Pneumonia

The management of pneumonia is based on 5 principles:

• The clinical features of pneumonia are non-specific
• Pneumonia can be caused by a wide range of organisms
• The relationship between specific clinical features and the causative organism is weak
• Epidemiological clues can be used to determine the most likely causative organisms. The most important of these clues are location at the time of onset (ie healthcare facility or community) and immunosuppression
• Early administration of appropriate antibiotics is important

Community acquired pneumonia

Definition

Acute infection of pulmonary parenchyma that:

• Is associated with at least some symptoms of acute infection
• Is accompanied by the presence of an acute infiltration on CXR or auscultatory findings consistent with pneumonia
• Occurs in a patient who is not hospitalized or residing in a long term care facility for at least 14 days prior to onset of symptoms

Aetiology

• Streptococcus pneumoniae is the most common cause
• Other important causes are Mycoplasma pneumoniae, Haemophilus influenzae, Legionella spp., Staphylococcus aureus, Chlamydia pneumoniae, Streptococcus pyogenes, Moraxella catarrhalis, Klebsiella pneumoniae, influenza, para-influenza and respiratory syncytial virus

Clinical features

Systemic

Fever, sweating, rigors and signs of dysfunction of other organs (severe cases).

Respiratory

• Cough, sputum production, pleuritic chest pain, dyspnoea, tachypnoea, pleural rub and inspiratory crackles are common
• Classic signs of consolidation in <25%

Diagnosis may be more difficult in the elderly. Although the vast majority have respiratory symptoms and signs, >50% may also have non-respiratory symptoms and >1/3 have no systemic signs of infection

Investigations

The aim of investigations is to confirm the diagnosis, identify causal factors, assess severity and detect complications. Important investigations that should be carried out in all patients:

• Chest X-ray
• Blood cultures x2 for patients with severe pneumonia, prior to giving antibiotics. These should be taken urgently so to avoid delay in administering antibiotics.
• Sputum for urgent Gram stain and culture for severe cases or for patients suspected to have infection with multi-resistant organisms (table 1), prior to antibiotics if specimens can be obtained urgently. The specimen should be transported to the laboratory and processed within 2 hours so that any organisms that may be present but require ideal conditions for successful culture do not die
• Nasopharygeal aspirate for influenza rapid molecular assay
• Pleural fluid aspiration for Gram stain, culture, pH and leucocyte count (if the patient has a pleural effusion >1 cm thick on a lateral decubitus film)
• Urinary legionella and pneumococcal antigen for patients with severe pneumonia
• Arterial blood gases or pulse oximetry
• Full blood count
• Renal and liver function tests
• Consider checking HIV status in areas of high prevalence or in patients with risk factors.

Features of severe pneumonia

• Severe respiratory failure
• Shock
• Multi-lobar pneumonia
• Confusion or disorientation
• Hypothermia
• Renal dysfunction
• Leukopaenia
• Thrombocytopaenia

Treatment

• High flow oxygen. In severe cases mechanical ventilation may be necessary
• Fluid to correct dehydration and provide maintenance requirements
• Organ support if there is other organ dysfunction

Antimicrobials

• NB Antibiotics should be administered urgently and administration should not be delayed to obtain sputum or pleural fluid samples. Ideally antibiotics should have been given before the patient leaves the emergency department
• Ideally each unit should have its own antibiotic guidelines based on local prevalence and sensitivity patterns as the likely organisms and their sensitivities varies from country to country, hospital to hospital and ward to ward
• In the absence of local guidelines, the following regimes can be used for patients with severe pneumonia in areas where high level penicillin resistant Streptococcus pneumoniae is uncommon
  • 3^rd generation cephalosporin (eg ceftriaxone or cefotaxime) plus macrolide (eg erythromycin, azithromycin or clarithromycin) or
  • ß lactam/ß lactamase inhibitor (eg ampicillin-sulbactam, amoxicillin-clavulanate) plus macrolide or
  • respiratory quinolone (eg levofloxacin, moxifloxacin). Less suitable in Asia due to high MIC for pneumococcus and risk of masking tuberculosis.
• Patients with risk factors for multi-resistant organisms (table 1) should receive anti-pseudomonal cephalosporin, carbapenem or ß-lactam/ ß-lactamase inhibitor (table 2) plus macrolide or quinolone.

Nosocomial pneumonia

Definition

Pneumonia developing more than 2-3 days after admission to a healthcare facility or in someone who has been discharged from a healthcare facility in the previous 2 weeks.

Pathogenesis

Major route of infection is thought to be micro-aspiration of bacteria from the upper respiratory tract. Micro-aspiration has been shown to occur in 45% of humans when asleep and the upper respiratory tract of 75% of critically ill patients is colonized by enteric Gram negative bacilli.

Management of nosocomial pneumonia is made even more difficult by the following:

• In hospitalized patients there are many conditions which may mimic pneumonia
• Respiratory specimens are contaminated by organisms colonizing the upper respiratory tract. Nevertheless culture of respiratory samples is still useful. Given that the predominant route of infection is micro-aspiration from the oropharynx, the absence of bacteria in respiratory secretions means that the patient is unlikely to have bacterial pneumonia. However the opposite is not true. If bacteria are grown, then the patient may or may not have pneumonia. The relevance of the organisms identified is similar (ie the absence of a specific organism eg Pseudomonas aeruginosa, means that it is unlikely that that specific organism is the cause of the pneumonia).

Diagnosis

A provisional diagnosis of nosocomial pneumonia is made on the basis of new or changed infiltrates on the chest X-ray plus two of the following:

• Purulent sputum
• Leucocytosis or leucopaenia
• Fever

Initial management

Initial selection of antimicrobials should be made on the basis of:

• risk factors for multi-drug resistant pathogens (table 1)
• local bacterial flora and resistance patterns
• antimicrobial therapy in past 2 weeks: try to avoid using the same class of antibiotic
• in the absence of local guidelines the regimes given in tables 1 & 2 may help

Do not delay initiation of antibiotic therapy to obtain lower respiratory tract specimens.

Subsequent management

Reassess management after 2-3 days or sooner if patient deteriorates. Subsequent management should be based on results of microbiological investigations and response to therapy (figure 3). If the patient is improving and the sensitivity of the pathogen is known, antibiotic cover can be narrowed. In high risk patients, the possibility of Mycobacterium tuberculosis should also be considered in those patients with negative cultures.

Remember that a large proportion of patients with nosocomial pneumonia and bacteraemia have another source of sepsis in addition to pneumonia.

Pneumonia in the immunocompromised

In this group, the possible aetiological agents include organisms which rarely cause pneumonia in the non-immunocompromised including Candida spp. and Pneumocystis carinii. These patients may also deteriorate rapidly and early specialist consultation is recommended to guide investigations and antibiotic treatment.