Across the country, hospitals are waging war against an invisible enemy. As the number of cases in the U.S. continues to rise, the health care system is becoming increasingly taxed — and in some hospitals, supplies are already running low.

Dr. Megan Ranney, an emergency room physician at Brown University, knows what medical providers are facing on the front lines of the pandemic. In an interview with "CBS Evening News" anchor Norah O'Donnell, Dr. Ranney explained what it's like to fight the virus firsthand.

Read O'Donnell's interview with Dr. Ranney below.

Norah O'Donnell: You know, we know our health care workers are like soldiers. What's it like to work under these circumstances?

Dr. Megan Ranney: We are scared. We are stressed. And we're worried about what comes next and about our ability to take care of our patients and our communities. As well as our ability to take care of ourselves.

Doctor, this is a difficult question — but what are some of the doctors and nurses and colleagues that you work with doing to prepare for the case that they may themselves catch COVID-19?

Norah, I already have dozens, literally dozens of friends in emergency medicine across the country who have been infected by COVID-19. A couple of them have been hospitalized, a couple are in intensive care.

My friends and colleagues are doing things like recording videos for their kids, writing letters to their spouses, or their kids or their grandkids, making sure that their wills are in order. Because we know that if we end up getting admitted to the hospital, we, like everyone else with COVID-19, would be isolated from our family and friends, and may not have the chance to say goodbye in person.

That's hard, to hear that.

It is unbelievably difficult. You know, as healthcare providers we run towards disaster, we are trained and ready to help anyone who needs it. We're not used to our helping putting us at such risk.

What are you seeing at your hospital in terms of COVID-19 patients and supplies?

My hospital, like every other hospital across the country, has day by day seen dramatic increases in the number of patients with symptoms consistent with COVID-19. We are also seeing dropping numbers of supplies.

A lot of the supplies that were intended for hospitals like mine have been diverted to New York.

What is something that people at home can do to help their local health care providers?

So the first and biggest thing that people at home can do is truly to stay home. I know how difficult social distancing is. But if you stay home, you can stop the spread of this virus and allow us in healthcare to better help you.

Well, doctor. We can't say thank you enough to you and to everyone who is caring for Americans and all around the world. Thank you.

Thank you, Norah.