Interplay of microbe and major histocompatibility complex: a family study.

We describe a 24-year-old man who developed reactive arthritis (ReA) after a dysenteric illness caused by Salmonella hadar. Serologic tests suggested recent exposure of family members to Salmonella. All members of the family were HLA-B27 positive, but no other family member developed acute ReA, although 2 of them had clinical evidence of previously existing B27 associated arthritis.