As coronavirus infections accumulate across America, hospitals are facing new urgency to keep their workers safe.

In China, where the virus was first discovered, protecting health care workers was a serious challenge. More than 3,300 nurses, doctors and other hospital staff members across the country were infected, many because of insufficient protective equipment.

In the United States, many hospitals are already struggling with limited supplies of masks, gowns and goggles, as health officials figure out the best way to protect workers. On Thursday, the U.S. surpassed China in total reported cases of Covid-19, the disease caused by the new coronavirus.

“We need to think about what the right thing is for patients, but also for our caregivers, to make sure they’re not exposed,” said Amy Compton-Phillips, chief clinical officer at the Providence St. Joseph Health, a hospital network headquartered in Washington State that is currently treating more than 400 confirmed coronavirus patients across seven states.

That means shoring up supplies of protective gear and making space to isolate and treat patients as cases mount.

Protective equipment: gowns, gloves, goggles and respirators

Current C.D.C. recommendations for health care workers Eye protection Goggles or face shield Respirator or medical mask N95 respirator, if available Gown Closed securely at the back Gloves Pulled up over gown sleeves Current C.D.C. recommendations for health care workers Eye protection Goggles or face shield Respirator or medical mask N95 respirator, if available Gloves Pulled up over gown sleeves Gown Closed securely at the back Current C.D.C. recommendations for health care workers Eye protection Goggles or face shield Respirator or medical mask N95 respirator, if available Gloves Pulled up over gown sleeves Gown Closed securely at the back

There is still some uncertainty about how the new coronavirus spreads, but experts agree it is most likely passed through close contact with people who are infected, and specifically the viral droplets they expel when they cough or sneeze.

The Centers for Disease Control and Prevention has advised health care workers to wear protective gowns, gloves, goggles and masks while treating potential and confirmed cases of Covid-19, to avoid exposure. But there has been some disagreement over which masks are needed.

Initially, the agency advised the use of respirator masks that fit tightly over the nose and mouth to filter out virus particles before they are inhaled, such as the N95. (Health care workers could also wear devices known as PAPRs, or powered air-purifying respirators, which cover the entire head.)

But with respirators in short supply across the country, the C.D.C. updated its recommendations in early March to allow the use of standard medical masks for most coronavirus patient care. These looser-fitting masks protect against droplet transmission from coughs and sneezes, but do not filter out airborne pathogens.

The change puts the agency in closer alignment with World Health Organization guidelines, which only require respirator masks during special procedures that may result in the spray of tiny viral particles. But it drew sharp rebuke from a national nurses union.

N95 respirator Surgical mask Tight fit; must be specially fitted. Filters out 95% of small particles. Loose fit around edges. Provides protection from large droplets. Surgical mask N95 respirator Loose fit around edges. Provides protection from large droplets. Tight fit; must be specially fitted. Filters out 95% of small particles. N95 respirator Tight fit; must be specially fitted. Filters out 95% of small particles. Surgical mask Loose fit around edges. Provides protection from large droplets.

A global surge in demand for protective gear and supply chain disruptions in China have led to dire shortages of both kinds of masks in many U.S. hospitals. Supplies of gowns, gloves and eyewear are also low.

“We have significant limitations on our high-level N95 masks, and even surgical masks are in short supply,” said Dr. Compton-Phillips of Providence St. Joseph Health.

“I cannot ask people to go into battle unarmed, and that’s what we would have to do if we ran out of PPE,” she said, using the acronym for personal protective equipment.

Representatives from hospitals across the country said they were taking steps to preserve their protective equipment supplies, including limiting the number of people who enter a patient’s room to essential personnel only, and grouping Covid-19 patients together so doctors and nurses don’t need to put on new gear for every interaction. Some health care workers are reusing disposable masks over multiple days. Under normal circumstances, masks and other equipment are discarded between patients.

“This pandemic is not a sprint, it’s like a marathon, and we’re trying to keep as many people as healthy as long as we can,” said Dr. Teresa Amato, chair of emergency medicine at Long Island Jewish Forest Hills, a hospital in Queens that is currently treating more than a 100 coronavirus patients.

Major manufacturers, like 3M, have increased mask production, and local companies have converted factories to join the effort. Governors in several states have tapped the nation’s safety net of emergency preparedness equipment: the Strategic National Stockpile, which contained about 13 million N95 respirator masks and 30 million surgical masks at the beginning of the outbreak. But some governors reported receiving less protective gear than they requested.

The U.S. surgeon general, Jerome M. Adams, last month urged the public to stop buying masks to lessen the strain on supply. Masks are not very effective for protecting casual wearers from Covid-19, he said, but are crucial for health care workers who are in close contact with infected patients.

Isolating patients with Covid-19

The C.D.C. recommends coronavirus patients be isolated in single rooms, behind closed doors, away from other patients. But more severe cases may require the use of a special room with negative pressure, which allows air to move inward but not escape back into general circulation.

