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Clinical Scenario: Bacillary Dysentery

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Q-1: Most Probable Causative Agent

Sherris & Ryan's Medical Microbiology, 8th Ed. — "All Shigella species are nonmotile… The genus is divided into four species defined by biochemical reactions and specific O antigens."

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Q-2: All Species of Shigella That Can Cause Dysentery

Red Book 2021 — "Four species (with more than 40 serotypes) have been identified."

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Q-3: Steps of Laboratory Diagnosis

Step 1 — Specimen Collection

• Fresh stool or rectal swab (pass immediately to lab within 2 hours, or use Cary-Blair transport medium at 4°C if delayed)
• Blood culture in severely ill/immunocompromised patients (bacteremia is rare)

Step 2 — Direct Microscopy

• Wet mount and methylene blue stained smear of stool
• Reveals: pus cells (neutrophils), RBCs, and macrophages → confirms invasive (exudative) diarrhea
• Fecal lactoferrin detection is sensitive for colitis (not specific for Shigella)

Step 3 — Culture

• MacConkey agar: Shigella produces pale/colorless (NLF) colonies (non-lactose fermenting)
• Deoxycholate citrate agar (DCA) or XLD agar (Xylose-Lysine-Deoxycholate): selective media for Shigella/Salmonella; Shigella forms pale pink/colorless colonies (no H₂S, unlike Salmonella)
• Selenite F broth or GN broth: enrichment media to improve yield
• Hektoen Enteric (HE) agar: another selective medium

Step 4 — Biochemical Identification

• Glucose fermented (with acid, no gas)
• Lactose not fermented
• H₂S not produced (unlike Salmonella)
• Urease negative
• Motility negative
• IMViC pattern: typically I+, M−, V−, C−

Step 5 — Serological Typing

• Slide agglutination with polyvalent and specific antisera (A, B, C, D serogroup antisera)
• Identifies the serogroup (A = S. dysenteriae, B = S. flexneri, C = S. boydii, D = S. sonnei)

Step 6 — Molecular Methods (Gold Standard)

• Multiplex PCR / NAAT (Nucleic Acid Amplification Tests): high sensitivity for detecting Shigella and differentiating from EIEC
• If PCR is positive, stool culture is still recommended to guide susceptibility testing
• Mass spectrometry (MALDI-TOF) cannot distinguish Shigella from E. coli — not recommended alone

Step 7 — Antibiotic Susceptibility Testing

• Mandatory due to widespread multidrug resistance

Red Book 2021, Medical Microbiology 9e

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Q-4: Treatment

1. Supportive (Mainstay)

• Oral rehydration solution (ORS) — severe dehydration is rare but fluid/electrolyte correction is essential
• Mild S. sonnei infections are self-limited (48–72 hrs) and may not require antibiotics

2. Antimicrobial Therapy

⚠️ Avoid: Loperamide and antidiarrheal agents (slow GI transit, worsen disease)

3. Infection Control

• Handwashing, proper disposal of soiled linens
• Isolation of cases to prevent fecal-oral spread

Harrison's Principles of Internal Medicine 22E — "With effective antibiotic therapy, clinical improvement occurs within 48 h, resulting in decreased risk of complications and death, shorter duration of symptoms, and elimination of Shigella from stools."

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Q-5: Hemolytic Uremic Syndrome (HUS)

1. Microangiopathic hemolytic anemia (MAHA)
2. Thrombocytopenia
3. Acute kidney injury (AKI)

Pathogenesis in Shigella

• Shiga toxin (Stx) produced by S. dysenteriae type 1 is the key virulence factor
• Stx is absorbed from the gut → enters bloodstream → binds Gb3 receptors on renal glomerular endothelial cells → disrupts protein synthesis → endothelial damage and microvascular thrombosis → occludes glomerular capillaries → acute renal failure
• Damaged RBCs are sheared through thrombi → hemolysis; platelet consumption → thrombocytopenia

Classification

• Typical (diarrhea-positive) HUS: 90% of cases — caused by Shiga toxin-producing organisms (E. coli O157:H7 most common; Shigella dysenteriae type 1; Streptococcus pneumoniae)
• Atypical (diarrhea-negative) HUS: 10% — hereditary complement dysregulation, pregnancy, malignancy, drugs

