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Pneumonia

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Pneumonia is an inflammation of the lung. The term is almost always used to refer specifically to infections of the lungs caused by bacteria, viruses, fungi or other parasites, but it is sometimes also used to denote lung injury caused by physical or chemical irritants. Infectious pneumonia may occur in patients of all age groups, but young children and the elderly, as well as immunocompromised and immune deficient patients, are especially at risk. Antimicrobial drugs are often used to treat pneumonia.

Diagnosis

To diagnose pneumonia, doctors rely on the patient's clinical history, findings on physical examination, and confirmatory testing. These often include chest X-rays, blood studies and sputum cultures.

In nosocomial pneumonia (pneumonia that was acquired while the patient was in hospital for something else) and in immunocompromised patients, a clear diagnosis of pneumonia can be difficult; sometimes, a chest CT scan is required to differentiate possible causes (e.g. pulmonary embolism). CT scanning may also be useful when the symptoms and physical examination suggest several possible causes for the complaints (e.g. vasculitis, sarcoidosis, lung cancer).

Symptoms

Symptoms of pneumonia commonly include:

  • Shortness of breath
  • Cough with greenish or yellow sputum
  • A high fever which may be accompanied with sweating, chills and rigors (shaking)
  • Sharp or stabbing chest pain, worsened by deep breaths or coughs
  • Rapid, shallow breathing (painful quick breathing)

Less commonly, there may be:

Pneumonia can progress to sepsis ("blood poisoning") and acute respiratory distress syndrome if untreated. These are the main causes of death in patients with untreated pneumonia.

Physical examination

Apart from the history, the physical examination is an essential part of the doctor's overall assessment of the patient. Important features to note include whether the patient is breathless, able to speak in full sentences, uses accessory muscles of respiration, or has signs of reduced oxygenation (for example, blue, cyanotic lips, or unexplained mental confusion). If this overall assessment is poor, admission to hospital is usually advised, whatever else the examination reveals.

The pulse rate, repiratory rate and temperature are measured. Feeling for the expansion movements of the chest wall (palpation) and tapping the chest wall (percussion) to find resonant and dull areas may provide clues to the underlying disease process affecting the patient's lungs. Finally, auscultation with a stethescope allows the doctor to listen for any areas of the lung which have reduced air flow, crackles (crepitus or 'rhonchi') or the crunch-sound (pleural rub) of pleurisy.

Pneumonia. Chest x-ray showing increased shadowing in right lung (left side of image). (Source: Center for Disease Control and Prevention.)

Chest X-rays and other tests

Some consider an increase in opacity in one or more lung fields on a chest X-ray — indicating consolidation in that region — to be the "gold standard" diagnostic finding. Supportive diagnostic tests include a raised white cell count, microbiological culture of sputum and/or blood. A full blood count often shows neutrophilia (except in some immunocompromised and all neutropenic patients). Renal function may have deteriorated if there is sepsis. There may be hyponatremia (low sodium levels), often due to secretion of antidiuretic hormone by pulmonary tissue; this is thought to be more frequent in tuberculosis and Legionaires' disease. Specific serological assays for atypical pathogens (Mycoplasma, Legionella and Chlamydia) are also available.

Differential diagnosis

The differential diagnosis of pneumonia includes:

Classification

There are several different classification schemes: microbiological, radiological, age-related, anatomical, point of acquiring infection. Generally, the following types are used:

  • lobar - an infection that involves, and is limited to, a single lobe of a lung (generally due to Streptococcus pneumoniae)
  • multilobar - pneumonia that involves more than one lobe
  • community-acquired - pneumonia in a patient who is not or has not recently been in the hospital
  • hospital-acquired or nosocomial - pneumonia in a patient in a hospital (or recently discharged)
  • ventilator-associated - pneumonia following intubation and mechanical ventilation for at least 48 hours
  • "walking" - outdated term, pneumonia in a patient who is still able to walk, a mild pneumonia, usually due to mycoplasma
  • pneumococcal - pneumonia due to S. pneumoniae.
  • atypical - pneumonia due to either Mycoplasma, Chlamydia, or Legionella.

The main classification used in medical journals is that between the point of infection: community-acquired and hospital-acquired. Furthermore, infections in the immunocompromised, as well as aspiration pneumonia, are usually treated as separate disease entities as they have other causal agents, as well as a different clinical course.

Aetiology

Many different infective agents can cause pneumonia. Of these, the most common cause of community acquired pneumonia (the most common form of pneumonia overall) is Streptococcus pneumoniae.

The more common infective causes of pneumonia include:

Types of pneumonia

Community-acquired pneumonia

Epidemiology

Community-acquired pneumonia (CAP) is a serious illness. It is the fourth most common cause of death in the UK, and sixth in the USA. 85% of cases of CAP are caused by the typical bacterial pathogens, namely, Streptococcus pneumoniae, Haemophilus influenzae, and Moraxella catarrhalis. The remaining 15% are caused by atypical pathogens, namely Mycoplasma pneumoniae, Chlamydia pneumoniae, and Legionella species. Unusual aerobic gram-negative bacilli (for example, Pseudomonas aeruginosa, Acinetobacter, Enterobacter) rarely cause CAP.

Clinical features

Typical symptoms include cough, purulent sputum production, shortness of breath, pleuritic chest pain, fevers and chills. On examination, one notes rapid respiratory rate and heart rate and signs of pulmonary consolidation. In the elderly, symptoms and signs are sometimes vague and non-specific. They may include headache, malaise, diarrhea, confusion, falling, and decreased appetite. Diagnosis is confirmed by physical examination and chest x-ray. In general, patients who present with symptoms consistent with CAP, without extrapulmonary findings on history, physical examination or in laboratory tests have a CAP caused by a typical pathogen. Patients who have pneumonia plus extrapulmonary physical findings or laboratory features (such as elevations in liver function test results) have an atypical pneumonia.

