"deadly condition" is correct and usable in written English. You can use it to describe a dangerous disease or serious medical condition that could have fatal consequences. Example sentence: "The cancer posed a deadly condition that could not be cured.".
The resulting loneliness, I argued, is a deadly condition, which kills as many people as smoking or obesity.
Jacob suffers from Duchenne muscular dystrophy, a rare and deadly condition that mainly strikes boys and causes steady deterioration of muscle tissue.
This is a potentially deadly condition in which the individual chambers of a heart beat out of phase with each other.
The best candidates are children with acute hepatic failure, a deadly condition in which the liver suddenly stops working, often for unknown reasons.
It also warned of potentially deadly conditions.
But researchers predict that these deadly conditions will only increase as the seasons pass by.
VIDEO Workers assembling iPads, iPhones and other products often work in abusive and sometimes deadly conditions.
Being a terminologist, I care about word choice. Ludwig simply helps me pick the best words for any translation. Five stars!
Maria Pia Montoro
Terminologist and Q/A Analyst @ Translation Centre for the Bodies of the European Union