Clinical Review - Community-acquired pneumonia

A clinical review of the diagnosis and management of pneumonia. By Consultant Chest Physician, Dr Simon Barry

Chest X-ray of a patient with CAP showing patchy right-sided airspace changes (Photograph: Author image)
Chest X-ray of a patient with CAP showing patchy right-sided airspace changes (Photograph: Author image)

Section 1: Epidemiology and aetiology

This review considers community-acquired pneumonia (CAP), which does not include chronic bronchitis, infective exacerbations of COPD, pneumonia in immunocompromised groups or pneumonia as a pre-terminal event.

The true incidence of CAP is difficult to determine, mainly because an accurate diagnosis requires changes on a chest X-ray, in the context of respiratory symptoms and other supporting clinical information. Most episodes of CAP are managed in the community and do not involve a chest X-ray.

The annual incidence of CAP in the UK is between five and 11 per 1,000 adult population, with higher rates in the very young and those over 60 years of age.1

Most of the financial costs of pneumonia relate to hospital admissions, which account for £1,700 to £5,100 per patient admitted, compared with £100 for community treatment.2

Bacteria predominate as the cause of CAP, with viruses accounting for about 10% of cases. In up to 45% of cases, no organism is identified. Streptococcus pneumoniae remains the most common infective pathogen, especially in the elderly and during the winter months. It has been argued that patients from nursing homes may have a different spectrum of pathogens causing pneumonia, although a recent study showed no significant differences.3

Mycoplasma pneumoniae tends to occur in epidemics with a four-year cycle, each lasting up to three years. Legionella pneumophila typically affects younger adults and half of all cases in the UK are acquired abroad, particularly after hotel stays and exposure to contaminated water systems.

Most of the pathogens that cause pneumonia can coexist in the oropharynx and this is especially true of Strep pneumoniae, Staph aureus, H influenzae and anaerobes. The main mechanism is by microaspiration of oropharyngeal secretions.

Factors that are significantly associated with an increased risk of pneumonia are those that impair host immune defences, such as smoking, alcoholism, HIV, immunoglobulin deficiency or structural lung damage such as bronchiectasis.

In other situations, particularly in more elderly patients, aspiration may be more profound and the burden of bacteria may overwhelm otherwise normal defences. Inhalation of aerosol droplets containing bacteria is the main mechanism of disease transmission in legionella and viral pneumonias.

Causes of community-acquired pneumonia
Pathogen Prevalence %
Strep pneumoniae 20–60
H influenzae 3–10
Chlamydia pneumoniae 5–17
M pneumoniae 4–13
Respiratory viruses 2–15
Staph aureus 3–5
L pneumophila 2–8
Moraxella catarrhalis 1–3  
Gram-negative bacilli 1–4

Section 2: Making the diagnosis

Theoretically, making a diagnosis of CAP in secondary care is straightforward, requiring the combination of symptoms and signs consistent with a lower respiratory tract infection, together with new radiological changes attributable to pneumonia.

Supporting laboratory information, such as inflammatory markers (CRP, WCC), is also invaluable.

Despite these advantages, a recent audit in our hospital demonstrated that as many as 57% of acute admissions with respiratory infections had their initial diagnosis changed after a review of the admitting chest X-ray by a consultant chest physician. Most of these involved making a definitive diagnosis of CAP, rather than 'lower respiratory tract infection' or 'chronic bronchitis' due to incorrect assessment of the admitting chest X-ray.

Making a diagnosis of CAP in primary care is more difficult. The British Thoracic Society (BTS) has defined CAP in the community as including:4

  • Symptoms of an acute lower respiratory tract illness (cough and at least one other lower respiratory tract symptom).
  • New focal chest signs on examination.
  • At least one systemic feature (fevers, sweats, rigors and/or a temperature of >38 degsC).
  • No other explanation for the illness, which is treated as CAP with antibiotics.

However, only 39% of those with new focal chest signs who were treated in the community with antibiotics actually had radiological evidence of CAP.1

In summary, clinical signs are notoriously unreliable and this begs the question whether there are new diagnostic tests that could aid diagnosis (and antibiotic prescription in primary care).

