Katy Perry was forced to cancel a concert in Michigan on Sunday (11Sep11) after finally succumbing to the illness that has dogged her for days.

The I Kissed a Girl hitmaker has been plagued by symptoms of a cold since last week (beg05Sep11), and she told fans how she was determined to perform in Louisiana and Kentucky despite suffering "snot, sweat, tears and all".

She had hoped to shake off the illness to perform in Grand Rapids, Michigan on the 10th anniversary of the 9/11 terror attacks on Sunday - but she ended up bedridden after she was diagnosed with an upper respiratory tract infection.

In a post on Twitter.com on Sunday, Perry wrote, "Sick in bed and watching the memorials today. Taking time to remember all the lost + all the heroes. GodBlessAmerica."

The Grand Rapids show has been rescheduled to 1 December (11). The next scheduled date on Perry's tour is in Columbus, Ohio, on Tuesday (13Sep11).