The patient has contracted a fatal illness. There is little chance of his recovery.

这个病人已病入膏肓， 没有多少痊愈的希望了。

《新英汉大辞典》

Everybody knew the little girl had a fatal illness, but they cheered her up by saying that she would recover soon.

每个人都知道这个小女孩的病是致命的，但他们还是跟她打气说她很快就可以康复了。

youdao

A fatal illness had kept the boy home, but he had been inclined to met me, and the principal knew it would mean a great deal to him.

一种致命的疾病把这个男孩困在家里，但他想见我一面，校长知道这对他来说意义重大。

youdao

At Sydney's Royal North Shore hospital a video linkup has allowed doctors from Vietnam and Japan to present case studies and to share their experiences in dealing with a potentially fatal illness.

VOA: standard.2009.08.25

She was SUFFERING from a FATAL ILLNESS for, at the very lease, the last five years of her life.

FORBES: Winehouse Death Renews Debate About Addiction and Choice

Hospice deploys nurses, doctors, and social workers to help people with a fatal illness have the fullest possible lives right now.

NEWYORKER: Letting Go

In the 1990s it was still comparatively unusual to see a fatal illness portrayed in anything like a candid way onstage or on the screen.

WSJ: Wit | The Motherf**cker With the Hat | Into the (Spot)light | Theater Reviews by Terry Teachout