Fastidious, short rod that does not Gram stain - an "atypical".
Lacks cell wall.
Person-to-person contact by respiratory droplets, and is exclusively a human pathogen.
Particularly common in school-aged children and other crowded environments.
Post-infectious syndromes from antibodies include:
Hemolysis from cold agglutinins
Rarely cardiac involvement
Diagnose by serology in general.
Difficult to culture.