What is Moraxella catarrhalis (Branhamella)? How do you get it?

K.N.

Moraxella (formerly Branhamella) catarrhalis is a bacterium that causes many common infections in children and adults. It colonizes the throat of about 5 percent of healthy children and a higher percentage of adults with chronic lung disease.

The most common infection caused by this organism is acute otitis media (middle-ear infection). In most medical research studies, M. catarrhalis is the third most common cause of ear infections in children. Since it is estimated that 80 percent of children will have at least one ear infection, and about 15 percent of ear infections are caused by this organism, then roughly 12 percent of all children will have an ear infection with M. catarrhalis. In general practice, we do not usually determine which organism is causing an ear infection, so most of these M. catarrhalis infections are not diagnosed as such. M. catarrhalis is also the third most common cause of sinusitis in adults. Again, the bacteria causing these infections are not identified in clinical practice, because we seldom culture the sinuses when we treat sinus infections.

M. catarrhalis is a common problem in people with chronic obstructive pulmonary disease (COPD), a term that encompasses emphysema and chronic bronchitis. Many exacerbations of COPD (which cause shortness of breath and productive cough) are caused, at least in part, by M. catarrhalis. In such patients, and in some elderly patients without COPD, the infection may lead to pneumonia. Pneumonia with M. catarrhalis is indistinguishable from pneumonia caused by most other bacteria. Sometimes, M. catarrhalis is responsible for pneumonia in patients on ventilators and in other hospitalized patients. In rare cases, it causes pneumonia in otherwise healthy adults.

M. catarrhalis is found only in humans. Presumably, it is spread from person to person. Once someone acquires the bacterium, it usually colonizes the person without causing any symptoms for at least a time. A symptomatic infection may come later. Treatment of this infection is straightforward. A variety of antibiotics are effective against the organism. However, amoxicillin (Amoxil) and ampicillin (Omnipen) are not usually effective.