Closing the Brief Case: Meningococcemia Leading to a Diagnosis of Complement Deficiency in a 23-Month-Old

ANSWERS TO SELF-ASSESSMENT QUESTIONS

1. What is the estimated rate of nasopharyngeal carriage of N. meningitidis in adolescents?

   • a.
     5 to 10%
   • b.
     20 to 25%
   • c.
     35 to 40%
   • d.
     50 to 55%

Answer: a. Most often, this organism is a harmless colonizer in the nasopharynx. Acquisition can occur from close contact or crowded spaces. As a result, carrier/colonization rates in dormitories or military barracks can be as high as 50%.

1. What 3 serogroups of N. meningitidis are most commonly seen in the United States?

   • a.
     A, B, C
   • b.
     B, C, X
   • c.
     B, C, Y
   • d.
     C, Y, W-135

Answer: c. At least 13 distinct serogroups have been defined, but these three represent the most common serotypes in the United States.

1. Which Neisseria species has been mistakenly reported as N. meningitidis by MALDI-TOF MS systems, and what test could be used to differentiate the two species?

   • a.
     N. sicca, observation of pigment
   • b.
     N. lactamica, colistin resistance
   • c.
     N. polysaccharea, 16S sequencing
   • d.
     N. subflava, gamma-glutamyltransferase (enzyme) detection

Answer: c. Definitive identification of N. meningitidis can be challenging. Many of the tests described in the question can be helpful for differentiation but would not be helpful when paired with the particular organism listed. N. sicca does not produce pigment, N. lactamica is colistin resistant, and N. subflava can produce the enzyme gamma-glutamyltransferase. All of these characteristics are shared by most strains of N. meningitidis. MALDI-TOF MS has been described to misidentify N. polysaccharea as N. meningitidis and vice versa. In at least one report, 16S sequencing was the only method able to definitively distinguish between these species.

TAKE-HOME POINTS

• Individuals with terminal complement deficiencies have a uniquely high risk of developing meningococcal disease, and identification of N. meningitidis from a sterile fluid should prompt consideration for immunodeficiency workup, including a CH50 level.

• Vaccination against N. meningitidis is recommended for all age groups with terminal complement deficiencies; however, vaccination alone does not prevent disease from all serotypes.

• Accurately differentiating N. meningitidis from nonpathogenic Neisseria spp. can be challenging, as MALDI-TOF MS as well as manual and automated biochemical methods are not 100% specific; therefore, results should be interpreted in the clinical context and with caution.

See https://doi.org/10.1128/JCM.01513-18 in this issue for case presentation and discussion.