Cases of congenital syphilis — syphilis passed from mother to baby during pregnancy — have more than doubled since 2013, according to the annual Sexually Transmitted Disease Surveillance Report released Tuesday by the Centers for Disease Control and Prevention.

Thirty-seven states, primarily in the South and West, have reported cases of congenital syphilis. In 2013, there were 362 reported cases, but the number increased to 918 in 2017 — the largest number of cases in 20 years.