Gonorrhea should be considered the most likely cause of acute suppurative arthritis in sexually active individuals; in some cases, multiple joints can be involved. In men, urethritis may occur with a gonorrheal infection. Borrelia burgdorferi causes Lyme disease, characterized by chronic arthritis that may mimic rheumatoid arthritis. Haemophilus influenzae is a short, gram-negative rod that can cause osteomyelitis in children. Staphylococcus aureus is the most common cause of osteomyelitis, but the Gram stain would show gram-positive cocci. Treponema pallidum infection, also a sexually transmitted disease, can lead to syphilitic gummas in the tertiary phase of syphilis that may produce joint deformity. There is no preceding urethritis, however. Tertiary syphilis may be preceded years earlier by a primary syphilitic chancre.