Community-acquired pneumonia (CAP) in adults is a common and potentially serious condition which is associated with high rates of morbidity and mortality in vulnerable patients.¹

Epidemiology

It is defined as an acute infection of the pulmonary parenchyma in a patient who has acquired the infection in the community, as compared to those who develop hospital-acquired (nosocomial) pneumonia. There is a seasonal variation, with most cases occurring during winter months.

The overall rate of CAP in adults is 5-11 per 1,000 of the adult population.² Between 22-42% of patients with CAP are admitted to hospital for treatment.³ In all, 1,974 people died from pneumonia in Ireland in 2006.⁴ Mortality is highest for people who require hospitalisation. Over half of deaths occur in elderly patients. Given the ageing population in our society, it is expected that the economic and social burden of this disease will increase.

Certain host conditions can lead to an increased risk of CAP. These include older age, malnutrition, smoking, alcohol use, chronic obstructive lung disease (COPD) and genetic disorders such as cystic fibrosis and Kartagener’s syndrome. 

Microbiology

There are more than 100 organisms that can cause CAP including bacteria, viruses, fungi and parasites. However, the majority are caused by a small number of micro-organisms. Streptococcus pneumoniae is the most common cause of pneumonia in Ireland. Other organisms such as Haemophilus influenzae and the atypical agents, such as Legionella pneumophila, Mycoplasma pneumoniae and Chlamydia pneumoniae, are being reported more frequently than in the past.⁵ In an individual patient, there are no clear findings from the history, physical examination or routine laboratory tests that allow the physician to clearly diagnose typical versus atypical pneumonia.

Influenza remains the most common cause of CAP. Other viruses responsible include adenovirus, respiratory syncytial virus (RSV), varicella and severe acute respiratory syndrome (SARS) coronavirus.

Clinical evaluation

The most common symptoms of CAP include fever, cough, dyspnoea and pleuritic chest pain. Patients may describe either scanty or mucopurulent sputum production. Other complaints include nausea and vomiting, diarrhoea, confusion and rigors.⁶

Physical examination may reveal pyrexia, however, pyrexia may be absent in elderly patients who instead may be found to have an altered mental status. Tachypnoea, tachycardia and cyanosis may be noted. On auscultation of the chest, crackles or reduced air entry may be detected. It is typically the combination of history and clinical features that leads to a diagnosis of CAP.

Investigations

General practice

General investigations are not usually necessary for patients with CAP who are managed in the community.⁷ Pulse oximetry allows for the simple assessment of oxygen saturation. It is not necessary to perform a chest radiograph in patients with suspected CAP unless the diagnosis is in doubt, progress following treatment is not satisfactory, or the patient is considered at risk of underlying lung pathology such as lung cancer.⁸

Microbiological investigations are not performed routinely in the community, but should be considered for patients who do not respond to empiric treatment.

Hospital

Routine investigations performed on admission to hospital for CAP include: full blood count (FBC), urea and electrolytes (U&E), C-reactive protein (CRP) and liver function tests (LFTs). Where necessary, arterial blood gases can be performed to guide oxygen therapy. 

Sputum cultures should be sent on all patients who are admitted to hospital for CAP, preferably before antibiotics have been administered.⁸ Sputum acid-fast bacillus (AFB) smear and TB culture should be performed if there is any possibility of pulmonary tuberculosis. Blood cultures are recommended for all patients with moderate-to-high severity CAP, also preferably before treatment is commenced. Further testing, including pneumococcal and legionella antigen testing, is recommended for patients with moderate-to-severe CAP. Sputum cultures should always be attempted for patients who are legionella antigen-positive as it can help aid outbreak and source investigation with the aim of preventing further cases of Legionnaires’ disease.¹

All patients who are reviewed in hospital with suspected CAP should have a chest radiograph performed to aid diagnosis.⁸ For patients who make a good recovery, the chest X-ray (CXR) need not be repeated during the admission. It is, however, important to repeat the CXR after an interval of six weeks to confirm resolution of consolidation, as other conditions such as bronchoalveolar carcinoma can mimic pneumonic consolidation. 

General management and antibiotic treatment

The decision to treat as an outpatient or inpatient can be difficult. The CURB-65 scoring system can inform a physician’s clinical judgement with regard to hospital admission. The score is an acronym for each of the points awarded (see Table 1). 

Patients who have a score of 0 are at low risk of death and normally do not require hospitalisation. Patients with a score of one or two are at increased risk of death, and should be considered for admission, particularly those with a score of two. Patients who have a score of three or more are at high risk of death. The British Thoracic Guidelines recommend that a patient at high risk of death on admission should be reviewed medically at least 12-hourly until shown to be improving.

