MD Microbiology Paper-I — Model Answers (PG Level)

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SECTION A: LONG ANSWER QUESTIONS (Attempt Any Two) — 2×20 = 40 Marks

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Q.1(a) Role of Microbes in Immune-Mediated Disorders, Non-Communicable Diseases (NCDs), and Mental Health

Introduction

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Part I: Microbes and Immune-Mediated / Autoimmune Disorders

1.1 Mechanisms of Microbial-Induced Autoimmunity

1.2 Specific Autoimmune Diseases and Microbial Triggers

• S. pyogenes pharyngitis is the obligate antecedent.
• M-protein epitopes (pepM5) cross-react with cardiac myosin; antibodies also target the valve endothelium.
• The Aschoff body represents the pathological hallmark: granuloma with multinucleate giant cells in the myocardium.
• Prevention: Complete 10-day penicillin course; secondary prophylaxis with benzathine penicillin G monthly.

• Triggered by Chlamydia trachomatis (urogenital), Salmonella, Shigella, Campylobacter (enteric), or Yersinia (enteric).
• HLA-B27 is positive in ~75% of cases.
• Classic triad: urethritis + arthritis + conjunctivitis ("can't see, can't pee, can't climb a tree").

• The "hygiene hypothesis" and "old friends" hypothesis explain the rising T1DM incidence in industrialized nations: reduced microbial diversity impairs Treg induction.
• Coxsackievirus B4 infects beta cells and triggers anti-GAD65 antibodies.
• Bacteroides species excess and reduced Firmicutes are observed pre-diabetes in at-risk children.

• Epstein-Barr virus (EBV) is strongly implicated; EBV nuclear antigen 1 (EBNA1) mimics GlialCAM (a myelin-associated protein).
• A landmark 2022 cohort of 10 million US military personnel showed EBV infection preceded MS with an OR of 32.4.
• Gut microbiome: reduced Butyricicoccus and Prevotella in MS patients → reduced short-chain fatty acids (SCFAs) → impaired Treg induction.

• Mycobacterium avium subsp. paratuberculosis (MAP) is implicated in Crohn's disease (Johne's disease analog).
• Adherent-invasive E. coli (AIEC) colonize ileal mucosa in Crohn's.
• Reduced Faecalibacterium prausnitzii (major butyrate producer) is consistently observed.

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Part II: Microbes in Non-Communicable Diseases (NCDs)

2.1 Cardiovascular Disease (CVD)

• Chlamydia pneumoniae can be detected within atherosclerotic plaques by PCR and electron microscopy.
• Proposed mechanisms: direct intimal infection → cytokine-mediated inflammation → foam cell formation; heat-shock protein 60 (Hsp60) molecular mimicry with host Hsp60 on endothelium.
• Porphyromonas gingivalis (periodontal pathogen): bacteremia → platelet aggregation (via FimA adhesin) → thrombus; also activates TLR-2 and TLR-4.
• Oral microbiome dysbiosis is an independent risk factor for CVD (INTERHEART study supporting data).

• Chronic valvular damage from streptococcal endocarditis leads to non-infective structural heart disease.

2.2 Diabetes Mellitus

• Gut microbiome in T2DM: ↑ Collinsella aerofaciens (promotes gut permeability, increases LPS translocation) and ↓ Akkermansia muciniphila (impairs mucus layer).
• Endotoxemia from gram-negative gut flora (metabolic endotoxemia) chronically activates TLR-4 on adipocytes and hepatocytes → NF-κB → insulin resistance.
• H. pylori infection associated with insulin resistance via chronic low-grade inflammation and ghrelin dysregulation.

2.3 Cancer

2.4 Chronic Kidney Disease (CKD)

• Urinary microbiome dysbiosis with uropathogens causing recurrent UTIs → progressive renal scarring.
• Gut-kidney axis: uremic toxins (indoxyl sulfate, p-cresol) produced by dysbiotic gut microbiota promote renal tubular injury.

2.5 Chronic Obstructive Pulmonary Disease (COPD)

• Haemophilus influenzae, Moraxella catarrhalis, S. pneumoniae cause acute exacerbations; repeated bacterial colonization promotes neutrophilic inflammation → emphysema progression.
• Microbiome dysbiosis in lung (↑ Proteobacteria) correlates with COPD severity.

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Part III: Microbes and Mental Health (The Gut-Brain Axis)

3.1 The Microbiota-Gut-Brain Axis

1. Vagal nerve signaling: Enteroendocrine cells sense microbial metabolites (SCFAs, secondary bile acids) and signal via the vagus nerve to the brainstem.
2. Neuroendocrine / HPA axis: Dysbiosis activates intestinal immune cells → systemic inflammation → glucocorticoid dysregulation → hippocampal neurogenesis impairment.
3. Neurotransmitter precursors: Gut bacteria produce or modulate serotonin (~95% of body 5-HT is gut-derived), GABA, dopamine, and acetylcholine. Lactobacillus rhamnosus modulates GABA-A receptor expression (Bravo et al., PNAS 2011).
4. Immune-mediated neuroinflammation: LPS translocation → microglial activation → neuroinflammation (implicated in depression, Alzheimer's disease).

3.2 Depression and Anxiety

• Germ-free mice demonstrate exaggerated HPA stress responses normalized by Bifidobacterium infantis colonization.
• Clinical studies show lower Lactobacillus and Bifidobacterium counts in depressed patients (Jiang et al., J Psychiatr Res 2015).
• Fecal microbiota transplant (FMT) from depressed humans to germ-free rats induces depressive-like behavior.
• The "psychobiotic" concept: Lactobacillus helveticus R0052 + Bifidobacterium longum R0175 reduce anxiety and cortisol in clinical trials.

