Introduction

Pneumonia is one of the most common presentations encountered in clinical practice. Strictly speaking it describes any inflammatory condition affecting the alveoli of the lungs, but in the vast majority of patients this is secondary to a bacterial infection.

Classification

Community vs. hospital-acquired pneumonia

The majority of patients develop pneumonia within the community, i.e. outside of hospital and these patients are said to have community-acquired pneumonia (CAP). Patients who develop pneumonia within hospitals are said to have hospital-acquired pneumonia. The distinction is important as the causative organisms vary and hence first-line antibiotic guidelines are also different.


Atypical pneumonia

Some type of infections give rise to atypical pneumonias. These are termed atypical and may have the following features:
  • symptoms may be subacute or less severe hence the term 'walking pneumonia'
  • absence of lobar consolidation on chest x-ray
  • not detectable on Gram stain
  • lack of response to penicillin antibiotics

Examples of atypical pneumonias include:
  • Legionella pneumonia
  • Mycoplasma pneumonia
  • Q fever secondary to Coxiella burnetii
  • psittacosis secondary to Chlamydophila psittaci

Epidemiology

  • Incidence: 500.00 cases per 100,000 person-years
  • Peak incidence: 70+ years
  • Sex ratio: 1:1
Condition Relative
incidence
Viral upper respiratory tract infections60.00
Acute bronchitis8.80
Musculoskeletal chest pain2.00
Acute exacerbation of COPD1.50
Pneumonia1
<1 1-5 6+ 16+ 30+ 40+ 50+ 60+ 70+ 80+

Aetiology

Risk factors:
  • Aged under 5 or over 65-years-old
  • Smoking cigarettes
  • Recent viral respiratory tract infection
  • Chronic respiratory diseases: e.g. cystic fibrosis and COPD
  • Immunosuppression: e.g. cytotoxic drug therapy and HIV
  • Patients at risk of aspiration: e.g. those with neurological diseases such as Parkinson's disease or those with oesophageal obstruction
  • IV drug users
  • Other non-respiratory co-morbidities: e.g. diabetes and cardiovascular disease

Pathophysiology

Bacterial pneumonia is by far the most common type of pneumonia seen in clinical practice. Other infective causes include:
  • viral
  • fungal (e.g. Pneumocystis jiroveci)

Once a pathogen has entered the lower respiratory tract an inflammatory cascade begins. Neutrophils migrate to the infected alveoli and release cytokines which activate an immune response and induce fever. This process leads to an accumulation of fluid and pus within the alveoli that impairs gaseous exchange, leading to a hypoxic state which is characteristic of pneumonia.

Clinical features

Signs and symptoms:

Symptoms:

Signs:
  • Signs of systemic infection: High temperature, tachycardia, hypotension, confusion
  • Tachypnoea
  • Low oxygen saturation (below 95% or below 88% in patients with COPD)
  • On auscultation, there may be reduced breath sounds, bronchial breathing, and crepitations/crackles
  • Dullness on percussion (fluid)

Management

Primary care setting

NICE recommends that patients should initially be assessed in primary care using the CRB65 criteria:


Criterion
Marker
CConfusion (abbreviated mental test score <= 8/10)
RRespiration rate >= 30/min
BBlood pressure: systolic <= 90 mmHg and/or diastolic <= 60 mmHg
65Aged >= 65 years

Patients are stratified for risk of death as follows:
  • 0: low risk (less than 1% mortality risk)
  • 1 or 2: intermediate risk (1-10% mortality risk)
  • 3 or 4: high risk (more than 10% mortality risk).

NICE recommend, in conjunction with clinical judgement:
  • home-based care for patients with a CRB65 score of 0
  • hospital assessment for all other patients, particularly those with a CRB65 score of 2 or more.

NICE also mention point-of-care CRP test. This is currently not widely available but they make the following recommendation with reference to the use of antibiotic therapy:
  • CRP < 20 mg/L - do not routinely offer antibiotic therapy
  • CRP 20 - 100 mg/L - consider a delayed antibiotic prescription
  • CRP > 100 mg/L - offer antibiotic therapy


Secondary care setting

Note that in hospital, once blood tests are available the CURB65, rather than the CRB65, can be used. This adds an extra criterion of urea > 7 mmol/L:


Criterion
Marker
CConfusion (abbreviated mental test score <= 8/10)
Uurea > 7 mmol/L
RRespiration rate >= 30/min
BBlood pressure: systolic <= 90 mmHg and/or diastolic <= 60 mmHg
65Aged >= 65 years

NICE recommend, in conjunction with clinical judgement:
  • consider home-based care for patients with a CURB65 score of 0 or 1 - low risk (less than 3% mortality risk)
  • consider hospital-based care for patients with a CURB65 score of 2 or more - intermediate risk (3-15% mortality risk)
  • consider intensive care assessment for patients with a CURB65 score of 3 or more - high risk (more than 15% mortality risk)

Investigations
  • chest x-ray
  • in intermediate or high-risk patients NICE recommend blood and sputum cultures, pneumococcal and legionella urinary antigen tests
  • CRP monitoring is recommend for admitted patients to help determine response to treatment

Management of low-severity community acquired pneumonia
  • amoxicillin is first-line
  • if penicillin allergic then use a macrolide or tetracycline
  • NICE now recommend a 5 day course of antibiotics for patients with low severity community acquired pneumonia

Management of moderate and high-severity community acquired pneumonia
  • dual antibiotic therapy is recommended with amoxicillin and a macrolide
  • a 7-10 day course is recommended
  • NICE recommend considering a beta-lactamase stable penicillin such as co-amoxiclav, ceftriaxone or piperacillin with tazobactam and a macrolide in high-severity community acquired pneumonia

Complications

  • sepsis
  • lung abscesses
  • pleural effusion
    • parapneumonic
    • empyema
  • acute respiratory distress syndrome

Prognosis

Discharge criteria and advice post-discharge

NICE recommend that patients are not routinely discharged if in the past 24 hours they have had 2 or more of the following findings:
  • temperature higher than 37.5°C
  • respiratory rate 24 breaths per minute or more
  • heart rate over 100 beats per minute
  • systolic blood pressure 90 mmHg or less
  • oxygen saturation under 90% on room air
  • abnormal mental status
  • inability to eat without assistance.

They also recommend delaying discharge if the temperature is higher than 37.5°C.

NICE recommend that the following information is given to patients with pneumonia in terms of how quickly their symptoms should symptoms should resolve:

TimeProgress
1 weekFever should have resolved
4 weeksChest pain and sputum production should have substantially reduced
6 weeksCough and breathlessness should have substantially reduced
3 monthsMost symptoms should have resolved but fatigue may still be present
6 monthsMost people will feel back to normal.

TYPES

Legionella pneumonia
Mycoplasma pneumonia
Psittacosis
Q fever