While most men trained to perform circumcisions remove blood from a baby using sterile pads, sponges or rubber suction bulbs, some Orthodox Jews insist that mohels use metzitzah b'peh, or suction by mouth.
"There is no reasonable doubt that the practice of metzitzah b'peh has infected several infants in New York City with the herpes virus, including one child who died and another who has evidence of brain damage," Health Commissioner Dr. Thomas Frieden said in the open letter.
Frieden also said some medical professionals had called for a government ban on the ancient practice, The New York Post reported Wednesday.
Earlier, Frieden agreed to allow a Jewish community court to decide whether to ban the practice, but the court has yet to rule.
Notable deaths of 2014 [PHOTOS]