3.3 Schizophrenia

• Prenatal Toxoplasma gondii and influenza virus infections increase schizophrenia risk (dopaminergic hypothesis: T. gondii increases brain dopamine synthesis).
• Gut dysbiosis in schizophrenia: elevated Lactobacillus phage phiadh correlates with symptom severity.

3.4 Autism Spectrum Disorder (ASD)

• Clostridium species overgrowth produces propionic acid (PPA), which disrupts mitochondrial function and modulates neurotransmission.
• The "leaky gut" in ASD allows microbial LPS and other metabolites to cross the blood-brain barrier.
• Dysbiosis with ↓ Bifidobacterium and ↑ Clostridium is a consistent finding.
• FMT in ASD children showed sustained behavioral improvement in clinical trials.

3.5 Alzheimer's Disease

• Porphyromonas gingivalis (periodontal pathogen) found in post-mortem AD brains; gingipain proteases cleave tau and promote amyloid-β deposition.
• Gut dysbiosis increases amyloid-β production (the "gut-brain amyloid highway").
• Clostridiales and Ruminococcaceae are reduced; Bacteroidetes enrichment correlates with elevated CSF Aβ42 levels.

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Conclusion

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Q.1(b) Bacterial Disease Outbreak — Typing, Enumeration, Differential Methods, and Reference Centers

Introduction

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Step 1: Case Definition and Outbreak Confirmation

• Epidemiological linkage exists (common source, time-place clustering)
• Laboratory-confirmed isolates from ≥2 unrelated cases are identified
• Isolates share identical or closely related typing profiles (molecular epidemiology)

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Step 2: Enumeration Methods for Bacteria

A. Direct Count (Total Count)

B. Viable Count (Colony Count)

C. Indirect Methods

• Turbidimetry (McFarland standards): OD600 correlates with cell density; McFarland 0.5 ≈ 1.5 × 10⁸ CFU/mL (used for antibiotic sensitivity testing inoculum preparation).
• ATP bioluminescence: Quantifies cellular ATP; proportional to viable cell number.
• Limulus Amoebocyte Lysate (LAL) test: Detects gram-negative endotoxin; useful for parenteral drug testing.

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Step 3: Bacterial Typing Methods

A. Phenotypic Typing

B. Genotypic Typing

WGS in Outbreak Investigation (Current Best Practice)

• Distinguish community clusters within a hospital transmission chain
• Detect recombination and horizontal gene transfer
• Generate phylogenetic trees to trace epidemic spread
• Identify novel resistance determinants

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Step 4: Reference Centers

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Step 5: Typing of Specific Organisms with Examples

• Typing sequence: Antibiogram → Phage typing → PFGE (SmaI) → spa typing → MLST (ST8, ST22, ST239) → WGS for final confirmation
• Transmission map based on cgMLST SNP differences (<5 SNPs = likely transmission event)

• Confirm V. cholerae O1 El Tor by agglutination and TCBS growth
• Biotype: El Tor vs. Classical (Voges-Proskauer, polymyxin B sensitivity, phage typing)
• Serotype: Ogawa vs. Inaba (antisera agglutination)
• Molecular: ctxB genotype (classical vs. El Tor variant), O139 screening
• Reference: NICED Kolkata

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Conclusion

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Q.1(c) Waterborne Disease Outbreak — Comprehensive Clinical Scenario Answer

Background

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Sub-question 1: Likely Waterborne Diseases Given Symptoms and Untreated River Water (2 marks)

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Sub-question 2: Microbiological Tests for Disease-Causing Microorganisms (6 marks)

A. Specimen Collection

• Stool (rectal swab in outbreak — Stuart's or Cary-Blair transport medium)
• Blood (for typhoid, febrile cases — blood culture in BHI/bile broth)
• Water samples: 500 mL–2L in sterile containers for quantitative analysis

B. Qualitative Methods

C. Quantitative Methods

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Sub-question 3: Presumptive and Differential Coliform Count — Principles, Procedures, and Significance (6 marks)

Rationale for Coliform Testing

• They are present in large numbers in human/animal feces
• They are easy to culture and quantify
• Their presence signals potential co-contamination with enteric pathogens

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A. Presumptive Coliform Count (MPN Method — Multiple Tube Fermentation Technique)

1. Preparation of sample dilutions: 10⁻¹, 10⁻², 10⁻³ using sterile distilled water.
2. Inoculation:
   • 5 tubes of double-strength lactose broth (DSB) + 10 mL water
   • 5 tubes of single-strength lactose broth (SSB) + 1 mL water
   • 5 tubes of SSB + 0.1 mL water
   • Each tube contains an inverted Durham tube.
3. Incubation: 37°C for 24–48 hours.
4. Reading: A tube is presumptive positive if:
   • Gas is present in Durham tube (≥10% displacement), AND
   • Turbidity is visible.
5. MPN calculation: Note the combination of positive tubes across all three dilution sets. Consult the MacCrady MPN table to obtain the MPN/100 mL value.
   Example: If 5/5, 3/5, 1/5 tubes positive → MPN = 110/100 mL (WHO potable water standard: <1 MPN/100 mL; total absence in treated water).
6. Note: This is only PRESUMPTIVE because gas can be produced by non-coliform organisms (e.g., Clostridium).

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B. Confirmed Coliform Count (Confirmatory Test)

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C. Differential (Fecal) Coliform Count — Eijkman Test

1. From confirmed positive BGBB tubes, transfer one loopful to:
   • EC broth (Escherichia coli broth: tryptose, lactose, bile salts, dipotassium phosphate)
   • Incubate at 44.5 ± 0.2°C (water bath — temperature must be precise) for 24h.
2. Reading: Gas production in inverted Durham tube = fecal coliform positive.
3. MPN of fecal coliforms: Apply MPN tables to positive EC broth tubes.

