Moraxella catarrhalis is a type of bacteria that can cause various infections in the body. It is prevalent in the respiratory system in many young children, but it only becomes an issue if it causes infections.

Although Moraxella catarrhalis is often present in young children, it can also affect adults, particularly those with underlying health conditions or a compromised immune system. Aside from the respiratory system, it can also cause infections in the:

Other names for M. catarrhalis include Neisseria catarrhalis and Branhamella catarrhalis. Although medical experts considered it harmless in the past, they are now aware of its significance as a bacterial pathogen. Keep reading to learn more.

a scientist studying Moraxella catarrhalis cells under a microscopeShare on Pinterest
Moraxella catarrhalis may cause infections in the respiratory system.

Moraxella catarrhalis is a bacterium that causes infection by sticking to a host cell. It does this using special proteins called adhesins that are on its outer membrane. Doctors usually treat M. catarrhalis infections with antibiotics, but this is becoming increasingly challenging due to antibiotic resistance.

According to a recent study in India, M. catarrhalis showed resistance to most antibiotics that doctors commonly use to treat respiratory tract infections. In this particular study, the researchers predominantly found the bacteria in males over 40 years of age with underlying respiratory conditions and lower immunity levels.

A person’s immune status is key to the severity of the symptoms, and diagnosis is rare in healthy adults.

M. catarrhalis has links with numerous conditions, such as:

Otitis media

M. catarrhalis is a common cause of otitis media (middle ear infections) in infants and children in whom the bacteria are naturally present in the nasopharynx. According to research, approximately 50–80% of children in the United States have at least one episode of otitis media by the age of 1 year. The study also states that otitis media costs the U.S. $3–5 billion a year.

Research in the journal Frontiers in Microbiology confirmed that acute otitis media is the most common reason for children to visit a doctor.

Learn more about ear infections here.

Chronic obstructive pulmonary disease (COPD)

Adults with COPD are more likely than those without COPD to develop infections with M. catarrhalis. It is the second most common cause of exacerbations in adults with COPD. A vaccine against M. catarrhalis could help protect people with COPD, and researchers are making progress in developing one.

Learn more about COPD here.


Pneumonia is the inflammation of the lungs. In most cases, the cause is an infection, which antibiotics can treat. M. catarrhalis is often present in adults with a weakened immune system who then develop pneumonia.

Community-acquired pneumonia (CAP) is a major cause of morbidity in children worldwide, and M. catarrhalis is the third most common causative pathogenic bacteria of CAP.

Learn more about pneumonia here.


M. catarrhalis can cause bronchitis, which is the inflammation of the airways and is very common. It generally affects older adults with underlying health conditions. Chronic bronchitis is a type of COPD.

Learn more about bronchitis here.


An inflammation of the upper respiratory system, sinusitis also has an association with M. catarrhalis. It can occur in children and adults of all ages, but it often affects those with a weakened immune system.

Learn more about sinusitis here.

Septic arthritis

M. catarrhalis can also lead to septic arthritis alongside bacteremia, which is the presence of bacteria in the blood. The symptoms of septic arthritis can range from a mild fever to life threatening sepsis.

Learn more about septic arthritis here.


Meningitis is an inflammation of the outer membranes covering the brain and spinal cord. It may affect newborns and people with a weakened immune system.

Learn about bacterial meningitis here.

Antibiotics are the standard treatment for M. catarrhalis infections. However, this bacterium produces an enzyme called beta-lactamase, which makes it resistant to certain antibiotics, such as penicillin, amoxicillin, and ampicillin. The doctor will, therefore, need to prescribe other antibiotics, such as amoxicillin-clavulanic acid, clarithromycin, or some types of cephalosporins.

The outlook for most people with community-acquired upper respiratory tract infections is positive, as they either have a natural recovery or respond to antibiotics. It is hospital inpatients, those with underlying lung disease, and the very young who are more vulnerable.

People can help prevent an M. catarrhalis infection by:

  • washing the hands regularly with soap and water and using an alcohol-based hand sanitizer outside the home
  • exercising regularly and eating a healthful diet to maintain a strong immune system
  • giving up smoking, if relevant, and avoiding secondhand smoke
  • visiting a doctor as soon as symptoms appear, as early detection is crucial to avoid serious illness, especially in the very young

Moraxella catarrhalis is a type of bacteria common in young children. It can often be harmless.

Those at risk of infection complications are people with underlying health conditions or a weakened immune system and those with socioeconomic risk factors.

There is not yet a vaccine for M. catarrhalis infections. However, the World Health Organization (WHO) have recognized antibiotic resistance as a global threat, and research into finding one is ongoing.