When worshippers clasp hands to "pass the peace" or share the communion cup and offering plates, religious leaders around the country want to be sure they don't also pass on swine flu.
Catholic churches in many dioceses with confirmed cases of the flu will not offer communion wine, and parishioners have been urged to bow or nod instead of offering a handshake.
Imams have been told the Friday communal prayer can be canceled and done privately. One rabbi is making hand sanitizer available to stave off germs that could be passed when the Torah is touched as it is carried throughout the synagogue.
In San Antonio, the University United Methodist Church ordered more than 3,000 individually wrapped communion wafers and juice packets for this week to avoid having to skip communion, which many Protestant churches serve the first Sunday of the month.
"In a time of fear, we just wanted people to have assurance we were doing everything we could do," said Shauna Forkenbrock, a church spokeswoman.
The Centers for Disease Control and Prevention and state officials have confirmed dozens of cases of swine flu across the country, though just one death in the United States has been reported, in Houston. In most confirmed U.S. cases, the patients are recovering.
But with warnings that the virus is spreading, houses of worship are cutting back on activities that require close contact.
In Miami and Austin, Texas, Roman Catholic officials have cut off serving communion wine, and many others are considering doing the same.
In the Diocese of Dallas, officials are assuring parishioners that "it's not a sin" to miss Mass if you're sick.
The Dallas diocese also is asking parishioners not to be offended if people don't want to shake hands during "the sign of peace," when parishioners traditionally greet one another. It's suggesting a slight bow of the head as a substitute.
Parishioners got similar advice from the Miami archdiocese, and that has been disheartening for Adelina Ramirez, 56, who spent her lunch break on church grounds.
"That part when you go up to the priest, and he offers you the bread and the wine, which stand for everything that is Jesus Christ, it is such an important part of Mass," she said. "Shaking the hands of whomever is sitting near you and wishing him or her that God be with you is just as important."
The communal Friday noon prayer for Muslims also could be affected if the flu worsens, said Ibrahim Hooper of the Council on American-Islamic Relations.
Islamic scholars consulted by CAIR said that the prayer time, when worshippers are often packed shoulder to shoulder, toe to toe, can be canceled, and done privately, in regions where flu cases are confirmed, Hooper said.
Hooper hadn't heard of any cancellations as of Thursday afternoon.
"At least we wanted to make sure that imams or the prayer leaders knew that was an option and that they were informing congregations as the crisis unfolds," he said.
Synagogue worship on Saturdays, when the Torah is removed from the ark and carried around the synagogue, offers chances for germs to spread. Worshippers touch the Torah with their prayer shawl, prayer book or hands. Then, they kiss whatever they used to touch the Torah.
Rabbi John Franken at Temple Ohabei Shalom outside of Boston said the temple is making hand sanitizers available and posting cautionary signs in the bathroom and Sabbath bulletins. But so far, it has not forbidden touching the Torah or other objects used in common worship.
Rabbi Mayshe Schwartz of The Chai Center in the Boston suburb of Brookline said he didn't want to overreact.
"Unfortunately, more people will probably die this weekend in car accidents of drunk drivers than of swine flu," Schwartz said. "The job is to create calm, not to create fear."
Catholic Bill Spain, who visited St. Anthony's Shrine in downtown Boston on Thursday, said he wasn't fazed by the various precautions his church could take. He said that he won't stop taking communion, or dipping his hand in holy water, but that if he can't shake hands at Mass for a while, so be it.
"So for one week we can just nod. I think that's great," said Spain, 71. "I'm still going to kiss my wife, so there's no problem with us