• Filter 100 mL through 0.45 μm cellulose nitrate membrane.
• Place filter on m-FC agar (rosolic acid medium).
• Incubate at 44.5°C for 24h.
• Blue colonies = fecal coliforms; count and express as CFU/100 mL.

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D. Completed Coliform Test (IMViC Confirmation for E. coli)

• I = Indole (+): E. coli produces tryptophanase; red ring with Kovac's reagent
• M = Methyl Red (+): Mixed acid fermentation → pH <4.4
• V = Voges-Proskauer (−): No acetoin production
• C = Citrate (−): Cannot use citrate as sole carbon source

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Sub-question 4: Interpretation of Results and Public Health Response (6 marks)

Interpreting Results

Immediate Interventions (Short-term)

1. Notify District Medical Officer (DMO) and State Health Department — mandatory under IDSP (Integrated Disease Surveillance Programme) Epidemic Prone Disease reporting.
2. Boil Water Advisory: Issue immediate advisory to boil all water for ≥1 min before consumption.
3. Oral Rehydration Therapy (ORT) centers: Set up in the village for active case management (particularly for cholera).
4. Chlorination of drinking water source: Distribute ORS sachets and sodium hypochlorite (bleach) solution (1% available chlorine, 0.5 mg/L residual in water).
5. Temporary water supply: Deploy tanker supply of safe treated water.
6. Mass mobilization: Identify all symptomatic cases via door-to-door survey; admit severe dehydration cases.
7. Isolate severe cases: Especially cholera patients — oral/IV rehydration; Doxycycline / Azithromycin single-dose.
8. Oral cholera vaccine (Shanchol): If cholera confirmed — reactive vaccination in outbreak setting (WHO recommendations).

Long-term / Structural Interventions

1. Water treatment infrastructure: Install community chlorination unit / slow-sand filter + chlorination at point of source.
2. Protected dug wells or borewell construction: With sanitary seal and apron to prevent runoff contamination.
3. Toilet construction (Swachh Bharat Mission): Eliminate open defecation — the primary source of fecal coliform contamination.
4. Household water treatment: Promote ceramic pot filters, SODIS (solar disinfection), or low-cost chlorine tablet distribution.
5. Water quality surveillance: Establish quarterly MPN and fecal coliform testing schedule under JALMA or PHED (Public Health Engineering Department).
6. Health education: Handwashing with soap — WASH (Water, Sanitation, Hygiene) program integration with ASHA workers.
7. Environmental mapping: Survey animal grazing patterns near river to control zoonotic fecal contamination (Cryptosporidium from calves).
8. Sentinel surveillance under IDSP: P, L, and S form reporting to maintain ongoing community surveillance.

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SECTION B: SHORT ANSWER QUESTIONS (Attempt Any Six) — 6×10 = 60 Marks

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Q.2(a) Mycoplasma: Unique Features, Pathogenesis and Diagnosis of Atypical Pneumonia

Unique Features of Mycoplasma

• Mycoplasma is the only class of self-replicating bacteria completely devoid of a peptidoglycan cell wall.
• This renders them naturally resistant to all β-lactam antibiotics (penicillins, cephalosporins) and vancomycin (all act on cell wall synthesis).
• Also resistant to cycloserine, bacitracin, and fosfomycin.

• Genome size: 580–1350 kbp (the smallest known genomes of free-living organisms).
• M. genitalium has only 470 genes — the metabolic minimum for autonomous life (requires exogenous cholesterol for membrane synthesis).

• Without a rigid cell wall, they form variable shapes — round, filamentous, branching — and cannot be Gram stained.
• Dienes stain (methylene blue-azure): Used for identification in culture.

• Unusual for prokaryotes; acquire cholesterol from the host or culture medium.
• Eaton's agar (PPLO — pleuropneumonia-like organism medium): Contains 20% horse serum for cholesterol.

• Colonies on PPLO agar (Hayflick medium): 0.1–0.3 mm, granular center embedded in agar (due to growth into gel) surrounded by flat peripheral fringe → resembles fried egg.
• Visible only under ×10 dissecting microscope.

• Generation time: 1–3 hours; primary isolation may take 7–21 days.

• Pass through 0.45 μm bacterial filters (historically confused with viruses).

• Digitonin sensitivity distinguishes Mycoplasma (sensitive) from Acholeplasma (resistant).

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Atypical Pneumonia (Primary Atypical Pneumonia — PAP)

• Mycoplasma pneumoniae — most common (up to 20% of community-acquired pneumonia)
• Chlamydophila pneumoniae (TWAR strain)
• Legionella pneumophila
• Coxiella burnetii (Q fever)
• Chlamydophila psittaci

• Gradual onset; constitutional prodrome (headache, malaise, myalgia) precedes respiratory symptoms
• Prominent dry, non-productive cough
• Minimal physical signs compared to radiological findings ("walking pneumonia")
• Does not respond to β-lactams
• Does not produce rust-colored sputum
• Sputum Gram stain shows no predominant organism
• Cold agglutinins may be positive

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Pathogenesis of Mycoplasma pneumoniae

