It has to be differentiated from laryngeal diphtheria.

Croup also can be laryngeal diphtheria, bacterial tracheitis, laryngotracheobronchitis, and laryngotracheobronchopneumonitis.

Others use the term more broadly, to include acute laryngotracheitis, spasmodic croup, laryngeal diphtheria, bacterial tracheitis, laryngotracheobronchitis, and laryngotracheobronchopneumonitis.

Corynebacterium diphtheriae causes laryngeal diphtheria; bacterial tracheitis, laryngotracheobronchitis, and laryngotracheobronchopneumonitis come from a virus infection, followed by a bacteria infection.

Laryngeal diphtheria is due to Corynebacterium diphtheriae while bacterial tracheitis, laryngotracheobronchitis, and laryngotracheobronchopneumonitis are usually due to a primary viral infection with secondary bacterial growth.