Pneumonia

Overview

Pneumonia describes the inflammation and infiltration of neutrophils in and around the alveoli and the terminal bronchioles. Pneumonia is usually caused by infection, most commonly by bacteria, then viruses, and certain fungi.

Classification

Pneumonia can be classified into:

• Community-acquired pneumonia (CAP): developed outside of hospital and most common
• Hospital-acquired pneumonia (HAP): developed in hospital (>48 hours after hospital admission)

This classification is important as the management of patients varies.

Causes

Community-Acquired Pneumonia

Typical bacteria:

• Streptococcus pneumoniae – most common cause
• Haemophilus influenzae
• Staphylococcus aureus
  • Usually seen following an influenza infection

Atypical bacteria:

• Mycoplasma pneumoniae
  • Flu-like symptoms (fever/malaise/myalgia) precede a dry cough
  • Some patients may develop erythema multiforme or erythema nodosum
• Legionella pneumophila
  • Classically spread by air-conditioning systems and in-building water systems
  • Patients have a dry cough
  • There may be diarrhoea, encephalopathy, and other neurological symptoms
  • There may be hyponatraemia, reduced lymphocytes, deranged LFTs, elevated creatine kinase
• Klebsiella pneumoniae
  • More common in alcoholics and diabetics
  • May happen after aspiration
  • Patients usually have sputum described as “red-currant”
• Chlamydia psittaci
  • Associated with bird-keepers
• Coxiella burnetii (Q fever)
  • Usually seen in farmers
  • AST and ALT may be raised

Fungal:

• Pneumocystis jirovecii
  • Usually clear chest and dry cough
  • Desaturations with exertion may be seen

Hospital-Acquired Pneumonia

Early-onset HAP (<5 days after hospital admission):

• Streptococcus pneumoniae

Late-onset HAP (>5 days after hospital admission):

• Methicillin-resistant Staphylococcus aureus
• Pseudomonas aeruginosa

Epidemiology

• Most episodes occur during the autumn or winter
• CAP results in around 100,000 hospital admissions a year
• The mortality rate is between 5-14%

Risk Factors

Community-Acquired Pneumonia

• Age >65 years
• Living in a nursing home/residential home
• COPD
• Smoking or exposure to cigarette smoke
• Alcohol abuse
• Poor dental hygiene

• Use of PPIs
  • Thought to be due to decreased gastric secretion allowing colonisation of the upper respiratory tract more easily
• Close contact/crowded spaces
• Diabetes mellitus
• Chronic liver disease
• Chronic renal disease
• Opioid use

Hospital-Acquired Pneumonia

• Poor hygiene or infection control
• Recent intubation and mechanical ventilation
• Exposure to MRSA and other multidrug-resistant bacteria
• Aspiration
• Use of PPIs
• Decreased consciousness
• Surgery in the chest or upper abdomen

Presentation

Community-acquired pneumonia

Patients have typical features of a lower respiratory tract infection with no other explanation for the symptoms (e.g. sinusitis, asthma, COPD etc.):

• Cough with or without sputum
• Dyspnoea
• Chest pain which may be pleuritic
• Fever
• Tachycardia
• Reduced oxygen saturations
• Coarse crackles on auscultation
• Reduced breath sounds on auscultation

Atypical pneumonia

Atypical pneumonias are usually community-acquired and seen in young people living in close proximity:

• Mycoplasma pneumoniae:
  • Flu-like symptoms (fever/malaise/myalgia) precede a dry cough
  • There may be erythema multiforme or erythema nodosum
• Legionella pneumoniae:
  • Classically spread by air-conditioning systems and in-building water systems
  • Dry cough
  • Diarrhoea
  • Encephalopathy
  • Hyponatraemia
  • Reduced lymphocytes
  • Deranged LFTs
  • Elevated creatine kinase
• Klebsiella pneumoniae:
  • More common in alcoholics and diabetics
  • May happen after aspiration
  • “Red-currant” sputum may be present
• Pneumocystis jirovecii:
  • Usually clear chest and dry cough
  • Desaturations with exertion may be seen
• Chlamydia psittaci:
  • Associated with bird-keepers
• Coxiella burnetii (Q fever):
  • Associated with farmers
  • AST and ALT may be raised

Differential Diagnoses

Acute bronchitis

• No shortness of breath
• No lung crackles
• Associated upper respiratory tract infection features may be seen e.g. sore throat or runny nose
• Wheeze may be present
• Fever is low-grade

Tuberculosis

• Duration of symptoms is usually longer
• There may be constitutional symptoms e.g. weight loss, anorexia, malaise, night sweats etc.
• Erythema nodosum may be present

Pneumothorax

• The onset is usually within minutes
• Auscultation may show unilaterally reduced breath sounds
• Auscultation may show unilateral hyper-resonance on percussion