All patients should receive appropriate oxygen therapy, with monitoring of oxygen saturations, with the aim to maintain them at 94-98% (SpO2). If a patient is at risk of hypercapnic respiratory failure, oxygen therapy should be controlled and guided by arterial blood gas measurement.

Patients should be assessed for volume depletion and receive intravenous fluid replacement if required. Venous thromboembolism prophylaxis with low molecular weight heparin should be considered in all patients who are not fully mobile. If a patient has difficulty with airway clearance and sputum expectoration, or if they have a pre-existing lung condition, then chest physiotherapy should be prescribed.

When deciding on antibiotic treatment, many factors must be taken into consideration. These factors include the patient’s age, comorbidities and severity of disease. Local guidelines can be helpful in choosing the most appropriate anti-microbial cover. 

The British Thoracic Guidelines recommend amoxicillin as the treatment of choice within the community, with doxycycline as an alternative or for those hypersensitive to penicillin. For patients admitted to hospital, the guidelines recommend treatment with amoxicillin and a macrolide such as clarithromycin. This can be given in an oral form if the CURB-65 score suggests a moderate severity, but should be given in intravenous form if the patient is deemed at high risk. If allergic to penicillin a second or third-generation cephalosporin is recommended. If a pathogen is isolated, this should further guide treatment. 

For patients who fail to improve, a full review including history, physical examination and investigations should be performed. Repeat CXR may be needed and referral to a respiratory physician should be considered. 

Complications

Typically patients begin to show signs of resolution after three to five days of treatment. Many factors can slow resolution, including severity of pneumonia, comorbidities (nutritional status and immunodeficiency) and older age. The pathogen causing the pneumonia can also affect rate of recovery. For example, resolution typically appears to be more rapid with Mycoplasma pneumoniae and more delayed with Moraxella catarrhalis. Alternative pathogens should be considered when clinical improvement is delayed, including Mycobacterium tuberculosis, fungi and Acintomyces. 

Dense consolidation can prevent an adequate concentration of antibiotics reaching the pathogen. Parapneumonic effusions occur in up to 40% of bacterial pneumonias. Parapneumonic effusions are usually small and resolve with antibiotic treatment. An empyema is a collection of pus in the pleural space. It occurs in less than 2% of patients with CAP. It should be suspected in any patients with unresolving infection. A moderate or large pleural effusion should prompt a diagnostic thoracocentesis. Empyema is diagnosed if frank pus is obtained from a pleural aspirate, if the pleural fluid pH is less than 7.2 or if a specific pathogen is cultured from the pleural fluid. A diagnosis of empyema should prompt intercostal drain insertion and consideration for surgical debridement of the pleural space if clinically appropriate.

A lung abscess is necrosis of the lung parenchyma caused by microbial infection. Patients with alcoholism, previous aspiration and seizure disorders are at higher risk of lung abscess. 

Also, certain micro-organisms are more likely to cause lung abscess or cavitating pneumonia, such as Staphylococcus aureus, Klebsiella pneumoniae, anaerobes and Pseudomonas aeruginosa. Most patients with lung abscess do well with conservative management and a prolonged course of parenteral antibiotics.

Follow-up

All patients should be reviewed at six weeks, either with their GP or in a hospital clinic. If a patient is at risk of underlying carcinoma (smokers and older patients), clinic review should be arranged and a CXR should be repeated to ensure resolution of the pneumonia.

Smoking cessation should be encouraged in all patients who are current smokers. All patients over 65 years who are at risk of invasive pneumococcal disease should receive the pneumococcal vaccine. Patients at risk of influenza should also be vaccinated.

References

1. Mandell LA, Wunderink RG, Anzueto A et al. Infectious Diseases Society of America/American Thoracic Society consensus guidelines on the management of community-acquired pneumonia in adults. Clin Infect Dis 2007; 44 Suppl 2: S27
2. Durrington HJ, Summers C; Recent changes in the management of community acquired pneumonia in adults. BMJ. 2008 Jun 21;336(7658):1429-1433
3. Guest JF, Morris A. Community-acquired pneumonia: the annual cost to the National Health Service in the UK. Eur Respir J 1997; 10: 1530–1534
4. Deaths from principle causes 1998-2006. The central statistics office Ireland
5. Johansson N, Kalin M, Tiveljung-Lindell A, et al. Etiology of community-acquired pneumonia: increased microbiological yield with new diagnostic methods. Clin Infect Dis 2010; 50:202
6. Macfarlane J. Lower respiratory tract infection and pneumonia in the community. Semin Respir Infect 1999;14: 151–62
7. Metlay JP, Kapoor WN, Fine MJ. Does this patient have community-acquired bpneumonia? Diagnosing pneumonia by history and physical examination. JAMA 1997; 278: 1440-14458. 
8. Guidelines for the management of community acquired pneumonia in adults, British Thoracic Society (2009)