Update: Hitchens spotted in D.C. Sunday night. Link here.
At reddit.com there are comments on Hitchens having breathing issues at the airport.
This would explain the latest event cancellations.
Twelve Publishers has removed his upcoming appearances this summer from their site. (The one left, June 28, is cancelled as well).
The Luncheon Society has been told by the publisher: He has a personal issue that requires his attention.
