Epidemiology

JIA is the most common chronic rheumatic disorder of childhood.

There are several limitations in the methods applied to study the epidemiology, including the use of different classification criteria. Epidemiological studies focusing on children seen in hospitals and clinics report lower prevalences compared with community-based studies. A population-based study in Rochester, Minnesota demonstrated a prevalence of 86.1 and an incidence of 11.7 per 100,000 children aged under 16 years.[5] A study in Nordic countries found that the incidence was 15 per 100,000 children per year.[6] One meta-analysis reported an incidence of 1.6 to 23 cases per 100,000 children per year and a prevalence of 3.8 to 400 cases per 100,000 children per year in Europe.[7]

JIA is 3 to 6.6 times more common in females than in males.[8] Oligoarticular JIA is the most common subtype (50% to 60% of cases), followed by polyarticular JIA (30% to 35% of cases).[9] Oligoarticular JIA and rheumatoid factor (RF)-negative JIA typically affect young, female children.[8] RF-positive polyarticular JIA is typically seen in teenage girls. Enthesitis-related JIA has male predominance, usually in boys after the age of 6 years.[10] Systemic-onset juvenile idiopathic arthritis (SoJIA) comprises 10% to 20% of all JIA and affects boys and girls equally.[9] Black, Indian, and Native American children are more likely to have polyarticular JIA.[11]

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