I have done a search in my Delphi e-edition, with no hits. Searching for parts, like ´good wine´, ´influenza´etc also did not give any results even remotely comparable to the quote above.
Google does not seem to have this quote attributed to anyone else, nor have I been able to find any variations/misspellings, which probably means that the attribution originated from one source only. This, however, does not mean the attribution is correct. If it is Jerome, it is probably from some uncollected article.
The Delphi edition includes the following:
Contents:The Novels
Three Men In A Boat (To Say Nothing Of The Dog)
Three Men On The Bummel
Paul Kelver
Tommy And Co.
They And I
All Roads Lead To Calvary
The Short Story Collections
Told After Supper
John Ingerfield And Other Stories
Sketches In Lavender, Blue And Green
The Observations Of Henry
The Passing Of The Third Floor Back, And Other Stories
The Angel And The Author And Others
Malvina Of Brittanythe Short Stories
List Of Short Stories In Chronological Order
List Of Short Stories In Alphabetical Order
The Plays
Fanny And The Servant Problem
The Master Of Mrs. Chilvers
The Non-Fiction
Idle Thoughts Of An Idle Fellow
On The Stage And Off
Stageland
The Diary Of A Pilgrimage, And Six Essays
Novel Notes
Second Thoughts Of An Idle Fellow
Tea-Table Talk
Idle Ideas In 1905
The Biography
Jerome K: Jerome: His Life And Works By Alfred Moss