Bacterial Meningitis

Epidemiology

• Streptococcus pneumoniae is the most common Gram-positive pathogen causing bacterial meningitis across all age groups except neonates, responsible for approximately 72% of cases in adults older than 16 years 1
• Listeria monocytogenes is the third most common pathogen in adults, particularly in older adults and immunocompromised patients 1
• Historically, the three main pathogens causing bacterial meningitis were H. influenzae type b, N. meningitidis, and S. pneumoniae, but after the introduction of vaccines, H. influenzae type b has virtually disappeared in vaccinated populations 1
• Streptococcus agalactiae (Group B Streptococcus) is the most common pathogen in neonates (58% of cases), followed by Escherichia coli (21% of cases) 1
• S. pneumoniae is only incidentally found in neonates (4% of cases) 1

Diagnosis

• Gram stain of CSF is highly valuable for rapid diagnosis, with S. pneumoniae having the highest detection rate on Gram stain (90% of cases) 2
• Visualization of S. pneumoniae on Gram stain depends on bacterial concentration in CSF (>105 CFU/mL yields 97% positive results) 2

Prevention

• The introduction of pneumococcal conjugate vaccines (PCVs) has reduced the incidence of pneumococcal meningitis, but serotype replacement has been observed in adults, highlighting the need for continued surveillance and vaccine development 1
• Streptococcus pneumoniae and Neisseria meningitidis are primarily spread through respiratory droplets when carriers cough or sneeze near others, and are the most common causes of community-acquired bacterial meningitis in children beyond neonatal age and adults 3, 1, 4
• Neisseria meningitidis is transmitted through large droplet respiratory secretions from patients or asymptomatic carriers, and serogroup B causes most meningococcal meningitis cases in both children and adults 1, 5, 4
• College freshmen living in dormitories are at higher risk for meningococcal disease and should be considered for vaccination, while asymptomatic carriers of N. meningitidis can transmit the pathogen to susceptible individuals through respiratory droplets 5
• Chemoprophylaxis is recommended for close contacts of patients with meningococcal meningitis, and vaccination with pneumococcal and influenza vaccines significantly reduces transmission risk in appropriate populations, as recommended by the CDC and ACP 5, 6, 7
• Respiratory hygiene, including covering coughs and sneezes, and disposing of tissues properly, is essential for preventing transmission, according to the WHO guidelines, while hand hygiene, including regular handwashing, especially after respiratory secretion contact, is crucial for preventing transmission, as stated by the IDSA 8
• Personal protective equipment, including masks and gloves, should be used by healthcare workers when caring for patients with contagious pneumonia, according to the OSHA guidelines, while isolation measures, including private rooms or cohorting, may be necessary for hospitalized patients with highly contagious pneumonia, as recommended by the CDC and SHEA 8
• Vaccination with pneumococcal and influenza vaccines significantly reduces transmission risk in appropriate populations, as recommended by the CDC and ACP, while Mycoplasma pneumoniae causes "atypical pneumonia", is particularly common in people 5-25 years of age, and is moderately contagious through close contact and respiratory droplets 6, 7, 9