Community-Acquired Pneumonia (CAP) – Adults

Definitions

CAP: pneumonia acquired outside the hospital, or within 48 hours of admission (includes pneumonia that develops in a nursing home resident)

Aetiology

Bacterial Causes

Bacteria are the most common cause of pneumonia in adults

• Most common bacterial cause of CAP: Streptococcus pneumoniae ^[Ref]

Some classic associations between the causative organisms and specific patient populations: ^[Ref]

‘Atypical’ bacterial pathogens (associated with CAP): ^[Ref]

• Mycoplasma pneumoniae – most common atypical pathogen
• Legionella species
• Chlamydia pneumoniae
• Zoonotic bacteria – Coxiella burentii (Q fever), Chlamydia psittaci (psittacosis), Francisella tularensis (tularemia)

Viral Causes

Viruses are the most common cause of pneumonia in children

Common causes: ^[Ref]

• Influenza viruses (A and B) – most common overall
  • Severe in the elderly, those with chronic comorbidities (e.g. heart failure, COPD), pregnancy, immunocompromised
• Respiratory syncytial virus – most common cause in young children and infants
• Parainfluenza and human metapneumovirus
• Rhinoviruses
• Coronaviruses

Clinical Features

Typical Bacterial Pneumonia

Sudden onset of: ^[Ref]

• High fever
• Productive cough with purulent sputum
  • Typically yellow-greenish
  • Rust-coloured sputum is typical of Streptococcus pneumoniae
  • Red currant sputum is typical of Klebsiella (from tissue necrosis and haemorrhage)
  • NB its possible to have a non-productive cough in pneumonia
• Dyspnoea, tachypnoea
• Pleuritic chest pain
• Chills, rigors, malaise

Typical respiratory examination findings: ^[Ref]

Pneumonia Caused by Atypical Pathogens

Shared features:

• Dry cough
• Low-grade fever
• Flu-like symptoms (e.g. headache, myalgia, malaise)
• Auscultation is often unremarkable

Organism-specific features (the exam-common ones are listed):

Viral Pneumonia

Similar to atypical vs typical bacterial pneumonia, viral and bacterial pneumonia cannot be reliably differentiated based solely on clinical presentation or radiographic findings.

However, certain features, as outlined in the table below, can aid differentiation. ^[Ref]

Complications

Main complications:

• Uncomplicated parapneumonic pleural effusion (common)
• Pleural infection (includes complicated parapneumonic effusion and empyema)
• Lung abscess
• Sepsis
• Respiratory failure

Uncomplicated parapneumonic pleural effusion vs complicated parapneumonic effusion vs empyema:

Assessment and Management

Step 1 – Risk Stratification and Choice of Setting

Risk stratification tools/scores such as CRB65/CURB65 are used in adults (NOT used in children) with a clinical diagnosis of CAP

Primary Care (CRB65 Score)

Calculate the CRB65 score, then use it to guide management

Interpretation:

• 0: low risk (<1% mortality risk)
• 1 or 2: intermediate risk (1-10% mortality risk)
• 3 or 4: high risk (>10% mortality risk)

CRB65 score-informed management setting:

Secondary Care (Hospital) (CURB65 Score)

Calculate the CURB65 score, then use it to guide management

Interpretation:

• 0 or 1: low risk (<1% mortality risk)
• 2: intermediate risk (3-15% mortality risk)
• 3 or 4 or 5: high risk (>15% mortality risk)

CURB65 score-informed management setting:

Step 2 – Investigation and Diagnosis

Primary Care

In primary care, a chest X-ray is not routinely required to diagnose CAP if the history and examination findings are typical (and given CRB65 score is low)

Secondary Care (Hospital)

1st line standard imaging: chest X-ray

The latest NICE guidelines emphasised the use of lung ultrasound for:

• Rapid point-of-care diagnosis in a sick or deteriorating patient, or
• Investigation for associated complications (e.g. pleural infection, parapneumonic effusion), or
• Investigation for a possible alternative diagnosis (e.g. heart failure)

Other tests to consider:

• Baseline CRP on admission
• Respiratory tract samples
  • Ideally, a sputum sample for microbiological testing
  • If not, nasopharyngeal swab for respiratory screen
• Blood cultures
• Pneumococcal urinary antigen test (to support use of narrow-spectrum antibiotic)
• Testing for atypical pathogens
  • Legionella urinary antigen test (if there are risk factors)
  • Mycoplasma pneumoniae serology (or if available, PCR of respiratory tract samples is preferred)

Step 3 – Choosing Antibiotic Therapy

Standard course: oral antibiotics for 5 days

• Give IV antibiotics or a prolonged course of antibiotics as per clinical judgement

Choice of antibiotics is based on the severity of disease (low, moderate, high)

• Disease severity is determined by 1) clinical judgement AND 2) the CRB65/CURB65 score, with an emphasis placed on clinical judgement

NICE also recommends considering IV hydrocortisone (alternative: dexamethasone) for 4-7 days or until discharge, in addition to antibiotics in high-severity CAP in adults.

