What are the causes of Neisseria meningitidis (Nm) infection, particularly in children, young adults, and individuals with underlying medical conditions such as asplenia or immunodeficiency?

Causes of Neisseria meningitidis Infection

Neisseria meningitidis infection is caused by transmission of the bacterium through direct contact with large respiratory droplets from patients or asymptomatic nasopharyngeal carriers, with humans being the only reservoir. 1

Transmission Mechanism

• N. meningitidis colonizes the mucosal surfaces of the nasopharynx and is transmitted through direct contact with large-droplet respiratory tract secretions from infected patients or asymptomatic carriers. 1
• The bacterium spreads through close contact, typically requiring proximity of less than 3 feet for transmission. 1
• Humans are the only host for this organism—there is no animal reservoir or environmental source. 1
• Nasopharyngeal carriage rates are highest in adolescents and young adults (ages 16-25), who serve as the primary reservoirs for transmission even when asymptomatic. 1
• Rare cases of urogenital and anorectal transmission have been documented, particularly following orogenital contact with oropharyngeal carriers, though this represents an uncommon route. 2

High-Risk Populations and Predisposing Conditions

Medical Conditions That Increase Susceptibility

• Complement deficiencies (particularly terminal complement pathway C3, C5-9) dramatically increase risk for acquiring meningococcal disease. 1, 3
• Anatomic or functional asplenia places individuals at substantially elevated risk for invasive meningococcal infection. 1, 3
• Patients on complement inhibitor therapy (such as Eculizumab/Soliris) face increased risk and require both vaccination and prophylactic antibiotics. 1
• HIV infection increases both incidence and mortality of meningococcal disease compared to HIV-negative patients. 1, 4

Environmental and Behavioral Risk Factors

• Household crowding and dormitory living (particularly college freshmen) increase transmission risk through prolonged close contact. 1
• Active and passive smoking are consistently associated with increased risk for meningococcal disease. 1
• Antecedent viral respiratory infection predisposes to secondary meningococcal infection. 1
• Bar or nightclub patronage and alcohol use have been associated with higher risk during outbreaks. 1
• Chronic underlying illness increases susceptibility. 1

Age-Related Risk Patterns

• Infants under 1 year have the highest disease rate at 9.2 per 100,000 population, with serogroup B causing over 50% of cases in this age group. 1
• A second peak occurs in adolescents and young adults (ages 11-25 years), with rates of 1.2 per 100,000 in the 11-19 age group. 1
• While disease rates are highest in infants, 62% of all meningococcal disease in the United States occurs in persons aged >11 years. 1

Serogroup Distribution

• Serogroups B, C, and Y each account for approximately one-third of cases in the United States, though distribution varies by age. 1
• Among persons aged ≥11 years, 73-75% of cases are caused by vaccine-preventable serogroups (C, Y, or W-135). 1
• Serogroup B predominates in infants and young children (>50% of cases under age 1), but no vaccine was available in the U.S. during the guideline periods. 1
• The proportion of serogroup Y cases increased dramatically from 2% (1989-1991) to 37% (1997-2002). 1

Epidemiologic Context

• Over 98% of meningococcal cases in the United States are sporadic rather than outbreak-associated. 1
• Despite widespread antibiotic availability, the case-fatality ratio remains 10-14%, with 11-19% of survivors experiencing permanent sequelae (neurologic disability, limb loss, hearing loss). 1
• Race and low socioeconomic status appear to be risk markers rather than independent risk factors—the true underlying risks relate to household crowding, smoking exposure, and recent respiratory illness. 1

Common Pitfall

Do not assume all close contacts require chemoprophylaxis—only those with direct exposure to respiratory secretions (household contacts, those sharing eating/drinking utensils, healthcare workers exposed during intubation without masks) warrant prophylactic antibiotics. 1 Casual contact, even in healthcare settings, does not require prophylaxis unless there was unprotected exposure to respiratory droplets. 1