Clinical Features

• Prodrome: bloody diarrhea, abdominal pain, fever
• After 5–10 days: pallor (anemia), oliguria/anuria, petechiae
• May have neurologic complications (seizures, altered consciousness from uremia/intracranial hemorrhage)

Management

• Supportive: IV fluids, electrolyte management, blood transfusion for severe anemia, dialysis if renal failure progresses
• Avoid antibiotics in EHEC-related HUS (lysis releases more Stx → worsens outcome)
• For Shigella HUS: antibiotics are generally used to treat the underlying infection
• Avoid: loperamide, antiperistaltics, platelet transfusion (unless significant bleeding)
• Atypical HUS: eculizumab (anti-C5 complement inhibitor), plasmapheresis, renal transplant in severe cases

Rosen's Emergency Medicine — "HUS consists of acute kidney injury, thrombocytopenia, and microangiopathic hemolytic anemia, occurring secondary to an inciting etiology." Janeway's Immunobiology 10e — "S. dysenteriae produces hemolytic uremic syndrome, named for its intravascular destruction of RBCs (hemolysis) and damage to kidney function (uremia)."

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Clinical Scenario: Syphilis

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Q-1: Most Probable Clinical Diagnosis

Harrison's Principles of Internal Medicine 22E — "The typical primary chancre usually begins as a single painless papule that rapidly erodes and becomes indurated, with a characteristic cartilaginous consistency on palpation of the edge and base of the ulcer."

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Q-2: Laboratory Diagnosis Tests for Syphilis

A. Direct Detection Methods

1. Darkfield Microscopy (Gold standard for primary syphilis)
   • Scrape the base of the chancre → place on slide → visualize under darkfield
   • T. pallidum appears as a corkscrew-shaped spirochete with characteristic motility
   • Immediate diagnosis; most useful in primary syphilis (before serology turns positive)
   • Limitation: requires specialized equipment and trained personnel
2. Direct Fluorescent Antibody Test (DFA-TP)
   • Uses fluorescence-labeled antibodies to identify T. pallidum in smears
   • Alternative to darkfield microscopy
3. PCR (Nucleic Acid Amplification Test)
   • Highly sensitive; detects T. pallidum DNA from lesion exudate, CSF, or blood
   • Research/reference labs; increasingly available clinically

B. Serological Tests

Non-treponemal (Screening) Tests — detect cardiolipin antibodies (non-specific)

• Sensitivity: ~70–80% in primary syphilis; rises to ~100% in secondary syphilis
• False positives: pregnancy, autoimmune diseases (SLE), endocarditis, viral infections, malaria
• Titers rise with active infection and fall after successful treatment → used to monitor treatment response

Treponemal (Confirmatory) Tests — detect anti-T. pallidum antibodies (specific)

• Once reactive, remain positive for life (even after cure) — NOT for monitoring treatment

C. Testing Algorithm

D. CSF Examination

• Required if neurosyphilis suspected (CSF-VDRL, cell count, protein)

E. Other Supporting Tests

• HIV serology (mandatory — strong STI co-association)
• Biopsy of lesion with silver staining (Warthin-Starry/Levaditi stain) to demonstrate spirochetes

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Q-3: Signs and Symptoms of Later Stages

Stage 2: Secondary Syphilis (4–10 weeks after primary; hematogenous dissemination)

• Generalized maculopapular rash — begins on trunk, spreads to palms and soles (hallmark — few other rashes involve palms and soles)
• May be macular, papular, papulosquamous, or pustular
• Condyloma lata — broad-based, flat, moist warty lesions on genitalia/perineum (highly infectious)
• Mucous patches — shallow erosions in mouth/throat
• "Moth-eaten" alopecia — patchy hair loss of scalp, eyebrows, beard (~5%)

• Generalized, nontender, rubbery lymphadenopathy
• Epitrochlear lymphadenopathy — particularly suggestive of secondary syphilis

• Low-grade fever, malaise, headache, myalgias, anorexia, weight loss

• Hepatitis (raised LFTs — 25% cases)
• Nephropathy — immune complex glomerulonephritis → nephrotic syndrome
• Uveitis/iritis — anterior uveitis (5–10%); risk of permanent blindness if untreated
• Otic syphilis — sensorineural hearing loss, tinnitus, vertigo
• Meningitis (early neurosyphilis)
• Arthritis, periostitis

