The fourth disease, 1900-2000.

Measles and scarlet fever were differentiated from one another in the 17th century. Rubella was accepted as the third distinct paediatric exanthem in 1881. Nil Filatow in 1885 and Clement Dukes in 1894 described two distinct forms of rubella, and in 1900 Dukes proposed that one of these forms of rubella was a separate entity which he called the fourth disease. For the past five decades, fourth disease has been considered a non-entity, perhaps a mild form of scarlet fever, but certainly not a distinct disease. In 1979 Keith Powell resurrected the idea of the fourth disease and argued that it was caused by exotoxin-producing Staphylococcus aureus. We present additional arguments for the existence of fourth disease, as well as information to link the disease to S. aureus.