See also separate articles on Aspiration Pneumonia, Pneumocystis, LRTI in Children.

Pneumonia is characterised by acute inflammation with an intense infiltration of neutrophils in and around the alveoli and the terminal bronchioles. The affected bronchopulmonary segment or the entire lobe may be consolidated by the resulting inflammation and oedema.

Epidemiology

The annual incidence of community-acquired pneumonia is 5-11 per 1,000 adult population. The illness results in about 83,000 hospital admissions each year and is the fifth leading cause of death in the UK. Most episodes occur during the autumn or winter.

Risk factors

• Age: especially infants, young children and the elderly.
• Lifestyle: smoking, alcohol.
• Preceding viral infections, e.g. influenza predisposing to Streptococcus pneumoniae infection.
• Respiratory: asthma, chronic obstructive pulmonary disease (COPD), malignancy, bronchiectasis, cystic fibrosis.
• Immunosuppression, AIDS, cytotoxic therapy - increased risk of infection with Staphylococcus spp., tuberculosis, Gram-negative bacilli and Pneumocystis jirovecii (carinii).
• Intravenous drug abuse, often associated with Staphylococcus aureus infection.
• Hospitalisation - often involving Gram-negative organisms.
• Aspiration pneumonia: patients with impaired consciousness, neurological disease such as cerebrovascular or Parkinson's disease, or patients with oesophageal obstruction are at risk of aspiration pneumonia which usually affects the right lung and is caused by anaerobes from the oropharynx.
• Underlying predisposing disease: diabetes mellitus, cardiovascular disease.

Community-acquired pneumonia¹

The presence of symptoms and signs consistent with acute lower respiratory tract infection, in association with new radiographic shadowing for which there is no alternative explanation, which is managed as pneumonia and is the main reason for seeking healthcare advice.²

Pathogenesis

Organisms include: Streptococcus pneumoniae, Mycoplasma pneumoniae, Haemophilus influenzae, Chlamydophila (Chlamydia) pneumoniae and respiratory viruses.²

Epidemiology

• The annual incidence of community-acquired pneumonia in the United Kingdom is 5-11 cases per 1000 adult population.²
• Community-acquired pneumonia (CAP) is the fifth leading cause of death in the UK.

Risk factors

• Winter months.
• The very young and the very old.
• Chronic lung, heart, renal and liver disease.
• Diabetes mellitus.
• Immunosuppression.

Presentation

• Symptoms: cough, purulent sputum which may be blood stained or rust coloured, breathlessness, fever, malaise.
• Diagnosis is unlikely if no focal chest signs and normal heart rate, respiratory rate and temperature.
• Elderly may present with mainly systemic complaints of malaise, fatigue, anorexia and myalgia. Young children may present with non-specific symptoms or abdominal pain.
• Signs: tachypnoea, bronchial breathing, crepitations, pleural rub, dullness with percussion.

Management

Patients with suspected CAP should be advised not to smoke, to rest, and to drink plenty of fluids. Other general measures include:¹

• Oxygen for hypoxia; ventilation if severe hypoxia.
• Fluids for dehydration.
• Analgesics: non-steroidal anti-inflammatory drugs (NSAIDs) and paracetamol - for mild pleuritic pain; more severe pain may require opiate analgesia but care is needed not to aggravate CO₂ retention.
• Nebulised saline may help expectoration.
• Chest physiotherapy has doubtful benefit. Physiotherapy may be more important in helping to mobilise the patient.