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Stage 3: Latent Syphilis

• No clinical signs/symptoms
• Positive serology with normal CSF
• Early latent: <1 year; Late latent: ≥1 year (or unknown)
• Patient may still transmit congenitally (to fetus)

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Stage 4: Tertiary/Late Syphilis (years to decades later; 25–40% of untreated)

• Gumma = granulomatous inflammatory lesion with central necrosis
• Affects skin, bones, liver, testes, brain
• Punched-out skin ulcers; bone pain; hepatosplenomegaly

• Aortitis (most common) — affects ascending aorta
• Aortic aneurysm (saccular, ascending aorta)
• Aortic regurgitation — widening of aortic root
• Narrowing of coronary ostia → angina

• Meningovascular syphilis — strokes in young people
• General Paresis (GPI — General Paralysis of the Insane):
  • Dementia, personality change, grandiosity, tremors, dysarthria, Argyll Robertson pupil
• Tabes Dorsalis:
  • Degeneration of posterior columns and dorsal roots
  • Lightning pains (lancinating), ataxia, loss of proprioception, Romberg positive
  • Argyll Robertson pupil — accommodates but does not react to light ("prostitute's pupil")
  • Charcot's joint (neuropathic arthropathy)

Rosen's Emergency Medicine — "Tertiary syphilis, which includes cardiovascular manifestations and gummatous disease, is uncommon in the United States. Aortitis, aortic aneurysm, and gummatous lesions of the skin, bones, and other organs may be seen."

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Q-4: What is Soft Chancre?

Key Features vs. Hard Chancre (Syphilitic Chancre):

Sherris & Ryan's Medical Microbiology, 8th Ed. — "The inflammation around the ulcer has caused the primary lesion to be called 'soft chancre' to distinguish it from the primary syphilitic chancre, which is typically indurated and painless."

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Q-5: Other Sexually Transmitted Infections (STIs)

Bacterial STIs

Viral STIs

Parasitic/Protozoan STIs

Rosen's Emergency Medicine — Broad categories of STI syndromes: (1) Genital ulcers — herpes, syphilis, chancroid, LGV; (2) Genital discharge — gonorrhea, chlamydia, NGU; (3) Epithelial cell lesions — genital warts (HPV), molluscum; (4) Ectoparasites — pubic lice, scabies.

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🩺 VIVA CASE — 2nd Year Microbiology

Pneumonia caused by Streptococcus pneumoniae (Pneumococcal Pneumonia)

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📋 CASE SCENARIO

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❓ VIVA QUESTIONS & ANSWERS

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Q1. What is the most probable diagnosis?

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Q2. What is the causative agent? Give its full classification.

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Q3. What are the virulence factors of S. pneumoniae?

1. Polysaccharide Capsule (most important)
   • Antiphagocytic — prevents opsonization and phagocytosis in the absence of specific anticapsular antibodies
   • 92+ antigenic serotypes — allows repeated infections
   • Binds mucus poorly → facilitates colonization of respiratory mucosa
   • Target of protective immunity and vaccines
2. Pneumolysin
   • Secreted pore-forming toxin
   • Inhibits ciliary function → impairs mucociliary clearance
   • Limits complement opsonization
   • Promotes inflammation via cytokine production and T-cell activation
   • Modulates reactive oxygen species
3. Pneumococcal Surface Proteins A and C (PspA, PspC)
   • Inhibit complement opsonization
4. IgA Protease
   • Cleaves secretory IgA → facilitates colonization of mucosal surfaces
5. Autolysin (LytA)
   • Causes autolysis → releases cell wall components that trigger inflammation
   • Basis for bile solubility test
6. Lipoteichoic Acid / C-substance (Cell Wall)
   • Activates complement, induces cytokine production

Murray & Nadel's Textbook of Respiratory Medicine — "S. pneumoniae is an obligate extracellular pathogen because it is killed rapidly after being phagocytosed by neutrophils or macrophages. Therefore, its virulence strategies have principally evolved to evade phagocytosis."

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Q4. What is the pathogenesis of pneumococcal pneumonia?

