Master Infectious Diseases
for MRCP Part 1

What the MRCP Part 1 Tests in Infectious Diseases

MRCP Part 1 Infectious Diseases tests the ability to diagnose and manage common and serious infections in adults, focusing on clinical presentations, pathogen-specific treatments, antibiotic stewardship, and public health measures. Candidates must know first-line and alternative antimicrobials for community-acquired pneumonia, meningitis, urinary tract infections, skin and soft tissue infections, and sepsis. Key areas include HIV-related opportunistic infections (e.g., PCP, toxoplasmosis, CMV), tuberculosis (treatment regimens, latent TB criteria), viral hepatitis (serology interpretation, treatment thresholds), and tropical diseases (malaria, typhoid, schistosomiasis). Vaccination schedules, post-exposure prophylaxis (e.g., rabies, HIV), and infection control (e.g., MRSA, C. difficile) are frequently tested. Guidelines from NICE, BASHH, and WHO are referenced, with emphasis on drug interactions, adverse effects, and resistance patterns.

High-Yield Concepts

• Community-Acquired Pneumonia (CAP) Severity Assessment: Use CURB-65: Confusion (new), Urea >7 mmol/L, Respiratory rate ≥30/min, BP systolic <90 or diastolic ≤60 mmHg, age ≥65. Score 0-1: home; 2: hospital; ≥3: severe, consider ICU. First-line antibiotics: amoxicillin 500mg-1g TDS for mild; doxycycline 200mg stat then 100mg OD if penicillin allergic. For moderate/severe: co-amoxiclav 1.2g TDS plus clarithromycin 500mg BD IV.
• Meningitis: Empirical Treatment and CSF Interpretation: Empirical: ceftriaxone 2g IV BD plus dexamethasone 10mg IV QDS (before or with first antibiotic) if suspected bacterial. Add amoxicillin 2g IV QDS if >55 years or immunocompromised (Listeria). CSF: bacterial – low glucose (<2.2 mmol/L), high protein (>1 g/L), neutrophils; viral – normal glucose, lymphocytosis; TB – low glucose, high protein, lymphocytosis. PCR for meningococcus, pneumococcus, enterovirus.
• HIV: Opportunistic Infection Prophylaxis and Treatment: Start ART when CD4 <350 cells/µL (now often regardless of CD4). PCP prophylaxis: co-trimoxazole 480mg OD if CD4 <200. Toxoplasma encephalitis: treat with pyrimethamine + sulfadiazine + folinic acid; primary prophylaxis with co-trimoxazole if CD4 <100 and IgG positive. CMV retinitis: valganciclovir or ganciclovir; prophylaxis if CD4 <50. TB: treat with rifampicin, isoniazid, pyrazinamide, ethambutol; check for IRIS.
• Tuberculosis: Treatment Regimens and Latent TB: Active TB: 2 months of rifampicin, isoniazid, pyrazinamide, ethambutol (RIPE) then 4 months rifampicin + isoniazid. Monitor LFTs. Latent TB: treat if positive IGRA (T-SPOT.TB) or Mantoux >5mm (immunocompromised) or >10mm (other risk). Regimens: 3 months rifampicin + isoniazid daily, or 6 months isoniazid alone. Check for drug interactions (rifampicin induces CYP450).
• Sepsis: Definitions and Management: Use qSOFA: altered mental state, RR ≥22, SBP ≤100 mmHg – if ≥2, suspect sepsis. Take blood cultures, lactate, start broad-spectrum antibiotics within 1 hour (e.g., piperacillin-tazobactam 4.5g QDS IV). Target MAP ≥65 mmHg with fluids and vasopressors (noradrenaline first). Source control (drain abscess, remove line). NICE guidelines: consider IV antibiotics for suspected sepsis without delay.
• Clostridioides difficile Infection: Diagnose with stool toxin test (GDH + toxin A/B). Severity: mild (WCC <15, creatinine normal) – oral metronidazole 400mg TDS 10 days; severe (WCC >15, creatinine >1.5x baseline) – oral vancomycin 125mg QDS 10 days; fulminant (ICU, ileus) – vancomycin 500mg QDS PO/NG + IV metronidazole 500mg TDS. Recurrence: fidaxomicin 200mg BD 10 days or bezlotoxumab.
• Malaria: Diagnosis and Treatment: Suspect in febrile traveler from endemic area. Thick and thin blood films; rapid diagnostic test (RDT) for P. falciparum. Uncomplicated P. falciparum: artemether-lumefantrine (Riamet) or atovaquone-proguanil (Malarone). Severe: IV artesunate 2.4 mg/kg at 0, 12, 24h then daily. Check G6PD before primaquine for P. vivax/ovale (radical cure).
• Viral Hepatitis: Serology and Management: Hep B: HBsAg positive = chronic; HBeAg positive = high replication; anti-HBc IgM = acute. Treat if HBV DNA >2000 IU/mL and ALT elevated (entecavir, tenofovir). Hep C: anti-HCV positive, then HCV RNA; genotype 1-6. Direct-acting antivirals (e.g., sofosbuvir/velpatasvir 12 weeks). Hep A: IgM anti-HAV; supportive care. Hep E: IgM anti-HEV; ribavirin in chronic (immunocompromised).

Common Traps in Infectious Diseases Questions

• Assuming all meningitis requires addition of ampicillin for Listeria; only if age >55, immunocompromised, or pregnant.
• Using co-trimoxazole for PCP prophylaxis without checking for G6PD deficiency or sulfa allergy.
• Thinking that all patients with HIV and fever have TB; always consider PCP, CMV, and IRIS first.
• Forgetting to stop prophylactic antibiotics after source control in sepsis; prolonged courses increase resistance and C. diff risk.
• Confusing latent TB treatment with active TB regimen; latent uses shorter, different drug combinations.
• Using vancomycin orally for C. diff without checking if patient has ileus (needs IV metronidazole).

How to Revise Infectious Diseases for the MRCP Part 1

For MRCP Part 1, prioritise memorising antibiotic first-line choices for common infections (CAP, UTI, cellulitis, meningitis) and their durations. Understand severity scores (CURB-65, qSOFA) and when to escalate therapy. Focus on HIV-related infection thresholds (CD4 counts for prophylaxis) and TB treatment phases. Practice interpreting serology panels (Hep B, HIV, syphilis) and CSF results. Questions often present a clinical scenario with a single lab value or travel history; link to the most likely pathogen and drug. Review NICE guidelines for sepsis and antibiotic stewardship. Use mnemonics for CURB-65 and qSOFA. Do not over-study rare tropical diseases; exam favours common presentations with classic epidemiology.

Practise it: MedLumen has 50 Infectious Diseases questions for the MRCP Part 1, each with a full explanation and references.