Those who fail to improve after 48 hours of treatment should be considered for hospital admission or a chest x-ray. All cases that cause concern should be referred for further investigation.²

Antibiotics

• Antibacterials are recommended in all suspected cases of pneumonia, starting as soon as possible.³
• Uncomplicated community-acquired pneumonia:⁴
  • Amoxicillin if previously healthy chest (or erythromycin/clarithromycin if penicillin-allergic).
  • Add flucloxacillin if staphylococci suspected, e.g. in influenza or measles (or vancomycin if MRSA suspected).
• Initial empirical treatment of adults with community-acquired pneumonia treated in hospital:²
  • Non-severe disease: oral amoxicillin plus erythromycin or clarithromycin; alternatively oral moxifloxacin or levofloxacin.
  • Severe disease: intravenous co-amoxiclav or cefuroxime or cefotaxime plus erythromycin/clarithromycin; alternatively intravenous levofloxacin plus benzylpenicillin.
• Severe community-acquired pneumonia of unknown aetiology:⁴
  • Cefuroxime (or cefotaxime) plus erythromycin.
  • Add flucloxacillin if staphylococci suspected (or vancomycin if MRSA suspected).

BTS guidelines suggest at least 7 days for patients managed in the community and 10 days for patients with severe disease.²

Pneumonias due to atypical pathogens

Pathogenesis

Formally known as "atypical pneumonias", these are most commonly due to pulmonary infection with:

• Mycoplasma pneumoniae.
• Chlamydophila (Chlamydia) pneumoniae.
• Legionella pneumophila.

Other microorganisms that cause similar patterns of presentation via pulmonary infection include:

• Chlamydophila psittaci (exposure to birds, particularly ill ones, is a useful clue in the history).
• Coxiella burnetii (presenting as Q fever).
• Viral pneumonias including influenza A, severe acute respiratory syndrome (SARS), RSV, adenoviridae and pneumonitis due to varicella (chickenpox pneumonitis).

Epidemiology

• It is thought that the three main atypical organisms might be implicated in up to 40% of community acquired pneumonias.⁵
• By the age of 20, 50% of people in the United States have detectable levels of antibody to Chlamydophila pneumoniae.⁵

Risk factors

• Mycoplasma and chlamydophila spread by person to person contact, and spread is most common in closed populations e.g. schools, offices.
• Legionellae are found most commonly in freshwater and man-made water systems.

Presentation

• Mycoplasma pneumoniae:⁶
  • Vague and slow-onset history over a few days or weeks of constitutional upset, fever, headache, dry cough with tracheitic ± pleuritic pain, myalgia, malaise and sore throat.
  • This is like many of the common viral illnesses, but the persistence and progression of symptoms is what helps to mark it out.
  • In otherwise healthy individuals, it usually resolves spontaneously over a few weeks.
  • The hacking, dry cough can be very persistent.
  • Extra-respiratory features include rashes such as erythema multiforme, erythema nodosum and urticaria; neurological complications like Guillain-Barré syndrome, transverse myelitis, cerebellar ataxia and aseptic meningitis; haematological complications such as cold agglutinin disease and haemolytic anaemia; joint symptoms like arthralgia and arthritis; cardiac complications such as pericarditis and myocarditis; rarely may cause pancreatitis.
• Chlamydophila pneumoniae:⁷
  • Gradual onset which may show improvement before worsening again; incubation period 3–4 weeks.
  • Initial non-specific URTI symptoms lead on to bronchitic or pneumonic features.
  • Most of those infected remain quite well or are asymptomatic.
  • Cough with scanty sputum is a prominent feature.
  • Hoarseness is a common feature.
  • Headache affects the majority of symptomatic sufferers.
  • Fever is relatively unusual.
  • Symptoms may drag on for weeks or months, despite a course of appropriate antibiotics.
  • Where it causes significant problems, this may be due to secondary infection or co-existing illness, e.g. diabetes.
• Legionella pneumophila:⁸
  • Tends to be the most severe of the pneumonias due to atypical pathogens. See Legionella and Legionnaires' Disease article.
  • Focal outbreaks centred around poorly-maintained air-conditioning or humidification systems (although this is often noted retrospectively by public health physicians).
  • 2–10 days incubation period.
  • Initial mild headache and myalgia leading to high fever, chills and repeated rigors; non-chest symptoms often predominate early on.
  • Cough is nearly always present, initially unproductive, but may lead to expectoration later.
  • Dyspnoea, pleuritic pain and haemoptysis are not uncommon.
  • Gastrointestinal upset such as diarrhoea, nausea and vomiting or loss of appetite/anorexia may occur.
  • There may be neurological complications such as confusion, disorientation and focal neurological deficit.
  • Arthralgia and myalgia are often reported.
  • Severe complications include pancreatitis, peritonitis, pericarditis, myocarditis, endocarditis and glomerulonephritis.

