“Hefur þú lært um Staphylococcus aureus?” I almost don’t recognize the bacteria name because my grandmother pronounces it differently in Icelandic.

“Já–” I’m about to translate my microbiology flashcard for her when she interrupts, her hands busy kneading the cookie dough and her eyes on my little sister near the oven.

That’s the bacteria that almost killed her eleven years ago, she tells me. I can hear her words building up. This is a story that has been waiting to be told often enough to be reconciled.

They did not know what was wrong with her. They thought maybe cancer, maybe tuberculosis — and I almost interrupt her story to tell her about Pott disease. That’s when tuberculosis from the lungs goes through the blood to the vertebrae and causes back pain, fever, night sweats and weight loss. I memorized the flashcard a few weeks ago.

My little sister stops doing handstands in the middle of the kitchen and comes to stand next to my chair. Together we watch Grandma roll the cookie dough as she continues talking.

It took the doctors a whole long time to figure out what was wrong with her. In the meantime, she was in so much pain from her back that she had to be on high doses of morphine. Codeine.

She could hear them yelling at each other in the next room, my great uncle, and the other doctor. The two internists had very different approaches. My great uncle wanted to identify what was going on before putting her up for surgery. The other doctor yelled at him that he was going to wait so long the woman would die.

My grandma stops her cookie cutting and sits across from me. She looks at me for a moment over her glasses and tells me how terrifying it is to know that your doctors don’t know what’s wrong with you.

My poor great uncle, I tell her — he was just trying to make sure that they didn’t make you worse by operating.

My grandma nods and describes how when they finally did agree to have her undergo surgery, my great uncle called the best surgeon in town and had him come back early from vacation to operate on her the next day. And good thing too, for when they did, they found that three of her vertebrae had been turned to dust.

With an infection like that, the surgeon said she was hours away from death.

My little sister stepped closer to me.

But they used bone from her hip and titanium steel to recreate the missing vertebrae, my grandma continued. Four months in the hospital, five days of morphine withdrawal, and eleven years later, she’s still walking around her kitchen making us cookies.

My sister runs off to continue her handstands, and I think to myself the scariest part of the story is that this bacteria that almost killed my grandmother lives on our skin. We have easy tests to confirm Staphylococcus aureus, and good antibiotics to kill it. But in my grandmother’s case, the doctors had no reason to suspect that she had a bacterial infection, much less that Staphylococcus aureus was growing to dangerous levels in her back when she had no evidence of the bacteria in her circulating blood.

I wonder if she has any idea how terrifying it is for doctors, to have someone expect you to save their life; to know that you’re good at what you do and yet you don’t have an answer. That you might never have an answer. And the crux of it is there’s only so far we can ethically go in treating someone when we don’t know what we’re dealing with. After all, the oath we swear is not just to heal — it is to do no harm.

Natalia Birgisson is a medical student who blogs at Scope, where this article originally appeared.