Pyogenic (Bacterial) Meningitis

Age-Stratified Aetiology

Older children/adults: S. pneumoniae + N. meningitidis (meningococcus) dominant. H. influenzae type b — historically major, now sharply DOWN with Hib vaccine (mirrors epidemiologic shift, see H. influenzae Infections topic). Neonates: separate aetiology — see Neonatal Meningitis topic.

Meningococcus: epidemic potential (meningitis belt sub-Saharan Africa), nasopharyngeal carriage/droplet spread. DISTINCTIVE petechial/purpuric rash — fulminant meningococcemia → Waterhouse-Friderichsen syndrome (bilateral adrenal hemorrhage, rapidly fatal). Rash = specifically meningococcal clinical clue.

Pathogenesis

Common route: nasopharyngeal colonization → bacteremia → BBB crossing → purulent subarachnoid exudate. Host INFLAMMATORY RESPONSE (not just direct toxicity) drives raised ICP, cerebral edema, long-term sequelae → basis for adjunctive steroid therapy (below).

Clinical

Classic triad: fever + neck stiffness + altered mental status (+ headache, photophobia). NOT always complete, esp. extremes of age. Kernig’s sign: pain/resistance on passive knee extension (hip flexed). Brudzinski’s sign: involuntary hip/knee flexion on passive neck flexion. Complications: seizures, coma, death if untreated. Survivors: HEARING LOSS (esp. pneumococcal — testable), other neuro deficits.

Diagnosis

LP + CSF analysis (full comparative table = CSF Examination in Meningitis topic). Bacterial pattern: ↑opening pressure, turbid/cloudy, NEUTROPHIL predominant, LOW glucose (bacterial consumption — key vs viral’s normal glucose), ↑protein. Gram stain: rapid, high-yield — GPC diplococci = pneumococcus; GNC diplococci = meningococcus; small GNC coccobacilli = H. influenzae. Culture: definitive + susceptibility, slower. Latex agglutination/PCR: rapid adjuncts, esp. valuable if prior antibiotics already sterilized culture.

Treatment

DO NOT DELAY empirical antibiotics for confirmation (rapid fatal progression). Empirical: 3rd-gen cephalosporin (ceftriaxone/cefotaxime) backbone + vancomycin (resistant pneumococcus concern) + AMPICILLIN added for Listeria coverage in neonates/elderly/immunocompromised. Adjunctive DEXAMETHASONE — given with/before 1st antibiotic dose — reduces inflammation-mediated complications, best evidence = reduced hearing loss in pneumococcal meningitis. Same “treat host inflammatory response, not just organism” principle as PCP/cysticercosis.

Prevention

Conjugate vaccines (pneumococcal, meningococcal, Hib) = primary strategy, drives aetiology shifts noted above. Chemoprophylaxis (rifampicin, or cipro/ceftriaxone alt) — CLOSE CONTACTS of confirmed meningococcal case specifically (secondary case clustering risk via droplets). Targeted, not routine.

Age-Stratified Aetiology

Rather than a single organism, bacterial meningitis’s causative agent is strongly determined by patient age — a distinction that sets up the separate, dedicated discussion of neonatal aetiology under Neonatal Meningitis. In older children and adults, the two dominant pathogens are Streptococcus pneumoniae and Neisseria meningitidis (meningococcus), with Haemophilus influenzae type b (Hib) historically a major third cause, now sharply reduced in vaccinating populations — a genuinely important, testable illustration of routine childhood immunization (Hib conjugate vaccine) changing a disease’s dominant epidemiology, directly paralleling the same vaccine-driven epidemiological shift covered under Haemophilus influenzae Infections. Meningococcus carries particular epidemic significance, causing outbreaks (classically in the “meningitis belt” of sub-Saharan Africa) via nasopharyngeal carriage and droplet spread, and is distinctively associated with a petechial/purpuric rash reflecting the organism’s propensity for bloodstream invasion and disseminated intravascular coagulation in fulminant meningococcemia (Waterhouse-Friderichsen syndrome, with bilateral adrenal haemorrhage, being the most severe, rapidly fatal presentation) — a genuinely distinctive clinical sign among the meningitis pathogens, worth remembering as specifically meningococcal.

