An encephalitis epidemic hit St. Louis in the summer of 1933. At that time, no one had a clue to the cause, incubation period, duration or transmission mechanisms. An entire floor at Barnes was opened for encephalitis patients. This was the first opportunity for a teaching hospital to study the disease on such a large scale. Researchers at Barnes and Washington University found a virus carried by the Culex mosquito caused the encephalitis. As a result, mosquito population control measures adopted nationwide helped reduce encephalitis outbreaks.