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Moraxella catarrhalis

Medical Professionals

Professional Reference articles are designed for health professionals to use. They are written by UK doctors and based on research evidence, UK and European Guidelines. You may find one of our health articles more useful.

Previously known as: Branhamella catarrhalis, Neisseria catarrhalis or Micrococcus catarrhalis.

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This is a Gram-negative, aerobic, oxidase-positive diplococcus. It is also known as Branhamella catarrhalis, It is considered to be a subgenus Branhamella of the genus Moraxella.

Moraxella catarrhalis is an exclusively human commensal and mucosal pathogen1.

It is a common commensal organism of the upper respiratory tract, particularly in children; however, it is increasingly being recognised as a pathological organism causing otitis media, sinusitis, ocular infection and occasionally laryngitis2. It may cause bronchitis or pneumonia in adults and children with underlying lung disease34.

Rarely, it may lead to bacteraemia and meningitis in the immunocompromised. Bacteraemic infection can lead to localised complications such as osteomyelitis and septic arthropathy. It can also cause nosocomial infection in a hospital setting, particularly in respiratory, paediatric and intensive care units.


  • The prevalence of M. catarrhalis colonisation is highly dependent on age.

  • Healthy adults are rarely colonised with this organism, whereas most infants have upper respiratory tract colonisation at some time in the first several years of life.

  • Carriage rates among populations of children vary from 28% to100%56.

  • M. catarrhalis has been shown to be positively cultured in at least one site in 42% of patients with sinusitis and 27% of well adults7.

  • In healthy adults the carriage rate is much lower at 1-10%. Carriage rates among those with underlying lung disease and the elderly are higher8.

  • It is a leading cause of otitis media in children9.

  • Only a proportion of positive bacteriological cultures occurring in children are thought to be of clinical significance (~9% in those aged <5 years and ~33% in those aged 6-10 years).

  • M. catarrhalis is estimated to cause ~10% of exacerbations in chronic obstructive pulmonary disease (COPD) patients1.

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In children

It may present with typical clinical features of:

In adults

In those with underlying respiratory disease such as COPD, it may present as:

  • Laryngitis.

  • Bronchitis.

  • Pneumonia.

  • Nosocomial outbreaks of infection (thought to be transferred from carers/visitors).

In the immunocompromised

This includes patients with cystic fibrosis. It rarely causes:

Sporadic cases

These include:

  • Neonatal ophthalmic infection.

  • Urinary tract infection.

  • Wound infection.

  • Peritonitis in patients undergoing chronic ambulatory peritoneal dialysis (CAPD).

There are no examination findings peculiar to, or discriminatory for, infection with M. catarrhalis and findings will be as expected for each of the disease entities it causes. Differentiation from other pathogens is on microbiological grounds.

Differential diagnosis

Bacteriological differential diagnosis is between those conditions that commonly cause infection in the sites listed above such as:

  • Streptococcus pneumoniae.

  • Haemophilus influenzae.

  • Causes of atypical pneumonia.

  • Viral causes of upper respiratory tract infection.

  • Viral causes of lower respiratory tract infection.

  • Fungal infection (should be considered as a possible cause of illness in the immunocompromised).

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  • FBC may reveal elevated WCC (predominantly neutrophils).

  • Gram-staining of sputum, middle-ear effusion fluid/aspirate, nasopharyngeal aspirate, sinus aspirate, transtracheal/transbronchial aspirate, blood, peritoneal fluid, wounds or urine will reveal Gram-negative diplococci.

  • The organism may be cultured from the same sources.

  • It may be difficult to discriminate M. catarrhalis from Neisseria spp. but use of differential culture media can help. Rapid test kits exploiting the ability of M. catarrhalis to hydrolise tributyrin are available.

  • Serological tests are not of much use due to significant cross-reactivity with Neisseria spp.

  • Imaging may be used to determine the site and extent of infection - eg, CT scan of sinuses and CXR.

  • Lumbar puncture and blood cultures are useful in diagnosing bacteraemic infection and meningitis.


  • The vast majority of isolates of M. catarrhalis are penicillin-resistant through the production of beta-lactamase.

  • Trimethoprim resistance is also common.

  • Macrolide antibiotics such as erythromycin and clarithromycin are useful. However, there is some resistance to these antibiotics11.

  • There is less resistance with newer macrolides such as azithromycin.

  • There is also low resistance with amoxicillin with clavulanate.

  • Quinolones such as ciprofloxacin and ofloxacin can be effective.

  • Second- or third-generation cephalosporins may be used12.

  • Tetracyclines are also active against this pathogen - eg, doxycycline.


  • Recurrence/failure to respond to antibiotic therapy.

  • Bacteraemia/systemic sepsis (mainly in the immunocompromised).

  • Meningitis (mainly in the immunocompromised).

  • Mastoiditis complicating otitis media.

  • Hearing impairment complicating otitis media.

  • Pleural effusion complicating pneumonia.

  • Death in advanced cases.