Step 4 – Monitoring Treatment

For those managed in hospital, consider measuring CRP or procalcitonin 3 or 4 days after starting treatment if there is a clinical concern about treatment failure:

• High levels of CRP or procalcitonin or levels that do not significantly improve with treatment are associated with treatment failure

Follow-Up

Patient Education

After starting treatment:

Explain to adults to expect the following recovery timeline (but rate of improvement will vary with the severity of the pneumonia):

• 1 week: fever should have resolved
• 4 weeks: chest pain and sputum production should have substantially reduced
• 6 weeks: cough and breathlessness should have substantially reduced
• 3 months: most symptoms should have resolved but fatigue may still be present
• 6 months: they will feel back to normal

Explain to parents or carers of children that for most children

• 3-4 days: resolution of fever (without use of antipyretics) AND dyspnoea
• Cough may persist for up to 4 weeks after discharge (despite gradual improvement), and does NOT usually require further review if the child is otherwise well

Follow-Up Chest X-Ray

Routine follow-up chest X-ray is NOT recommended

Follow-up chest X-ray at 6 weeks following discharge should be considered if:

• Risk factors for lung cancer / other underlying respiratory disease (e.g., smokers or >50 y/o, OR
• Persisting or deteriorating symptoms, OR
• Unexplained weight loss

Community-Acquired Pneumonia (CAP) – Paediatrics

The management of CAP in babies, children, and young people (<18 years; abbreviated as ‘BCY’ in this article) is largely similar to adult guidelines. This section highlights the key differences, particularly in diagnosis, risk stratification, and antibiotic duration.

Assessment and Risk Stratification

Risk stratification tools like CRB65 and CURB65 are NOT used in BCY (they should only be used in adults)

Severity assessment is based solely on severity of symptoms/signs & clinical judgement. Severe signs / symptoms of CAP include:

• Difficulty breathing
• SpO₂ <90%
• Raised heart rate
• Grunting
• Severe chest indrawing
• Inability to breastfeed or drink
• Lethargy / Reduced level of consciousness

Investigations

Investigations are largely the same as adults guidelines, with one minor difference:

• Urinary antigen tests are NOT routinely carried out for BCY with severe CAP (although indicated for adults with moderate-severe CAP)

Management

Referral

On clinical diagnosis of CAP → consider hospital referral or seek specialist paediatric advice on further investigation and management

Antibiotic Therapy

Duration

Duration of antibiotics therapy:

• Non-severe disease: depends on age
  • 3 months to 11 y/o (without complications) → 3 days
  • <3 months AND 12-17 y/o → 5 days (same as adults)

• Severe disease → 5 days (same as adults)

Choice of Antibiotics

Similar to adults, with minor differences (mainly that doxycycline should NOT be used in <12 y/o)

Corticosteroid Therapy

Corticosteroids (e.g., IV hydrocortisone or dexamethasone) are considered for high-severity CAP in adults, but the recommendation is NOT made for BCY with pneumonia

Hospital-Acquired Pneumonia (HAP)

Key difference from CAP is that the causative agent is usually different, therefore different antibiotics are recommended.

Definitions

• Hospital-acquired pneumonia: defined by pneumonia onset at least 48 hours after hospital admission, or those who presented to hospital with pneumonia but were discharged (from hospital) within the last 7-10 days

Aetiology

Up to 80% caused by: ^[Ref1][Ref2]

• Gram -ve bacilli (esp. Pseudomonas aeruginosa, Klebsiella species, E. coli, Acinetobacter species)
• Staphylococcus aureus

A significant proportion of HAP is due to multidrug-resistant strains

Management

Unlike CAP, the NICE guidance for HAP is essentially the same for adults and children. The only notable differences relate to paediatric dosing and certain alternative second-line antibiotic options, which fall outside the scope of this article.

Antibiotic choice is specifically based on:

1. Disease severity
   • The key distinction for HAP is that, unlike CAP, there are no specific scoring systems (like CRB65 or CURB65) recommended for assessing mortality risk and severity.
   • The severity of hospital-acquired pneumonia is determined primarily based on clinical judgement (as per NICE, severe disease is indicated for example by symptoms/signs of sepsis)
2. Local hospital and ward-based antimicrobial resistance data

Non-Severe Disease and Not High Risk of Resistance

Offer oral antibiotics. Choice of antibiotics:

• 1st line: co-amoxiclav 500/125mg TDS for 5 days
• 2nd line options:
  • Doxycycline
  • Cefalexin
  • Co-trimoxazole (off-label)
  • Levofloxacin (only if switching from IV levofloxacin)

Severe Disease or High Risk of Resistance

Offer IV antibiotics. Choice of antibiotics:

• Tazocin (piperacillin with tazobactam) – usually 1st line in hospital guidelines (but not explicitly stated in NICE guideline)
• Various cephalosporins (ceftazidime / ceftriaxone / cefuroxime / ceftazidime with avibactam)
• Meropenem
• Levofloxacin

Suspected or Confirmed MRSA

Offer IV dual antibiotic therapy; a 1st line antibiotic PLUS one of the following:

• Vancomycin
• Teicoplanin
• Linezolid (only if vancomycin cannot be used)

References