The gates are closed at the entrance to the pub chain on Parliament Street, and Wetherspoons have issued a statement.
Wetherspoon spokesman Eddie Gershon said: “Management took the decision to close the pub after a number of staff reported ill. The pub will be closed until Friday morning.
“In the interim a professional clean will take place at the pub. We apologise to customers for this, but believe it is the right action to take.”