1. Attachment: M. pneumoniae possesses a specialized attachment organelle — a tip structure at one pole with adhesin proteins P1 (molecular weight 169 kDa) and P30. These bind sialic acid residues on respiratory epithelial cell surface glycoproteins (especially CD43 and glycophorin A analogs on bronchial epithelium).
2. Gliding motility: The terminal organelle facilitates gliding along the cilia.
3. Ciliary damage:
   • M. pneumoniae produces hydrogen peroxide and superoxide radicals that damage ciliated epithelium.
   • Cilia become non-functional → impaired mucociliary clearance → bacterial colonization.
4. Inflammation:
   • Mononuclear cell infiltration (lymphocytes, plasma cells, macrophages) of peribronchial and perivascular spaces → lymphoid hyperplasia.
   • TNF-α, IL-6, IL-8 released from macrophages.
   • Histology: Interstitial pneumonitis pattern (not consolidation).
5. Immune-mediated injury:
   • Cold agglutinins (IgM anti-I antigen on red blood cells): Develop in 50% of patients; can cause hemolytic anemia in severe cases.
   • The I antigen on RBCs shares structural similarity with Mycoplasma antigens → antibody cross-reactivity.
   • Extrapulmonary complications (Stevens-Johnson syndrome, myocarditis, meningoencephalitis, hemolytic anemia) are largely immune-mediated.
6. Extrapulmonary Spread (rare): Can involve heart, CNS, joints, skin.

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Diagnosis of Mycoplasma Pneumonia

Clinical Diagnosis

• Insidious onset; low-grade fever; nonproductive cough lasting >2 weeks
• CXR: Bilateral patchy interstitial infiltrates (often worse than physical signs suggest)
• WBC count: Normal or mildly elevated (lymphocytosis)

Laboratory Diagnosis

• Specimen: Nasopharyngeal swab, throat swab, BAL, sputum
• Medium: Hayflick (PPLO/SP4 broth) + Eaton's agar
• Incubation: 37°C, 5% CO₂, up to 21 days
• Identification: "Fried egg" colonies; β-hemolysis of guinea pig red blood cells; glucose fermentation (acid); manganese chloride-tetrazolium salt (MT) reduction test positive.

• Cold agglutinin test (rapid screening, bedside):
  • Positive if ≥1:32 titer; present in ~50% of cases
  • Method: 4°C — agglutination occurs; 37°C — agglutination dissolves
  • Non-specific; also positive in viral pneumonia, EBV
• Complement fixation test (CFT):
  • Antigen: Mycoplasma lipid antigen; fourfold rise in paired sera (acute + convalescent, 2–3 weeks apart) is diagnostic
  • IgM appears at 7–10 days; peaks at 3–4 weeks
• ELISA (IgM + IgG): Most widely used today; IgM positivity indicates acute/recent infection
• Particle Agglutination Test: Rapid, simple, commercially available

• Real-time PCR (RT-PCR): Targets P1 adhesin gene, 16S rRNA gene; sensitivity >95%, specificity ~100%
• Specimen: Throat swab or NP aspirate
• Turnaround: 4–6 hours
• Simultaneously can detect Chlamydophila, Legionella (multiplex respiratory panel)

• Direct fluorescent antibody (DFA): Less sensitive; mainly research use

• Macrolides (Azithromycin, Clarithromycin) — first line, especially in children; caution with macrolide-resistant strains (prevalent in Japan/China, emerging globally)
• Tetracyclines (Doxycycline) — first line in adults
• Fluoroquinolones (Levofloxacin, Moxifloxacin) — for resistant cases or adults

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Q.2(b) Zoonotic Diseases — Bacterial Zoonoses and Specific Example

Definition

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Enumeration of Bacterial Zoonotic Diseases

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Specific Example: Leptospirosis — Pathogenesis and Diagnosis

Epidemiology

Organism

Pathogenesis

1. Entry: Penetration through abraded skin, mucous membranes, or conjunctiva following contact with contaminated water or soil (occupational — rice farmers, sewer workers, veterinarians; recreational — flood wading).
2. Leptospiremia (Days 1–7 — Leptospiremic Phase):
   • Rapid multiplication in blood; hematogenous spread to all organs.
   • LPS and hemolysin (sphingomyelinase C) → vascular endothelial injury → vasculitis.
   • Clinical: High fever, severe myalgia (especially calf muscles — pathognomonic), headache, conjunctival suffusion.
3. Immune / Leptospiruric Phase (Days 7–28):
   • IgM antibodies develop → antibody-mediated clearance from blood → deposited in kidney tubules.
   • Leptospires appear in urine.
   • Platelet destruction + DIC → thrombocytopenia → hemorrhagic manifestations.
4. Weil's Disease (severe icteric leptospirosis — 5–15% of cases):
   • Jaundice + Acute Kidney Injury + Hemorrhagic manifestations = Weil's triad.
   • Hepatocellular dysfunction (direct endothelial injury; not hepatocyte necrosis).
   • Tubulointerstitial nephritis → oliguria/anuria.
   • Pulmonary haemorrhage syndrome (LPHS) — major cause of death in severe disease.
   • Myocarditis with arrhythmias.
   • Uveitis (late sequela — can persist months after infection).
5. Immunopathology: Immune complex deposition in glomeruli → glomerulonephritis; antileptospiral antibodies bind kidney tubule antigens.

Diagnosis

• Phase I (leptospiremic, days 1–7): Blood (EDTA, heparin), CSF
• Phase II (leptospiruric, days 7+): Urine (pH neutralized with buffer to prevent lysis)
• At autopsy: Kidney, liver

• Elevated CK (myositis), elevated bilirubin, elevated creatinine, thrombocytopenia, elevated liver enzymes (typically AST > ALT, conjugated hyperbilirubinemia).
• CSF: Aseptic meningitis pattern (lymphocytes, normal glucose) in neurological disease.

• Mild: Doxycycline 100 mg BD × 7 days
• Severe: IV Penicillin G 6 million units/day × 7 days OR IV Ceftriaxone 1g/day × 7 days
• Prophylaxis: Doxycycline 200 mg once weekly (occupationally exposed); Human leptospira vaccine available in India (Leptavac — L. biflexa serovars).