CT scan showing cavitation and an area of consolidation (Photograph: Author image)

New diagnostic tests
One of the most promising tests is procalcitonin, which reliably distinguishes bacterial infection from viral infection or inflammation. A Swiss RCT involving 550 patients attending primary care physicians with acute respiratory infection compared clinical outcomes and antibiotic prescribing between a group where antibiotics were recommended above a procalcitonin threshold of 0.25ng/ml with a control group based on the clinicians' decisions.5

There were no differences in adverse outcomes at 14 days in the procalcitonin group when compared to the controls, but there was a 41.6% reduction in antibiotic prescribing (21.5% in the procalcitonin group versus 36.7% in the control group).

Although results are encouraging, procalcitonin remains impractical in primary care, because it requires a blood test to be sent to a laboratory and the result received in a timely fashion.

Section 3: Managing the condition

The two important decisions to be made in primary care are whether to prescribe antibiotics and whether to refer for hospital admission.

As discussed previously (above), many patients are prescribed antibiotics who probably do not need them, but this remains a practical solution in the absence of other discriminatory tests. The BTS recommends the use of a severity score assessment in the community, CRB65 (see box).4

Pneumonia severity assessment using CRB65

C Confusion (new disorientation or mini mental test score 8 or less)
R Respiratory rate >30 resps per min
B Systolic BP <90mmhg or="" diastolic="" bp="" 60mmhg="" br=""> Age >65 years

Score one point for each

CRB score
0 Likely to be suitable for home treatment
1 or 2 Consider hospital referral
3 or 4 Urgent hospital referral

Considerable debate has been generated regarding which are the most discriminatory measurements in assessing pneumonia severity, although the focus of these studies has been mainly in the secondary care setting, with a particular focus on high-dependency care.

CRB65 remains a convenient assessment tool in the community, but clinical judgment, particularly in the frail and elderly, should be a vital component of any decision regarding admission to hospital. The measurement of oxygen saturations is also helpful and recommended by the BTS. Admission should certainly be considered in patients with suspected pneumonia who have newly documented hypoxaemia. Patients managed in the community should be reviewed in 48 hours to ensure clinical improvement.

Microbiological tests are not usually helpful in CAP. However, failure of the sputum purulence to clear and a requirement for repeated courses of antibiotics should prompt a sputum sample being sent for culture.

This is particularly important in patients with chronic respiratory disease (cystic fibrosis, bronchiectasis, COPD), in whom colonisation with organisms such as pseudomonas that do not respond to conventional antibiotics is not uncommon.

It is worthwhile ensuring that samples are also sent for mycobacterial culture.

Antibiotic therapy
Patients with a CRB65 score of zero should be treated with oral amoxicillin or alternatively, and in those with penicillin allergy, clarithromycin or doxycycline.

Patients who require admission to hospital do not normally need antibiotics to be given before admission, unless the pneumonia is considered to be life-threatening (for example, significant hypotension suggestive of severe sepsis). In this case, penicillin G 1.2g IV or amoxicillin 1g orally should be administered.

In 2007 in the UK, 9% of Strep pneumoniae isolates were resistant to erythromycin and 4% were resistant to penicillin.

All patients over 65 years old with CAP who have not already been vaccinated should be given the conjugate pneumococcal vaccine when well.

Smoking cessation

All smokers with CAP should be counselled about smoking and referred to smoking cessation services.

Section 4: Prognosis

The physician Sir William Osler famously described pneumonia as 'the friend of the aged' and it remains one of the most common terminal events in patients dying from other incurable diseases.

Even in the 21st century, it is the biggest killer in children worldwide, accounting for 2m deaths in children under five years old, more than malaria, measles and HIV combined.

However, in resource-rich settings with universal access to healthcare, the outcomes are favourable. The mortality of patients with pneumonia managed in the community is less than 1%.1 The purpose of the CRB65 and CURB (confusion, urea, respiratory rate and BP) 65 severity scores is to identify patients at high risk of death, to ensure they are managed in an appropriate care environment.

For example, those patients with a CURB65 score of four or five have mortality rates of up to 40% and should be managed in a high-dependency setting.

Chest X-ray revealed patchy alveolar shadowing in the right mid and lower zones (Photograph: Author image)

Section 5: Case study

A 29-year-old Italian chef presented with a two-week history of fever, together with a cough productive of purulent sputum, dyspnoea and general malaise.