1. Colonization — S. pneumoniae colonizes the nasopharynx (carried asymptomatically by 5–40% of healthy adults and up to 50% of children)
2. Predisposing factors weaken defenses — viral URTI (e.g., influenza), smoking, alcohol, immunosuppression → impair mucociliary clearance, cough reflex, alveolar macrophage function
3. Aspiration into lower airway — bacteria reach alveoli; if alveolar macrophages cannot clear them (especially without opsonizing antibodies), infection establishes
4. Neutrophil recruitment — macrophages signal via TLR2, NLR inflammasomes → recruit neutrophils → robust inflammatory response
5. Inflammatory exudate — fills alveoli → consolidation → impaired gas exchange → hypoxia
6. Bacteremia — occurs in 25–30% of cases; spread to meninges, heart valves, joints

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Q5. What are the four pathological stages of Lobar Pneumonia?

If resolution fails → organization (fibrosis) or lung abscess (rare in S. pneumoniae)

Robbins, Cotran & Kumar Pathologic Basis of Disease — "In the first stage of congestion, the lung is heavy, boggy, and red… Red hepatization: neutrophils, red cells, and fibrin fill the alveolar spaces. The lobe is red, firm, and airless, with a liver-like consistency."

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Q6. What are the clinical features of pneumococcal pneumonia?

• Sudden with shaking rigors (classic!)
• High-grade fever (39–40°C), tachycardia, tachypnea

• Productive cough with rust-colored (rusty/blood-tinged) sputum — pathognomonic
• Pleuritic chest pain — sharp, worse on breathing/coughing
• Dyspnea

• Dullness to percussion (consolidation)
• Increased vocal fremitus/resonance
• Bronchial breath sounds, crepitations
• Pleural friction rub

• Lobar consolidation — homogeneous opacity of one lobe (classic)
• Air bronchograms may be seen

• Sustained fever 5–10 days → sudden "crisis" (sudden fall in temperature + improvement) = antibody-mediated opsonization overwhelms bacteria

Sherris & Ryan's Medical Microbiology, 8th Ed. — "Pneumococcal pneumonia begins abruptly with a shaking chill and high fever. Cough with production of sputum pink to rusty in color and pleuritic chest pain are common."

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Q7. What are the laboratory diagnostic tests for pneumococcal pneumonia?

Step 1 — Specimen Collection

• Sputum (early morning, deep cough, before antibiotics)
• Blood (for cultures — bacteremia in 25–30%)
• Urine (for antigen test)
• Pleural fluid (if effusion present)
• CSF (if meningitis suspected)

Step 2 — Direct Microscopy

• Gram Stain of sputum:
  • Gram-positive, lancet-shaped (flame-shaped) diplococci
  • Surrounded by halo = capsule
  • Numerous neutrophils (pus cells) in good-quality sputum
  • Absence of other predominant flora = strongly suggestive

Step 3 — Culture

• Blood agar with 5–10% CO₂ at 37°C overnight
• Colonies: small, grey, mucoid, with α-hemolysis (green zone = partial hemolysis)
• Colonies may show central dimpling (due to autolysis) with time

Step 4 — Identification Tests

Step 5 — Blood Culture

• Aerobic blood culture bottles; incubate 37°C
• Identifies bacteremia; same identification tests applied
• Sensitivity decreased if antibiotics given before culture

Step 6 — Rapid Tests

• Urinary Pneumococcal Antigen Test (immunochromatographic strip)
  • Detects C-polysaccharide (pneumococcal cell wall antigen) in urine
  • Sensitivity ~70–80%; Specificity >95%
  • Useful when cultures negative (e.g., after antibiotics)
  • Cannot provide antibiotic susceptibility information
• Multiplex PCR / FilmArray Respiratory Panel
  • Detects S. pneumoniae DNA from BAL or sputum
  • High sensitivity; increasingly available

Step 7 — Antibiotic Susceptibility Testing (AST)

• E-test or Kirby-Bauer disc diffusion for penicillin, macrolides, cephalosporins
• MIC determination: Penicillin susceptible ≤2 μg/mL; resistant ≥8 μg/mL
• Mandatory due to increasing resistance rates

Step 8 — Chest X-Ray / CT Chest

• Lobar consolidation, air bronchograms
• Rule out effusion, abscess, empyema

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Q8. What are the complications of pneumococcal pneumonia?

