Parents who are fearful of vaccines should not intentionally expose their children to the measles, California health officials warned Monday, amid rumors of “measles parties” in local media.

The California Department of Health said it “strongly recommends against the intentional exposure of children to measles. It unnecessarily places the exposed children at potentially grave risk and could contribute to further spread.”

No known “measles parties” have been thrown to date, but the expression started cropping up in local media reports after a San Francisco radio station reported that a local mother had offered to arrange a play date between sick and healthy children.

Officials have confirmed 59 cases of the measles across the state, 42 of which have spread through Disney (DIS) theme parks.