Rheumatism or rheumatic disorders are conditions causing chronic, often intermittent pain affecting the joints or connective tissue. Rheumatism does not designate any specific disorder but covers at least 200 different conditions including arthritis and non-articular rheumatism. There is a close overlap between the term soft tissue disorder and rheumatism. Sometimes the term "soft tissue rheumatic disorders" is used to describe these conditions. The term "Rheumatic Diseases" is used in MeSH to refer to connective tissue disorders. The branch of medicine devoted to the diagnosis and therapy of rheumatism is called rheumatology. Many rheumatic disorders of chronic, intermittent pain (including joint pain, neck pain, or back pain) have historically been caused by infectious diseases. Their etiology was unknown until the 20th century and not treatable, like Lyme disease (in the Northern and Northeastern US), coccidiomycosis or valley fever (in the Western US), and chikungunya in India and a myriad of causes for postinfectious arthritis also known as reactive arthritis-like, for example, the once very common rheumatic fever after Group A Streptococcus infection up to the rare Whipple's disease.