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Community Acquired Pneumonia

Author: Jason B Lee / Editor: Jason M Kendall / Codes: CAP6, HAP6 / Published: 31/03/2013 / Review Date: 31/03/2017

 

Introduction

Context

This module focuses on community acquired pneumonia (CAP) which is by far the commonest form of pneumonia seen in the Emergency Department. Many countries have developed national guidelines for the treatment of CAP. The British Thoracic Society (BTS) guidelines1, updated in 2009, form the basis for the recommendations made in this module. These guidelines are not applicable to children, patients with COPD, immunosuppressed patients, inpatients or patients that have left hospital in the preceding 10 days.

The annual incidence of CAP in the UK is approximately 10 per 1000 population but is higher in children and the elderly. The proportion of adults with CAP that require hospital admission in the UK has been reported as being between 22% and 42%. Mortality for patients with CAP treated in the community is very low (<1%) but is greater than 5% for patients requiring hospital admission, and greater than 30% for patients requiring intensive care input. Pneumonia remains one of the commonest causes of in-hospital death and carries a significant burden of cost to the UK health system, mainly due to the cost of inpatient care. In 1993 this cost was estimated at 441 million2. Hospital admissions for pneumonia rose by 34% between 1997 and 2005 and today the annual cost may exceed 1billion.

Basic science and pathophysiology

Chest infection is a lay term, which is used to describe a spectrum of respiratory tract infections. Only 5-12% of lower respiratory tract infections diagnosed clinically by GPs and treated with antibiotics have pneumonia, which strictly defined is an infection of the lung parenchyma. Lung parenchyma inflammation causes local alveoli to fill with fluid and exudates, which accounts for the clinically apparent features of productive cough and reduced oxygenation.

Aetiology

A single pathogen is identified in 85% of patients where an aetiology is found, however the true frequency of polymicrobial CAP is not clear. Streptococcus pneumoniae is the most frequently identified pathogen (39%). Chlamydophilia pneumonia is identified in 13% of hospitalised patients but the incidence in community cases is unknown. Mycoplasma pneumoniae occurs in epidemics spanning three winters every four years and therefore its incidence is variable. Although legionella species and staphylococcus aureus are identified more frequently in patients managed on the ICU, streptocoocus pneumoniae is still the most frequent isolated organism in this setting. Gram-negative enteric organisms, chlamydophila psittaci and coxiella burnetii are uncommon causes of CAP. Legionella and mycoplasma species are less commonly isolated in elderly patients with CAP but otherwise the causative organisms have a similar frequency as those found in younger patients.

Table 1- Pooled data of causative organisms in UK patients diagnosed with CAP(1)

Organism Hospital (%) Community (%)
Streptococcus pneumoniae 39 36
None identified 31 45
Mixed 14 11
All viruses 13 13
Chlamydophila pneumoniae 13 not known
Inluenza A and B 11 8
Mycoplasma pneumoniae 11 1
Haemophilus influenzae 5 10
Legionella species 4 0.4
Chlamydophila psittaci 3 1
Staphylococcus aureus 2 0.8
Moraxella catarrhalis 2 not known
Other 2 2
Coxiella burnetii 1 0
Gram negative bacteria 1 1

Atypical pneumonia

The BTS considers the term atypical pneumonia misleading, as it incorrectly implies a distinct clinical pattern. Instead, the term atypical pathogen is preferred. Atypical pathogens (eg Mycoplasma pneumoniae, C pneumoniae, Coxiella burnetii, C psittaci) are usually sensitive to antibiotics other than beta-lactams such as macrolides or fluoroquinolones which act intracellulary where these organisms replicate. Legionella species share some characteristics but are not considered atypical as there are different species which can be acquired both in the community and hospital environment.

