The phrase "a severe illness" is correct and usable in written English.
You can use it when discussing a serious health condition that significantly impacts a person's well-being.
Example: "After several tests, the doctor diagnosed her with a severe illness that required immediate treatment."
Alternatives: "a serious disease" or "a critical health condition."
Pandemics, he said, can start out mild, and over the course of several months become a severe illness, as was the case during the devastating flu pandemic of 1918.
Variations in frequencies observed in the different studies could be related to the severity of the meningitis since a severe illness could exhibit a higher risk of sequelae [ 25].
She danced with the vitality of a young woman when she was seventy she wrote a book of reminiscences a year later, and even after a severe illness the beauty of her complexion and of her eyes still remained.
He was reported to have fallen ill on 26 January and was diagnosed with a severe illness on 31 January.
TUCHMAN--Judith, died November 3, 2004, after a valiant attempt to live with a severe illness.
His composing career was abruptly terminated by a severe illness in 2005.
Approaching 50, this prominent Spanish court painter had contracted a severe illness that was to leave him permanently deaf.
Her family were able to use their connections to get her out after a year, claiming that she suffered a severe illness.
"After a severe illness Goran Hadžić died today," said the state-run Tanjug news agency, quoting the regional hospital of Serbia's Vojvodina province.
In the following year he returned to England in the hope of recovering from a severe illness, but died in Chelsea, London, and was buried in Westminster Abbey.
A new edition of Dante's Paradiso doesn't just crown Robert Hollander 's5's long study of the Italian poet; it also marks his recovery from a severe illness.
