5. Infection (Bacterial, Viral, Fungal, Tuberculosis)

📄Definition

Respiratory infections involve inflammation of lung tissue due to pathogenic microorganisms, typically categorised as:

  • Bacterial (e.g. Streptococcus pneumoniae, Haemophilus influenzae)

  • Viral (e.g. Influenza, RSV, COVID-19)

  • Fungal (e.g. Aspergillus, Pneumocystis jirovecii)

  • Mycobacterial (Tuberculosis – Mycobacterium tuberculosis)

🎯 EXAM ANCHOR – CORE CONCEPT (PARA)

  • Respiratory infection = lung inflammation due to pathogenic organisms

  • Classified as bacterial, viral, fungal, or mycobacterial (TB)

📌 PARA commonly asks:

How are respiratory infections broadly classified?

🛡️Causes (Aetiology)

Mnemonic: “B-FIT”

  • Bacterial – S. pneumoniae, H. influenzae, Legionella

  • Fungal – Aspergillosis, Pneumocystis jirovecii

  • Influenza viruses – Influenza A/B, RSV, COVID-19

  • Tuberculosis – M. tuberculosis (airborne)

🎯 EXAM ANCHOR – BACTERIAL vs VIRAL (PARA)

  • Bacterial → acute onset, focal signs, raised CRP/WCC

  • Viral → diffuse symptoms, bilateral changes, normal/mild WCC rise

📌 PARA commonly asks:

Which features suggest bacterial rather than viral pneumonia?

📋 Risk Factors

🧠 Mnemonic: HOPE SCAR

  • HIV/immunosuppression

  • Overcrowding (TB)

  • Poor vaccination uptake

  • Elderly

  • Smoking

  • Chronic lung disease (e.g. COPD, asthma)

  • Alcoholism

  • Recent hospitalisation or travel

📋 Clinical Features

🧠Mnemonic: FEVER COPS

  • Fever

  • Exertional dyspnoea

  • Vomiting/cough +/- sputum

  • Elevated CRP/WCC

  • Rales or crepitations on auscultation

  • Chest pain (pleuritic)

  • O2 desaturation

  • Productive cough (± purulent)

  • Shivering or rigors

🩺 Examination Findings

  • ↓ Chest expansion

  • Dullness to percussion

  • Bronchial breathing or crackles

  • Tracheal deviation (TB cavity/effusion-related)

  • Lymphadenopathy (TB, fungal)

Investigations 

LevelInvestigationWhen to Use
🟢 First-LineCXR – consolidation, effusion, cavitationAll suspected pneumonia, TB, COVID, fungal infections
 Bloods – FBC, CRP, U&Es, LFTsBaseline and inflammatory markers
 O2 sats / ABGHypoxia, suspected respiratory failure
 Sputum cultureModerate–severe infections or poor response to empiric therapy
 PCR (viral swab)If viral infection suspected (COVID, flu, RSV)
🟡 Second-LineBlood culturesIf sepsis suspected or severe pneumonia
 ProcalcitoninGuide bacterial vs viral aetiology (esp. in hospital)
 Tuberculin skin test / IGRASuspected TB, especially latent or extrapulmonary
 HIV testAll cases of Pneumocystis jirovecii pneumonia or suspected immunosuppression
🔴 SpecialistHRCT ChestSuspected fungal lung disease, unresolved pneumonia, cavitary lesions
 Bronchoscopy + BALImmunocompromised, non-resolving pneumonia, suspected TB/fungal disease

🎯 EXAM ANCHOR – DIAGNOSIS (PARA)

  • CXR is first-line imaging for suspected pneumonia or TB

  • Normal CXR does not exclude early TB

📌 PARA commonly asks:

What is the first-line investigation in suspected pneumonia?

🎯 EXAM ANCHOR – MICROBIOLOGY (PARA)

  • Sputum culture indicated in moderate–severe infection or poor response

  • Identifies causative organism and resistance

📌 PARA commonly asks:

When should sputum cultures be sent in respiratory infection?

🎯 EXAM ANCHOR – IMMUNOCOMPROMISED HOST (PARA)

  • Consider fungal and atypical infections early
  • Pneumocystis jirovecii → HIV, raised LDH, hypoxia
  •  

📌 PARA commonly asks:

Which infection should be suspected in an immunocompromised patient with hypoxia and diffuse infiltrates?

Severity Assessment (CAP Specific)

📊 CURB-65 Score – NICE NG138 (2023)

ComponentCriteriaPoints
ConfusionAMT ≤8+1
Urea>7 mmol/L+1
Respiratory rate≥30 breaths/min+1
Blood pressureSystolic <90 or Diastolic ≤60+1
Age ≥65 +1

Score Interpretation:

  • 0–1: Home treatment

  • 2: Hospital referral

  • ≥3: Urgent hospital + consider ICU

CRB-65 (Primary Care) vs. CURB-65 (Secondary Care)

NICE makes a clear distinction that is frequently tested:

  • In Primary Care: Use CRB-65 (Urea is unavailable). A score of 1 or more should prompt consideration for hospital referral.

  • In Secondary Care: Use CURB-65.

  • Correction: Ensure your summary specifies that Urea is the “hospital-only” component.

Management

🧠 Mnemonic: ABC + PATH

  • Antibiotics – based on local guidelines & CURB-65

🎯 EXAM ANCHOR – SEVERITY (CAP)

  • CURB-65 assesses pneumonia severity
  • Guides site-of-care decision
  •  

📌 PARA commonly asks:

Which scoring system is used to assess severity in community-acquired pneumonia?