Definition

Hospital diagnosis is based on new radiographic changes on a chest radiograph in addition to symptoms and signs suggestive of pneumonia. Recognised features of pneumonia include fever, dyspnoea, pleuritic chest pain, productive cough, tachypnoea and focal crepitations or bronchial breathing on chest auscultation. However, no prediction rules have shown reliable accuracy for diagnosing pneumonia in the absence of a chest radiograph. The 2009 BTS guidelines propose the following definitions for community acquired pneumonia:

(a) Patients managed in the community (without a chest radiograph)

  • Symptoms of an acute lower respiratory tract illness (cough and at least one other lower respiratory tract symptom eg breathlessness, pleuritic chest pain)
  • and new focal chest signs on examination
  • and at least one systemic feature (either a symptom complex of sweating, fevers, shivers, aches and pains and/or temperature of 38 C or more)
  • and no other explanation for the illness, which is treated as CAP with antibiotics.

(b) Patients admitted to hospital (with a chest radiograph)

  • symptoms and signs consistent with an acute lower respiratory tract infection associated with new radiographic shadowing for which there is no other explanation (e.g. not pulmonary oedema or infarction);
  • and the illness is the primary reason for hospital admission and is managed as pneumonia.

Clinical assessment

History

Although a confident diagnosis of pneumonia cannot be made on the basis of history alone it is unlikely that the patient with none of the following symptoms will have pneumonia.

  • Fever
  • Productive cough
  • Sweating
  • Shivering
  • Myalgia
  • Dyspnoea
  • Pleuritic chest pain

The history should also identify factors which may influence the management plan if a diagnosis of pneumonia is made.

These would include the following:

  • Prior or current antibiotic use
  • Allergies
  • Current medications
  • Known respiratory disease eg COPD
  • Co-morbidities (eg congestive cardiac failure, chronic renal failure)
  • Immunosuppression (through disease, or medication)
  • Social circumstances
  • Smoker
  • Age >50 years
  • New confusion reported by friend, relative or carer

Only 20% of UK cases of Chlamydia psittaci pneumonia have a history of bird contact, less than 10% of cases of Coxiella burnetii have a history of occupational exposure to animal sources (usually sheep) and less than a quarter of legionella cases occur in clusters. The low frequency of CAP caused by atypical pathogens coupled with the likely high prevalence of the relevant risk factors in the general population means that routine enquiry about such factors is likely to be misleading . Only in those with severe illness, where the frequency of legionella and staphylococcal infection is higher, does the BTS consider questioning about foreign travel and influenza symptoms to be of predictive value.

Organism specific features

Whilst the BTS community acquired pneumonia guidelines acknowledge that certain features occur more frequently with particular organisms (see below), they consider none to be specific enough to influence the initial choice of antibiotic.

Streptococcus pneumoniae

  • Increasing age, co-morbidity, acute onset, high fever and pleuritic chest pain

Legionella pneumophila

  • Younger patients, smokers, absence of co-morbidity, diarrhoea, neurological symptoms, more severe infection, evidence of multisystem involvement (e.g. abnormal liver function tests, elevated serum creatinine kinase). Legionella infection peaks in autumn in the UK and in 50% of cases is related to travel abroad. Less frequently cases occurs in clusters due to contaminated water cooling systems.

Mycoplasma pneumoniae

  • Younger patients, less multisystem involvement. Epidemics occur in UK spanning 3 winters every 4 years.

Staphylococcus aureus

  • Incidence peaks in winter and occurs more commonly in intravenous drug users or debilitated patients, particularly those with influenza. It is relatively more prevalent in patients on intensive care but even in this setting strep. pneumoniae remains the most common cause of pneumonia.

Learning Bite

Whilst certain features occur more frequently with particular organisms none are specific enough to influence the initial choice of antibiotic

Examination

A thorough examination of the cardio-respiratory system should be made to identify features consistent with pneumonia eg bronchial breathing, dullness to percussion, crepitations on auscultation of the chest, pyrexia, tachypnoea and tachycardia. Alternatively, the findings on chest examination may point to an alternative diagnosis such as pulmonary oedema, pleural effusion or pneumothorax.

As a minimum the following parameters should be recorded:

  • Temperature
  • Blood pressure
  • Pulse
  • Respiratory rate
  • Oxygen saturations

Dependent on the predominant presenting symptom the examination should also focus on areas (e.g. throat, legs) that may reveal features consistent with an alternative diagnosis (e.g. URTI, DVT/PE).

