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New York (CNN) -- Two more infants have contracted the herpes virus after undergoing an ultra-Orthodox Jewish type of circumcision, which has been linked to the spread of the potentially deadly virus to newborn boys, according to the New York City Health Department.
In the ritual, known as metzitzah b'peh, after removing the foreskin of the penis the person performing the procedure places his mouth briefly over the wound, sucking a small amount of blood out, which is discarded. Antibacterial ointment is applied and the wound is bandaged. The health department says the procedure is dangerous because the contact with the mouth could transmit diseases such as herpes.
Most adults are infected with the herpes simplex virus type 1, and while they may have no symptoms, the virus may be present in their saliva, according to the health department. (It is different from herpes simplex virus type 2, which is usually transmitted sexually.)
"While HSV-1 in adults can cause the common cold sore, HSV-1 infection in newborns is very serious," a department statement says.
Since 2000, there have been 13 reports in New York City of infants contracting HSV-1, two of whom died from the virus. The health department reported that an estimated 20,493 infants in New York City were exposed to the practice in that period.
In the most recent case, the infant developed a fever seven days after circumcision and vesicular lesions the following day, according to a press release from the city health department. Seventy percent of neonatal herpes cases show lesions and only 40% produce a fever.
The DOH passed a regulation in September requiring all those who perform the ritual to get parental consent on a form stating that the procedure can lead to health risks. Several Jewish groups and three rabbis filed a lawsuit in federal District Court in Manhattan arguing that "the government cannot compel the transmission of messages that the speaker does not want to express -- especially when the speaker is operating in an area of heightened First Amendment protection, such as a religious ritual."
Dr. Thomas A. Farley, commissioner of the city's health department, claimed the consent requirement was "lawful, appropriate and necessary" in a September press release. "The city's highest obligation is to protect its children; therefore, it is important that parents know the risks associated with the practice," he said.
Baby boys whose circumcisions likely involved the ritual between April 2006 and December 2011 had an estimated risk of contracting neonatal HSV-1 infection of 24.4 per 100,000 cases, 3.4 times greater than other infants, according to the health department.
"There is no safe way to perform oral suction on any open wound in a newborn," Farley said.
While Jews regularly practice circumcision as part of their religion, metzitzah b'peh is limited to a relatively small number of ultra-Orthodox Jews.
CNN's Erinn Cawthon and Pauline Kim contributed to this story.