Signs

• Vital signs should be checked.
• Look for evidence of extra-thoracic involvement if an atypical pathogen is suspected.
• On the whole, chest signs are not helpful. Indeed, it is often the discordance between the chest signs and the illness of the patient, or the floridity of initial CXR appearance, that raises the suspicion of an atypical pathogen.
• Non-specific chest signs and evidence of consolidation may be found, but this is much less common than in the 'standard' pneumonias.
• There may be signs in other systems due to complications of the infection.

Management

Pneumonias due to atypical pathogens are usually treated as for other community-acquired pneumonias, at least initially.

• There is no evidence that routinely giving antibiotics active against atypical organisms leads to better outcomes in non-severe community-based cases of pneumonia.⁹
• Macrolides, such as erythromycin, clarithromycin and azithromycin, have been shown to be effective in the treatment of all three infective organisms.
• Erythromycin tends to be less well tolerated, and although effective in the treatment of mycoplasma and chlamydophila, there are few trials demonstrating its efficacy in the treatment of legionella.⁵
• Severe legionella infections may require rifampicin as well as a macrolide.
• Tetracycline, doxycycline and fluoroquinolones are also effective against all three infective organisms.

Hospital-acquired pneumonia

This is defined as a new infection of lung parenchyma appearing more than 48 hours after admission to the hospital.¹⁰

• It occurs mostly in patients who are severely debilitated, immunocompromised or mechanically ventilated.
• Infection occurring during the first four days of the hospital stay is usually caused by S. pneumoniae, H. influenzae and M. catarrhalis.
• Onset more than four days after admission is more often caused by Gram-negative enterobacteria, S. aureus or L. pneumophila.
• Hospital-acquired pneumonia is often caused by multiple organisms.

Differential diagnosis

• Different organism responsible.
• Pulmonary oedema.
• Pleural effusion.
• Pneumothorax.
• Pulmonary embolus.
• Asthma.
• Chronic obstructive pulmonary disease (COPD).
• Bronchiectasis.
• Fibrosing alveolitis.
• Neoplasm.
• Sarcoidosis.
• Pneumonia complication e.g. empyema, lung abscess.

Investigations

General investigations are not necessary for the majority of patients who are managed in the community. Pulse oximeters allow for simple assessment of oxygenation. When a patient is admitted to hospital:

• Full blood count with differential white cell count.
• C-reactive protein to aid diagnosis and as a baseline measure.
• Renal function and electrolytes.
• Liver function tests.
• Blood cultures.
• Chest x-ray: the Royal College of Radiologists recommends a follow-up chest x-ray 6 weeks after recovery from pneumonia for all adults who have persistent symptoms or signs, or who are at higher risk of underlying malignancy (smokers and those aged over 50 years). Follow-up chest x-ray in children is recommended only if there are persisting clinical symptoms or signs.
• Sputum examination and culture.
• Cold agglutinins to detect Mycoplasma pneumoniae.
• Immuno-electrophoresis: pneumococcal antigen from sputum or blood.
• Pulse oximetry or blood gases.
• Acute and convalescent serology to detect antibodies to viruses and atypical pathogens.
• Aspiration of pleural fluid (for biochemistry and culture).

Hospital admission for community-acquired infection

• The decision to admit is based on a variety of factors including severity of illness, age, underlying health problems and social circumstances.
• The British Thoracic Society guidelines for community-acquired pneumonia in adults recommend use of the CURB-65 score. A 6-point score, one point for each of Confusion, Urea >7 mmol/L, Respiratory rate 30 breaths/minute or more, systolic Blood pressure below 90 mm Hg (or diastolic below 60 mm Hg), age 65 years or older.
  • Patients who have a CURB-65 score of 0 are at low risk of death and do not normally require hospitalisation for clinical reasons.
  • Patients who have a CURB-65 score of 1 or 2 are at increased risk of death and hospital referral and assessment should be considered, particularly with a score of 2.
  • Patients who have a CURB-65 score of 3 or more are at high risk of death and require urgent hospital admission.