Tension pneumothorax

• Tracheal deviation to the contralateral side
• Sweating
• Haemodynamic instability: tachycardia and hypotension

Pulmonary embolism

• Sudden onset shortness of breath and pleuritic chest pain
• Chest sounds are clear
• Tachycardia is usually seen
• Cough is usually non-productive but there may be haemoptysis
• There may be risk factors e.g. recent surgery/immobilisation/cancer
• There may be features of a deep vein thrombosis e.g. calf swelling

Lung cancer

• Constitutional symptoms present e.g. weight loss, fatigue, anorexia, malaise etc.
• Haemoptysis may be present

Empyema

• Features similar to pneumonia but usually develop over weeks
• May have a history of recent pneumonia and failure to respond to antibiotics or worsening of symptoms
• Constitutional symptoms may be present e.g. weight loss, fatigue, anorexia, malaise etc.
• Dullness to percussion present
• Signs of sepsis

Assessment

In primary care

CRB-65 is used to guide whether a patient should be managed in the community or hospital. Scores are stratified for the risk of death.

The following table shows features and their thresholds for scoring. Each feature is given one point if met:

Table 1 – the CRB-65 score

The scores should be interpreted as follows:

• 0 (low risk, mortality <1%): consider treating the patient at home
• 1-2 (moderate risk, mortality 1-10%): consider hospital referral for assessment and treatment
• ≥3 (high risk, mortality >10%): admit to hospital immediately

In secondary care

In hospitals, it is possible to have blood tests with results performed in a relatively quick timeframe. For this reason, CURB-65 is used. It is effectively the same as CRB-65 but has an additional feature of urea.

Table 2 – the CURB-65 score

The scores should be interpreted as follows:

• 0-1 (low risk, mortality <3%) – consider outpatient treatment
• 2 (moderate risk, mortality 3-15%) – consider hospital-based care
• ≥3 (high risk, mortality >15%) – consider intensive care assessment and management

Investigations

All patients

• Chest x-ray – not routinely done in primary care unless there is diagnostic doubt:
  • May show consolidation
  • May show atypical features e.g. cavitation, pleural effusion, multifocal consolidation etc. then other investigations should be considered
• Full blood count (FBC):
  • May show raised white cell count
  • The white cell count can be used to monitor treatment
• C-reactive protein (CRP):
  • Usually elevated
  • This can be monitored to see how patients respond to treatment

Other investigations

Other investigations are considered in specific scenarios:

• Blood cultures:
  • If patients are moderate-/high-risk according to CURB-65
• Sputum culture and gram stain – ideally before giving antibiotics:
  • If patients are moderate-/high-risk according to CURB-65 or
  • If patients do not improve with treatment
• Legionella urinary antigen:
  • If Legionella pneumonia is suspected
• Pneumococcal urinary antigen:
  • Can be considered as urinary testing is less affected by antibiotics
• Polymerase chain reaction and/or serological testing:
  • If the following are suspected:
    • Mycoplasma pneumoniae
    • Chlamydophila psittaci
    • Coxiella burnetii
    • Pneumocystis jirovecii

Management

In the community

• Low-severity (CRB-65 0):
  • 1^st-line: oral amoxicillin
  • If penicillin-allergic/atypical pathogens suspected: doxycycline or clarithromycin or erythromycin if pregnant
• Moderate-risk (CRB-65 1-2): consider hospital referral + amoxicillin + clarithromycin
  • 1^st-line: oral amoxicillin + clarithromycin (if atypical pathogen suspected)
  • If penicillin-allergic: doxycycline or clarithromycin
• High-risk (CRB-65 ≥3): urgent hospital admission via ambulance

Monitoring

In hospital

• The CRP and white cell count can be used to monitor a patient’s response to treatment:
  • White cell counts change much faster than CRP. CRP often “lags” behind during the course of the illness

In the community

• If a sample has been sent for microbiological analysis, consider changing the antibiotic to a narrower-spectrum one that the pathogen is sensitive to
• Consider a chest x-ray after 6 weeks for:
  • Signs and symptoms that persist despite treatment
  • People at risk of malignancy, particularly smokers and >50 years

Patient Advice

• Patients should seek help if:
  • Symptoms worsen rapidly or significantly
  • Symptoms do not improve within 3 days or as expected
  • They become systemically unwell
• Patients should be advised on when to expect to feel better. In general:
  • 1 week – fever resolves
  • 4 weeks – chest pain + sputum reduced
  • 6 weeks – cough + breathlessness reduced
  • 3 months – symptoms resolve but fatigue may remain
  • 6 months – all symptoms gone
• Patients should stop smoking and should be offered help with this

Complications

• Pleural effusion
• Sepsis
• Empyema
• Lung abscess
• Pneumothorax
• Acute kidney injury
• Post-infective bronchiectasis

Prognosis

• A higher CRB-65/CURB-65 score is associated with a worse prognosis