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Q.2(c) Syndemic of TB and AIDS — NTEP, AIDS Control Programs, and Modern Approaches

The Concept of Syndemic

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Biological Synergism Between TB and HIV

• India has the highest TB burden globally (28% of global cases, WHO 2023)
• ~5.5% of TB patients are HIV-co-infected (NACO data)
• HIV-TB co-infection increases mortality risk 3–4 fold
• HIV+ patients present with atypical TB (extrapulmonary TB more common; smear-negative TB; miliary TB; lower bacillary load → diagnostic challenge)

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NTEP (National Tuberculosis Elimination Programme) Approach to HIV-TB

1. TB/HIV Collaborative Activities (Bidirectional screening — 3Is):
   • Intensified TB Case Finding (ICF): Screen all HIV+ patients for TB (symptom screening: cough ≥2 weeks, fever, weight loss, night sweats) at every clinical visit.
   • Isoniazid Preventive Therapy (IPT): All HIV+ individuals without active TB receive Isoniazid 300 mg/day × 6 months (or Isoniazid + Rifapentine weekly × 12 weeks — 3HP regimen).
   • Infection Control: Airborne precautions in ART centers; HEPA filtration, UV germicidal irradiation.
2. Diagnostic Integration:
   • CBNAAT (Cartridge-Based Nucleic Acid Amplification Test — GeneXpert MTB/RIF): WHO-mandated as the preferred initial test for HIV-TB (simultaneously detects rifampicin resistance). All HIV+ presumptive TB cases → GeneXpert as first test.
   • LF-LAM (Lateral Flow Lipoarabinomannan): Urine-based bedside test for TB in advanced HIV (CD4 <200 cells/μL); recommended by WHO 2015.
   • Liquid culture (MGIT — Mycobacteria Growth Indicator Tube): Gold standard for smear-negative, extrapulmonary TB.
   • Truenat MTB: Made-in-India real-time PCR (microchip-based); approved by NTEP as equivalent to GeneXpert for primary testing; deployed at district and sub-district level.
3. Treatment Integration:
   • Anti-TB therapy first, then ART within 2 weeks (regardless of CD4 count) per WHO/NTEP 2022 guidelines (reduces mortality).
   • Exception: TB meningitis — ART may be delayed to 8 weeks to avoid IRIS.
   • Drug interactions: Rifampicin is a potent CYP3A4 inducer → reduces plasma levels of PIs and NNRTIs.
     • Preferred ART: Efavirenz-based regimen (EFV dose may need to be 800 mg).
     • Rifabutin (less CYP induction) substituted for Rifampicin when using PIs.
   • Immune Reconstitution Inflammatory Syndrome (IRIS): Watch for paradoxical worsening after ART initiation; managed with corticosteroids.
4. Nikshay Portal: Digital patient tracking for every TB patient registered under NTEP; integrates with ART centers for HIV-TB co-management.
5. PMDT (Programme Management of Drug-Resistant TB): HIV+ patients with DR-TB are treated per NTEP PMDT guidelines (Bedaquiline + Pretomanid + Linezolid — BPaL regimen, or standard MDR regimen with 6 months BPaL).

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NACO's AIDS Control Programme Approach to TB-HIV

1. All ART centers screen for TB at every visit using standardized symptom screening tool.
2. Refer screen-positive patients to Designated Microscopy Centre (DMC) or CBNAAT facility.
3. Provide IPT to all TB-negative HIV+ patients.
4. Link TB patients to ART centers via referral forms; ensure HIV testing of all TB patients (Provider Initiated Testing and Counselling — PITC).
5. Fast-track ART initiation: India adopted the "Test and Treat" policy (2017) — every HIV-positive person should start ART regardless of CD4 count.

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Recent Approaches for Screening and Early Diagnosis

• WHO-endorsed computer-aided detection tools for CXR analysis in TB screening.
• Deployed in India at high-risk HIV+ population screening sites.
• Sensitivity ~90%; used as triage before molecular confirmation.

• WGS (Whole Genome Sequencing) of MTB: Full drug resistance profiling from a single positive culture; identifies XDR-TB, novel resistance mutations.
• CBNAAT Xpert Ultra: Replaces earlier Xpert MTB/RIF; 4× lower LOD; can detect smear-negative TB and low-burden HIV-TB cases.

• Point-of-care antigen detection test.
• Specifically useful in HIV+ patients with CD4 <100 cells/μL.
• Reduces time-to-diagnosis in critically ill patients.

• Indigenous Indian real-time PCR deployed at sub-district health centres.
• Truenat MTB Plus + Truenat MTB-RIF Dx provide rapid diagnosis and rifampicin resistance detection.

• Novel approach for pediatric and HIV-associated extrapulmonary TB where sputum is unavailable.
• WHO-endorsed; particularly valuable for HIV-positive children.

• 3HP (Weekly Isoniazid 900 mg + Rifapentine 900 mg × 12 doses) is more convenient than 6H.
• India scaling up TPT under End TB Strategy (target: 90% reduction in TB deaths by 2030).

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Q.2(d) Role of Helicobacter pylori in Peptic Ulcer Disease and Diagnostic Methods

Historical Background

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Microbiology of H. pylori

• Gram-negative, microaerophilic, spiral-shaped bacillus with 4–6 unipolar sheathed flagella (essential for motility through mucus).
• Urease enzyme: Highly active; hydrolyzes urea → NH₃ + CO₂ → alkaline microenvironment → neutralizes gastric acid locally → organism survival.
• Oxidase +, Catalase +, Urease + (the three hallmark biochemical tests).
• Grows on blood agar, chocolate agar, Skirrow's agar (Campylobacter-selective: vancomycin + trimethoprim + polymyxin B) at 37°C for 3–5 days under microaerophilic conditions (5% O₂, 10% CO₂).