• Pleural effusion — ~25% of cases
• Empyema — purulent pleural fluid (less common)
• Lung abscess — rare (more common with serotype 3)
• ARDS

• Pneumococcal Meningitis — most feared complication; high mortality and neurological sequelae
• Septicemia / Septic shock
• Endocarditis — can affect normal or damaged valves
• Arthritis (septic)
• Peritonitis (especially in cirrhosis/ascites)
• Otitis media, Sinusitis — common in children

• Asplenia/splenectomy → fulminant pneumococcemia, high mortality
• Elderly, immunocompromised, multiple myeloma, HIV, chronic lung disease, diabetes

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Q9. What is the treatment for pneumococcal pneumonia?

1. General / Supportive

• Bed rest, adequate hydration, nutrition
• Supplemental oxygen if SpO₂ <94%
• Antipyretics (paracetamol) for fever and pleuritic pain
• Treat underlying conditions

2. Antibiotic Therapy

• β-Lactam + Macrolide (e.g., ceftriaxone + azithromycin) — evidence suggests better outcomes

• Due to altered penicillin-binding proteins (PBPs) — NOT β-lactamase production
• Anti-pneumococcal cephalosporins (ceftriaxone, cefotaxime) retain activity against 75–95% of resistant strains
• Avoid antibiotics used in previous 90 days

• Non-dysenteriae strains: 5–7 days (outpatient mild)
• Hospitalized: 7–14 days guided by clinical response

Clinical response with appropriate antibiotics expected within 24–48 hours.

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Q10. What is the prevention? What vaccines are available?

• Smoking cessation
• Influenza vaccination (influenza predisposes to pneumococcal superinfection)
• Good nutrition, treatment of underlying diseases
• Infection control in hospitals

PCV has markedly decreased invasive pneumococcal infections in children, with secondary reduction in adults through herd immunity (reduced colonization = reduced transmission).

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Q11. What are other diseases caused by S. pneumoniae?

1. Lobar Pneumonia (most common serious infection)
2. Meningitis — leading cause in adults; high mortality and neurological sequelae
3. Otitis Media — most common cause in children
4. Sinusitis — common bacterial cause
5. Bacteremia — primary bacteremia, especially in children and asplenic patients
6. Endocarditis — infective endocarditis (normal or damaged valves)
7. Peritonitis — spontaneous in cirrhosis/nephrotic syndrome
8. Septic arthritis

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Q12. How do you differentiate S. pneumoniae from Viridans streptococci on culture?

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Q13. What is the Quellung (Neufeld) reaction?

1. Confirm the presence of a capsule on S. pneumoniae
2. Identify the specific serotype

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Q14. What is the significance of rust-colored sputum?

• Inflammatory exudate in alveoli contains red blood cells (RBCs)
• RBCs break down → hemoglobin degradation products give the sputum its characteristic rust/blood-tinged appearance
• Indicates alveolar hemorrhage as part of the exudative consolidation
• Seen in the red hepatization stage of lobar pneumonia
• Highly characteristic of S. pneumoniae pneumonia (though not pathognomonic)

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Q15. What is the CURB-65 score? (Bonus clinical question)

• Score 0–1: Low severity → outpatient treatment
• Score 2: Moderate → supervised outpatient or short admission
• Score 3–5: High severity → hospital admission / consider ICU

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📌 QUICK REVISION SUMMARY

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🩺 VIVA CASE — 2nd Year Microbiology

MENINGITIS — Complete Viva Guide

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📋 CASE SCENARIO

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❓ VIVA QUESTIONS & ANSWERS

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Q1. What is the most probable diagnosis?

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Q2. Define Meningitis. What are the types?

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Q3. What are the causative agents of bacterial meningitis — by age group?

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Q4. What are the signs of meningeal irritation? Describe them.

1. Nuchal Rigidity (Neck stiffness) — patient cannot flex the neck; resistance to passive flexion due to paraspinal muscle spasm
2. Kernig's Sign — with patient supine and hip flexed at 90°, attempt to extend the knee → pain and resistance (hamstring spasm) — positive if extension limited to <135°
3. Brudzinski's Sign
   • Neck sign: passive flexion of neck → involuntary flexion of knees and hips
   • Contralateral leg sign: flexion of one leg → involuntary flexion of opposite leg
4. Photophobia — sensitivity to light (meningeal inflammation)
5. Phonophobia — sensitivity to sound
6. Jolt accentuation — worsening of headache on horizontal head rotation (2–3 times/sec) — sensitive sign for meningitis

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Q5. Describe the pathogenesis of bacterial meningitis.

