Unusual infection by anatomical site Unusual musculoskeletal infection Increased susceptibility to infection of bones, joints, or muscles, as manifested by recurrent or severe osteomyelitis, septic arthritis, or infectious myositis, or by musculoskeletal infection caused by an atypical or opportunistic organism. Recurrent musculoskeletal infections are characteristic of phagocyte defects, sickle cell-related asplenia, and combined immunodeficiencies.