What is the pathophysiology of Moraxella catarrhalis infection?

Updated: Mar 22, 2021
  • Author: Michael Constantinescu, MD; Chief Editor: Michael Stuart Bronze, MD  more...
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Studies have shown that M catarrhalis colonizes the upper respiratory tract in 28-100% of humans in the first year of life. In adults, the colonization rate is 1-10.4%. Colonization appears to be an ongoing process with an elimination-colonization turnover of various strains. Transmission is believed to be due to direct contact with contaminated secretions by droplets.

The endotoxin of M catarrhalis, a lipopolysaccharide similar to those found in Neisseria species, may play a role in the disease process. Some strains of M catarrhalis have pili or fimbriae, which may facilitate adherence to the respiratory epithelium. Some strains produce a protein that confers resistance to complement by interfering with the formation of the membrane attack complex. M catarrhalis also expresses specific proteins for iron uptake that act as receptors for transferrin and lactoferrin.

M catarrhalis has been shown to have increased cell adhesion and proinflammatory responses when cold shock (26°C for 3 hours) occurs. Physiologically, this may occur with prolonged exposure to cold air temperatures, resulting in coldlike symptoms. [1]

Humoral responses against M catarrhalis appear to be age-dependent, with the titer of immunoglobulin G (IgG) gradually increasing in children. Antibody responses to outer-membrane proteins have been obtained, predominantly in the IgG3 subclass.

Although the commensal status of M catarrhalis in the nasopharynx is still accepted, the organism is a common cause of otitis media and sinusitis and an occasional cause of laryngitis. M catarrhalis causes bronchitis and pneumonia in children and adults with underlying chronic lung disease and is occasionally a cause of bacteremia and meningitis, especially in immunocompromised persons. Bacteremia can be complicated by local infections, such as osteomyelitis or septic arthritis. M catarrhalis is also associated with nosocomial infections.

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