Pathogenesis

All three major organisms share a common general route to meningitis: nasopharyngeal colonization, followed by bloodstream invasion (bacteraemia), and finally crossing the blood-brain barrier to seed the meninges and cause a purulent (pyogenic) inflammatory exudate within the subarachnoid space — the resulting inflammatory response, more than direct bacterial toxicity alone, drives much of the clinical picture (raised intracranial pressure, cerebral oedema, and the risk of long-term neurological sequelae from inflammation-mediated tissue injury), which is precisely why adjunctive anti-inflammatory therapy (below) has a genuine, evidence-based role alongside antibiotics.

Clinical Manifestations

The classic triad — fever, neck stiffness (nuchal rigidity), and altered mental status — together with headache and photophobia, defines the syndrome, though genuinely worth remembering that the complete triad is not always present, particularly at the extremes of age. Kernig’s and Brudzinski’s signs are the classic bedside tests for meningeal irritation (Kernig’s: pain/resistance on passive knee extension with the hip flexed; Brudzinski’s: involuntary hip/knee flexion on passive neck flexion), taught as complementary confirmatory findings though neither is perfectly sensitive. Untreated or inadequately treated disease can progress rapidly to seizures, coma, and death, with survivors at real risk of long-term sequelae including hearing loss (a genuinely important, specifically testable complication, particularly associated with pneumococcal meningitis) and other neurological deficits.

Laboratory Diagnosis

Lumbar puncture with CSF analysis is the diagnostic cornerstone (see CSF Examination in Meningitis for the detailed comparative CSF-parameter framework across meningitis types) — bacterial meningitis classically shows markedly elevated opening pressure, cloudy/turbid CSF appearance, a neutrophil-predominant pleocytosis, markedly low glucose (reflecting bacterial glucose consumption — a genuinely important, specifically testable distinguishing feature from the normal-glucose pattern of viral meningitis), and elevated protein. Gram stain of CSF, feasible rapidly at the bedside/laboratory, often directly visualizes and reasonably reliably suggests the causative organism by its stain and morphology (gram-positive diplococci suggesting pneumococcus, gram-negative diplococci suggesting meningococcus, small gram-negative coccobacilli suggesting H. influenzae), making it a genuinely high-yield, rapid test disproportionate to its simplicity. CSF culture remains the definitive confirmatory test and allows antimicrobial susceptibility testing, though results take longer than the Gram stain’s immediate turnaround; latex agglutination and PCR-based rapid antigen/molecular panels are increasingly used adjuncts, particularly valuable when prior antibiotic treatment has already sterilized the CSF culture.

Treatment

Empirical antibiotic therapy should not be delayed for diagnostic confirmation given the disease’s rapid, potentially fatal progression — a third-generation cephalosporin (ceftriaxone or cefotaxime) forms the backbone of empirical coverage against the major pathogens, with vancomycin added where resistant pneumococcal strains are a concern, and ampicillin added specifically to cover Listeria monocytogenes in neonates, the elderly, and the immunocompromised (a genuinely important, age/immune-status-triggered addition to the standard regimen, distinct from the core three-organism coverage). Adjunctive dexamethasone, given concurrently with or just before the first antibiotic dose, has a genuine, evidence-based role — specifically in reducing inflammation-mediated complications, most robustly demonstrated for reducing hearing loss in pneumococcal meningitis — directly illustrating, alongside PCP and cysticercosis, the broader principle that the host’s own inflammatory response to organism killing can itself be a meaningful target of adjunctive treatment, separate from antimicrobial therapy targeting the organism.

Prevention

Conjugate vaccines against the three major pathogens — pneumococcal conjugate vaccine, meningococcal conjugate vaccine, and Hib conjugate vaccine — form the primary public-health prevention strategy and are responsible for the substantial epidemiological shifts in causative-organism frequency noted above. Chemoprophylaxis (typically rifampicin, or alternatively ciprofloxacin/ceftriaxone) is specifically indicated for close contacts of a confirmed meningococcal meningitis case, given the organism’s genuine potential for secondary case clustering via respiratory droplet transmission — a targeted, contact-triggered intervention distinct from routine population-wide vaccination.