Can Streptococcus pneumoniae cause meningitis, especially in individuals with compromised immune systems, chronic medical conditions, or those at high risk due to age or past pneumococcal infections?

Can Streptococcus pneumoniae Cause Meningitis?

Yes, Streptococcus pneumoniae is definitively a major cause of bacterial meningitis and has become the most common cause of bacterial meningitis in the United States following the introduction of Haemophilus influenzae type b vaccines. 1

Epidemiologic Evidence

S. pneumoniae causes meningitis across all age groups with distinct patterns:

• In the United States, the estimated overall annual incidence of pneumococcal meningitis is 1-2 cases per 100,000 population. 1

• The incidence is highest among children aged 6-24 months and persons aged ≥65 years. 1

• Following the dramatic decrease in H. influenzae type b meningitis after conjugate vaccine introduction, S. pneumoniae has become the most common cause of bacterial meningitis in the United States. 1

• Among adults, pneumococcal meningitis accounts for approximately 29% of identified bacterial meningitis cases overall, but this proportion increases significantly to approximately 72% in adults over 50 years of age. 2

High-Risk Populations

Certain groups face substantially elevated risk for pneumococcal meningitis:

Age-Related Risk

• Children aged 6-24 months have peak incidence rates for pneumococcal meningitis. 1
• Adults over 65 years have incidence rates of 50-83 cases per 100,000 population for invasive pneumococcal disease, with meningitis being one manifestation. 1
• Middle-aged adults (45-64 years) have the highest overall incidence of bacterial meningitis at 1.21 per 100,000 population. 3

Racial and Ethnic Disparities

• Rates for blacks are twice as high as those for whites and Hispanics. 1
• Alaskan Natives have rates for meningitis that are 8-10 fold higher than other U.S. population groups. 1
• Specific American Indian groups (e.g., Apache) have the highest incidence rates for any U.S. population. 1

Immunocompromised States

• Immunosuppression from cancer, immunosuppressive therapy, or HIV/AIDS substantially increases the risk of pneumococcal meningitis. 3
• In immunocompromised patients, cancer patients, diabetics, and alcoholics, S. pneumoniae remains the leading cause of bacterial meningitis. 3, 2
• Patients with sickle-cell disease are at increased risk for developing pneumococcal infections. 4

Chronic Medical Conditions

• Diabetes mellitus increases the risk of bacterial meningitis, with pneumococcus being a major pathogen. 3
• Alcoholism significantly increases susceptibility to pneumococcal infections. 3

Clinical Significance and Mortality

The mortality associated with pneumococcal meningitis is substantial:

• Case-fatality rates are highest for meningitis and bacteremia, with the highest mortality occurring among the elderly and patients with underlying medical conditions. 1

• The mortality rate for pneumococcal meningitis is up to 30% in adults, increasing with age, which is higher than the approximately 20% mortality for all-cause bacterial meningitis. 1, 2

• Pneumococcal infection causes an estimated 40,000 deaths annually in the United States, accounting for more deaths than any other vaccine-preventable bacterial disease. 1

• In children, death from pneumococcal infection is relatively uncommon except among those who have meningitis, are immunocompromised, or have undergone splenectomy. 1

Pathophysiology

S. pneumoniae causes invasive disease through specific mechanisms:

• Pneumococcus can colonize the upper respiratory tract and is transmitted through contact with respiratory droplets, with certain colonized persons developing invasive pneumococcal disease including meningitis. 1

• Invasive pneumococcal disease is defined as infection of normally sterile sites, including meningitis, pneumonia with bacteremia, osteomyelitis, septic arthritis, and bacteremia without a focus. 1

• Pneumococcal meningitis can also manifest as meningoencephalitis with widespread brain lesions and parenchymal injury, sometimes associated with immunologically mediated necrotizing vasculitis. 5

Prevention Context

The burden of pneumococcal meningitis is vaccine-preventable:

• Approximately half of the 40,000 annual deaths from pneumococcal infection could potentially be prevented through the use of vaccine. 1

• Current ACIP recommendations specify the use of either PCV20 alone or PCV15 in series with PPSV23 for all adults aged ≥65 years and for adults aged 19-64 years with certain underlying medical conditions or other risk factors. 1

• During 2018-2019, approximately 60-75% of all invasive pneumococcal disease in adults was caused by the 24 pneumococcal serotypes included in commercially available vaccines. 1