The city Health Department admitted Thursday that it is often unable to identify practitioners who infect newborns with herpes through a controversial ritual Jewish circumcision — because of a code of silence in the ultra-­Orthodox community.

Since 2015, there have been six neonatal cases of herpes linked to the ancient practice known as metzitzah b’peh, which requires a mohel, the person performing the circumcision, to suck blood from the incision on an infant’s penis.

But only two mohelim have been identified for endangering the lives of infants since then.

The Health Department has yet to find the mohel behind the most recent case, first reported Wednesday. It issued a statement Thursday night noting potential obstacles to its investigation.

“Identifying a mohel has always been challenging, and it generally takes time,” the statement read.

“Unfortunately, some in the community are resistant. We are hopeful that won’t happen with this new case, but we don’t know yet.”

The practice has pitted public health officials against leaders in the Hasidic community, who see regulation as an infringement on a religious ritual.