individuals from the general population for each patient with pertussis, matched on sex and year of birth. Inpatient or hospital-based outpatient diagnosis of pertussis. Cumulative incidence and hazard ratio of time to hospital-based epilepsy diagnosis (pertussis cohort vs general population cohort), adjusted for birth year, sex, maternal history of epilepsy, presence of congenital malformations, and gestational age. Unique personal identifiers permitted unambiguous data linkage and complete follow-up for de...

Chondrolysis is a rare disease with destruction of cartilage of joints. Incidence and risk factors have not been studied in a formal epidemiologic population-based setting. We used the Danish National Registry of Patients (NRP) covering all Danish hospitals to identify all cases of chondrolysis from 1994 to 2008. Incidence rates were estimated using the general population as the denominator. For each chondrolysis patient, 10 age-matched population controls were sampled for a case-control analysis. For cases and controls, we ascertained in the NRP history of diabetes, rheumatoid arthritis, orthopedic surgery, including surgery of shoulder and upper arm, injury to shoulder girdle or upper arm, and treatment with pain pump. We determined the prevalence of these risk factors in cases and controls, and computed odds ratios (OR). We identified 43 patients with chondrolysis in the 15-year study period. The incidence rate was 5.5 per 10,000,000 person-years. Diabetes was more prevalent in chondrolysis cases, compared with the 430 controls (OR = 6.7; 95% confidence intervals [CI]: 1.1-39.9). Orthopedic surgery was also associated with an increased risk of chondrolysis (OR = 28.8, 95% CI: 11.0-75.6), while previous injury was not (OR = 0.8; 95% CI: 0.1-5.9). Chondrolysis was rarely diagnosed in Denmark. Diabetes and orthopedic surgery may be risk factors.

Infant respiratory distress syndrome (IRDS) is the most common respiratory disease in preterm infants, and is associated with considerable morbidity and mortality. Valid data on IRDS are important in clinical epidemiological research. The objective of this study was to estimate the positive predictive value (PPV) of the IRDS diagnosis registered in the population-based Danish National Patient Registry according to the International Classification of Diseases, 8th and 10th revisions. Between January 1, 1977 and December 31, 2008, we randomly selected three patients per year, 96 in total, who were registered with an IRDS diagnosis in the Danish National Patient Registry and living in the northern part of Denmark. Data on the infants included information on the presence of predefined clinical symptoms. We defined IRDS as the presence of at least two of four clinical symptoms (tachypnea, retractions or nasal flaring, grunting, and central cyanosis), which had to be present for more than 30 minutes. Using medical record review as the reference standard, we computed the positive predictive value of the registered IRDS diagnosis including 95% confidence intervals (CIs). We located the medical record for 90 of the 96 patients (94%), and found an overall PPV of the IRDS diagnosis of 81% (95% CI 72%-88%). This did not vary substantially between primary and secondary diagnoses. The PPV was higher, at 89% (95% CI 80%-95%), for preterm infants born before 37 weeks of gestation. The PPV of the IRDS diagnosis in the Danish National Patient Registry is reasonable when compared with symptoms described in the corresponding medical records. The Danish National Patient Registry is a useful data source for studies of IRDS, particularly if restricted to preterm infants. Nonetheless, the potential impact of misclassification of the IRDS diagnosis must be considered.

Atrial fibrillation is a major risk factor for ischemic stroke. However, the prognostic impact of atrial fibrillation among patients with stroke is not fully clarified. We compared patient characteristics, including severity of stroke and comorbidity, quality of in-hospital care and outcomes in a cohort of first-time ischemic stroke patients with and without atrial fibrillation. Based on linkage of public medical databases, we did a population-based follow-up study among 3,849 stroke patients from the County of Aarhus, Denmark admitted in the period of 2003-2007 and prospectively registered in the Danish National Indicator Project. Atrial fibrillation was associated with an adverse prognostic profile but not with an overall poorer quality of in-hospital care. Patients with atrial fibrillation had a longer total length of stay (median: 15 vs 9 days), and were at increased risk of in-hospital medical complications (adjusted relative risk = 1.48, 95% CI: 1.23-1.79) and recurrent stroke (adjusted hazard ratio = 1.30, 95% CI: 0.93-1.82) when compared with patients without atrial fibrillation. The adjusted hazard ratios for 30 days and one year mortality were 1.55 (95% CI: 1.20-2.01) and 1.55 (95% CI: 1.30-1.85), respectively. Patients not eligible to oral anticoagulant treatment had an increased risk of recurrent stroke (adjusted hazard ratio = 1.92, 95% CI: 1.19-3.11). Atrial fibrillation is associated with a poor outcome among patients with ischemic stroke particularly among patients, who are not eligible to oral anticoagulant treatment.