Investigation Strategies

CT chest

CT has no role in the routine investigation of patients with CAP.

Chest radiograph

The chest radiograph is the single most useful test available in the ED for diagnosing pneumonia. It is also in the identification of alternative diagnoses such as pulmonary oedema and exclusion of others e.g. pneumothorax. The BTS guidelines1 recommend that chest radiographs are performed on all patients being admitted from the ED with CAP in order to confirm or refute the diagnosis.

Chest radiographs are not necessary on patients discharged from the ED with a diagnosis of CAP unless the diagnosis is in doubt or the patient is considered at risk of underlying pathology such as lung cancer.

Chest radiograph changes consistent with pneumonia

The lung parenchymal inflammation and fluid filled alveoli are seen as areas of consolidation on the chest radiograph. The areas of infection are usually limited by pleural surfaces to a specific lobe of one lung but occasionally it may involve more than one lobe or both lungs. Small pleural effusions are common and usually reactive. Occasionally, chest radiographs may appear normal in the early stages of pneumonia. AP films performed on very unwell in the resuscitation room are often of poor quality and distinguishing between pulmonary oedema and pneumonia can be difficult. The following signs may help to confirm a diagnosis of pneumonia:

Silhouette sign:

The silhouette sign refers to the loss of the normal border between structures e.g.

  • middle lobe pneumonia, where the right heart margin is classically lost
  • right lower lobe pneumonia, where the border of the diaphragm on the right side is obscured, while the right heart margin remains clear

Air bronchogram:

As the bronchi branch a point is reached where the cartilaginous bronchial walls are too thin to visualise (unless calcified) and it is not possible to distinguish air in the bronchi from air in the surrounding alveoli. However, if the surrounding alveoli fill with fluid or pus then branching radiolucent air passages (air bronchograms) may be seen.

Learning Bite

Left lower lobe pneumonia may be missed if the area behind the cardiac shadow is not routinely inspected

Blood tests

The BTS guidelines recommend that the following tests be performed on all patients admitted with CAP:

Full Blood count

A white cell count >15 x 109/l is suggestive of a bacterial pneumonia.

Urea and electrolytes

Urea forms part of the CURB-65 scoring system. Occasionally, patients will be identified with unsuspected renal failure or hyponatraemia.

C- Reactive Protein (CRP)

CRP levels on admission have not proven to be clinically useful either diagnostically or prognostically but forms a baseline for later comparison. Failure of the CRP level to fall 72 hours after admission suggests treatment failure.

Liver Function Tests (LFTs)

The value of routine measurement of LFTs in patients that are not jaundiced, with non-severe pneumonia is unclear.

Arterial Blood Gases/Lactate

The BTS guidelines recommend that ABGs only be performed in patients with oxygen saturations below 94%3. However, the measuring of lactate levels (which is now routinely measured on most blood gas analysers) is essential for identifying tissue hypo-perfusion in patients who are not yet hypotensive but who are at risk for septic shock. A raised lactate (particularly levels >4mmol/l) is a poor prognostic indicator independent of the CURD-65 score. Early goal directed therapy using sepsis bundle pathways on intensive care have been shown to increase the chance of survival for patients with severe sepsis8,9.

Microbiology Blood cultures

Blood cultures are not necessary in the following groups:

Overall, blood cultures have a low sensitivity in CAP (<10% cases). The yield is particularly low for patients with non-severe CAP and no co-morbid disease, and for those who have received antibiotic therapy prior to admission4,5.

The BTS guidelines recommend that blood cultures are taken from all patients with moderate or severe CAP and most other patients admitted with CAP, preferably before antibiotic therapy is commenced.

However, blood cultures may be omitted if the following criteria are met-

  • a diagnosis of CAP has been definitely confirmed

and

  • the patient has low severity pneumonia

and

  • the patient has no significant co-morbid disease

Learning Bite

Blood cultures are not required for patients with confirmed low severity pneumonia in the absence of co-morbid conditions

Microbiology Sputum culture

Purulent sputum samples should be sent for culture and sensitivity from patients with the following characteristics1:-

  • Severe pneumonia
  • Moderate pneumonia that have not received prior antibiotics
  • Failure to improve with treatment
  • Patients who test positive for urine legionella antigen

Since the aim is to deliver antibiotics within 4 hours of arrival at the ED, purulent sputum samples that are produced by patients being admitted with CAP should in general be sent for culture and sensitivity. Samples obtained later on the ward will have a lower yield due to antibiotic administration in the ED.

