Meningococcemia classification

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Cafer Zorkun, M.D., Ph.D. [2]

Overview

13 serotypes of meningococci have been isolated based on their polysacchride capsule out of which five of them causes clinically severe diseases. They are also classified according to outer membrane protein.

Classification

• Meningococci are classified by using serologic methods based on the structure of the polysaccharide capsule.
• 13 Serotypes are described based on capsular polysaccharide: A, B, C, D, X, Y, Z, E, W-135, H, I, K, and L.
• Serogroup A usually with epidemics in less developed nations and an attack rate of as high as 500 cases per 100,000 population.
• Serogroup B usually in developed nations with attack rate of 50-100 cases per 100,000 population.
• Serogroup C usually in both developed and less developed populations and an attack rate of up to 500 per 100,000 population.
• Some strains, often those found to cause asymptomatic nasopharyngeal carriage, are not groupable and do not have a capsule.
• Almost all invasive disease is caused by one of five serogroups: A, B, C, Y, and W-135.
• The relative importance of each serogroup depends on geographic location, as well as other factors, such as age. For instance, serogroup A is a major cause of disease in sub-Saharan Africa but is rarely isolated in the United States.
• Meningococci are further classified on the basis of certain outer membrane proteins. Molecular subtyping using specialized laboratory techniques (e.g., pulsed-field gel electrophoresis) can provide useful epidemiologic information.

Classification of Clinical Presentations

• They present with a wide range of clinical conditions from transient bacteremia to rapidly progressing septicemia.
• Most of them develop meningitis as meningococci invade the meninges.
• Meningococcal infections are classified into four different clinical groups based on the following conditions:

• Presence or absence of signs of septic shock.
• Presence or absence of clinical symptoms and laboratory signs of distinct meningitis.

Clinical group	Characteristic feature	Case fatality
Fulminent meningocccal septicemia	Persistent and severe septic shock, which lasts for more than 24 hours, associated with minimal pleocytosis or lack of clinical manifestations of meningitis.	25-55%
Distinct meningitis	Marked pleocytosis or distinct clinical signs of meningitis.	10-25%
Distinct meningitis and persistent septic shock	Marked pleocytosis or distinct signs of meningitis associated with severe septic shock.	<5%
Mild systemic meningococcal infection	Mild meningococcemia without signs of meningitis or persistent septic shock.	0%
Table adapted from Handbook of meningococcal disease