Usually, the Occupy D.C. protesters battle corporate greed and taxes. This week, their biggest battle has been against hypothermia.

As temperatures dipped into the teens, the city’s two Occupy encampments began to resemble ghost towns, with protesters fleeing to bunk on friends’ couches or in church shelters. Tent covers surrendered themselves to wind gusts, only to reveal no one snuggled underneath them.

“I’m 62. I have arthritis in my knees. It got cold and uncomfortable,” said Crystal Zevon, a writer from Greenfield, Mass., who lent her tent to another protester. She said she is moving indoors to help plan the group’s big spring protests.

“I feel I’m just as much a part of it as I ever was,” she added. “But I’m not a masochist.”

She’s among about half of the protesters who will begin moving indoors in the coming days to expand their efforts. Even though she’s leaving Freedom Plaza, Zevon said, she and fellow protesters are not leaving the occupation.

The dwindling number of residents who stayed behind zipped up their tents, swallowed vitamins and swaddled themselves in clothing to battle the elements. Medics in both camps said Wednesday that they were passing out vitamin C tablets and Theraflu but had no official cases of hypothermia — yet. Good Samaritans streamed by to drop off blankets, and a collection was started to raise money to buy propane for heaters.

Meantime, there were increased sightings of rats nestling under pallets strewn with sleeping bags, and occupiers in McPherson Square voluntarily shuttered their kitchen for 48 hours for what they said was a monthly cleaning. Protesters were eating donated food brought in by supporters.

Mahlori Isaacs, a spokeswoman for the D.C. Department of Health, said health officers had been closely monitoring the camps for health and safety violations throughout the week, passing out literature on hypothermia and tips to avoid the flu and other illnesses.

“Our main concern is the public health and safety of District residents and visitors . . . making sure that people don’t get sick,” Isaacs said.

D.C. health inspectors will be visiting again early next week, she said, but they have little power to correct any problems they observe because the camps are on federal land.

The final call on whether to close the camps over health and sanitation concerns must come from the National Park Service, Isaacs said.

The Park Service has said that the protesters have a First Amendment right to continue their “24-hour vigil” at the two encampments but that the agency will move in to evict protesters if sanitation conditions warrant.

This week, occupiers at Freedom Plaza — whose permit was extended by the Park Service last month through the end of February — began to erect three large canvas tents for the winter, which will be warmed with kerosene heaters and serve as a kitchen and communal gathering space.

Organizer Kevin Zeese said half of the 70 protesters in Freedom Plaza will move to homes owned by supporters in Northwest Washington and Mount Rainier in Prince George’s County to expand their operations and make plans for spring marches and other events.

“Don’t think it is just about the cold — the real purpose is to use indoor space to work more effectively to build the movement,” Zeese wrote in an e-mail.

The group had debated its future for several weeks last month, and a small group was adamant that some protesters remain on the plaza despite the chilly weather.

At Freedom Plaza during a wintry night this week, the wind gusted, and tempers began to fray.

“People get a little bit more irritated,” protester Kyle Szolsek said as he jumped up and down in the frigid air. “I’m from Maine, so it’s not so bad. I think I might go inside our warming center and teach an aerobics class.”

Blair Rush, a 41-year-old homeless woman in her tent on Tuesday night, knows cold. She said she has been without a permanent home for four years, since she stopped being able to make her mortgage payments. She doesn’t stay in shelters because she has a dog, she said.

“Thank God I have blankets,” she said, her body warmed by at least three layers of clothing. “I don’t do cold.”

Her tent, big enough to hold nine, was covered in blankets that sat atop more blankets. She sat on a blanket-covered milk crate in front of her hot plate, huddling over a pot of steaming water.

Watching the camp empty out as winter arrived reaffirmed to Rush that there were class divisions among the 99 percent: those who can’t go home again and those who choose not to. When the mercury began to sink, Rush noticed there were fewer occupiers occupying. Some went home for the holidays, and many spend hours out of the wind in nearby restaurants and coffee shops.

Not that Rush faults those who spend the cold nights in a heated place with a roof over their heads. She’d do the same if she could.

Jerry Jackson, another occupier, said he wondered whether the temperature will do what the police and politicians haven’t: Shut the place down.

“I’m here as long as we need to be here to make our point,” he said. “The people that are going to stay are the people who truly believe they are making a difference. The other people will just blow away.”