Medicine chapters
Pneumonia, atypical pneumonia and lung abscess
Community-acquired, hospital-acquired and aspiration pneumonia with CURB-65 severity scoring, the clues to atypical organisms (Mycoplasma, Legionella, Chlamydia, Q fever), and the causes, diagnosis and treatment of lung abscess.
- Assess community-acquired pneumonia with CURB-65 (Confusion, Urea >7, RR ≥30, BP <90/≤60, age ≥65): 0–1 home oral amoxicillin, 2 admit (amoxicillin + clarithromycin), 3–5 severe (IV co-amoxiclav or ceftriaxone + clarithromycin).
- Atypical organisms (Mycoplasma, Legionella, Chlamydophila, Coxiella) give dry cough and systemic features, a normal or modest white count, and are not killed by penicillins; use a macrolide, doxycycline or a quinolone.
- Lung abscess follows aspiration (anaerobes), Staph. aureus or Klebsiella: swinging fever, foul copious sputum, cavity with an air–fluid level; treat with 4–6 weeks of antibiotics and postural drainage; surgery is rarely needed.
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Overview
Pneumonia is infection and inflammation of the lung parenchyma with consolidation. It is classified by where it was caught, because this predicts the organism:
- Community-acquired pneumonia (CAP).
- Hospital-acquired pneumonia (HAP): starts more than 48 hours after admission; ventilator-associated pneumonia (VAP) is a subtype.
- Aspiration pneumonia.
- Pneumonia in the immunocompromised (e.g. Pneumocystis in HIV).
The TOS stresses atypical pneumonia and lung abscess.
Community-acquired pneumonia
Organisms
| Organism | Clues |
|---|---|
| Streptococcus pneumoniae (commonest) | Abrupt fever, rigors, pleuritic pain, rusty sputum, lobar consolidation, labial herpes, high WCC and CRP |
| Haemophilus influenzae | COPD, smokers |
| Moraxella catarrhalis | COPD exacerbations |
| Staphylococcus aureus | After influenza, IV drug users; cavities and thin-walled pneumatoceles |
| Klebsiella pneumoniae | Alcoholics and diabetics, upper lobe, red currant jelly sputum, cavitation and abscess |
| Atypical organisms | See below |
| Viruses | Influenza, SARS-CoV-2, RSV |
In many patients no organism is found.
Clinical features
- Fever, cough (dry or productive), breathlessness, pleuritic chest pain, sometimes haemoptysis.
- Signs of consolidation: dull percussion, bronchial breathing, increased vocal resonance, coarse crackles, pleural rub.
- The elderly may present only with confusion or falls.
Investigations
- Chest X-ray in all admitted patients; repeat at about 6 weeks in smokers and over-50s to exclude an underlying lung cancer.
- FBC, urea and electrolytes, LFTs, CRP; ABG if SpO2 <94%.
- Blood and sputum cultures (before antibiotics) in moderate and severe disease.
- Urinary antigens for pneumococcus and Legionella in severe disease.
- PCR or serology for atypical organisms and viruses; offer an HIV test.
CURB-65 severity score (1 point each)
| Letter | Criterion |
|---|---|
| C | New confusion (AMT ≤8) |
| U | Urea >7 mmol/L |
| R | Respiratory rate ≥30/min |
| B | BP: systolic <90 or diastolic ≤60 mmHg |
| 65 | Age ≥65 years |
| Score | Severity | Where and what |
|---|---|---|
| 0–1 | Low | Home; oral amoxicillin (clarithromycin or doxycycline if penicillin-allergic), usually 5 days |
| 2 | Moderate | Admit; amoxicillin + clarithromycin |
| 3–5 | High | Admit, consider ICU; IV co-amoxiclav (or ceftriaxone) + clarithromycin; levofloxacin if allergic |
In the community, CRB-65 (no urea) is used.
Man of 70, newly confused, urea 9 mmol/L, RR 32/min, BP 100/70 mmHg
C 1 + U 1 (9 >7) + R 1 (32 ≥30) + B 0 (100/70) + 65 1 = 4
Score 4 → high severity → IV co-amoxiclav + clarithromycin, senior and ICU review
General management
- Oxygen to 94–98% (88–92% in CO2 retainers), IV fluids, analgesia for pleuritic pain, thromboprophylaxis.
- Give antibiotics within 1 hour in severe pneumonia; switch to oral once afebrile for 24 hours and improving.
- Low-severity CAP: 5 days; severe or complicated: longer (7–10 days, more for Staph. aureus or Legionella).
- Vaccinate: pneumococcal and influenza vaccines for at-risk groups.
