WASHINGTON — With U.S. public health experts warning of a cresting wave of coronavirus infections in the coming weeks, rates of transmission among the nation's front-line fighters — doctors, nurses and other medical staff — are setting off alarm bells.

Disparities in testing and tracking in many states — and the lack of national data — make the actual infection rates among medical personnel difficult to pin down. Still, state health departments in Ohio and Minnesota are reporting that up to 20 percent of those infected are health care professionals, a number in line with Italy and other hard-hit regions of the world.

In Ohio, the percentage of health care workers infected recently ticked up to 18 percent from 16 percent of all coronavirus cases, health department spokesperson Melanie Amato told NBC News. In Minnesota, as of early this week, the Department of Health confirmed approximately 1 in 5 diagnosed cases were health workers, with the caveat that health workers probably have better access to testing.

In Italy, the country hardest hit by the virus so far, 20 percent of health care professionals have become infected, according to a recent update in the medical journal The Lancet. Most of those were in the country's northern Lombardy region, where the virus has been especially lethal.

Dr. Barak Mevorak, a U.S.-trained doctor and health technology expert advising governmental health departments worldwide, said the U.S. lags behind Asian countries in knowing how to protect front-line workers. Asia,and China in particular, were hit hard by outbreaks of avian flu in the early 2000s and swine flu in 2009.

"What China learned a while ago is the supplies were not the bottleneck at the end. The bottleneck was the staff because everybody was sick," Mevorak said. "That's something the U.S. hasn't learned yet."

At issue is the availability of personal protective equipment (PPE) for health care workers in the U.S.

In China and South Korea, doctors treating COVID-19 — the illness caused by the coronavirus — are typically clothed in full-body Tyvek jumpsuits and N95 masks. U.S. medical personnel, by contrast, are often left to treat highly infectious patients in standard cloth gowns and surgical masks. Some hospitals are even threatening to fire health-care workers who publicize their working conditions, Bloomberg News reported.

Governors across the country are pleading for additional PPE for their states. The situation has grown so dire that many health care workers have taken to social media to plead for adequate protective gear. The Centers for Disease Control and Prevention also relaxed its standards, including encouraging professionals to reuse masks and even use bandanas if necessary.

A physician at a New York City hospital who spoke on the condition of anonymity said that while it is difficult to determine precisely, more than 20 percent of the hospital's staff could have COVID-19, including doctors, nurses and aides. "We are short of everything and everybody."

"As an American, I feel ashamed." the doctor said, emphasizing a belief that the lack of PPE supplies has contributed to the transmission to health care workers.

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"It feels like the rest of the country has abandoned us — we are on our own. We shouldn't have to be scrounging for masks. The government has failed us."

While New York is currently the epicenter of the pandemic, front-line health care workers are at risk throughout the country.

In Connecticut, some 200 nurses are in quarantine due to a lack of testing, Healthline reported. In Washington state, dozens of staffers at a nursing home tested positive for the coronavirus; in Pittsfield, Massachusetts, 160 employees of Berkshire Medical Center have been quarantined due to exposure to the virus.

Dr. William Jaquis, president of the American College of Emergency Physicians, saidthat the standard of protective gear in the U.S. is much closer to that of Italy than South Korea or China, where the rate of transmission has begun to come under control and individuals are returning to work.

The true scale of the problem remains unknown. NBC News has reached out to state public health departments around the country, but many have said that they do not keep data on infection among health care workers specifically. Health care worker deaths have been reported in New York, Florida, California and Georgia.

In California, Los Angeles County Director of Public Health Barbara Ferrer told reporters Monday that "dozens and dozens" of local health care workers have tested positive for the virus. The city's Public Health Department did not supply exact figures.

In some cases, health care workers are now caring for their own colleagues with COVID-19.

"When you look at the list of who is in the ICU, we realize we recognize many of the names," a physician at Montefiore Medical Center in New York said. "These are our colleagues, our leadership at the hospital, trusted specialists," the doctor said. "It's awful."

"We have multiple staff members ranging from surgeons to technicians who have tested positive for COVID-19 and are out sick," a spokesperson from Montefiore said. "Some are in the hospital as inpatients and others are recovering at home. The same is true at hospitals around the world. The sobering reality of this virus is that everyone is at risk."

The emotional toll on health care workers can be severe.

Dr. Mindy Oshrain, a North Carolina psychiatrist, said that some doctors and nurses are traumatized because they have no control over their personal safety. Some have taken to calling the day-to-day anticipatory worry over working conditions "pre-TSD" — pre-traumatic stress disorder.

"There's a sense that the people in charge ... are not there for them," Oshrain said.

National Nurses United, the largest union of registered nurses in the United States, said in a recent statement that PPE supplies are "drastically short of what is needed to stem the danger of becoming infected and exposing patients, family members and other health care staff."

The union said it has filed over 126 complaints with Occupational Safety and Health Administration offices in 17 states charging individual hospitals with failing to provide safe workplaces.

President Donald Trump has pointed to volunteer efforts by major U.S. companies to produce much-needed masks and other protective gear. Yet for weeks experts have been warning that severe shortages are looming — and the president's suggestion that hospitals have what they need does not match the experiences of many doctors and nurses on the front lines.

In early March, as the coronavirus pandemic reached the U.S., Robert Kadlec, assistant secretary for preparedness and response at the Department of Health and Human Services, told Congress that the U.S. had 35 million masks on hand. But in the case of a pandemic, Kadlec warned, the U.S. would need 3.5 billion N95 masks over a year.

In a March 21 letter to Kadlec and Secretary Alex Azar, Democrats on the House Oversight Committee wrote: "Although President Trump announced that the federal government will order 500 million respirator masks to address these shortages, it may take up to 18 months for orders to be fulfilled despite the immediate need for this lifesaving equipment."

The government has begun releasing supplies from the Strategic National Stockpile, the nation's emergency supply of drugs and medical devices. But multiple states previously reported that they have received only 10 to 25 percent of their requests.

In an interview late last week, Dr. Kamal Kalsi, an emergency room doctor and Army officer practicing in hospitals in New York and New Jersey, raised concerns about protective gear and the CDC's new guidelines.

"It was just such a slap in the face. We work so hard," Kalsi said. "It's a high-stress environment, it's really tough to work there and now you're putting us on the front lines without an adequate plan, preparation or protection."

Contacted on Tuesday, Kalsi said he is now home with a fever awaiting his coronavirus test results.

Heidi Przybyla reported from Washington, and Sarah Fitzpatrick from New York.