The Basics - Community-acquired pneumonia

Clinical features depend on patient factors and the infecting organism, explains Dr Harry Brown.

Pneumonia acquired in the community may be due to H influenzae (Photograph: SPL)
Pneumonia acquired in the community may be due to H influenzae (Photograph: SPL)

Pneumonia is a lower respiratory tract infection defined as an inflammation of the lung parenchyma. It is often associated with an underlying respiratory disease, such as COPD.

Pneumonia can be classified into various different types either by anatomical site, microbiological cause or by being community or hospital acquired. This article will concentrate on community-acquired pneumonia (CAP).

1. Aetiology
Streptococcus pneumoniae is the most common cause of CAP. This organism can affect all age groups, while Chlamydia pneumoniae and Mycoplasma pneumoniae tend to affect younger people. Haemophilus influenzae will often be seen in patients with underlying lung disease, such as COPD, and hence is more likely to be seen in an older age group. Legionella pneumophila is associated with contaminated water systems.

Viral pneumonia is relatively uncommon; however it has a destructive effect on the airways, which in turn can lead to bacterial infection.

Transmission of the infection is often by inhalation of respiratory droplets from an infected patient. Host factors play an important role in the genesis and aggressiveness of pneumonia. These include:

  • Increasing age
  • Immunosuppression (either due to underlying disease or treatment by chemotherapy or steroids)
  • Cigarette smoking
  • Underlying lung disease, such as COPD or bronchiectasis
  • Preceding upper respiratory tract infection
  • Excess alcohol consumption.

Hospital-acquired pneumonia is defined as being acquired 48 hours after admission. The range of organisms isolated may resemble those found in the community. Prolonged hospital stays are sometimes associated with Gram-negative bacterial infections.

2. Clinical features
Clinical features are determined by both host and infecting organism factors. For example, in the elderly confusion may be the only presenting sign of pneumonia.

The symptoms will often have a relatively acute onset and may have systemic and respiratory components.

The systemic symptoms include feeling generally unwell, fever and lethargy. The respiratory component may include cough, purulent sputum, haemoptysis, breathlessness and pleuritic-type chest pain.

Physical signs may be numerous or absent but should always be sought. These include the findings of pyrexia, hypotension and tachypnoea. With a stethoscope focal signs such as a pleural rub or evidence of consolidation may be heard.

Different infecting organisms may be associated with a variety of symptoms and signs, though there is significant overlap. The very old and very young may have quite different and far from typical presentations.

3. Investigations
Other investigations may include pulse oximetry and chest X-ray. Radiological signs do not necessarily correlate with the clinical state and course of the illness.

A chest X-ray may help to detect underlying malignancies or flag the presence of complications or other abnormalities. If abnormalities persist on a chest X-ray then consider a malignancy and further investigations may then be necessary.

A chest X-ray should return to normal - unless there is an underlying abnormality - within about six weeks. Ideally, all patients with new or abnormal chest X-ray appearances should have a follow-up chest X-ray after about six weeks. This advice could apply in particular to smokers and those older than 50 years of age. An FBC and a sputum culture may assist in the diagnostic process.

4. Prevention
Offer preventive care to patients with suspected or confirmed pneumonia. Smoking cessation advice and referral to an appropriate service may be useful for someone interested in quitting. Advice on yearly influenza and pneumococcal vaccination will also be appropriate in some patients, such as those aged 65 years and over and patients with chronic heart, respiratory, renal or liver disease.

5. Management
In primary care, if the patient is not too unwell, has no other significant comorbidities and has a supportive social background then treating with antibiotics without the need to perform further investigations may be appropriate.

It is not always easy to decide who to treat in the community and who to admit. CRB-65 is a useful scoring system used to assess the severity of CAP.

One point is awarded for each of the following features:

  • Confusion
  • Respiratory rate 30 breaths/minute or greater.
  • BP - systolic ≤90 mmHg or a diastolic ≤60 mmHg.
  • 65 years of age or older.

A score of 0 is likely to be compatible with treatment in the community, 1 or 2 may need to be seen at hospital, while 3 or 4 will require urgent admission.

For patients with CAP, the first-line drugs are usually amoxicillin, or doxycycline, erythromycin or clarithromycin if the patient is allergic to penicillin. The duration of antibiotics is likely to be one week.

An otherwise healthy patient would be expected to respond to antibiotics in two to three days. Failure to respond may make it necessary to reconsider the diagnosis or managment, such as a chest X-ray, if not already done, or consider admission.

Patients should be encoura-ged to increase their fluid intake, and take appropriate pain relief if they have pleuritic-type pain. They should also be encouraged to seek medical advice if their symptoms do not improve or they have side-effects from any prescribed medication.

Key points
  • Streptococcus pneumoniae is the most common cause of CAP.
  • Symptoms often have acute onset.
  • Discuss smoking cessation and yearly vaccinations as preventive treatment.
  • Treating with antibiotics in the community may be appropriate.

Dr Brown is a GP in Leeds

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