Acute pyogenic infection of the meninges — neurologic emergency requiring empiric antibiotics within 1 hour.
Also known as: bacterial meningitis, meningococcal meningitis, pneumococcal meningitis, acute meningitis
Overview
Acute pyogenic infection of the leptomeninges and subarachnoid space, characterized by inflammation, neutrophilic CSF pleocytosis, and high morbidity/mortality without prompt antibiotic therapy.
Epidemiology
Incidence in the US ~1-2 per 100,000 adults annually; higher in infants and young children. Vaccination has dramatically reduced Haemophilus influenzae type b and Streptococcus pneumoniae meningitis. Outbreaks of Neisseria meningitidis occur in close-contact settings (college dormitories, military barracks).
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Question 1Infectious DiseaseEasy
A 24-year-old woman at 20 weeks of gestation comes to the emergency department the morning after her live-in boyfriend was admitted with meningitis. His blood cultures have grown Neisseria meningitidis. They have shared a bed and eaten from the same dishes throughout the past week. She is asymptomatic, her temperature is 36.9 C, and her examination is normal. She has no drug allergies. Which of the following is the most appropriate chemoprophylaxis for her?
ARifampin 600 mg PO every 12 hours for 2 days
BCiprofloxacin 500 mg PO given as a single dose
CErythromycin 500 mg PO every 6 hours for 7 days
DBenzathine penicillin G 2.4 million units IM once
ECeftriaxone 250 mg IM given as a single dose
Reveal answer & full explanation
Correct answer: E — Ceftriaxone 250 mg IM given as a single dose
ARifampin 600 mg PO every 12 hours for 2 days
BCiprofloxacin 500 mg PO given as a single dose
CErythromycin 500 mg PO every 6 hours for 7 days
DBenzathine penicillin G 2.4 million units IM once
ECeftriaxone 250 mg IM given as a single dose✓
Why Ceftriaxone 250 mg IM given as a single dose is correct
She is a household close contact of invasive meningococcal disease: she lives with the patient and shared his bed in the 7 days before his illness, so CDC recommends chemoprophylaxis, given as soon as possible and ideally within 24 hours of identifying the index patient
Prophylaxis works by eradicating nasopharyngeal carriage; rifampin, ciprofloxacin and ceftriaxone are each 90-95% effective, and in a nonpregnant adult any of the three is acceptable, so her pregnancy is the deciding fact
CDC lists rifampin and ciprofloxacin as not recommended for pregnant women, which leaves single-dose ceftriaxone as the preferred agent for a pregnant contact; the dose for ages 15 and older is 250 mg IM once (125 mg IM under age 15)
She is afebrile with a normal examination, so she needs prophylaxis, not a sepsis workup or treatment-dose antibiotics
Why the others are wrong
Ciprofloxacin 500 mg PO given as a single dose - the most convenient regimen for a nonpregnant adult contact, but CDC does not recommend ciprofloxacin for pregnant women (fluoroquinolones cause arthropathy in juvenile animals), and since 2024 CDC has advised replacing it in areas where ciprofloxacin-resistant cases reach a set local threshold (the trap is reaching for the usual one-pill adult default)
Benzathine penicillin G 2.4 million units IM once - safe in pregnancy and given as one injection, but penicillins do not reliably eradicate nasopharyngeal carriage of N. meningitidis, so no penicillin is an accepted chemoprophylaxis agent (the trap is choosing on pregnancy safety alone)
