The death toll from mysterious lung illnesses linked to vaping across the U.S. has risen to 37, according Thursday to the nation’s health protection agency.

The cases of vaping-related illnesses jumped to 1,888, said the Centers for Disease Control and Prevention (CDC) in a statement.

Last week, the agency verified more than 1,600 confirmed and probable cases in 49 of the U.S.’s 50 states. Alaska is the sole exception.

Officials are continuing to search for a cause for the outbreak.

Read more: Vaping-related deaths in US rise to 37: health agency