Atypical pneumonia
"Atypical" organisms live inside cells or lack a normal cell wall, so β-lactams (penicillins, cephalosporins) do not work. They respond to macrolides (clarithromycin, azithromycin), tetracyclines (doxycycline) or fluoroquinolones.
Typical pattern: gradual onset, dry cough, prominent headache, myalgia and malaise, X-ray changes out of proportion to chest signs, and a normal or only mildly raised WCC.
| Organism | Who | Special features | Diagnosis | Treatment |
|---|---|---|---|---|
| Mycoplasma pneumoniae | Young adults, students; epidemics every few years | Cold agglutinins with haemolytic anaemia (IgM); erythema multiforme, Stevens–Johnson syndrome; bullous myringitis; myocarditis, pericarditis; meningoencephalitis, Guillain–Barré | PCR, serology; cold agglutinin test; Coombs test positive | Clarithromycin or doxycycline |
| Legionella pneumophila | Middle-aged smokers; air-conditioning and cooling towers, hotel water systems, travel | High fever, confusion, diarrhoea, abdominal pain, hyponatraemia, raised liver enzymes, lymphopenia, haematuria | Urinary antigen (quick), culture on special media, PCR | Clarithromycin or a fluoroquinolone (levofloxacin) |
| Chlamydophila pneumoniae | All ages | Mild illness, sore throat, hoarseness | PCR, serology | Macrolide or doxycycline |
| Chlamydia psittaci (psittacosis) | Bird contact (parrots, pigeons, poultry) | Headache, high fever, splenomegaly, rash, hepatitis | Serology | Doxycycline |
| Coxiella burnetii (Q fever) | Farm and abattoir workers, sheep, goats, raw milk | Flu-like illness, pneumonia, hepatitis; chronic form gives culture-negative endocarditis | Serology (does not grow on routine culture) | Doxycycline |
Mycoplasma has no cell wall, which is why penicillins are useless and why it does not Gram stain.
Pneumonia plus hyponatraemia, diarrhoea and confusion after air-conditioning exposure is Legionella; the fastest test is the urinary antigen.
Cold agglutinins and anaemia point to Mycoplasma, not Legionella. Lymphopenia, hyponatraemia and abnormal LFTs point to Legionella.
"My CAT": Mycoplasma = Cold agglutinins, Anaemia (haemolysis), Target lesions (erythema multiforme).
Pneumocystis jirovecii pneumonia (PCP)
- HIV with CD4 <200, or long-term steroids, transplant and methotrexate patients.
- Dry cough, fever, marked desaturation on exertion, few chest signs.
- Chest X-ray: bilateral perihilar ("bat-wing") interstitial shadowing; may be normal early; pneumothorax.
- Diagnosis: immunofluorescence or PCR on induced sputum or BAL.
- Treatment: high-dose co-trimoxazole, plus steroids if hypoxic in HIV. Prophylaxis with co-trimoxazole when CD4 <200.
Hospital-acquired and aspiration pneumonia
Hospital-acquired and ventilator-associated pneumonia
- Gram-negative bacilli (Pseudomonas, Klebsiella, E. coli, Acinetobacter), Staph. aureus including MRSA, anaerobes.
- Treat according to local resistance patterns: e.g. piperacillin–tazobactam or a carbapenem, adding vancomycin or linezolid for MRSA.
Aspiration pneumonia
- Risk: reduced consciousness (alcohol, seizures, stroke, anaesthesia), dysphagia, bulbar palsy, poor dentition.
- Site: the right main bronchus is wider, shorter and more vertical, so aspirate enters the right lower lobe when upright; when lying supine it reaches the posterior segment of the upper lobe and the apical (superior) segment of the lower lobe.
- Mendelson syndrome: chemical pneumonitis after aspirating acidic gastric contents, classically during obstetric anaesthesia.
- Organisms: oral anaerobes and Gram-negatives.
- Treatment: co-amoxiclav (or a cephalosporin plus metronidazole); correct the swallowing or airway problem.
Complications of pneumonia
- Parapneumonic effusion and empyema: suspect with persistent swinging fever and rising CRP despite antibiotics. Aspirate under ultrasound. Pus, positive Gram stain or culture, or pleural fluid pH <7.2 → chest drain (plus antibiotics); surgery for organised empyema.
- Lung abscess.
- Respiratory failure, sepsis and shock, ARDS.
- SIADH (hyponatraemia), AF, delirium.
- Slow resolution: think of wrong antibiotic, resistance, empyema, underlying cancer or foreign body, TB, PE, organising pneumonia.
Lung abscess
A localised collection of pus within the lung with necrosis, forming a cavity, usually containing an air–fluid level.