Rifampin 600 mg PO every 12 hours for 2 days - the correct adult regimen and effective for nonpregnant contacts, but CDC does not recommend rifampin for meningococcal prophylaxis in pregnant women (it is still used for tuberculosis in pregnancy, where the benefit outweighs the risk); it also induces CYP enzymes that lower hormonal contraceptive, warfarin and some antiseizure drug levels, turns urine and tears orange, and stains soft contact lenses (the trap is reaching for the classic textbook agent without checking who the contact is)
Erythromycin 500 mg PO every 6 hours for 7 days - a macrolide generally considered safe in pregnancy and familiar from pertussis and diphtheria contact prophylaxis, but erythromycin is not among the agents CDC recommends for meningococcal chemoprophylaxis and lacks good evidence that it eradicates nasopharyngeal carriage of N. meningitidis, so it cannot be counted on to protect her (the trap is borrowing a pregnancy-safe prophylaxis regimen from another droplet-spread infection)
Additional high-yield points
Close contacts are household members, child care contacts and anyone directly exposed to the patient's oral secretions (kissing, mouth-to-mouth resuscitation, endotracheal intubation or tube management) in the 7 days before symptom onset; classmates and coworkers without such exposure do not need prophylaxis
Health care personnel need prophylaxis only after unprotected exposure to respiratory secretions, such as intubation, airway suctioning or mouth-to-mouth resuscitation without a mask
Prophylaxis started more than 14 days after the index patient's illness onset is of limited or no benefit, and nasopharyngeal cultures are not useful for deciding who receives it
Give chemoprophylaxis to close contacts regardless of their meningococcal vaccination status
Azithromycin 500 mg once is not recommended routinely but is an alternative where ciprofloxacin resistance is a problem; CDC (2024) advises stopping ciprofloxacin in a local catchment area once, over a rolling 12 months, 2 or more cases are caused by resistant strains and those cases make up at least 20% of all reported cases, using rifampin, ceftriaxone or azithromycin instead; ciprofloxacin is also a poor choice for contacts of an index patient whose isolate is known to be ciprofloxacin-resistant
The prophylaxis dose of ceftriaxone is 250 mg IM, not the 500 mg IM dose now used for gonorrhea
An index patient treated with ceftriaxone or cefotaxime needs no further carriage eradication; one treated with another agent, such as penicillin, needs rifampin, ciprofloxacin or ceftriaxone before discharge
Question 2Infectious DiseaseMedium
A 68-year-old male presents with fever, altered mental status, and stiff neck. A non-blanching petechial rash is progressing rapidly to purpura. BP is 80/50 and he is obtunded. Blood cultures are drawn. Which of the following is the most appropriate immediate next step?
ACT head with contrast
BLumbar puncture before antibiotics
CEmpiric IV doxycycline
DEmpiric IV antibiotics and dexamethasone
EEmpiric IV acyclovir
Reveal answer & full explanation
Correct answer: D — Empiric IV antibiotics and dexamethasone
ACT head with contrast
BLumbar puncture before antibiotics
CEmpiric IV doxycycline
DEmpiric IV antibiotics and dexamethasone✓
EEmpiric IV acyclovir
Why Empiric IV antibiotics and dexamethasone is correct
Non-blanching petechial/purpuric rash with septic shock indicates Neisseria meningitidis meningococcemia — a life-threatening emergency; do not delay antibiotics for LP or CT
Give IV ceftriaxone 2 g q12h immediately plus vancomycin for resistant pneumococcal coverage and IV ampicillin 2 g q4h for Listeria, because he is older than 50
