Bacterial Meningitis — Adult

Key Points

• Antibiotics are time critical; a required CT scan must not postpone empiric treatment.
• Obtain blood cultures before antibiotics when this can be accomplished immediately, but never trade treatment time for perfect sampling.
• Use selective, not routine, CT before lumbar puncture based on clinical risk for mass effect or focal intracranial disease.
• Vancomycin plus ceftriaxone is common community-acquired empiric therapy; add ampicillin for meaningful Listeria risk.
• Dexamethasone should precede or accompany the first antibiotic dose when bacterial meningitis, especially pneumococcal disease, is suspected.
• CSF findings can be altered by prior antibiotics, immune compromise, and early disease.
• A petechial or purpuric rash with systemic illness should raise concern for meningococcemia and septic shock.
• Close-contact prophylaxis is organism specific and should be coordinated promptly for meningococcal or selected Haemophilus influenzae exposures.

Algorithm

1. Recognize a compatible syndrome and stabilize airway, breathing, circulation, glucose, and seizures.
2. Draw two sets of blood cultures and routine emergency laboratory studies without delaying therapy.
3. Decide whether clinical features require CT before lumbar puncture.
4. If CT is needed or LP will be delayed, give dexamethasone and empiric antibiotics immediately.
5. Perform lumbar puncture as soon as safely possible; obtain cell count, differential, protein, glucose with paired serum glucose, Gram stain, culture, and appropriate molecular tests.
6. Tailor empiric coverage to age, immune status, neurosurgical history, trauma, and local resistance.
7. Narrow therapy when microbiology and susceptibility data return and address complications in a monitored setting.
8. Implement droplet isolation, public health measures, and close-contact prophylaxis when indicated by the identified or suspected pathogen.

Clinical Synopsis & Reasoning

Classic fever, neck stiffness, and altered mental status occur together in only a subset of adults, so absence of the complete triad does not exclude meningitis. Headache, photophobia, vomiting, confusion, lethargy, seizure, focal neurologic deficits, petechial or purpuric rash, and signs of sepsis should increase concern. Older adults and immunocompromised patients may present subtly. Immediately assess airway, ventilation, circulation, mental status, seizures, and shock. Obtain blood cultures promptly, but do not allow cultures to create a treatment delay. Lumbar puncture is preferred without preceding head CT when no clinical feature suggests a substantial risk of mass effect. Neuroimaging before lumbar puncture is generally reserved for selected patients with focal neurologic deficit, new-onset seizure, papilledema, markedly impaired consciousness, significant immune compromise, known central nervous system lesion, or another reason to suspect elevated intracranial pressure or a focal process. If CT is indicated, draw blood cultures and start dexamethasone and empiric antibiotics before transport rather than waiting for imaging and LP. Typical bacterial CSF shows neutrophilic pleocytosis, elevated protein, and low CSF glucose relative to serum, but partially treated infection can be atypical. CSF Gram stain, culture, and molecular testing are complementary. Consider encephalitis, subarachnoid hemorrhage, brain abscess, parameningeal infection, fungal or tuberculous meningitis, and noninfectious inflammatory disease when the presentation or CSF pattern is not typical.

Treatment Strategy & Disposition

For most immunocompetent adults younger than about 50 years with community-acquired bacterial meningitis, empiric intravenous vancomycin plus a third-generation cephalosporin such as ceftriaxone is a common regimen. Add ampicillin when Listeria monocytogenes risk is meaningful, including age 50 years or older, pregnancy, or impaired cell-mediated immunity. Post-neurosurgical, penetrating-trauma, shunt-associated, and health care-associated meningitis require antipseudomonal and resistant gram-positive coverage tailored to the context. Give dexamethasone shortly before or at the time of the first antibiotic dose when pneumococcal meningitis is a possibility; benefit is reduced when started after antibiotics have already been given. Manage shock using sepsis principles, correct hypoxemia and hypoglycemia, treat seizures promptly, and avoid hypotonic fluids. Narrow therapy once organism and susceptibilities are available, and use organism-specific treatment duration. Suspected meningococcal disease requires droplet precautions until effective therapy has been given for the recommended interval, public health notification according to jurisdiction, and prompt chemoprophylaxis for qualifying close contacts. Neurosurgical consultation is needed for hydrocephalus, abscess, infected hardware, or another structural complication.

Epidemiology / Risk Factors

• Streptococcus pneumoniae is a leading cause of community-acquired bacterial meningitis in adults.
• Neisseria meningitidis remains important in adolescents and young adults and can cause rapidly progressive meningococcemia.
• Listeria risk rises with older age, pregnancy, alcoholism, malignancy, transplantation, and impaired cell-mediated immunity.
• Vaccination against pneumococcus, meningococcus, and Haemophilus influenzae type b has changed the epidemiology but has not eliminated adult bacterial meningitis.
• Postsurgical and device-associated disease has a different pathogen distribution and requires broader empiric coverage.

Investigations

Empiric Therapy (Adults)

Pharmacology

Prognosis / Complications

• Mortality and neurologic disability remain substantial, particularly with pneumococcal meningitis, septic shock, delayed therapy, advanced age, and severe impairment of consciousness.
• Survivors may experience hearing loss, vestibular dysfunction, cognitive impairment, seizures, focal deficits, or fatigue.
• Early appropriate antibiotics and management in an experienced acute-care setting improve the chance of favorable outcome.
• Meningococcal disease can deteriorate over hours and may cause shock, disseminated intravascular coagulation, limb ischemia, and adrenal injury.
• Follow-up should address hearing, cognition, mood, seizure risk, rehabilitation, and vaccination when appropriate.

Patient Education / Counseling

• Explain that bacterial meningitis is treated before every test is complete because treatment delay can be dangerous.
• If a transmissible pathogen is suspected, tell close contacts that prophylactic antibiotics are recommended only for defined exposure categories and should be arranged promptly through clinical or public health services.
• Discuss possible neurologic and hearing complications even when acute infection improves.
• Review vaccine indications after recovery, including organism-specific recommendations and risk-based schedules.
• Advise urgent reassessment for recurrent fever, worsening headache, confusion, seizure, new weakness, or hearing change after discharge.

Notes

The key operational principle in suspected bacterial meningitis is parallel processing. Resuscitation, blood cultures, the decision about CT, lumbar puncture preparation, dexamethasone, and antimicrobial therapy should move forward together rather than sequentially. The patient who needs neuroimaging before LP is also the patient in whom it is especially important not to wait for the scan before starting treatment. Once microbiology is available, targeted therapy, complication surveillance, infection-control measures, contact prophylaxis, and post-discharge hearing and neurologic follow-up complete the care pathway.

References

1. IDSA Clinical Practice Guideline for Bacterial Meningitis — Link