- To determine whether there is a seasonal peak onset of systemic juvenile rheumatoid arthritis (SOJRA) suggestive of an infectious etiology. We examined the seasonal variability of SOJRA in Israel. A multicenter retrospective chart review of 59 patients with SOJRA, enrolled from 10 rheumatology units or pediatric departments in Israel. All patients met defined criteria of SOJRA. Fifty-nine patients (31 female, 28 male) were followed from 1982 to 1997. Their mean age was 7.1 +/- 4.3 years (range 0.9-16). Forty-six were Jewish and 13 were Arabs or of Bedouin origin. Eighteen patients (31%) had disease onset in the winter, 16 (27%) in the spring, 12 (20%) in the summer, and 13 (22%) in the fall. Twenty-eight patients had a monophasic disease subtype, while 31 had a chronic or cyclic subtype. The seasonal onset in the patients with the monophasic type versus the chronic or the cyclic type shows 7 versus 11 in the winter, 7 versus 9 in spring, 8 versus 4 in summer, and 6 versus 7 in fall, respectively. There is no seasonal pattern to SOJRA disease onset in Israel. However, the disease onset of patients having the chronic or the polycyclic subtype tends to be more common in winter and spring. Since patients with this type have more severe disease, it is possible that another specific infectious agent is one of the factors involved in the pathogenesis of the disease. Larger sampling and multicenter studies are required to clarify this point.