The vast majority of cases of community-acquired upper respiratory tract infection will recover spontaneously or respond to antibiotics, without complications or sequelae.

Prognosis among the immunocompromised, those with underlying lung disease, those in hospital, the elderly and the very young is variable but tends to be worse.


  • Nosocomial outbreaks can be prevented by good hygiene techniques in hospitals, particularly hand washing/use of alcohol gel hand rubs.

  • It is thought that the infection may spread from person to person via droplet infection from expectorated sputum; it may help to isolate confirmed cases in hospital where this is possible and give attention to general hygiene measures to prevent spread in community cases.

  • Smoking cessation should reduce susceptibility to infection in those with respiratory disease.

  • Vaccines are currently in development13.

Further reading and references

  • Raveendran S, Kumar G, Sivanandan RN, et al; Moraxella catarrhalis: A Cause of Concern with Emerging Resistance and Presence of BRO Beta-Lactamase Gene-Report from a Tertiary Care Hospital in South India. Int J Microbiol. 2020 Feb 7;2020:7316257. doi: 10.1155/2020/7316257. eCollection 2020.
  • Murphy TF, Brauer AL, Pettigrew MM, et al; Persistence of Moraxella catarrhalis in Chronic Obstructive Pulmonary Disease and Regulation of the Hag/MID Adhesin. J Infect Dis. 2019 Apr 16;219(9):1448-1455. doi: 10.1093/infdis/jiy680.
  1. Aebi C; Moraxella catarrhalis - pathogen or commensal? Adv Exp Med Biol. 2011;697:107-16.
  2. Shaikh SB, Ahmed Z, Arsalan SA, et al; Prevalence and resistance pattern of Moraxella catarrhalis in community-acquired lower respiratory tract infections. Infect Drug Resist. 2015 Jul 31;8:263-7. doi: 10.2147/IDR.S84209. eCollection 2015.
  3. Ren D, Pichichero ME; Vaccine targets against Moraxella catarrhalis. Expert Opin Ther Targets. 2015 Aug 23:1-15.
  4. de Vries SP, Eleveld MJ, Hermans PW, et al; Characterization of the molecular interplay between Moraxella catarrhalis and human respiratory tract epithelial cells. PLoS One. 2013 Aug 6;8(8):e72193. doi: 10.1371/journal.pone.0072193. Print 2013.
  5. Thors V, Morales-Aza B, Pidwill G, et al; Population density profiles of nasopharyngeal carriage of five bacterial species in pre-school children measured using quantitative PCR offer potential insights into the dynamics of transmission. Hum Vaccin Immunother. 2015 Sep 14:0.
  6. Coughtrie AL, Whittaker RN, Begum N, et al; Evaluation of swabbing methods for estimating the prevalence of bacterial carriage in the upper respiratory tract: a cross sectional study. BMJ Open. 2014 Oct 30;4(10):e005341. doi: 10.1136/bmjopen-2014-005341.
  7. Rawlings BA, Higgins TS, Han JK; Bacterial pathogens in the nasopharynx, nasal cavity, and osteomeatal complex during wellness and viral infection. Am J Rhinol Allergy. 2013 Jan;27(1):39-42. doi: 10.2500/ajra.2013.27.3835.
  8. Ramadan O et al; Significance of Moraxella catarrhalis as a causative organism of lower respiratory tract infections. Egyptian Journal of Chest Diseases and Tuberculosis, 66(3), p459-464, 2017.
  9. Hassan F; Molecular mechanisms of moraxella catarrhalis-induced otitis media. Curr Allergy Asthma Rep. 2013 Oct;13(5):512-7. doi: 10.1007/s11882-013-0374-8.
  10. Shaikh SB, Ahmed Z, Arsalan SA, et al; Prevalence and resistance pattern of Moraxella catarrhalis in community-acquired lower respiratory tract infections. Infect Drug Resist. 2015 Jul 31;8:263-7. doi: 10.2147/IDR.S84209. eCollection 2015.
  11. Iwata S, Sato Y, Toyonaga Y, et al; Genetic analysis of a pediatric clinical isolate of Moraxella catarrhalis with resistance to macrolides and quinolones. J Infect Chemother. 2015 Apr;21(4):308-11. doi: 10.1016/j.jiac.2014.11.002. Epub 2014 Nov 14.
  12. Mpenge MA, MacGowan AP; Ceftaroline in the management of complicated skin and soft tissue infections and community acquired pneumonia. Ther Clin Risk Manag. 2015 Apr 7;11:565-79. doi: 10.2147/TCRM.S75412. eCollection 2015.
  13. Van Damme P, Leroux-Roels G, Vandermeulen C, et al; Safety and immunogenicity of non-typeable Haemophilus influenzae-Moraxella catarrhalis vaccine. Vaccine. 2019 May 21;37(23):3113-3122. doi: 10.1016/j.vaccine.2019.04.041. Epub 2019 Apr 24.

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The information on this page is written and peer reviewed by qualified clinicians.

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