Background Last decade a resurgence of post streptococcal reactive arthritis (PSRA) is observed in the Netherlands. As throat cultures often remain negative, dicrimination between cases due to group A streptococci (GAS) versus non-group A streptococci (NGAS) may be strived for by using serologic responses in anti-strepto-lysin-O (ASO) and anti-deoxyribonuclease-B (antiDNase-B). Previous studies have shown: lower ASO/antiDNase-B ratio 1.45 for NGAS infection.

Study design Prospective observational inception cohort study of consecutive PSRA patients, presenting to our Dept of Rheumatology from April 1998 until Dec 2000. Alternative causes of arthritis were excluded.

Results 20 female, 15 male PSRA patients were included; 1 male was excluded after half a year as he developed a RF positive erosive RA. The 24 remaining patients did not meet Jones’ criteria. A sore throat was recalled by 19/24 = 79%. Throat culture was positive in 7/24 = 29%: GAS in 4, GGS in 2, and GCS in 1 patient. Patients were subgrouped according to ASO/antiDNase-B ratio. At least a 1-yr-period of monthly penicillin prophylaxis was advised to patients in whom GAS was the presumed causative microbe. So far follow-up was uneventful with respect to carditis/chorea: complication rate <1/427 mos. In 1 patient from the NGAS group, a fulminant arthritis with pneumonitis recurred 6 mos after a 2-yr-period of penicillin prophylaxis: arthritis recurrency rate 1/304 NGAS-patient mos.

Conclusion Serologic analysis in PSRA gives additive information. A higher ASO/anti-Dnase-B ratio suggests primary NGAS infection, is associated with a signifiantly less polyarticular presentation of arthritis, and with a significantly more rapid recovery. The exact role for penicillin prophylaxis warrants further investigation.