Serology

A number of serological tests are available for identification of specific organisms but are of little relevance to management of the patient in the ED.

The BTS guidelines recommend the following:

Pneumococcal urine antigen

All patients with moderate or severe CAP should be tested.

Legionella urine antigen

Patients with severe pneumonia, specific risk factors and all patients during epidemics should be tested.

PCR

PCR testing is available for mycoplasma pneumonia, Chlamydophila and respiratory viruses but should be selectively requested by respiratory physicians.

ECG

Pneumonia is not associated with specific ECG changes though sinus tachycardias are common. In the elderly it is not uncommon for pneumonia to trigger atrial fibrillation or rate related ischaemia.

Risk stratification

The CURB-65 score is made up from the following components (1 point for each):

  • Confusion (new onset disorientation in time, place or person) OR an AMT score of (< 8/10)
  • Urea: > 7mmol/l
  • Respiratory rate: > 30/min
  • Blood pressure: low blood pressure (systolic BP < 90 mm Hg or diastolic BP < 60 mm Hg)
  • Age: >65 years

Abbreviated Mental Test (AMT) score

Patients with new confusion (disorientation in time, place or person) secondary to pneumonia are stratified by the CURB-65 system into a higher mortality risk group than those that are not confused. It is not uncommon to meet confused patients in the ED that have been brought by ambulance from care homes and be unsure whether their confusion is old or new. In this situation a score of 8 or less on the AMT is substituted for confusion in the CURB-65 score.
Pneumonia mental test

Learning Bite

Confusion (new onset disorientation in time, place or person) OR an AMT score of ( 8/10) scores 1 point on the CURB-65 score

CURB-65

The possible score ranges from 0-5 and the mortality from pneumonia rises exponentially with the CURB-65 score as seen in the table below7.

Pneumonia curb-65

The BTS adopted this scoring system in 2004 as it is easy to use (being a single step system compared to previous multi-step systems) and it is clinically useful in determining the disposition of patients. The BTS classifies patients scoring 3 or more are as having severe pneumonia and recommends that these patients are admitted urgently. Hospital treatment should be considered for those scoring 2 but outpatient management is acceptable in selected cases. Most patients with CAP who have CURB-65 scores of 0 or 1 can be managed in the community.

Learning Bite

A CURB-65 score of 3 or more indicates a severe pneumonia

Other factors suggesting a need for admission

The vast majority of patients with a CURB-65 score of 0 or 1 can be discharged. However, the BTS considers additional factors that are adversely related to prognosis to be important in deciding whether patients require in-patient treatment or not, irrespective of their CURB-65 score. These include:

    • Hypoxaemia (SaO2 <94% or PaO2 <8 kPa) regard less of FiO2.
    • Bilateral or multi-lobe involvement on the chest radiograph.
    • Presence of a co-existing disease e.g. Congestive cardiac failure, chronic renal failure
    • Age over 50 years

Some elderly patients with no adverse factors (other than age) will require admission solely for social reasons.

Learning Bite

The CURB-65 score should not be used in isolation to risk stratify patients

Management

General management

Patients should be given the following advice(1):

  • rest
  • drink plenty of fluids
  • stop smoking

Patients discharged from the ED should be advised to see their GP for review within 48 hours or sooner if clinically indicated.

Specific management

Antibiotics

Local guidelines should be adhered to but listed below are pragmatic antibiotic regimes that the BTS support.

Patients with low severity pneumonia that are either discharged or admitted (for social reasons or because of significant co-morbidities) and most with moderate severity pneumonia should be prescribed oral antibiotics if they are able to swallow:

Amoxicillin 500mg po tds for 1 week is the preferred regime. Clarithromycin 500mg po tds for one week is an alternative if the patients is allergic to penicillin and Levofloxacin can be used for patients allergic to both drugs mentioned above.