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Role in Peptic Ulcer Disease — Pathogenesis

• H. pylori penetrates mucus layer using flagellar motility and BabA adhesin (binds fucosylated Lewis b blood group antigen on gastric epithelium).
• Localizes to the gastric antrum (non-acid-secreting region).

• VacA and CagA → direct epithelial damage
• NH₃ from urease → mucosal cytotoxicity
• Prostaglandin E₂ production reduced (weakened mucosal defense)
• Direct impairment of bicarbonate secretion in duodenum

• ~70% of duodenal ulcers and ~50% of gastric ulcers worldwide are H. pylori-related.
• Eradication leads to long-term ulcer remission in >90% of cases.
• Progression to gastric adenocarcinoma and MALT lymphoma in a subset of patients.

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Diagnostic Methods

A. Non-Invasive (No Endoscopy Required)

B. Invasive (Endoscopy-Based)

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Treatment (Standard Triple Therapy / Clarithromycin-based)

• PPI + Clarithromycin 500 mg + Amoxicillin 1 g (or Metronidazole 400 mg) × 14 days
• Bismuth quadruple therapy (BQT): Bismuth + PPI + Tetracycline + Metronidazole × 14 days — preferred where clarithromycin resistance >15%
• Test of cure: UBT or SAT — 4–8 weeks after completing therapy.

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Q.2(e) Legionnaires' Disease

Introduction

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The Organism

• Gram-negative, aerobic, non-spore-forming, motile rod (1 flagellum + type IV pili).
• Gram stain: Weakly gram-negative; frequently stains poorly — Dieterle silver impregnation stain or Warthin-Starry stain visualizes Legionella in tissue.
• Special requirement: Cysteine and iron supplementation in culture media.
• Culture: BCYE agar (Buffered Charcoal Yeast Extract agar) + α-ketoglutarate; 35°C; 5% CO₂; grows in 3–7 days.
• 15 species, >60 serogroups; L. pneumophila serogroup 1 accounts for ~80% of human disease.

Ecology and Epidemiology

• Environmental reservoir: Warm freshwater (thermocline 25–45°C) — rivers, lakes.
• Amplification sites: Air conditioning cooling towers, hospital hot water systems, whirlpool spas, fountains, humidifiers, shower heads — aerosolized water droplets are the primary vehicle.
• NOT transmitted person-to-person.
• At-risk: Immunocompromised, elderly, smokers, chronic lung disease, renal transplant patients.
• In India: Underdiagnosed; hospital water systems are a major source.

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Pathogenesis

1. Inhalation of aerosolized contaminated water droplets (2–5 μm respirable particles).
2. Alveolar macrophage uptake: Legionella binds complement receptors (C3bi) on macrophages using Msp (Macrophage infectivity potentiator) protein; phagocytosed but arrests phagosomal maturation.
3. Intracellular survival: Forms a Legionella-containing vacuole (LCV) — recruits ER-derived vesicles (Dot/Icm type IV secretion system); avoids lysosomal fusion by remodeling phagosomal membranes.
4. Dot/Icm T4SS: Injects >300 effector proteins into host cytoplasm → hijacks host vesicle trafficking, inhibits NF-κB, modulates ubiquitin pathways.
5. Intracellular multiplication → macrophage lysis → release → infects new macrophages → lobar/bronchopneumonia.
6. Histology: Fibrinopurulent consolidation with alveolar macrophages and polymorphs; "dirty necrosis."

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Clinical Features

• Relative bradycardia (pulse-temperature dissociation)
• Hyponatremia (SIADH)
• Elevated liver enzymes
• Microscopically: Gram-negative rods NOT visible on sputum Gram stain (despite severe pneumonia)
• Neurological symptoms (confusion, headache)
• Diarrhea (~50%)
• CXR: Rapidly progressing, bilateral consolidation

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Laboratory Diagnosis

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Treatment

• Azithromycin 500 mg IV/oral × 5–10 days — first line (penetrates macrophages; intracellular activity; well-tolerated)
• Fluoroquinolones (Levofloxacin 500 mg BD or Moxifloxacin) — equivalent efficacy; may be superior in severe immunocompromised patients
• Rifampicin — historically added for severe cases (synergistic); now less commonly used
• β-lactams are ineffective (intracellular organism)
• Prevention: Legionella water management plans (regular hot water flushing >60°C, hyperchlorination, water sampling of hospital water systems per ASHRAE 188 / local guidelines).

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Q.2(f) Laboratory Diagnosis of Lyme Disease

Introduction

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Clinical Stages

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Laboratory Diagnosis

Clinical Diagnosis

• Stage 1 (EM present): Diagnosis is clinical; laboratory confirmation NOT needed for EM >5 cm with epidemiological exposure. Treatment should be initiated immediately.
• All other stages: Serological confirmation required.

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Standard Two-Tier Testing (STTT) Algorithm (CDC Recommended)

• Detects total antibody (IgM + IgG) to B. burgdorferi whole cell lysate or recombinant antigens (VlsE, C6 peptide).
• High sensitivity (90–99%), lower specificity (false positives with EBV, SLE, other spirochetes, rheumatoid arthritis).
• Negative result → NO further testing; disease unlikely.
• Equivocal or positive → proceed to Western Blot.

• IgM: Use only in first 4 weeks; IgM persists — a positive IgM alone in late disease is unreliable.
• IgG: Use if illness >4 weeks; positive in all patients with late Lyme disease (arthritis, neuroborreliosis).

