There are separate articles on Aspiration Pneumonia, Pneumocystis Jirovecii Pneumonia and Lower Respiratory Tract Infection 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.
- Age: especially infants, young children and the elderly.
- Lifestyle: smoking, alcohol.
- Preceding viral infections, eg 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 P. jirovecii.
- 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.
This is defined as 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. This is managed as pneumonia.
The most likely organisms are: S. pneumoniae, S. aureus, Mycoplasma pneumoniae, Haemophilus influenzae, Chlamydophila pneumoniae and respiratory viruses. Mixed pathogens occur up to 25% of the time.
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- The annual incidence of community-acquired pneumonia (CAP) in the UK is 5-11 cases per 1,000 adult population.
- CAP is the fifth leading cause of death in the UK.
- CAP results in about 83,000 hospital admissions each year, with most episodes occurring during the autumn or winter.
- Symptoms: cough, purulent sputum which may be blood-stained or rust-coloured, breathlessness, fever, malaise.
- Diagnosis is unlikely if there are no focal chest signs and heart rate, respiratory rate and temperature are normal.
- The elderly may present with mainly systemic complaints of malaise, fatigue, anorexia and myalgia. Young children may present with nonspecific symptoms or abdominal pain.
- Signs: tachypnoea, bronchial breathing, crepitations, pleural rub, dullness with percussion.
Patients with suspected CAP should be advised not to smoke, and to rest and drink plenty of fluids. Other general measures include:
- Oxygen for hypoxia; ventilation if there is 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 CXR. All cases that cause concern should be referred for further investigation. Community patients should be advised to return if their symptoms do not resolve after three weeks.
- Antibacterials are recommended in all suspected cases of pneumonia, starting as soon as possible.
- Uncomplicated CAP:
- Amoxicillin or tetracycline if the patient has a previously healthy chest (or erythromycin/clarithromycin if there is a known allergy).
- Add flucloxacillin if staphylococcal infection is suspected, eg in influenza or measles (or vancomycin if meticillin-resistant S. aureus (MRSA) is suspected).
- Initial empirical treatment of adults with CAP treated in hospital:
- 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.
Flucloxacillin should be added if staphylococcal infection is suspected (or vancomycin if MRSA suspected).
British Thoracic Society (BTS) guidelines suggest at least seven days for patients managed in the community and ten days for patients with severe disease.
Pneumonias due to atypical pathogens
Formally known as 'atypical pneumonias', these are most commonly due to pulmonary infection with:
- Mycoplasma pneumoniae
- Chlamydophila pneumoniae
- Legionella pneumophila
Other micro-organisms 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), respiratory syncytial virus (RSV), adenoviridae and pneumonitis due to varicella (chickenpox pneumonitis).
It is thought that the three main atypical organisms might be implicated in up to 30% of community-acquired pneumonias (CAP).
- Mycoplasma and chlamydophila spread by person-to-person contact, and spread is most common in closed populations, eg schools, offices.
- Legionellae are found most commonly in fresh water and man-made water systems.
- Mycoplasma pneumoniae:
- 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:
- Gradual onset, which may show improvement before worsening again; incubation period is 3-4 weeks.
- Initial nonspecific upper respiratory tract infection (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, eg diabetes.
- Legionella pneumophila:
- This tends to be the most severe of the pneumonias due to atypical pathogens. See separate article Legionella and Legionnaires' Disease.
- 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.
- 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.
- Nonspecific 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.
Pneumonias due to atypical pathogens are usually treated as for other CAP, at least initially. There is little value in serological testing for most patients with CAP.
- There is no evidence that routinely giving antibiotics active against atypical organisms leads to better outcomes in non-severe community-based cases of pneumonia.
- Macrolides, such as erythromycin, clarithromycin and azithromycin, have been shown to be effective in the treatment of all three most common infective organisms. Resistance to macrolides is a growing concern.
- Severe legionella infections may require rifampicin as well as a macrolide.
- Tetracycline, doxycycline and fluoroquinolones are also effective against all three of the common infective organisms.
This is defined as a new infection of lung parenchyma appearing more than 48 hours after admission to the hospital.
- 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 Moraxella 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.
- Different organism responsible.
- Pulmonary oedema.
- Pleural effusion.
- Pulmonary embolus.
- Chronic obstructive pulmonary disease (COPD).
- Fibrosing alveolitis.
- Pneumonia complication, eg empyema, lung abscess.
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:
- FBC with differential white cell count.
- CRP (to aid diagnosis and as a baseline measure).
- Renal function and electrolytes.
- Blood cultures.
- CXR. (A follow-up CXR six weeks after recovery from pneumonia is recommended.)
- Sputum examination and culture.
- Pulse oximetry or blood gases.
- 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 BTS guidelines for community-acquired pneumonia (CAP) in adults recommend use of the CURB-65 score. A 6-point score, one point for each of C onfusion, U rea >7 mmol/L, R espiratory rate 30 breaths/minute or more, systolic B lood 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.
- Pleural effusion that is 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.
- Pyopneumothorax - eg 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.
Mortality from community-acquired pneumonia (CAP) is less than 1% in those well enough to be managed in the community. Patients in hospital have mortality rates of approximately 6-12%. This rises to over 50% in patients requiring intensive care.
Legionella has the most severe course and may cause significant morbidity if not treated early. The mortality rate is around 10%.
- Early appropriate antibiotic therapy reduces mortality and morbidity.
- Influenza and pneumococcal vaccination.
- Targeted risk reduction, such as smoking cessation.
Further reading & references
- Respiratory tract infections, NICE Clinical Guideline (July 2008)
- Kamangar N et al; Bacterial Pneumonia, Medscape, Jan 2012
- Guidelines for the management of community acquired pneumonia in adults, British Thoracic Society (2009)
- Durrington HJ, Summers C; Recent changes in the management of community acquired pneumonia in adults. BMJ. 2008 Jun 21;336(7658):1429-33.
- Guidelines for the management of adult lower respiratory tract infections, European Respiratory Society and European Society of Clinical Microbiology and Infectious Diseases (September 2011)
- Chest infections - adult, Prodigy (August 2007)
- Bartlett JG; Is activity against "atypical" pathogens necessary in the treatment protocols for Clin Infect Dis. 2008 Dec 1;47 Suppl 3:S232-6.
- MJ Bono, Mycoplasmal Pneumonia, Medscape, Mar 2011; concise overview from A&E perspective
- Oba Y, Chlamydial Pneumonias, Medscape, Mar 2011; overview of infection with the three main chlamydial species that cause respiratory disease in humans
- Smeeks FC, Legionnaires Disease in Emergency Medicine, Medscape, Mar 2011
- Robenshtok E, Shefet D, Gafter-Gvili A, et al; Empiric antibiotic coverage of atypical pathogens for community acquired Cochrane Database Syst Rev. 2008 Jan 23;(1):CD004418.
- Thiem U, Heppner HJ, Pientka L; Elderly patients with community-acquired pneumonia: optimal treatment strategies. Drugs Aging. 2011 Jul 1;28(7):519-37. doi: 10.2165/11591980-000000000-00000.
- Guidelines for the management of hospital-acquired pneumonia in the UK, British Society for Antimicrobial Chemotherapy (2008)
- Fiumefreddo R, Zaborsky R, Haeuptle J, et al; Clinical predictors for Legionella in patients presenting with community-acquired BMC Pulm Med. 2009 Jan 19;9:4.
|Original Author: Dr Colin Tidy||Current Version: Dr Hayley Willacy||Peer Reviewer: Prof Cathy Jackson|
|Last Checked: 19/04/2012||Document ID: 2624 Version: 26||© EMIS|
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