The city's intervention has angered many Orthodox leaders, and the issue has left the city struggling to balance its mandate to protect public health with the constitutional guarantee of religious freedom.
"This is a very delicate area, so to speak," said Health Commissioner Thomas R. Frieden.
The practice is known as oral suction, or in Hebrew, metzitzah b'peh: after removing the foreskin of the penis, the practitioner, or mohel, sucks the blood from the wound to clean it.
It became a health issue after a boy in Staten Island and twins in Brooklyn, circumcised by the same mohel in 2003 and 2004, contracted Type-1 herpes. Most adults carry the disease, which causes the common cold sore, but it can be life-threatening for infants. One of the twins died.
Since February, the mohel, Rabbi Yitzchok Fischer, 57, has been under court order not to perform the ritual in New York City while the health department is investigating whether he spread the infection to the infants.
Pressure from Orthodox leaders on the issue led Mayor Michael R. Bloomberg and health officials to meet with them on Aug. 11. The mayor's comments on his radio program the next day seemed meant to soothe all parties and not upset a group that can be a formidable voting bloc: "We're going to do a study, and make sure that everybody is safe and at the same time, it is not the government's business to tell people how to practice their religion."
The health department, after the meeting, reiterated that it did not intend to ban or regulate oral suction. But Dr. Frieden has said that the city is taking this approach partly because any broad rule would be virtually unenforceable. Circumcision generally takes place in private homes.
Dr. Frieden said the department regarded herpes transmission via oral suction as "somewhat inevitable to occur as long as this practice continues, if at a very low rate."
The use of suction to stop bleeding dates back centuries and is mentioned in the Talmud. The safety of direct oral contact has been questioned since the 19th century, and many Orthodox and nearly all non-Orthodox Jews have abandoned it. Dr. Frieden said he hoped the rabbis would voluntarily switch to suctioning the blood through a tube, an alternative endorsed by the Rabbinical Council of America, the largest group of Orthodox rabbis.
But the most traditionalist groups, including many Hasidic sects in New York, consider oral suction integral to God's covenant with the Jews requiring circumcision, and they have no intention of stopping.
"The Orthodox Jewish community will continue the practice that has been practiced for over 5,000 years," said Rabbi David Niederman of the United Jewish Organization in Williamsburg, Brooklyn, after the meeting with the mayor. "We do not change. And we will not change."
David Zwiebel, executive vice president of Agudath Israel, an umbrella organization of Orthodox Jews, said that metzitzah b'peh is probably performed more than 2,000 times a year in New York City.
The potential risks of oral suction, however, are not confined to Orthodox communities. Dr. Frieden said in March that the health department had fielded several calls from panicked non-Orthodox parents who had hired Hasidic mohels unaware of what their services entailed.
Defenders of oral suction say there is no proof that it spreads herpes at all. They say that mohels use antiseptic mouthwash before performing oral suction, and that the known incidence of herpes among infants who have undergone it is minuscule. (The city's health department recorded cases in 1988 and 1998, though doctors in New York, as in most states, are not required to report neonatal herpes.)
Dr. Kenneth I. Glassberg, past president of the New York section of the American Urological Association and director of pediatric urology at Morgan Stanley Children's Hospital of New York-Presbyterian, said that while he found oral suction "personally displeasing," he did not recommend that rabbis stop using it.
"If I knew something caused a problem from a medical point of view," said Dr. Glassberg, whose private practice includes many Hasidic families, "I would recommend against it."
But Rabbi Moshe Tendler, a microbiologist and professor of Talmud and medical ethics at Yeshiva University, said that metzitzah b'peh violates Jewish law.
"The rule that's above all rules in the Torah is that you cannot expose or accept a risk to health unless there is true justification for it," said Dr. Tendler, co-author of a 2004 article in the journal Pediatrics that said direct contact posed a serious risk of infection.
"Now there have been several cases of herpes in the metro area," he said. "Whether it can be directly associated with this mohel nobody knows. All we're talking about now is presumptive evidence, and on that alone it would be improper according to Jewish law to do oral suction."
The inconsistent treatment of Rabbi Fischer himself indicates the confusion metzitzah b'peh has sown among health authorities, who typically regulate circumcisions by doctors but not religious practitioners.
In Rockland County, where Rabbi Fischer lives in the Hasidic community of Monsey, he has been barred from performing oral suction. But the state health department retracted a request it had made to Rabbi Fischer to stop the practice. And in New Jersey, where Rabbi Fischer has done some of his 12,000 circumcisions, the health authorities have been silent.
Rabbi Fischer's lawyer, Mark J. Kurzmann, said that absent conclusive proof that the rabbi had spread herpes, he should be allowed to continue the practice. Rabbi Fischer said through Mr. Kurzmann that the twin who died and the Staten Island boy both had herpes-like rashes before they were circumcised and were seen by a pediatrician who approved their circumcision. The health department declined to comment on its investigation.