Dexamethasone 0.15 mg/kg q6h should be given before or with the first antibiotic dose — reduces mortality and neurologic sequelae
Add IV fluids and vasopressors for septic shock; LP can follow after antibiotics if the patient stabilizes
Why the others are wrong
Lumbar puncture before antibiotics — must not delay antibiotics in suspected bacterial meningitis with septic shock (premature procedure)
Empiric IV acyclovir — is added when HSV encephalitis is suspected but never replaces or delays empiric antibacterial therapy (right-concept-wrong-pathogen)
CT head with contrast — should not delay antibiotic administration in this presentation (anchoring on imaging)
Empiric IV doxycycline — a febrile illness with a petechial rash and altered mentation can suggest Rocky Mountain spotted fever, for which doxycycline is the drug of choice at any age; but meningismus with a petechial rash progressing to purpura and shock points to meningococcemia with meningitis, and doxycycline is not adequate therapy for bacterial meningitis, which needs ceftriaxone plus vancomycin (with ampicillin at his age); when rickettsial disease is also a concern, doxycycline is added to that regimen rather than substituted for it (confused-with Rocky Mountain spotted fever)
Additional high-yield points
Prior antibiotics may render cultures negative within hours, but Gram stain and antigen testing remain useful
Chemoprophylaxis for close contacts: ciprofloxacin 500 mg single dose or rifampin
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Viral (aseptic) meningitis — Less ill-appearing; lymphocytic CSF, normal glucose, mildly elevated protein, negative gram stain; enterovirus most common
Encephalitis (HSV, arboviral) — Prominent altered mental status, seizures, focal deficits; HSV with temporal lobe involvement on MRI
Subarachnoid hemorrhage — Thunderclap headache; LP with RBCs and xanthochromia; CT head before LP if clinical suspicion
Brain abscess — Focal deficits, ring-enhancing lesion on imaging; LP often contraindicated due to mass effect
Tuberculous meningitis — Subacute course (1-2 weeks), basilar meningitis, cranial nerve palsies, lymphocytic CSF with high protein, very low glucose, AFB smear/PCR/culture
LP CSF studies: opening pressure, cell count and differential, protein, glucose (with simultaneous serum glucose), Gram stain, culture, latex agglutination/multiplex PCR (meningitis/encephalitis panel), HSV PCR, cryptococcal antigen if at risk, AFB stain/culture/PCR if TB suspected, cytology in older patients
Typical bacterial CSF: WBC >1000 (PMN predominant), glucose <40 (or CSF:serum ratio <0.4), protein >200, opening pressure elevated (>250 mm H2O)
Imaging
CT head BEFORE LP only if any of: immunocompromise, history of CNS disease (mass, stroke, focal infection), new seizure within 1 week, papilledema, abnormal level of consciousness, focal neurologic deficit, age >60 — to exclude mass effect and risk of herniation
DO NOT delay antibiotics for imaging or LP — give empiric antibiotics immediately if any delay anticipated
MRI brain if focal findings, suspected complications (abscess, ventriculitis, infarct)
Diagnostic algorithm
Parameter
Bacterial
Viral
Fungal/TB
Normal
Opening pressure (mm H2O)
Elevated (>250)
Normal or mildly elevated
Elevated
70-180
WBC (cells/µL)
>1000 (often 1000-5000)
10-500
100-500
0-5
WBC predominance
Neutrophils (PMN)
Lymphocytes
Lymphocytes
—
Glucose (mg/dL)
Low (<40) or CSF:serum <0.4
Normal
Low
50-80 (~2/3 serum)
Protein (mg/dL)
High (>200)
Mildly elevated (50-150)
Very high (>250)
<45
Gram stain
Often positive
Negative
Negative (AFB/India ink)
Negative
Typical CSF profiles by etiology of meningitis.
