Then she bursts into infectious laughter.
Times, Sunday Times (2006)
Our world will be a bleaker place without him, his infectious laughter and fantastic sense of humour.
Times, Sunday Times (2010)
Think how infectious laughter is - no matter that you " know not why "- it is a subconscious reaction to humour.
Mansfield, Patricia Why Am I Afraid to be Assertive? (1994)