Pneumonia

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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.

Contents

Clinical features

Symptoms

LogoWarningBox4.pngComplete collapse of one lobe due to pneumonia may not produce any signs in the chest. Beware tachypnoea without other signs.
  • Cough
  • Breathlessness
  • Rigors
  • Fever
  • Pleuritic chest pains
  • Phlegm - often dry at first but then productive usually yellow, bloodstained or rust-coloured.
  • Confusion
  • Herpes labialis

Signs

Can be unilateral or bilateral. Physical examination has a limited sensitivity and specificity.[1]

  • Tachypnoea
  • Reduced expansion
  • Reduced breath sounds
  • Crepitations
  • Dull percussion note
  • Increased vocal resonance and tactile vocal fremitus

Wheeze virtually always indicates a viral cause.

Radiology

Sagittal CT slice showing left lower lobe pneumonia.

Epidemiology

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[2]. In the elderly and immunosuppressed incidence is up to 14/1000 per year.

Risk groups

  • Post splenectomy
  • Elderly.
  • Heart disease
  • Chest disease
  • Diabetics
  • Immunocompromised
  • Alcoholics

Genetic factors

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[3]. TLR6 polymorphisms appear to be associated with disease caused by Klebsiella pneumoniae infection[4] and Legionnaires disease[5] as well as other infections.

Assessing severity

One method of assessing the severity of community acquired pneumonia is to use the CURB65 score[6][7] Scoring one point for each of:

  • Confusion
  • 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.

Prevention

  • 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)

Treatment

  • 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 British Thoracic Society published revised treatment guidelines for community acquired pneumonia (CAP) in 2004 (here) Use the CURB65 score for risk stratification.

Aetiology

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[8]:

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 &microg/L.[9][10][11]
  • Microbiology testing is only recommended where probability of changing the initial empirical antibiotic is high such as hospitalised CAP[12]:
    • 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[12]
  • 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[13]. These cover most aspects including prevention of ventilator associated pneumonia in detail. Some highlights include:

Prevention

  • Non-invasive positive pressure ventilation should be used rather than ventilation whenever possible - A grade recommendation[13]
  • Stress ulcer prophylaxis should be avoided where possible in ventilated patients - A grade recommendation[13]
    • If indicated, sucralfate preferred unless high risk GI bleed - A grade recommendation[13]
  • 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[13]
  • Subglottic drainage and positioning in ventilated patients to reduce aspiration - B grade recommendation[13]
  • Legionella control of hospital water - B grade recommendation[13]
  • Ventilate in semi-recumbent position (30–45°) if no contraindications - B grade recommendation[13]
  • Avoid red cell transfusions if possible - C grade recommendation[13]
  • Physiotherapy:
    • Post-operative ventilated patients - beneficial[13]
    • Other ITU patients - unknown effectiveness[13]

Treatment


Atypical pneumonia

Causes of atypical pneumonia include (list needs expanding):

Viruses such as human metapneumovirus are potentially grossly under recognised and the dangers of not considering viruses such as MERS to other patients and healthcare personnel are considerable

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[13].

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)
  • Influenza
  • 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
  • Pneumonitis
  • Congestive heart failure
  • Pulmonary embolism
  • Myocardial infarction
  • Pneumothorax
  • Drug-induced injury
  • Radiation-induced injury

Complications

External links

References

  1. 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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