Nasopharyngeal Carriage of Neisseria meningitidis
Nasopharyngeal carriage rates of Neisseria meningitidis are highest in adolescents and young adults, serving as the primary reservoir for transmission. 1
General Population Carriage Rates
The available evidence indicates that asymptomatic nasopharyngeal colonization varies significantly by age and population characteristics:
Overall carriage rates range from approximately 2% to 16.7% in general population studies, with substantial variation based on age group and risk factors 2, 3
Adolescents and young adults demonstrate the highest carriage rates, which explains why this age group serves as the primary reservoir for meningococcal transmission in communities 1
In a large UK study of approximately 14,000 teenagers, 16.7% were found to be carriers of N. meningitidis 2
Canadian studies during non-outbreak periods found carriage rates between 1.9% and 5.4% in asymptomatic individuals 3
Age-Related Variation in Carriage
Age greater than 6 years is the primary factor associated with colonization with N. meningitidis 3:
Carriage rates peak during adolescence and young adulthood (approximately ages 15-24 years) 1
Younger children and older adults have substantially lower carriage rates 3
Risk Factors That Increase Carriage Rates
The carriage percentage increases dramatically with specific behavioral risk factors 2:
Baseline carriage of 7.8% in individuals with no risk factors 2
Carriage increases to 32.8% in those with all three major risk factors: pub/club attendance, intimate kissing, and cigarette smoking 2
Each of these factors (pub/club attendance, intimate kissing, and smoking) independently and strongly increases carriage risk (p<0.001) 2
Passive smoking is also linked to higher carriage rates 2
Notably, sex, social deprivation, home crowding, and school characteristics have little to no effect on carriage rates 2
Clinical Significance
Approximately 500 million people worldwide are carriers of N. meningitidis in their nasopharynx, representing the global reservoir for this pathogen 4:
Invasive disease is an infrequent consequence of nasopharyngeal colonization 1
The vast majority of carriers never develop invasive disease, but they serve as the transmission source for susceptible individuals 1, 4
Multiple factors beyond carriage determine whether invasive disease develops, including nasopharyngeal mucosal damage, strain virulence, absence of bactericidal antibodies, and complement system deficiencies 4
Important Caveats
Social behavior rather than demographic characteristics explains the higher carriage frequency among teenagers 2:
This finding has public health implications, as interventions targeting smoking in public places may reduce transmission risk 2
During outbreak investigations, the specific outbreak clone may not be present among carrier strains in the affected population, as demonstrated in Ontario where the outbreak strain was not found among carriers despite elevated carriage rates 3
Carriage rates can vary substantially between geographic regions and during different epidemiological periods (endemic versus outbreak scenarios) 4, 3