Yesterday, I received a text from a colleague whose sister is in charge of nursing at one of my city’s major hospitals. Two of her nurses had just quit, in tears. “They were fed up,” she said. “They couldn’t take it any longer.”

As anyone, like me, who has worked in a hospital, clinic or emergency room knows, this was very bad news. Because all of us who care for patients are intimately familiar with this calculus: As the ratio of patients to doctors and nurses increases, the quality of care diminishes. Waiting rooms fill up, providers scramble and patients get an increasingly abridged version of care, if they are seen at all.

Over the last few weeks, as coronavirus has spread across the country, many have been sounding the alarm about our country’s lack of critical resources like ventilators and hospital beds. But the worst shortage we face is that of doctors and nurses — the health care professionals who can staff those beds, administer the life-supporting intravenous medications and run the ventilator machines.

Even in the best case situation, with a shortage of skilled doctors and nurses, caring for Covid-19 patients with life-threatening respiratory distress will be like using a Band-Aid to stop a carotid artery bleed.

Some of the most important specialties needed to fight the coronavirus pandemic are intensivists and critical care nurses — the physicians and nurses specially trained to manage ventilators and life-supporting medications essential for critically ill patients. There are currently fewer than 65,000 physicians, physician assistants and advanced practice nursing intensivists and just over 100,000 critical care nurses in the United States. Those physicians who have been trained to care for patients in the hospital, known as hospitalists, are another crucial specialty, but there are only a little over 50,000 in the United States.

Further complicating the provider shortage is the nature of coronavirus, which is highly contagious. Like foot soldiers marching at the front of an assault, first-line doctors and nurses need robust layers of backup personnel in case they fall ill and become an infectious risk to others.

To do that, doctors and nurses have had to become creative. Retired health care providers are volunteering to operate telehealth centers so that younger colleagues can go into the hospital and serve as backup. Surgeons, anesthesiologists, recovery room nurses who have some experience with critically ill patients are being called in to care for Covid-19 patients in the intensive care unit. “We are thinking of this as an all-hands-on-deck approach,” said Dr. Sumant Ranji, chief of the division of hospital medicine at Zuckerberg San Francisco General Hospital.

But perhaps the biggest barrier to mobilizing the insufficient health care force that we have is the disease itself. Most doctors and nurses are accustomed to “covering” one another, working longer hours or making do when there are not enough health care providers. Few, however, have labored under the constant threat of becoming ill with something for which we have no cure or treatment, nor lived under the crippling fear of infecting loved ones at home. The fear is multiplied as supplies of masks and equipment dwindle and health care workers are asked to work longer hours with little respite or protection.

“Even though we are protecting, we have had instances where inadvertent exposure has occurred and the reaction has been, ‘I need to self-quarantine and self-monitor, but am I going to die?’” said Dr. Vineet Chopra, chief of the division of hospital medicine at Michigan Medicine and the University of Michigan Medical School. “That fear is not irrational.”

There is no way to immediately train the hundreds of thousands of doctors and nurses needed to care for our worst case scenario. There is no way to mobilize sufficient numbers of health care professionals even if we include those who are retired or only tangentially familiar with critical care, hospital medicine, emergency medicine and infectious disease. There is no way to address the very real fears of doctors and nurses who put their own lives at risk every time they go to work.

The only way we can address the most serious shortage of all is by doing what we can to slow the spread of the disease.

Wash your hands frequently and at length. Stay at home even if you are feeling well. If you must go to work, don’t go if you feel sick. Avoid the hospital, urgent care clinics and emergency rooms unless your problem is urgent. And call first — don’t visit — your doctor’s office if you have questions.

All these seemingly minor changes in our usual behavior will not only save yourself potential exposure to coronavirus but will also preserve and support health care providers, one of the country’s scarcest resources.

Because as anyone who has studied calculus knows, every variable counts.