Moraxella catarrhalis is a gram-negative aerobic diplococcus that belongs to the Neisseriaceae family. In the past, it has been known as Micrococcus catarrhalis, Neisseria catarrhalis, and Branhamella catarrhalis. It commonly inhabits the upper respiratory tract. For many years, it was considered a nonpathogenic member of the resident flora of the nasopharynx. Over the past 30 to 35 years, it has been recognized as a genuine mucosal pathogen and is now considered an important cause of otitis media and sinusitis in healthy children and adults. It also causes lower respiratory tract infections and exacerbation of bronchitis in adults with chronic lung disease. Occasionally, it can cause a variety of severe infections, including septicemia, pneumonia, and meningitis, especially in immunocompromised hosts.
PATHOGENESIS AND EPIDEMIOLOGY
M catarrhalis, an exclusively human pathogen, is an aerobic gram-negative diplococcus that has a striking resemblance to meningococcus and gonococcus, except that it is unencapsulated. After the nasopharynx is colonized, the organism appears to spread contiguously from its respiratory colonizing position to the infection site and cause mainly otitis media and sinusitis in children and less often pneumonia in adults. There is no pathognomic feature of M catarrhalis otitis media, sinusitis, or pneumonia. The mode of transmission of the organism is presumed to be direct contact with contaminated respiratory tract secretions and/or droplet spread.
In children, pneumonia may develop in those with intercurrent viral infection, underlying lung disease, prematurity, or immunoglobulin deficiency. Risk factors for development of bacterial tracheitis and pneumonia in children in an intensive care setting include endotracheal intubation and frequent suctioning.
The predominant bacteria associated with otitis media in children are Streptococcus pneumoniae, nontypeable Haemophilus influenzae, and M catarrhalis. Since 1980, there has been an increase in the isolation of M catarrhalis from middle ear exudates. Presently, it accounts for 15% to 20% of pathogens recovered from middle ear fluids of children with acute otitis media (AOM); however, these isolation rates might be an underestimation. In a study using polymerase chain reaction (PCR), M catarrhalis DNA was detected in 46.4% of 97 middle ear specimens compared to 54.6% for H influenzae DNA and 29.9% for S pneumoniae DNA. The increase in the isolation rate of M catarrhalis has been accompanied by the appearance of β-lactamase-producing strains, which now account for approximately 95% to 100% of the isolates. In a cohort of 306 infants followed from birth through 12 months to determine frequency and duration of nasopharyngeal colonization and risk of AOM and otitis media with effusion (OME), M catarrhalis was the most common bacterium isolated. Infants colonized at 3 months of age or younger were at increased risk of AOM and OME. Early colonization with M catarrhalis revealed the greatest risk (relative risk [RR] = 1.24), especially for OME (RR = 1.57). A strong relationship was noted between the frequency of colonization and OM (r = 0.37, P < .001) for ...