Objective: To find the incidence and prevalence of juvenile chronic arthritis (JCA) in the urban area of San José, Costa Rica.
Methods: During the year preceding our 2 year prospective, population based study, we conducted an educational program on JCA. The physicians caring for children < 16 years of age from all centers in the study area followed the program. They were asked to refer all cases of possible JCA according to EULAR criteria. The children were all evaluated at the National Children's Hospital.
Results: Of 189 children referred, 48 fulfilled EULAR criteria for JCA. The 2 year incidence rate for JCA was 13.7 per 100,000 children < 16 years old. This corresponds to an annual incidence per 100,000 children of 6.8 (95% CI 4.1-9.6). The incidence rate for pauciarticular onset JCA was 3.9 per 100,000. At the prevalence date, 122 cases of JCA were recorded, corresponding to a prevalence of 34.9 per 100,000 children < 16 years. When patients in remission were excluded, the prevalence was 31.4 per 100,000 (95% CI 25.5-37.2). The pauciarticular onset form was the most common, 71% of all prevalence cases. The highest incidence and prevalence were noted for pauciarticular girls with late onset JCA. No incidence peak was found in preschool age. The girl-to-boy ratio was 1.5/1. Antinuclear antibodies (ANA) were positive in only 7 cases (6.3%). IgM rheumatoid factor was found in 13 children (10.6%). Chronic iritis was observed in 4 cases, all of them ANA negative and older than 7 years of age at onset of arthritis.
Conclusion: The incidence and prevalence observed were lower than those reported in other population based studies, but within the confidence intervals of their data. The incidence rate for pauciarticular JCA was significantly lower than that reported in other comparable studies. ANA positive pauciarticular preschool girls and associated uveitis were rarely encountered.