Complications

• Pleural effusion - usually sterile.
• Empyema: a reactive effusion can occur but is trivial. Empyema is potentially more serious and presents as the persistence of fever and leukocytosis after 4-5 days of appropriate antibiotic therapy.
• Lung abscess: can occur in disease due to S. pneumoniae and is classically seen in patients with klebsiella or staphylococcal pneumonia.
• Pneumatocele.
• Pneumothorax.
• Pyopneumothorax - e.g. following rupture of a staphylococcal lung abscess in the pleural cavity.
• Deep vein thrombosis.
• Septicaemia, pericarditis, endocarditis, osteomyelitis, septic arthritis, cerebral abscess, meningitis (particularly in pneumococcal pneumonia).
• Postinfective bronchiectasis.
• Acute renal failure.

Prognosis

Mortality from community-acquired pneumonia is about 1% but, for patients in hospital, mortality is approximately 13-15% and it ranges from 22-54% in patients requiring intensive care.
The prognosis for Mycoplasma pneumoniae is generally good with most patients making a full recovery. The mortality rate is approximately 1.4%, with the majority of deaths occurring in the elderly or patients with co-existing pathologies.⁵Most cases of chlamydophilal infection are mild. The mortality rate is approximately 9%, usually associated with secondary infection or underlying disease.⁵
Legionella has the most severe course, and may cause significant morbidity if not treated early. The mortality rate is 14%.⁵

Prevention

• Early appropriate antibiotic therapy reduces mortality and morbidity.
• Influenza and pneumococcal vaccination.
• Targeted risk reduction, such as smoking cessation.

Document references

1. Guidelines for the management of community acquired pneumonia in adults. British Thoracic Society (2009)
2. Durrington HJ, Summers C; Recent changes in the management of community acquired pneumonia in adults. BMJ. 2008 Jun 21;336(7658):1429-33.
3. Marrie TJ, Carriere KC, Jin Y, et al; Factors associated with death among adults <55 years of age hospitalized for community-acquired pneumonia. Clin Infect Dis. 2003 Feb 15;36(4):413-21. Epub 2003 Jan 22. [abstract]
4. BNF; Section 5.1; Antibacterial drugs.
5. Thibodeau KP, Viera AJ; Atypical pathogens and challenges in community-acquired pneumonia. Am Fam Physician. 2004 Apr 1;69(7):1699-706. [abstract]
6. MJ Bono, Mycoplasma Pneumonia, eMedicine, Apr 2010; Concise overview from A&E perspective
7. Oba Y, Chlamydial Pneumonias, eMedicine, Jun 2010; Overview of infection with the three main chlamydial species that cause respiratory disease in humans
8. Smeeks F, Savage S; Legionnnaires Disease, eMedicine, June 2009.
9. Mills GD, Oehley MR, Arrol B; Effectiveness of beta lactam antibiotics compared with antibiotics active against atypical pathogens in non-severe community acquired pneumonia: meta-analysis. BMJ. 2005 Feb 26;330(7489):456. Epub 2005 Jan 31. [abstract]
10. Guidelines for the management of hospital-acquired pneumonia in the UK, British Society for Antimicrobial Chemotherapy (2008)

Internet and further reading

• Respiratory tract infections, NICE Clinical Guideline (July 2008); Prescribing of antibiotics for self-limiting respiratory tract infections in adults and children in primary care
• Chest infections - adult, Clinical Knowledge Summaries (2007)
• Pneumococcal disease. Professor Brian Duerden, CBE, explains how pneumococcal disease can cause pneumonia and other invasive infections. He describes the effects of the disease on older people and children, and what you can do to prevent it. Short video from NHS Choices (June 2009)

Acknowledgements