| Septic arthritis | Occurs in 10% of patients |
| Extracellular, encapsulated bacteria ( S. pneumoniae , H. influenzae ), S. aureus | |
| Mycoplasma , particularly Ureaplasma urealyticum | |
| Enteroviruses, particularly echovirus and coxsackie virus | |
| Aseptic, possibly autoimmune, arthritis | Usually mono- or oligoarticular; involves large joints; rarely destructive; rheumatoid factor and ANA absent. Occurs in 10% of patients |
| Dermatomyositis-like syndrome associated with progressive enterovirus (ECHO) CNS infection | Presents with rash and muscle weakness |
