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)

🛡️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)

📋 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

Severity Assessment (CAP Specific)

📊 CURB-65 Score – NICE NG138 (2023)

Component Criteria Points
Confusion AMT ≤8 +1
Urea >7 mmol/L +1
Respiratory rate ≥30 breaths/min +1
Blood pressure Systolic <90 or Diastolic ≤60 +1
Age ≥65   +1

Score Interpretation:

  • 0–1: Home treatment

  • 2: Hospital referral

  • ≥3: Urgent hospital + consider ICU

Management

🧠 Mnemonic: ABC + PATH

  • Antibiotics – based on local guidelines & CURB-65

  • 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)

🧰 Summary Table for PARA Recall

Infection TypeKey OrganismKey ClueFirst-line Tx (Empirical)
CAPStrep pneumoniaeLobar consolidationAmoxicillin (± clarithromycin)
HAPStaph aureus, GNB>48h in hospitalPiperacillin-tazobactam
TBM. tuberculosisUpper lobe, cavitationRIPE: Rifampicin, Isoniazid, etc.
PCPP. jiroveciiHIV, ↑LDH, ground-glassCo-trimoxazole ± steroids
AspergillosisAspergillus spp.Cavities, immunocompromisedVoriconazole
COVID-19SARS-CoV-2PCR+, ground-glass CXROxygen + dexamethasone ± abx

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

🔎 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: July 2025
🔒 PASSMAP ensures all content is NICE-aligned and reviewed for Physician Associate Registration Assessment (PARA) success.

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