Treatment
First-line
Empiric antibiotics within 1 hour of presentation — do not delay for imaging or LP if not immediately available:
Adults 18-50: ceftriaxone 2 g IV q12h + vancomycin 15-20 mg/kg IV q8-12h (covers pneumococcus with ceftriaxone resistance); ceftriaxone is a third-generation cephalosporin (beta-lactam) that binds penicillin-binding proteins and blocks transpeptidase cross-linking of peptidoglycan
Adults >50 or immunocompromised, alcoholic, pregnant: ADD ampicillin 2 g IV q4h to cover Listeria monocytogenes
Children 1 month-18 years: ceftriaxone + vancomycin
Post-neurosurgery/penetrating head trauma: vancomycin + cefepime (or ceftazidime or meropenem) — covers Pseudomonas, MRSA, gram-negatives
Dexamethasone 0.15 mg/kg IV q6h x 4 days, FIRST DOSE 10-20 minutes BEFORE OR WITH first antibiotic dose — reduces mortality and neurologic sequelae (especially hearing loss) in pneumococcal meningitis (de Gans & van de Beek NEJM 2002); continue if pneumococcus confirmed
Acyclovir IV 10 mg/kg q8h if HSV encephalitis cannot be excluded
Second-line / adjunct
Narrow antibiotics once Gram stain/culture/sensitivities return:
S. pneumoniae (gram-positive diplococci): ceftriaxone (continue vancomycin until sensitivities confirm)
N. meningitidis (gram-negative diplococci): ceftriaxone or penicillin G
H. influenzae (gram-negative coccobacilli): ceftriaxone
L. monocytogenes (gram-positive rods): ampicillin ± gentamicin
Group B Streptococcus: penicillin G or ampicillin
Standard duration: meningococcus 7 days, H. influenzae 7-10 days, pneumococcus 10-14 days, GBS 14-21 days, Listeria 21 days, gram-negative bacilli 21 days
Chemoprophylaxis for close contacts of meningococcus: rifampin 600 mg PO BID x 2 days, ciprofloxacin 500 mg PO x 1, or ceftriaxone 250 mg IM x 1 (preferred in pregnancy)
Vaccinate close contacts of vaccine-preventable cases (meningococcal, Hib, pneumococcal); update routine vaccinations in survivors and high-risk patients
Audiology screening on recovery (CN VIII injury, especially pneumococcal)
Complications
Death (mortality ~10-30% adults; up to 50% pneumococcal in elderly)
Sensorineural hearing loss (~10-30%, especially pneumococcal)
Cognitive impairment, memory deficits
Seizure disorder
Cranial nerve palsies
Hydrocephalus, cerebral infarction
Subdural empyema, brain abscess
Septic shock, DIC, adrenal hemorrhage (Waterhouse-Friderichsen with meningococcemia)
Limb necrosis from purpura fulminans
PANCE pearls
Empiric antibiotics within 1 hour. If CT before LP is needed, give blood cultures and antibiotics FIRST.
Add ampicillin for Listeria in patients >50, immunocompromised, alcoholic, or pregnant.
Dexamethasone before/with first antibiotic in suspected pneumococcal meningitis — reduces mortality and hearing loss.
Petechial rash with meningismus = meningococcemia until proven otherwise; isolate, treat, and notify public health.
Vaccination: MenACWY (preteens, college students, military, asplenia, complement deficiency); MenB (high-risk patients and outbreaks; shared clinical decision-making for ages 16-23); pneumococcal: PCV15 or PCV20 in children, and for adults ≥50 or younger adults at risk, PCV20 or PCV21 alone or PCV15 followed by PPSV23; Hib in children.
Close contacts of meningococcus require chemoprophylaxis within 24 hours.
In suspected partially treated meningitis (prior antibiotics), Gram stain and culture may be negative — multiplex PCR helpful.
Recurrent meningitis suggests anatomic defect (CSF leak from basilar skull fracture, dermal sinus tract) or complement deficiency.
References
IDSA 2004 — Practice Guidelines for the Management of Bacterial Meningitis (Tunkel et al., Clin Infect Dis 2004; updates pending)
ESCMID 2016 — van de Beek D, Cabellos C, Dzupova O, et al. ESCMID guideline: diagnosis and treatment of acute bacterial meningitis. Clin Microbiol Infect 2016;22 Suppl 3:S37-S62
de Gans NEJM 2002 — Dexamethasone in Adults with Bacterial Meningitis (de Gans & van de Beek, NEJM 2002)
CDC ACIP — ACIP Recommendations for Meningococcal Vaccination
CDC ACIP 2025 — Kobayashi M, Leidner AJ, Gierke R, et al. Expanded recommendations for use of pneumococcal conjugate vaccines among adults aged ≥50 years: recommendations of the Advisory Committee on Immunization Practices — United States, 2024. MMWR Morb Mortal Wkly Rep 2025;74(1):1-8
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