Hospital-acquired pneumonia

Hospital-acquired pneumonia, also called nosocomial pneumonia, is a lung infection acquired after hospitalization for another illness or procedure. It is considered a separate clinical entity from CAP because the causes, microbiology, treatment and prognosis are different. Up to 5% of patients admitted to an hospital for other causes subsequently develop a pneumonia. Hospitalized patients have a variety of risk factors for pneumonia, including mechanical ventilation, prolonged malnutrition, underlying cardiac and pulmonary diseases, achlorhydria and immune disorders. Additionally, pathogens thrive in hospitals that could not survive in other environments. These pathogens include resistant aerobic gram-negative rods, such as Pseudomonas, Enterobacter and Serratia, resistant gram positive cocci, such as MRSA. Because of risk factors, underlying morbidity and resistant bacteria, hospital-acquired pneumonia tends to be more deadly than its community counterpart.

Gold standard of therapy based on determination of aetiological agent holds but a specific pathogen is identified in only 50% of patients even with extensive evaluation. Due to seriousness of the disease treatment should not be delayed. Antibiotics used for hospital-acquired pneumonia include aminoglycosides, fluoroquinolones, carbapenems, and vancomycin. Multiple antibiotics are administered in combination in order to cover all the possible organisms effectively and rapidly, before the infectious agent can be known. Antibiotic choice varies from hospital to hospital as the likely pathogens and resistance patterns vary similarly.

Other pneumonias

Pathophysiology

The vast majority of pneumonias are infectious diseases; whether a patient is prone to develop pneumonia depends not only the presence of pathogens but equally on the patient's immune system and other factors. Most pneumonias are not epidemic, although infection with influenza virus can be so defined.

Breathing problems, as often present in patients after a stroke, in Parkinson's disease, hospitalisation or surgery and mechanical ventilation can all increase the likelihood of pneumonia. Similarly, inability to clear sputum (as in cystic fibrosis) or retention of sputum (as in bronchiectasis) can lead to pneumonia.

After splenectomy (removal of the spleen), a patient is more prone to pneumonia due to the spleen's role in developing immunity against the polysaccharides on pneumococcus bacteria.

Therapy

Antibiotics are the treatment of choice for pneumonia of bacterial origin. They are not effective in viral pulmonary infections, but are sometimes used due to frequent concommitant bacterial superinfection. The antibiotics that are used depend on the nature of the pneumonia, the microbes known to typically cause pneumonia in the geographical region, and the immune status of the patient. In the United Kingdom, Amoxicillin is used as first-line therapy in the vast majority of patients who acquired pneumonia in the community, sometimes with added clarithromycin. In North America, where the "atypical" forms of community-acquired pneumonia are becoming more common, clarithromycin, azithromycin, and the fluoroquinolones have displaced the penicillin-related drugs as first-line therapy. In hospitalized patients and immune deficient patients, local guidelines generally determine which combination of (generally intravenous) antibiotics is used.

Patients who have significantly compromised respiratory function due to pneumonia may require supplemental oxygen. Severely affected patients may require artificial ventilation as a life-saving measure while their immune system fights off the infective cause with the help of antibiotics and other drugs.

In cases of viral (interstitial) pneumonia where influenza A or B are thought to be causative agents, patients who are seen within 48 hours of symptom onset may be treated with oseltamivir or zanamivir. There is no known efficacious treatment for pneumonia caused by SARS coronavirus, adenovirus, hantavirus, or parainfluenza virus; treatment is largely supportive.

Complications

Prognosis and mortality

The clinical state of the patient at time of presentation is a strong predictor of the clinical course. Many clinicians use the Pneumonia Severity Score to calculate whether a patient requires admission to hospital, based on the severity of symptoms, underlying disease and ageinformation Administrator note. In the United States, mortality from pneumococcal pneumonia is 1 in 20. In cases where the disease progresses to blood poisoning (bacteremia), 2 of 10 die. When the disease affects the brain (meningitis), 3 of 10 die. information Administrator note

Prevention

Vaccination with the pneumococcal polysaccharide vaccine is recommended for adults older than 65, patients with chronic disease and in patients with known immune compromise (includes AIDS, Nephrotic syndrome and Asplenia).information Administrator noteinformation Administrator note. Pneumoccocal pneumonia kills more Americans than all other diseases combined that could be partially prevented by vaccinationinformation Administrator note.

These same groups should also have annual Flu vaccination and so avoid secondary bacterial infections after influenza infection.

Epidemiology

Pneumonia is mainly a disease of young children and the elderly. Young adults rarely get the disease. It occurs more often during winter and spring than during summer and autumn.

History of pneumonia

Before the advent of antibiotics, pneumonia was often fatal. When penicillin was discovered in the 20th century, it was the first causal therapy. Most community-acquired strains of S. pneumoniae are still penicillin-sensitive. According to The Acorn Newspaper (Conejo Valley, Southern California), pneumonia was the leading cause of death in the United States in 1904.

See also

Notes

  1. Template:Anb National guideline clearninghouse clinical practice guideline (USA): adult preventive health care - immunizations
  2. Template:Anb Center for Disease Control, United States, regarding vaccination with the pneumococcal polysaccharide vaccine (PDF)
  3. Template:Anb Halm EA, Teirstein AS. Management of community-acquired pneumonia. N Engl J Med 2002;347:2039-45. PMID 12490686.
  4. Bartlett JG, Dowell SF, Mandell LA, File TM Jr, et al: Practice guidelines for the management of community-acquired pneumonia in adults. Clin Infect Dis. 2000;31:347-82.
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