How can a patient's history help diagnose the etiology of meningitis?

How History Can Diagnose the Etiology of Meningitis

Patient age is the single most powerful historical factor for predicting meningitis etiology, with viral meningitis predominating in adults aged 20s-40s, meningococcal disease in adolescents and young adults, and pneumococcal or Listeria infections in those over 50-60 years. 1

Age-Based Etiologic Patterns

• Young adults (20s-40s): Viral meningitis is more common than bacterial, with a second peak of meningococcal disease occurring in late teens/early 20s 1
• Adults over 50 years: Pneumococcal disease becomes increasingly common 1
• Adults over 60 years: Listeria monocytogenes becomes a significant consideration, though it remains relatively rare 1

Critical Historical Features That Identify Specific Pathogens

Presence and Type of Rash

• When a rash is present with meningitis, Neisseria meningitidis is the causative organism in 92% of cases (petechial in 89% of these cases) 1
• However, 37% of meningococcal meningitis cases present without any rash, so absence does not exclude this diagnosis 1
• Meningococcal meningitis is more likely to present with rash than pneumococcal meningitis 1

Source of Infection

• Co-existing upper respiratory tract infection (otitis media, sinusitis) strongly suggests pneumococcal meningitis 1
• History of recent trauma or neurosurgery suggests pneumococcal meningitis and raises concern for recurrent disease 1
• Evidence of rhinorrhea or otorrhea indicates possible CSF leak and pneumococcal etiology 1

Travel History

• Travel to the Mediterranean suggests Toscana virus 1
• Travel to Central/Eastern Europe raises concern for Tick Borne Encephalitis virus 1
• Travel to the meningitis belt in Africa increases risk of meningococcal disease 1
• Travel to the USA suggests West Nile virus or Lyme disease (with appropriate exposure) 1
• Travel to areas with warm, fresh, or brackish water (globally) raises concern for parasitic meningitis such as Naegleria fowleri 1
• Travel to South America or parts of Africa suggests trypanosomiasis 1
• Travel to areas with penicillin-resistant pneumococci necessitates empiric vancomycin coverage 2

Contact History

• Contact with another person with meningitis or sepsis should always be ascertained and taken seriously 1

Immunocompromise and Underlying Conditions

HIV Status

• HIV infection increases risk of pneumococcal and meningococcal meningitis with higher mortality 1
• Cryptococcal meningitis is most common with CD4 count <100 cells/μL but should be considered with CD4 <200 cells/μL or <14% 1
• TB meningitis is an important consideration at all CD4 counts 1
• All patients with meningitis should have an HIV test performed 1

Other Immunocompromising Conditions

• Asplenia increases risk from all encapsulated bacteria (Streptococcus pneumoniae, Neisseria meningitidis, Haemophilus influenzae) 1
• Complement deficiency increases risk of meningococcal disease 1
• Risk factors for Listeria include alcohol dependency, diabetes, malignancy, and immunosuppression from illness or medication 1
• Patients ≥60 years or immunocompromised require empiric ampicillin coverage for Listeria 2, 3

Recurrent Meningitis

• History of skull fracture or CSF leak suggests pneumococcal meningitis and risk for recurrence 1
• Previous lymphocytic meningitis suggests HSV-2 as the commonest cause of recurrent disease 1
• Two or more episodes of meningococcal or pneumococcal meningitis warrant immunological investigations 1
• Family history of more than one episode of meningococcal disease requires immunological studies 1

Common Pitfalls to Avoid

• Do not rely on the "classic triad" (neck stiffness, fever, altered consciousness) as it is present in less than 50% of bacterial meningitis cases 1
• Elderly patients are more likely to have altered consciousness and less likely to have neck stiffness or fever, making diagnosis more challenging 1
• Kernig's and Brudzinski's signs have high specificity (up to 95%) but very low sensitivity (as low as 5%), making them unreliable for ruling out meningitis 1
• Clinical features alone cannot distinguish between viral and bacterial meningitis, necessitating CSF analysis 1
• Concern from the referring doctor or a relative should always be taken seriously, even when clinical features are not clear-cut 1

Algorithmic Approach to History-Taking

1. Document patient age to establish baseline risk for viral vs. bacterial pathogens and specific organisms 1
2. Assess for rash (presence, type, distribution) to identify possible meningococcal disease 1
3. Identify source of infection (otitis media, sinusitis, recent trauma/surgery) suggesting pneumococcal etiology 1
4. Obtain detailed travel history to assess for geographically-specific pathogens 1
5. Determine immune status (HIV, asplenia, complement deficiency, immunosuppressive medications, chronic diseases) 1
6. Inquire about contact with meningitis cases 1
7. Review for history of recurrent meningitis or family history of meningococcal disease 1