BOSTON — A deadly infection that has now spread to three states is puzzling disease investigators. The illness is caused by Elizabethkingia anophelis, a bacterium commonly found in soil and water and that, until now, has rarely caused problems.

Public health authorities in Wisconsin first reported the outbreak to the U.S. Centers for Disease Control and Prevention in early January. At that time, six people were ill with symptoms that include fever, difficulty breathing and cellulitis. The outbreak has now spread to 63 people in Wisconsin, one in Illinois and one in Michigan. Most patients are over 65. About 30 percent have died from the infection.

An investigation team led by the CDC has been unable to determine how the E. anophelis is spreading or why it has become so fatal. It was first found in the