1. Colonization of nasopharynx by organism (e.g., N. meningitidis, S. pneumoniae)
2. Local invasion — organisms cross mucosal barrier → enter bloodstream → bacteremia
3. Seeding of meninges — bacteria cross the blood-brain barrier (BBB) via:
   • Transcytosis through endothelial cells
   • Paracellular passage (aided by bacterial surface proteins)
   • Trojan horse mechanism (via infected monocytes)
4. Subarachnoid space infection — organisms multiply in CSF (poor immune defense: low Ig, complement, phagocytes in CSF)
5. Inflammatory cascade — bacterial cell wall components (LPS in Gram-negatives; teichoic acid in Gram-positives) activate macrophages and microglia → release IL-1β, TNF-α, IL-6, IL-8
6. BBB disruption → cerebral edema (vasogenic + cytotoxic)
7. Complications: raised intracranial pressure, cerebral ischemia, cranial nerve palsies, hydrocephalus, sensorineural hearing loss

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SECTION A: ACUTE BACTERIAL (PYOGENIC) MENINGITIS

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Q6. What are the clinical features of acute bacterial meningitis?

• Fever (>38°C)
• Neck stiffness
• Altered mental status/confusion

• Severe headache ("thunderclap" — worst of life)
• Photophobia, phonophobia
• Nausea, vomiting
• Seizures (~30%)
• Cranial nerve palsies (III, IV, VI, VII)
• Papilledema (raised ICP)
• Petechial/purpuric rash — specific to N. meningitidis (meningococcemia)
• Waterhouse-Friderichsen syndrome (meningococcal adrenal hemorrhage → septic shock)

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Q7. Describe the CSF findings in Acute Bacterial Meningitis.

"High WBC (>1000/mm³) with neutrophil predominance, low glucose (<40 mg/dL or <40% of blood glucose), and high protein (>160 mg/dL) are nearly diagnostic of acute bacterial meningitis." — Textbook of Family Medicine 9e

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Q8. What are the laboratory investigations for acute bacterial meningitis?

Step 1 — Blood Tests (before LP if mass lesion suspected)

• CBC — leukocytosis (raised WBC), neutrophilia
• Blood cultures × 2 (before antibiotics — positive in 50–80%)
• CRP, Procalcitonin — markedly elevated; help distinguish bacterial from viral
• Blood glucose (for CSF:blood glucose ratio)
• Serum electrolytes, renal function (SIADH is a complication)
• Coagulation profile — DIC in meningococcemia

Step 2 — Imaging (before LP if indicated)

• CT head — mandatory BEFORE LP if: papilledema, focal neurological signs, seizures, immunocompromised, or GCS <10 (risk of herniation)
• MRI with gadolinium — shows meningeal enhancement, hydrocephalus, cerebritis

Step 3 — Lumbar Puncture (LP) — MOST IMPORTANT

• Appearance, opening pressure
• Cell count & differential
• Glucose + simultaneous blood glucose
• Protein
• Gram stain (60–90% sensitivity)
• Culture & sensitivity (gold standard — >70% sensitivity)
• Latex agglutination test — rapid antigen detection for S. pneumoniae, N. meningitidis, H. influenzae, Group B Strep
• PCR / FilmArray panel — detects 14 organisms simultaneously (bacterial + viral + yeast); high sensitivity; increasingly preferred

Step 4 — Special Microbiological Tests

• Countercurrent immunoelectrophoresis (CIE) — antigen detection (now largely replaced by PCR)
• Limulus amoebocyte lysate (LAL) test — detects Gram-negative endotoxin; rapid but non-specific

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Q9. What are the specific causative agents, their Gram stain appearance, and key features?

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Q10. What is the treatment of acute bacterial meningitis?

Principle: Medical EMERGENCY — antibiotics within 60 minutes of arrival

Empirical Treatment (before organism identified):

Pathogen-Directed Therapy:

Adjunctive Therapy:

• Dexamethasone 0.15 mg/kg IV q6h × 4 days — started 20–30 minutes BEFORE or with first antibiotic dose
• Reduces TNF-α and IL-1β production → decreases BBB disruption, cerebral edema, meningeal inflammation
• Proven benefit for S. pneumoniae meningitis (reduces neurological sequelae, sensorineural hearing loss, mortality)
• Give before antibiotics — no benefit if given after

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SECTION B: TUBERCULOUS (TB) MENINGITIS — Subacute

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Q11. What is Tuberculous Meningitis? Who gets it?

