It is a gram-negative diplococcus that commonly lives as a commensal in the upper respiratory tract. It was previously called Branhamella catarrhalis. Its pathogenicity increases after prolonged exposure to cold conditions.

It may cause otitis media, sinusitis (third most common cause), laryngitis, bronchitis, pneumonia, and meningitis.

Diagnosis is made by:

• Gram stain showing the typical diplococcal morphology
• Culture on chocolate agar or blood agar

Key laboratory features include:

• Oxidase positive
• Does not ferment glucose, maltose, sucrose, or lactose
• DNase positive
• Reduces nitrate and nitrite

Apart from biochemical features, it can be differentiated from Neisseria by a rapid test based on hydrolysis of tributyrin:

• Positive in Moraxella
• Negative in Neisseria

Treatment options include amoxicillin-clavulanic acid, second- and third-generation cephalosporins, and azithromycin/clarithromycin.