Outside Air vent Bathroom HEPA filter Area of lower air pressure Hallway Anteroom Negative pressure allows air to flow inwards, but not out of the room. Outside Air vent Bathroom HEPA filter Hallway Area of lower air pressure Anteroom Negative pressure allows air to flow inwards, but not out of the room. Outside Air vent Bathroom HEPA filter Hallway Area of lower air pressure Anteroom Negative pressure allows air to flow inwards, but not out of the room. Outside Air vent Bathroom HEPA filter Hallway Area of lower air pressure Anteroom Negative pressure allows air to flow inwards, but not out of the room. Outside Air vent Bathroom HEPA filter Hallway Area of lower air pressure Anteroom Negative pressure allows air to flow inwards, but not out of the room. Outside Air vent Bathroom HEPA filter Hallway Area of lower air pressure Anteroom Negative pressure allows air to flow inwards, but not out of the room. Note: This is one possible layout for a negative pressure isolation room; an anteroom is optional, and air flow systems may vary.

Negative pressure isolation rooms are recommended for special procedures that may result in the spray of tiny viral particles, like intubation for patients who need help breathing, or bronchoscopy, a procedure that allows doctors to examine a patient’s lungs. Respirator masks are required during these procedures, too.

Most people infected with the new coronavirus do not require hospitalization, but medical systems in many cities and states are already straining as the outbreak accelerates. Many hospitals are cancelling nonessential procedures to free up beds as they anticipate an influx of new patients.

Patients with mild coronavirus infections and no underlying medical conditions are also being asked to quarantine at home. “If you are healthy — even if you have Covid but are not ill enough to be in a hospital — we don’t want to treat you in the hospital,” said Dr. Compton-Phillips.

According to the W.H.O., 80 percent of Covid-19 patients in China experienced a mild or moderate form of the illness, 14 percent had a severe form, and 6 percent became critically ill. Older people and those with prior health conditions were at the highest risk.

“Hopefully most of the people who are sick can be cared for at home and only those with serious respiratory conditions and the elderly who need I.C.U. care are the ones who get admitted to a hospital,” said Dr. Gabor D. Kelen, the director of the Johns Hopkins Office of Critical Event Preparedness and Response and the emergency medicine department. “But if we really get inundated the way they did in some parts of China, you get to the point that you can’t operate normally.”

Determining the proper precautions

The gear health care workers need to protect themselves and how they isolate patients depends largely on how an illness is transmitted.

Airborne spread up to 100 ft Measles, tuberculosis Smaller, lighter aerosol droplets can linger in the air. Influenza, whooping cough, and most likely Covid-19, per W.H.O. Larger, heavier viral droplets fall to the ground after being expelled. DROPLET SPREAD Up to 6 feet Influenza, whooping cough, and most likely Covid-19, per W.H.O. Larger, heavier viral droplets fall to the ground after being expelled. AIRBORNE SPREAD Up to 100 feet Measles, tuberculosis Smaller, lighter aerosol droplets can linger in the air. Airborne spread up to 100 ft Measles, tuberculosis Smaller, lighter aerosol droplets can linger in the air. Influenza, whooping cough, and most likely Covid-19, per W.H.O. Larger, heavier viral droplets fall to the ground after being expelled. DROPLET SPREAD Up to 6 feet Influenza, whooping cough, and most likely Covid-19, per W.H.O. Larger, heavier viral droplets fall to the ground after being expelled. AIRBORNE SPREAD Up to 100 feet Measles, tuberculosis Smaller, lighter aerosol droplets can linger in the air.

Some illnesses, like measles and tuberculosis, can spread far and wide through the air. Their ability to linger in the air for hours and travel long distances after a sneeze or cough makes them highly contagious.

These illnesses are treated at a high level of precaution that requires health care workers to wear respirator masks and patients to be isolated under negative pressure to keep the germs from spreading.

But experts think that other respiratory illnesses, like the flu, do not stay airborne for long. Instead, the viral droplets that leave a person’s mouth or nose end up falling to the ground within six feet or less. Think of it more like a sprinkle of rain than a cloud of mist.

The W.H.O. has said Covid-19 is most likely spread through this droplet route.

Such illnesses are usually transmitted through close contact, within family groups or during large gatherings, and can also be transferred by touching infected surfaces.

Health care workers routinely treat droplet-borne illnesses at a lower level of precaution than fully airborne ones, using medical masks rather than respirators. But for new diseases, like Covid-19, health authorities may recommend higher-level protections while the transmissibility question remains unsettled. And those guidelines can evolve over time.

“During the outbreak, you’re going to see changing guidance for hospital workers,” said Amesh Adalja, an infectious disease physician at the Johns Hopkins Center for Health Security. Where the new coronavirus falls in terms of mortality and risk perception “will change as we start to get more data within the United States,” he said.

The most recent C.D.C. guidelines — which suggest the use of medical masks while treating coronavirus patients when respirators are not available — drew criticism from some health care professionals, notably nurses.

“Now is not the time to be weakening our standards and protections, or cutting corners,” said Bonnie Castillo, a registered nurse and executive director of National Nurses United, a union that represents about 150,000 nurses across the country. “If nurses and health care workers aren’t protected, that means patients and the public are not protected,” she said.

Other medical experts said the new recommendations did not go far enough to clarify how health care workers dealing with the outbreak should be protected.

“We want health care workers to be confident they are being kept safe,” Dr. Adalja said.