Pneumonia in its most common form is an infection of the lung air spaces. Can be caused by a variety of micro-organisms - viruses, bacteria, fungi and parasites. Pneumonia can also be caused by aspiration of irritants such as corrosive chemicals or noxious fumes.
The causative organism depends on many factors including exposure to infection, host immunity and others. Viral disease may predispose to bacterial secondary infection, as seen in influenza. Pneumonia is a common disease, can affect the young & healthy, and in some patients can be lethal.
- Pleuritic chest pains
- Phlegm - often dry at first but then productive usually yellow, bloodstained or rust-coloured.
- Herpes labialis
Can be unilateral or bilateral. Physical examination has a limited sensitivity and specificity.
- Reduced expansion
- Reduced breath sounds
- Dull percussion note
- Increased vocal resonance and tactile vocal fremitus
Wheeze virtually always indicates a viral cause.
- Usually diagnosed on plain chest radiography.
Pneumonia is commoner in children under 5, those elder than 65 years, males compared to females. It can for clinical purposes be subdivided into community acquired, hospital acquired and atypical as causative organisms and treatment is different, but however classified it remains the second largest cause of death worldwide. The age standardised death rate as of 2013 was 42 per 100,000 population. In the elderly and immunosuppressed incidence is up to 14/1000 per year.
- Post splenectomy
- Heart disease
- Chest disease
Some common variants of the FER gene that encodes a non-receptor protein tyrosine kinase are protective. Mortality in ITU patients was 9·5% in patients carrying the CC genotype, 15% in those carrying the TC genotype, and 25% in those carrying the TT genotype. This effect is likely to be due to modulation of neutrophil chemotaxis and endothelial permeability. TLR6 polymorphisms appear to be associated with disease caused by Klebsiella pneumoniae infection and Legionnaires disease as well as other infections.
- Urea >7 mmol/l
- Respiratory rate >30/min
- BP - Systolic <90mmHg or diastolic <60mmHg
- >65 years old
A score >3 diagnoses severe community-acquired pneumonia usually requiring admission and intravenous antibiotics.
Mortality in Western countries of those not admitted according to these criteria is less than 1%, but 30 day mortality of those needing admission is at least four times this, and some series have reached 18%, or up to 50% if ITU admission is required.
- Good hygiene and basic healthy living choices
- Immunisation against viral respiratory pathogens such as influenza appears to reduce secondary pneumonia in at risk groups
- Good infection control practices (as SARS and MERS have shown it is likely to be inadequate due to inconvenience and resource implications)
- Use narrowest spectrum antibiotic choice consistent with relevant local isolation and susceptibility patterns
- This means respect local antimicrobial advice and only use national or other advice when
such advice is not available
- Commence antibiotic treatment as soon as possible (within an hour of diagnosis !)
Community acquired pneumonia
The main isolated pathogen is Streptococcus pneumoniae, explaining 35% of presentations in Europe, with some variation by population and time of year (typically winter peaks of metapneumovirus, influenza A and B viruses, RSV, Staphylococcus aureus, and Streptococcus pneumoniae. For example in those from the USA requiring hospitalisation it is somewhat rarer in terms of potential pathogen's actually isolated/demonstrated by PCR where recent figures were:
- Pathogen was detected in 38%
Intensive care need doubles the rate of Streptococcus pneumoniae to 8%, increases rate for Staphylococcus aureus by five times to 5% and enterobacteriaceae by three times to 3%. Such data is important as it suggests in Western countries that the viral load may have been underestimated and that we have an incomplete understanding of aetiology based upon extrapolation. Indeed some have difficulty with assigning viruses as the cause of pneumonia given classic pathophysiology teaching. Also important is that organisms such as Pseudomonas aeruginosa, ESBL+ enterobacteriaceae and MRSA are much commoner in the immunocompromised.
Guides to treatment
- Antibiotics (at least 5 days) consistent with local guidelines (which may include biomarker measurement to determine duration)
- In primary community treatment CRP measurement can reduce exposure to antibiotics safely and NICE recommends no use of antibiotics if chest symptoms without convincing evidence of CAP and CRP<20 ng/L.
- Procalcitonin (PCT) is increasingly being used in the ITU and new dysponea hospital presentations to distinguish between bacterial and non-bacterial presentations. The cut off is 0.25 µg/L.
- Microbiology testing is only recommended where probability of changing the initial empirical antibiotic is high such as hospitalised CAP:
- Sputum culture should be universal if productive of sputum
- Blood culture, legionella and pneumococcal urinary antigen if moderately ill
- Role of corticosteroids unclear but they appear to reduce hospital length of stay
- Follow up interval minimum is 72 hours, shorter if hospitalised.
Hospital acquired pneumonia
The British Society for Antimicrobial Chemotherapy treatment guidelines were published in 2008. These cover most aspects including prevention of ventilator associated pneumonia in detail. Some highlights include:
- Non-invasive positive pressure ventilation should be used rather than ventilation whenever possible - A grade recommendation
- Stress ulcer prophylaxis should be avoided where possible in ventilated patients - A grade recommendation
- Selective decontamination of the digestive tract (SDD) should be considered in ITU where mechanical ventilation will be for ≥48 hours (prevents ventilator associated pneumonia) - A grade recommendation
- Subglottic drainage and positioning in ventilated patients to reduce aspiration - B grade recommendation
- Legionella control of hospital water - B grade recommendation
- Ventilate in semi-recumbent position (30–45°) if no contraindications - B grade recommendation
- Avoid red cell transfusions if possible - C grade recommendation
- Antimicrobial monotherapy where possible - A grade recommendation and if response to therapy, the routine duration should be no longer than 8 days - C grade recommendation 
- Activated protein C - likely to be beneficial
- Physiotherapy -unknown effectiveness but one RCT with no benefit
- Steroids - unlikely to be benefical but poor evidence base
- Granulocyte-colony stimulating factor - likely to be ineffective or harmful 
Causes of atypical pneumonia include (list needs expanding):
Pneumonia in the immunocompromised
- This has several implications, including choice of antimicrobials. For example with building work steps should be taken to minimize exposure to Aspergillus - B grade recommendation.
Causes of pneumonia in the immunocompromised include(source - Medscape):
- Bacterial organisms
- Coccidioides species
- Cytomegalovirus (CMV)
- Tuberculosis (TB)
- Histoplasma species
- Aspergillus species
- Mycobacterium avium complex (MAC)
- Pneumocystis (carinii) jiroveci (PCP)
- Herpes simplex virus (HSV)
- Varicella-zoster virus (VZV)
- Legionella species
- Nocardia species
- Cryptococcus neoformans
- Mucoraceae species
- Strongyloides species
- Toxoplasma species
- Capnocytophaga species
Non-infectious causes of pneumonia in immuno-compromised patients include the following (source - Medscape):
- Pulmonary haemorrhage
- Congestive heart failure
- Pulmonary embolism
- Myocardial infarction
- Drug-induced injury
- Radiation-induced injury
- NICE Pneumonia: Diagnosis and management of community- and hospital-acquired pneumonia in adults. Clinical Guideline 191 December 2014
- this is a link to the Medscape Pneumonia in Immunocompromised Patients page.)
- ↑ Saeed S, Body R. Towards evidence based emergency medicine: best BETs from the Manchester Royal Infirmary. Auscultating to diagnose pneumonia. Emergency medicine journal : EMJ. 2007 Apr; 24(4):294-6.(Link to article – subscription may be required.)
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- ↑ BTS GUIDELINES FOR THE MANAGEMENT OF COMMUNITY ACQUIRED PNEUMONIA IN ADULTS - 2004 UPDATE
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