Admitted patients with low and moderate severity pneumonia that are unable to swallow should be given intravenous antibiotics:

Admitted patients with severe pneumonia

Patients with severe pneumonia should be given intravenous antibiotics as soon as possible after the diagnosis made:

The BTS guidelines recommend Co-amoxiclav 1.2g plus Clarithromycin 500mg for 7-10 days as an appropriate first line treatment. However, local resistance patterns and other factors may mean that some hospitals recommend alternative first line therapy. In this situation local guidelines should be followed.

If penicillin allergic:
Cefuroxime plus Clarithromycin

If penicillin and clarithromycin allergic:
Levofloxacin orally

Learning Bite

Antibiotics should be started in the ED as soon as possible after the diagnosis is made (usually on chest radiography) and within 4 hours of arrival in all cases. Local antibiotic guidelines should be followed

Oxygen

The BTS oxygen guidelines3 should be followed. Oxygen should be prescribed and administered if the oxygen saturations are below 94% on air or the arterial oxygen tension PaO2 is less than 8kPa.

Steroids

Steroids are not recommended in the routine treatment of pneumonia of any severity.

Chest physiotherapy

Classical chest clearance techniques are not routinely recommended for patients admitted with pneumonia but may have a place in patients with pre-existing lung conditions.

NIV

CPAP and NIV have not been demonstrated to improve mortality in patients with respiratory failure secondary to pneumonia and their routine use is not recommended.

Para-pneumonic effusions

Para-pneumonic effusions are found in up to a half of all patients admitted with CAP. Thoracocentesis is recommended in all cases to identify those that are infected (empyemas).

Where there is evidence that the pleural aspirate is infected (clear but pH<7.2 or cloudy /pus) a pleural drain should be inserted.

Prognosis & Followup strategies

Follow up

A letter should be sent to the GP recommending that a chest radiograph be repeated 6 weeks after completion of treatment for the following patient groups:

  • Persistence of symptoms or signs.
  • Patients at higher risk of malignancy (especially smokers and those aged over 50 years).

Safety pearls and Pitfalls

Pitfalls

  • Applying CAP guidelines to children, immunosuppressed patients or patients with COPD.
  • Decision making based on the CURB-65 score alone.
  • Prescribing intravenous antibiotics for all patients.
  • Failure to send sputum samples before antibiotics are administered.
  • Failure to recognise the patient with sepsis.

References

  1. British Thoracic Society Guidelines for the Management of Community Acquired Pneumonia in Adults. 2009 Guidelines. Thorax 2009;64:(suppl III)
  2. Guest JF, Morris A. Community-acquired pneumonia: the annual cost to the National Health Service in the UK. Eur Respir J. 1997;10(7):1530-4
  3. ODriscoll B, Howard LS, et al on behalf of the British Thoracic Society. Guideline for emergency oxygen use in adult patients. Thorax 2008;(63):suppl VI
  4. Campbell SG, Marrie TJ, et al. Utility of blood cultures in the management of adults with community acquired pneumonia discharged from the emergency department. Emerg Med J. 2003;20(6):521-3
  5. Campbell SG, Marrie TJ, et al. The contribution of blood cultures to the clinical management of adult patients admitted to the hospital with community-acquired pneumonia: a prospective observational study. Chest. 2003;123(4):1142-50.
  6. Hodkinson HM; Evaluation of a mental test score for assessment of mental impairment in the elderly. Age Ageing. 1972 Nov;1(4):233-8.
  7. Lim W.S., M.M. van der Eerden et al. Defining community acquired pneumonia severity on presentation to hospital: an international derivation and validation study. Thorax 2003;58:377 382.
  8. Rivers E, Nguyen B et al. Early Goal-Directed Therapy in the Treatment of Severe Sepsis and Septic Shock. N Engl J Med. 2001 Nov 8;345(19):1368-77.
  9. Shapiro N, Howell M et al. Serum Lactate as a Predictor of mortality in Emergency Department patients with infection. Ann Emerg Med. 2005;45(5):524-528

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