• Immunocompromised (HIV/AIDS — most important)
• Children <5 years
• Malnourished
• Chronic alcohol use
• Homeless, overcrowded conditions
• Migrants from TB-endemic regions

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Q12. What are the clinical features of TB meningitis?

• Malaise, fatigue, loss of appetite
• Low-grade fever, night sweats
• Weight loss
• Behavioral changes, irritability

• Severe headache (persistent, progressive)
• Neck stiffness (meningismus)
• Vomiting
• Photophobia

• Cranial nerve palsies — CN III, IV, VI (basal meningitis affects basal cisterns)
• Hydrocephalus (communicating — blockage of CSF reabsorption)
• Stroke — tuberculous arteritis → focal deficits
• Seizures
• Coma

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Q13. What are the CSF findings in Tuberculous Meningitis?

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Q14. What are the laboratory diagnostic tests for TB Meningitis?

1. CSF Examination

• ZN (Ziehl-Neelsen) stain for AFB — sensitivity only 10–20% (low, but if positive = very specific)
• Multiple LP increases yield — repeat 3× on large volumes (≥10 mL)

2. CSF Culture (Gold Standard)

• Lowenstein-Jensen (LJ) medium or BACTEC MGIT 960 (automated liquid culture)
• Sensitivity: 45–80% (variable; takes 4–8 weeks for LJ)
• BACTEC MGIT: faster (1–3 weeks), higher sensitivity

3. Molecular Diagnosis

• GeneXpert MTB/RIF (Xpert assay) — real-time PCR; sensitivity ~80%; specificity >98%
• Preferred initial test per WHO guidelines
• Negative result does NOT exclude TB — requires further workup
• Also detects rifampicin resistance simultaneously

4. CSF ADA (Adenosine Deaminase)

• Level >8 U/L: rule-in for TB meningitis
• Level <4 U/L: rule-out
• Cannot distinguish from bacterial meningitis — use with clinical context

5. Other Supportive Tests

• Chest X-ray — miliary TB pattern in 50% of TB meningitis
• Mantoux/TST (tuberculin skin test) — may be negative in immunocompromised
• IGRA (Interferon Gamma Release Assay) — QuantiFERON-TB Gold
• CT/MRI brain — basal meningeal enhancement, hydrocephalus, periventricular infarcts, tuberculoma = characteristic
• Sputum AFB culture — positive in 40–50% (helps confirm diagnosis)

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Q15. What is the treatment of TB Meningitis?

Total duration = 12 months (longer than pulmonary TB because of poor CNS drug penetration)

• 0.4 mg/kg/day IV (tapering over 6–8 weeks)
• Reduces mortality by ~25% (meta-analysis)
• Reduces CSF inflammation and ICP
• Caution: No proven benefit in HIV-positive patients (recent trial)

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SECTION C: VIRAL (ASEPTIC) MENINGITIS

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Q16. What is Aseptic Meningitis? What are its causes?

1. Enteroviruses (most common — 85–95% of viral meningitis): Echovirus, Coxsackievirus A/B
2. Herpes Simplex Virus-2 (HSV-2) — recurrent aseptic meningitis (Mollaret's meningitis)
3. Mumps virus (rare now with vaccination)
4. HIV (acute seroconversion illness)
5. VZV (Varicella-Zoster Virus)
6. Arbovirus (West Nile Virus, Japanese Encephalitis)
7. Lymphocytic Choriomeningitis Virus (LCMV)

• Drugs (NSAIDs, trimethoprim, IVIG)
• Carcinomatous meningitis
• Sarcoidosis
• SLE (systemic lupus erythematosus)

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Q17. What are the CSF findings in Viral (Aseptic) Meningitis?

Key point: In early viral meningitis (first 48h), PMNs may predominate — this can mimic bacterial meningitis. Repeat LP after 24h shows shift to lymphocytes.

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Q18. What are the laboratory diagnostic tests for Viral Meningitis?

