Once thought a nonpathogenic inhabitant of the human respiratory tract, Moraxella catarrhalis is now recognized as an important etiologic agent of otitis media in children, sinusitis in children and adults, and pneumonia in adults with chronic obstructive pulmonary disease (COPD).

Moraxella catarrhalis is a gram-negative kidney-shaped diplococcus similar in morphology to the Neisseria. The bacterium was first described by Ghon and Pfeiffer as Micrococcus catarrhalis in 1902 and has since undergone several reclassifications. In 1970 it was placed into the genus Branhamella based on fatty acid content and DNA homology. In 1979 the name Moraxella (Branhamella) catarrhalis was proposed, and this is the most widely accepted nomenclature at this time.

EPIDEMIOLOGY

Moraxella catarrhalis has been recovered exclusively from humans and is a normal inhabitant of the upper respiratory tract. Colonization rates are highest in infants and young children (40%–70%), decreasing into adulthood (1%–5%). The organism is recovered with increased frequency in children with recurrent otitis media and in adults with chronic lung disease.

Infection with M. catarrhalis is seasonal with an increase in prevalence during winter and spring months.

PATHOGENESIS

The pathogenesis of infection is complex with both host and bacterial factors determining the evolution from colonization to clinical disease. Moraxella catarrhalis expresses adhesion factors and several outer membrane proteins that facilitate preferential binding to human pharyngeal and middle ear epithelial cells. Some strains of M. catarrhalis demonstrate an ability to form biofilms in sequestered sites such as the middle ear.