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

Pathogenesis

This is a Gram-negative, aerobic, oxidase-positive diplococcus. The genera Moraxella (including the former Branhamella), Acinetobacter and Psychrobacter currently belong to the family Moraxellaceae; the classification is currently under review.

It is a common commensal organism of the upper respiratory tract, particularly in children, but is increasingly being recognised as a pathological organism causing otitis media, sinusitis, ocular infection and occasionally laryngitis.¹ It may cause bronchitis or pneumonia in adults and children with underlying lung disease.

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.²

Epidemiology

• Carriage rates among populations of children vary from 28-100%. In common-cold episodes 29% were found to be due to bacterial pathogens - including M. catarrhalis.³
• In healthy adults the carriage rate is much lower at 1-10%. Carriage rates among those with underlying lung disease and the elderly are higher.⁴
• Carriage rates are higher in autumn and winter than in spring/summer.
• In the USA it is the third most common cause of otitis media and sinusitis in children (after Streptococcus pneumoniae and Haemophilus influenzae).²
• In the USA it is thought to cause 3-4 million cases of otitis media each year.²
• 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).²
• M. catarrhalis is estimated to cause ~10% of exacerbations in chronic obstructive pulmonary disease (COPD) patients.¹
• It is thought that any isolate in adults is of clinical significance.²
• There may be a male preponderance with one study showing an overall male:female ratio of 1.6:1.²

Differential diagnosis

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

• S. pneumoniae.
• H. influenzae.
• Causes of atypical pneumonia.
• Viral causes of upper/lower respiratory tract infection.
• Fungal infection (should be considered as a possible cause of illness in the immunocompromised).

Investigations

• 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.
• Other methods that allow distinction of M. catarrhalis from similar organisms include DNase detection (positive), reduction of nitrate and nitrite and ability to hydrolyse tributyrin.²
• 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, e.g. CT scan of sinuses and CXR.
• LP and blood cultures are useful in diagnosing bacteraemic infection and meningitis.

Management

• The vast majority of isolates of M. catarrhalis are penicillin-resistant through the production of beta-lactamase.⁵
• Trimethoprim resistance is also common.
• Macrolide antibiotics such as erythromycin and clarithromycin are useful. Treatment with oral azithromycin 500 mg once daily for three days has been found to be comparable with a 10-day course of oral clarithromycin (500 mg twice daily) for acute exacerbation of chronic bronchitis.⁶
• Quinolones such as ciprofloxacin and ofloxacin are effective.⁷
• Second- or third-generation cephalosporins may be used, e.g. cefalexin, cefaclor.
• Tetracyclines are also active against this pathogen, e.g. doxycycline.

Complications

• 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.

Prognosis

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. Mortality in the three months following pneumonia due to M. catarrhalis in one study was as high as 33%.²

Prevention

• 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.
• Children prone to otitis media may be less likely to be infected if they are not exposed to passive smoking.^8,9
• Vaccines are currently in development.¹⁰

Document references

1. Aebi C; Moraxella catarrhalis - pathogen or commensal? Adv Exp Med Biol. 2011;697:107-16. [abstract]
2. Constantinescu M et al; Moraxella Catarrhalis Infections, Medscape, Sep 2011
3. Pappas DE, Hendley JO, Hayden FG, et al; Symptom profile of common colds in school-aged children. Pediatr Infect Dis J. 2008 Jan;27(1):8-11. [abstract]
4. Verduin CM, Hol C, Fleer A, et al; Moraxella catarrhalis: from emerging to established pathogen.; Clin Microbiol Rev. 2002 Jan;15(1):125-44. [abstract]
5. Morrissey I, Robbins M, Viljoen L, et al; Antimicrobial susceptibility of community-acquired respiratory tract pathogens in the UK during 2002/3 determined locally and centrally by BSAC methods.; J Antimicrob Chemother. 2005 Feb;55(2):200-8. Epub 2005 Jan 13. [abstract]
6. Swanson RN, Lainez-Ventosilla A, De Salvo MC, et al; Once-daily azithromycin for 3 days compared with clarithromycin for 10 days for acute exacerbation of chronic bronchitis: a multicenter, double-blind, randomized study. Treat Respir Med. 2005;4(1):31-9. [abstract]
7. Sahm DF, Brown NP, Thornsberry C, et al; Antimicrobial susceptibility profiles among common respiratory tract pathogens: a GLOBAL perspective. Postgrad Med. 2008 Sep;120(3 Suppl 1):16-24. [abstract]
8. Brook I, Gober AE; Recovery of potential pathogens and interfering bacteria in the nasopharynx of otitis media-prone children and their smoking and nonsmoking parents.; Arch Otolaryngol Head Neck Surg. 2005 Jun;131(6):509-12. [abstract]
9. Kum-Nji P, Meloy L, Herrod HG; Environmental tobacco smoke exposure: prevalence and mechanisms of causation of infections in children.; Pediatrics. 2006 May;117(5):1745-54. [abstract]
10. Mawas F, Ho MM, Corbel MJ; Current progress with Moraxella catarrhalis antigens as vaccine candidates. Expert Rev Vaccines. 2009 Jan;8(1):77-90. [abstract]

Internet and further reading

• Community management of lower respiratory tract infection in adults, Scottish Intercollegiate Guidelines Network - SIGN (2002)
• Wald E; Beginning antibiotics for acute rhinosinusitis and choosing the right treatment.; Clin Rev Allergy Immunol 2006 Jun;30(3):143-52.