• Recent CDC approval: Replace Western blot with a second EIA using different antigens (e.g., C6 peptide ELISA or Vidas test); equal or better performance.

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Other Diagnostic Tests

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Pitfalls and Caveats

1. Early stage (EM): Serology may be negative (antibodies not yet produced at day 3–10); treat empirically.
2. Seronegative Lyme: A real entity; some immunocompromised patients may not mount adequate antibody response.
3. Treated Lyme: Antibodies persist for years; serology cannot confirm active vs. past infection.
4. False positives: Syphilis (Treponema pallidum cross-reacts — share flagellin), EBV, CMV, autoimmune diseases, other Borrelia species.
5. Chronic Lyme disease: A controversial entity; standard two-tier testing remains the diagnostic standard; the CDC does not recommend repeat antibiotics beyond standard course.

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Treatment

• Stage 1 (EM): Doxycycline 100 mg BD × 14–21 days; Amoxicillin 500 mg TDS × 14–21 days (children, pregnancy)
• Neuroborreliosis / severe: IV Ceftriaxone 2g/day × 14–28 days

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Q.2(g) Audit of Antibiotic Prescribing Practice in a Tertiary Care Hospital

Definition

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Background: Why Antibiotic Stewardship?

• Antimicrobial resistance (AMR) is a global health emergency; India has one of the highest rates of multi-drug resistant (MDR) organism burden globally.
• Inappropriate antibiotic use (wrong drug, dose, duration, indication) drives resistance, increases C. difficile infection risk, prolongs hospital stays, and increases costs.
• The National Action Plan on AMR (NAPAMR 2017–2021) and WHO GLASS (Global Antimicrobial Resistance Surveillance System) mandate hospital-level stewardship programs.

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Types of Antibiotic Audits

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Components of Antibiotic Audit (Donabedian Framework)

Structure Criteria

• Is an Antibiotic Stewardship Programme (ASP) committee in place?
• Is there a hospital antibiogram (updated annually)?
• Is there an approved hospital formulary listing restricted antibiotics?
• Is an Infectious Disease (ID) consultant available?
• Is there a pharmacy-based stewardship pharmacist?

Process Criteria (Core of the Audit)

1. Indication: Is antibiotic prescribed for a proven or suspected bacterial infection? (Not viral respiratory tract infections, asymptomatic bacteriuria unless high-risk)
2. Choice of antibiotic: Consistent with hospital antibiogram and local guidelines? Narrowest spectrum appropriate?
3. Culture before antibiotics: Was a culture (blood culture, urine culture, wound swab) collected before initiating antibiotics?
4. Dose: Correct for indication, renal/hepatic function (pharmacokinetic/pharmacodynamic — PK/PD — dosing)?
5. Route: Oral conversion possible? (IV-to-oral switch at 48–72h in stable patients with functioning GI tract)
6. Duration: Is stop date/review date documented? Duration conforms to guidelines?
7. De-escalation: After culture results, was antibiotic narrowed from broad-spectrum empiric to targeted therapy?
8. Antibiotic approval: Were restricted antibiotics (carbapenems, colistin) prescribed with prior approval per hospital formulary?
9. Surgical prophylaxis: Single pre-operative dose? Not continued >24h post-op?

• Defined Daily Dose (DDD)/100 bed-days: Standard WHO metric for antibiotic consumption
• Days of Therapy (DOT)/1000 patient-days: More clinically meaningful than DDD
• Length of therapy (LOT)
• Appropriateness rate: % of prescriptions meeting all criteria

Outcome Criteria

• Incidence of hospital-acquired infections (HAIs) — CLABSI, VAP, SSI
• Rates of MDR organism isolation (MRSA, ESBL, CRE, CRAB)
• C. difficile infection rate
• 30-day mortality, ICU length of stay

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Audit Methodology

• IDSA/ESCMID/NABH/hospital guidelines for common infections
• Hospital antibiogram (annual cumulative susceptibility report)

• Sample: All prescriptions on a given day (PPS) OR consecutive admissions (retrospective)
• Data: Patient demographics, diagnosis, antibiotics prescribed, duration, culture sent/result, adherence to stop dates
• Tool: Structured proforma / WHONET software / EMR module

• Calculate DDD/100 bed-days per antibiotic class
• % prescriptions with documented indication
• % prescriptions with prior culture
• % de-escalation rate
• % surgical prophylaxis compliance

• Present findings to department heads, Infection Control Committee, pharmacist, and administrative leadership.
• Identify outlier departments/wards.

• Education sessions, antibiogram dissemination
• Clinical Decision Support System (CDSS) alerts in EMR
• Restricted antibiotic prior authorization (pre-authorization for carbapenems/colistin)
• Automatic stop orders for surgical prophylaxis
• ID/pharmacist consult requirement for >7 days IV antibiotics

• Repeat audit after 6–12 months to assess improvement (PDCA cycle — Plan, Do, Check, Act).

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ICMR National ASP Guidelines Recommendations (India)

• Every hospital >100 beds should have a functioning ASP committee.
• Carbapenem restriction policies should be implemented in all tertiary care hospitals.
• Electronic reporting of antibiotic consumption data to national AMR surveillance network.