Causes and organisms
| Cause | Typical organisms |
|---|---|
| Aspiration (alcohol, seizures, dental sepsis, dysphagia) | Anaerobes (Bacteroides, Fusobacterium, Peptostreptococcus), Streptococcus milleri |
| Necrotising pneumonia | Staph. aureus, Klebsiella pneumoniae |
| Bronchial obstruction | Tumour (often squamous cell), inhaled foreign body |
| Septic emboli | Staph. aureus (IV drug users with tricuspid endocarditis, infected lines) |
| Spread from below the diaphragm | Amoebic liver abscess (right lower lobe, "anchovy-sauce" sputum) |
| Partially treated pneumonia; tuberculosis | M. tuberculosis, fungi |
Clinical features
- Persisting or worsening pneumonia, swinging fever, night sweats, weight loss.
- Large volumes of foul-smelling, purulent sputum (anaerobes), sometimes haemoptysis.
- Finger clubbing if chronic; signs may be few.
- Normocytic anaemia, high ESR and CRP.
Investigations
- Chest X-ray: thick-walled cavity with an air–fluid level.
- CT chest: confirms the abscess, separates it from empyema (abscess is round with a thick wall and acute angle to the chest wall; empyema is lens-shaped and compresses lung) and looks for an obstructing lesion.
- Sputum and blood cultures, AFB smears for TB.
- Bronchoscopy to remove a foreign body, exclude a tumour or obtain samples.
Treatment
- Prolonged antibiotics, usually 4–6 weeks, guided by culture: e.g. IV then oral co-amoxiclav, or a cephalosporin with metronidazole for anaerobic cover; clindamycin is an alternative; anti-staphylococcal or anti-Klebsiella cover when indicated.
- Postural drainage and physiotherapy.
- Percutaneous drainage or surgical resection only if it fails to resolve, is very large, or there is massive haemoptysis or an underlying tumour.
A lung abscess does not always need surgical drainage. Most resolve with prolonged antibiotics and postural drainage.
In a smoker over 40 with a cavity, always exclude a cavitating squamous cell carcinoma; in Pakistan also exclude tuberculosis.
Complications of lung abscess
- Empyema and bronchopleural fistula.
- Massive haemoptysis.
- Brain abscess and other metastatic infection.
- Bronchiectasis, chronic abscess.
Expect: CURB-65 items and cut-offs with the matching antibiotic plan, Strep. pneumoniae as the commonest cause, Klebsiella with red currant jelly sputum and upper lobe cavitation, Staph. aureus after influenza, Mycoplasma with cold agglutinins, haemolysis and erythema multiforme, Legionella with hyponatraemia, diarrhoea, abnormal LFTs and urinary antigen, Mycoplasma lacking a cell wall, Q fever and psittacosis exposures, Pneumocystis in HIV with CD4 <200, aspiration into the right lower lobe, empyema with pH <7.2 needing a drain, and lung abscess causes, foul sputum, air–fluid level and 4–6 weeks of antibiotics without routine surgery.
Quick revision
- CURB-65: confusion, urea >7, RR ≥30, BP <90/≤60, age ≥65.
- 0–1 home amoxicillin; 2 admit amoxicillin + clarithromycin; 3–5 IV co-amoxiclav + clarithromycin.
- Atypicals: macrolide, doxycycline or quinolone (no cell wall or intracellular).
- Mycoplasma: young, cold agglutinins, haemolysis, erythema multiforme.
- Legionella: air-conditioning, hyponatraemia, diarrhoea, LFTs, urinary antigen.
- Psittacosis: birds, doxycycline. Q fever: farm animals, doxycycline.
- Empyema: pH <7.2 or pus → chest drain.
- Lung abscess: aspiration (anaerobes), Staph, Klebsiella; air–fluid level; 4–6 weeks antibiotics.
Written by The House Job from standard references (Kumar and Clark's Clinical Medicine).
FAQ
What makes a pneumonia "atypical"?
The organism (Mycoplasma, Legionella, Chlamydophila, Coxiella) is intracellular or has no normal cell wall, gives prominent systemic symptoms with a dry cough, and does not respond to penicillins.
What is the quickest test for Legionella?
A urinary antigen test, which can be positive within hours of admission; culture needs special media and takes days.
Which antibiotic is used for Mycoplasma pneumonia?
A macrolide such as clarithromycin or azithromycin, or doxycycline in adults.
Does every lung abscess need an operation?
No. Most settle with 4–6 weeks of antibiotics and postural drainage; drainage or resection is kept for failures, very large abscesses, massive haemoptysis or an underlying tumour.