1. CSF PCR — gold standard; FilmArray Meningitis/Encephalitis (ME) Panel detects:
   • HSV-1, HSV-2, VZV, Enterovirus, HHV-6, Human Parechovirus
   • Very high sensitivity; result in 1 hour
2. Enterovirus RT-PCR — most sensitive test for enteroviral meningitis
3. HSV PCR — highly sensitive and specific for HSV meningitis/encephalitis
4. Viral cultures — slow, low sensitivity (mostly replaced by PCR)
5. West Nile Virus — CSF IgM (more sensitive than PCR for WNV)
6. Serology (paired sera) — 4-fold rise in antibody titre in convalescent vs acute phase
7. Throat swab, stool — Enteroviruses can be isolated from these sites

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SECTION D: FUNGAL / CRYPTOCOCCAL MENINGITIS

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Q19. What is Cryptococcal Meningitis?

• HIV/AIDS (CD4 <100 cells/μL) — most important; commonest life-threatening fungal infection in HIV
• Organ transplant recipients
• Corticosteroid therapy
• Lymphoma, sarcoidosis
• Rare in immunocompetent hosts

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Q20. What are the CSF findings in Cryptococcal Meningitis?

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Q21. What are the laboratory diagnostic tests for Cryptococcal Meningitis?

1. India Ink Preparation (Negative Stain) (classic test)
   • CSF + India ink on slide → yeast cells appear as clear halos (unstained polysaccharide capsule) against black background
   • Sensitivity: 50–80% in HIV patients; lower in immunocompetent
   • Rapid, cheap, widely available
2. Cryptococcal Antigen (CrAg) Detection (most sensitive test)
   • Latex agglutination or lateral flow assay (LFA) in CSF or serum
   • Sensitivity: >90%; Specificity: >95%
   • Also used for serum screening in HIV patients (CrAg screening programme)
   • Positive CrAg in serum = high risk for developing cryptococcal meningitis
3. CSF Fungal Culture
   • Sabouraud Dextrose Agar (SDA)
   • Cryptococcus grows as mucoid, cream-colored colonies
   • Definitive identification; urease positive; melanin production on birdseed/Niger seed agar
   • Takes 1–5 days
4. Mucicarmine stain / PAS stain (on tissue/biopsy) — stains polysaccharide capsule red
5. CT/MRI Brain — pseudocysts ("soap bubble lesions"), dilated Virchow-Robin spaces, hydrocephalus

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Q22. What is the treatment of Cryptococcal Meningitis?

• Serial LPs or CSF drainage — critical to manage extremely high intracranial pressure
• ART (antiretroviral therapy) in HIV — delay for 4–6 weeks after antifungal treatment started (to prevent IRIS)

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THE MASTER CSF COMPARISON TABLE

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ADDITIONAL VIVA QUESTIONS

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Q23. What is the significance of the petechial rash in meningitis?

• Mechanism: Endotoxin (LPS) → DIC (disseminated intravascular coagulation) → thrombocytopenia → small vessel thrombosis + hemorrhage into skin
• Starts as petechiae → coalesces into purpura → can progress to purpura fulminans (extensive skin necrosis)
• Indicates meningococcemia (meningococcal septicemia) — medical emergency
• Non-blanching on glass tumbler test

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Q24. What is Waterhouse-Friderichsen Syndrome?

• Massive bilateral adrenal hemorrhage → acute adrenal insufficiency
• Results from DIC and endotoxin-mediated vascular damage to adrenal glands
• Features: Sudden cardiovascular collapse, high fever, widespread purpuric rash, shock, coma, death
• Treatment: Immediate antibiotics + IV hydrocortisone + fluid resuscitation
• Mortality very high without immediate treatment

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Q25. What is the role of Dexamethasone in meningitis?

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Q26. What are the complications of meningitis?

• Septic shock, DIC (especially meningococcal)
• Raised ICP → cerebral herniation (most common cause of death)
• Seizures
• SIADH (hyponatremia)
• Cerebral vein thrombosis

• Sensorineural hearing loss (most common — especially S. pneumoniae, H. influenzae meningitis)
• Cognitive impairment, learning difficulties
• Hydrocephalus (communicating)
• Cranial nerve palsies
• Epilepsy
• Stroke/hemiplegia (TB arteritis)
• Visual impairment
• In neonates: cerebral palsy, intellectual disability

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Q27. What are the vaccines available for prevention of meningitis?

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📌 QUICK REVISION SUMMARY

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