  • Barrier nursing for TB/COVID

  • Community vs Hospital admission decision (CURB-65)

  • Public Health notification (TB, COVID)

  • Anti-viral/fungal agents if indicated

  • Treat underlying immunodeficiency

  • Hydration, oxygen, and supportive care

📝 Example: TB Treatment

  • 6-month RIPE: Rifampicin, Isoniazid, Pyrazinamide, Ethambutol (first 2 months)

  • Then Rifampicin + Isoniazid (4 months)

  • Screening for Latent TB involves IGRA (Interferon-Gamma Release Assay) or Mantoux; Active TB requires Sputum Smears (AFB) and Culture.

TB Medication Side Effects (High-Yield PARA Topic)

PARA almost always asks about their specific toxicities:

  • Rifampicin: Red/Orange secretions (tears/urine); Cytochrome P450 inducer.

  • Isoniazid: Peripheral neuropathy (must co-prescribe Vitamin B6/Pyridoxine); Hepatotoxicity.

  • Pyrazinamide: Hyperuricaemia (can trigger Gout); Hepatotoxicity.

  • Ethambutol: Optic neuritis (blurred vision/red-green colour blindness). “E for Eye.”

🎯 PARA Decision Matrix: IGRA vs. Mantoux vs. Sputum

TestBest Used For…PARA Key Fact
MantouxInitial screening for Latent TB.Can give false positive if the patient had a BCG vaccine.
IGRAConfirming Latent TB (if Mantoux is positive or if the patient had a BCG).Highly specific; no false positives from BCG.
Sputum Smear/CultureDiagnosing Active TB.Requires 3 samples (one early morning). Smear uses Ziehl-Neelsen stain.

📌 PARA commonly asks:

A patient with suspected TB has had a prior BCG vaccination. Which test is most appropriate to screen for latent infection while minimizing false-positive results?

🎯 EXAM ANCHOR – INFECTION CONTROL (PARA)

  • TB requires isolation and contact tracing

  • Infection control decisions are examinable

📌 PARA commonly asks:

Which respiratory infection requires airborne isolation?

🦠 Bacterial & Atypical Pneumonia (The “Host” Clues)

OrganismPARA Clue (The “Trigger”)NICE Treatment (UK)
S. pneumoniaeRusty sputum + Lobar consolidation.Amoxicillin (5 days)
L. pneumophilaHyponatraemia + Travel + Deranged LFTs.Clarithromycin
M. pneumoniaeYoung + Erythema Multiforme (Target rash).Clarithromycin
S. aureusWorsening immediately after Flu recovery.Flucloxacillin
KlebsiellaAlcoholic + “Red currant jelly” sputum.Cefotaxime
HAP (>48h)Hospitalized patient + new fever/cough.Tazocin

🤧 Viral & Fungal (The “Host” Clues)

InfectionPARA Clue (The “Trigger”)NICE / UK Management
PCPHIV + Desaturation on exertion + ↑LDH.Co-trimoxazole
AspergillusImmunosuppressed + Haemoptysis + Cavity.Voriconazole
InfluenzaAbrupt onset, myalgia, headache.Supportive (± Oseltamivir)

🏔️ Tuberculosis (The “Safety” Clues)

DrugPARA Toxicity (The “Fail” Point)Mandatory Intervention
RifampicinOrange urine/tears (P450 Inducer).Warn patient.
IsoniazidPeripheral neuropathy.Give Vitamin B6.
PyrazinamideGout (Hyperuricaemia).Monitor Uric Acid.
EthambutolOptic Neuritis (Red-green color loss).Baseline Visual Acuity.

Red Flags

  • Rapid deterioration

  • Sepsis/shock

  • Haemoptysis or cavitation

  • Multi-lobar involvement

  • Unresponsive to antibiotics after 48–72h

⚠️ Complications

  • Lung abscess

  • Empyema

  • Sepsis / ARDS

  • Cavitation (TB)

  • Bronchiectasis (post-infective)

Differential Diagnoses

  • PE

  • Lung cancer

  • Heart failure

  • Pneumothorax

  • Autoimmune ILD

✅ Review & Safety Netting

  • Always assess for deterioration: NEWS2

  • Escalate if CURB-65 ≥2 (hospital referral)

  • Contact tracing for TB

🔎  Key PARA Exam Traps 

💡 Bacterial pneumonia → acute onset, fever, focal chest signs, raised CRP/WCC

💡 Viral pneumonia → diffuse symptoms, bilateral infiltrates, normal or mildly raised WCC

💡 CRP is non-specific → indicates inflammation, not organism

💡 Sputum cultures should be sent before antibiotics in severe

💡  Vitamin B6 (Pyridoxine) is given with Isoniazid to prevent peripheral neuropathy.” or recurrent infection

💡 Failure to respond to antibiotics → think resistant organism, wrong diagnosis, or complication

💡 Immunocompromised patients → consider atypical and fungal infections early

💡 Fungal infection (e.g. Aspergillus) → haemoptysis, cavitation, immunosuppression history

💡 TB presents insidiously → weight loss, night sweats, haemoptysis, upper-lobe disease

💡 Normal CXR does not exclude early TB

💡 Always assess infection control risk (TB isolation is an exam favourite)

🔎 Last updated in line with:

  • NICE NG138 – Community-acquired pneumonia in adults

  • NICE NG33 – Tuberculosis

  • NICE NG186 – COVID-19 rapid guideline

  • NICE NG164 – Fungal infections: risk prediction and management in critically ill

Published: March 2020 • Last updated: May 2023
Last reviewed: February 2026
🔒 PASSMAP ensures all content is NICE-aligned and reviewed for Physician Associate Registration Assessment (PARA) success.

Educational platform. Not medical advice.

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