The Danish Infection Cohort: a resource for population based infectious disease epidemiology

Infections are a major cause of morbidity and mortality, but many aspects of the epidemiology of infections are unknown or unclear because key data are lacking. We created The Danish Infection Cohort by linking Danish National Health Survey data (including self-reported behavioral, health, and other information) to data on diagnoses and medications in Danish national health registries. We included individuals ≥ 18 years of age in surveys from 2010, 2013, 2017, and 2021. We identified evidence of infection in the 365 days post-survey by using two definitions: hospital-diagnosed infections, via primary or secondary discharge diagnoses in the Danish National Patient Registry (containing all Danish hospital-based outpatient, emergency, and inpatient encounters); and community-treated infections, via systemic anti-infective prescription redemptions at community pharmacies in the Danish National Prescription Registry. Overall, among 609,224 individuals, 196,980 (32.3%) had one or more infections within 365 days post-survey: 11,850 hospital-diagnosed and 185,130 community-treated. Because more than one infection occurred in some individuals, the total number of infections was 315,689: 25,385 hospital-diagnosed and 290,304 community-treated. The most common diagnoses were respiratory infections (34.9%), and the most common anti-infectives were antibiotics (80.6%). This cohort, with nearly 200,000 individuals with infections, and more than 315,000 infections overall, includes data on smoking, weight, physical activity, diet, alcohol use, and other factors, enabling a wide range of investigations including infectious disease patterns and etiologies over time.