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Q.2(h) Bacterial Meningitis in a 6-Year-Old — Clinical Diagnosis, Laboratory Diagnosis, and Causative Organisms

Clinical Scenario

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Probable Clinical Diagnosis

• Viral meningitis (Enteroviruses, Herpes simplex)
• Tuberculous meningitis (subacute; lymphocytic pleocytosis; very high protein; very low glucose)
• Fungal meningitis (immunocompromised child; India ink in CSF)
• Brain abscess

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Steps in Laboratory Diagnosis

Step 1: Specimen Collection — Lumbar Puncture

• Collect 3 sterile tubes:
  • Tube 1: Biochemistry (protein, glucose, LDH)
  • Tube 2: Microbiology (Gram stain + culture — this tube used even if blood-tinged)
  • Tube 3: Cell count + cytology
• Simultaneously collect blood glucose (within 30 min of LP for CSF:blood glucose ratio).
• Collect blood cultures × 2 before antibiotic administration.
• Transport immediately to laboratory at 37°C or room temperature — NOT refrigerated (N. meningitidis is cold-sensitive).

Step 2: CSF Analysis

• Color: Turbid/milky → bacterial (>500 cells/mm³ or high protein).
• "Cobweb clot" → TB meningitis.
• Xanthochromia → subarachnoid haemorrhage.

• Neubauer chamber counting
• Differential staining (Leishman stain): >80% neutrophils (PMNs) → strongly suggests bacterial meningitis

• Protein by biuret method or Lowry method
• Glucose by hexokinase method
• CSF: Serum glucose ratio <0.4 → bacterial; <0.3 → strongly bacterial

• Spread on glass slide, heat-fix, Gram stain
• Examine under ×1000 oil immersion:
  • Gram-positive diplococci (lancet-shaped): S. pneumoniae
  • Gram-negative diplococci (kidney-bean shaped): N. meningitidis
  • Gram-negative coccobacilli: H. influenzae
  • Gram-positive rods: Listeria monocytogenes (less common in this age)
• Sensitivity: ~70–80% in untreated cases; drops to <30% if antibiotics started.

• Inoculate directly from tube 2 (uncentrifuged or after centrifugation):
  • Blood agar (5% sheep blood): All organisms
  • Chocolate agar (lysed blood agar): H. influenzae, N. meningitidis (require factor X and V)
  • MacConkey agar: Gram-negative enteric organisms (relevant in neonates)
• Incubate at 37°C, 5–10% CO₂, 18–24h; examine at 24h, 48h, 72h.
• Identification: Colony morphology → Gram stain of colony → biochemical tests (API 20E/NE, VITEK) → MALDI-TOF MS (rapid, definitive identification in minutes).
• Antibiotic sensitivity by Kirby-Bauer disk diffusion or E-test (MIC determination for CSF penetrating antibiotics: penicillin, ceftriaxone, chloramphenicol, vancomycin).

• Detects capsular antigens of common meningeal pathogens:
  • S. pneumoniae (Quellung reaction or latex antigen test)
  • N. meningitidis A, B, C, Y, W135
  • H. influenzae type b
  • E. coli K1
  • Group B Streptococcus
• Useful in partially treated meningitis where Gram stain and culture are negative.
• Sensitivity: 60–90%; specificity: >99%.

• Real-time PCR (FilmArray Meningitis/Encephalitis Panel): Simultaneously detects 14 pathogens (bacteria, viruses, fungi) in CSF within 1 hour.
• Detects: S. pneumoniae, N. meningitidis, H. influenzae, Listeria, E. coli K1, S. agalactiae + major viruses (HSV-1/2, Enterovirus, CMV, VZV) + Cryptococcus.
• Sensitivity 97–100%; specificity 98%; extremely valuable when Gram stain/culture negative after prior antibiotics.
• Important limitation: Cannot provide antibiotic susceptibility information.

• Negative in bacterial meningitis; positive (capsule visible around budding yeast) in Cryptococcus neoformans meningitis.

• If child is immunocompromised; serum and CSF CrAg.

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Most Likely Causative Organisms — Age Group Correlation

1. Neisseria meningitidis (Meningococcus):
   • Gram-negative diplococcus; polysaccharide capsule (serogroups A, B, C, Y, W135)
   • Serogroup A/C — epidemic meningitis (India: "Meningitis Belt" pattern during pilgrimages/mass gatherings)
   • Exotoxins + endotoxin → septicemia + Waterhouse-Friderichsen syndrome (bilateral adrenal hemorrhage)
   • Characteristic purpuric/petechial rash
   • Very rapid course; can die within 24h of symptoms.
2. Streptococcus pneumoniae (Pneumococcus):
   • Gram-positive lancet-shaped diplococci; α-hemolytic on blood agar.
   • Most common cause of bacterial meningitis across all ages in India (due to low Hib/PCV vaccination coverage historically).
   • Pneumococcal meningitis has higher morbidity (deafness, cognitive impairment) than meningococcal.
   • Penumococcal conjugate vaccine (PCV13) now included in UIP India.
3. Haemophilus influenzae type b (Hib):
   • Gram-negative coccobacillus; requires X factor (hemin) and V factor (NAD).
   • Was the leading cause of bacterial meningitis in children <5 years pre-vaccination.
   • India introduced Hib vaccine (Pentavalent vaccine) into UIP in 2011; dramatic reduction in Hib meningitis observed.
   • Satellite phenomenon on blood agar around S. aureus streak (provides V factor).

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Empiric Treatment (Pending Culture Results)

• Ceftriaxone 100 mg/kg/day IV divided Q12h (covers all three organisms; excellent CSF penetration).
• Add Vancomycin if penicillin-resistant S. pneumoniae suspected (MIC-based dosing).
• Add Dexamethasone 0.15 mg/kg Q6h × 4 days (begin 15–30 min before or with first antibiotic dose; reduces sensorineural hearing loss, especially for Hib and pneumococcal meningitis).
• Chemoprophylaxis for close contacts (meningococcal): Rifampicin 10 mg/kg BD × 2 days (children) OR single-dose Ciprofloxacin 500 mg (adults) OR Ceftriaxone IM.