On the day of admission, the patient attended his GP surgery and was noted to be unwell, febrile at 38.5 degsC, tachycardic at 110bpm and tachypnoeic at 28rpm.

Chest auscultation revealed coarse crepitations on the right side. His saturations on air were 96%. He was referred to hospital for admission.

On review in the medical assessment unit at the hospital, the patient was noted to be febrile at 39.6 degsC and mildly tachypnoeic, but normotensive.

A chest X-ray demonstrated patchy alveolar shadowing in the right mid and lower zones, and blood tests demonstrated a significant inflammatory response, with a CRP of 337mg/L, and raised WCC with a neutrophilia of 15.5x109/L. His renal function was normal, with a urea of 3.1mmol/L. A diagnosis of CAP was made with a CURB65 score of zero.

Low assessment score
The patient was clinically unwell so he was admitted, despite the low CURB65 score. He was started on IV co-amoxiclav and oral clarithromycin.

The patient's serum albumin was 25g/L and an HIV test was negative. In the course of the following 10 days, he remained unwell, with intermittent fevers and a CRP level of more than 200mg/L.

The antibiotics were changed to piperacillin/tazobactam and a repeat chest X-ray demonstrated partial resolution of the airspace change, with cavitation in the right upper lobe, confirmed on CT scan.

A presumptive diagnosis of staphylococcal pneumonia causing cavitation was made and his antibiotics were then switched to flucloxacillin.

There was no microbiological confirmation of the causative organism. The patient was discharged home after a 14-day inpatient stay and on review in outpatients one month later, he reported that he was feeling much better. It was also noted that the right-sided changes had resolved with minimal scarring remaining.

This patient's case highlights a number of learning points concerning the management of CAP, which are presented in the box (below).

Learning points
  • The CURB65 score does not always reflect illness severity and an overall clinical assessment needs to be made before deciding whether admission is necessary.
  • Young patients requiring hospital admission with pneumonia (or other severe infections) should undergo HIV testing as a routine procedure.
  • Staphylococcus is an important cause of severe pneumonia, frequently complicating preceding viral URTIs, and is a cause of cavitating pneumonia.

Section 6: Evidence base


  • Lim WS, Baudouin SV, George RC et al. British Thoracic Society guidelines for the management of community acquired pneumonia in adults: update 2009. Thorax 2009; 64: supp iii.
  • Burkhardt O, Ewig S, Giersdorf S et al. Procalcitonin guidance and reduction of antibiotic use in acute respiratory tract infection. Eur Respir J 2010; 36: 601-7.

For an alternative view:

  • Infectious Disease Society of America/American Thoracic Society Consensus Guidelines on the Management of Community Acquired Pneumonia in Adults. Clin Infect Dis 2007; 44: supp 2.



This excellent resource centre collects worldwide data on CAP and has resulted in a number of publications, which are available on the website.

Click here to take a test on this article and claim a certificate on MIMS Learning


These further action points may allow you to earn more credits by increasing the time spent and the impact achieved.

  • Make a CRB65 template on your clinical system.
  • Audit which patients presenting with pneumonia in the past year were given smoking cessation advice.
  • Develop a fast-track integrated care pathway for patients with potential community-acquired pneumonia, to reduce the need for admission.

1. Woodhead MA, Macfarlane JT, McCracken JS et al. Prospective study of the aetiology and outcome of pneumonia in the community. Lancet 1987; i: 671-4.

2. Guest JF, Morris A. Community acquired pneumonia: the annual cost to the National Health Service in the United Kingdom. Eur Respir J 1997; 10: 1530-4.

3. Lim WS, Mcfarlane JT. A prospective comparison of nursing home acquired pneumonia with community acquired pneumonia. Eur Respir J 2001; 18(2): 362-8.

4. Lim WS, Baudouin SV, George RC et al. British Thoracic Society guidelines for the management of community acquired pneumonia in adults: update 2009. Thorax 2009; 64: supp iii.

5. Burkhardt O, Ewig S, Giersdorf S et al. Procalcitonin guidance and reduction of antibiotic use in acute respiratory tract infection. Eur Respir J 2010; 36: 601-7.

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