Epidemiology of juvenile rheumatoid arthritis in Manitoba, Canada, 1975-92: cycles in incidence.

Objective: To determine the yearly incidence of juvenile rheumatoid arthritis (JRA) and to seek correlations between this and cyclic infections occurring in the province of Manitoba, Canada, during the same period.

Methods: An estimate of the incidence of JRA in Manitoba was determined from a disease registry of the Pediatric Rheumatology Clinic, Children's Hospital, Winnipeg. The numbers of confirmed Mycoplasma pneumoniae and viral respiratory infections were determined from annual reports of Cadham Provincial Laboratory. Both facilities provide centralized services for the province.

Results: Between 1975 and 1992 the onset of JRA occurred in 261 patients (136 with pauciarticular, 91 polyarticular, and 34 systemic onset). The average annual incidence of JRA for this period was 5.34/100,000. However, a cyclic incidence was apparent with peaks in 1979, 1982, 1986, and 1990-91. Increases in confirmed M. pneumoniae infections were concurrent with peaks in the incidence of JRA. A significant correlation was found between the incidence of JRA and the number of M. pneumoniae infections detected in the province between 1985 and 1992 (R = 0.76, p = 0.044). In contrast, there was no consistent variation in the incidence of seronegative spondyloarthropathies in children (n = 103 patients).

Conclusion: These data suggest the need for further study of a possible infectious etiology for JRA.