Clinical Immunology And Allergy: Pneumonia

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Pneumonia is an inflammatory condition of the lung affecting primarily the small air sacs known as alveoli. Typically, symptoms include some combination of productive or dry cough, chest pain, fever and difficulty breathing. The severity of the condition is variable.

Pneumonia is usually caused by infection with viruses or bacteria and less commonly by other microorganisms, certain medications or conditions such as autoimmune diseases. Risk factors include cystic fibrosis, chronic obstructive pulmonary disease (COPD), asthma, diabetes, heart failure, a history of smoking, a poor ability to cough such as following a stroke and a weak immune system. Diagnosis is often based on the symptoms and physical examination. Chest X-ray, blood tests, and culture of the sputum may help confirm the diagnosis. The disease may be classified by where it was acquired, such as community- or hospital-acquired or health care-associated pneumonia.

Vaccines to prevent certain types of pneumonia are available. Other methods of prevention include hand washing and not smoking.Treatment depends on the underlying cause. Pneumonia believed to be due to bacteria is treated with antibiotics. If the pneumonia is severe, the affected person is generally hospitalized. Oxygen therapy may be used if oxygen levels are low.

Pneumonia affects approximately 450 million people globally (7% of the population) and results in about 4 million deaths per year. Pneumonia was regarded by Canadian pathologist William Osler in the 19th century as "the captain of the men of death".With the introduction of antibiotics and vaccines in the 20th century, survival greatly improved. Nevertheless, in developing countries, and also among the very old, the very young and the chronically ill, pneumonia remains a leading cause of death. Pneumonia often shortens suffering among those already close to death and has thus been called "the old man's friend".

Cause

The bacterium Streptococcus pneumoniae, a common cause of pneumonia, imaged by an electron microscope

Pneumonia is due to infections caused primarily by bacteria or viruses and less commonly by fungi and parasites. Although there are over 100 strains of infectious agents identified, only a few are responsible for the majority of the cases. Mixed infections with both viruses and bacteria may occur in roughly 45% of infections in children and 15% of infections in adults.A causative agent may not be isolated in approximately half of cases despite careful testing.

The term pneumonia is sometimes more broadly applied to any condition resulting in inflammation of the lungs (caused for example by autoimmune diseases, chemical burns or drug reactions); however, this inflammation is more accurately referred to as pneumonitis.

Factors that predispose to pneumonia include smoking, immunodeficiency, alcoholism, chronic obstructive pulmonary disease, asthma, chronic kidney disease, liver disease, and old age.Additional risks in children include not being breastfed, exposure to cigarettes or air pollution, malnutrition, and poverty.The use of acid-suppressing medications – such as proton-pump inhibitors or H2 blockers – is associated with an increased risk of pneumonia.Approximately 10% of people who require mechanical ventilation develop ventilator associated pneumonia, and people with gastric feeding tube have an increased risk of developing of aspiration pneumonia. For people with specific variants of FER gene, the risk of death is reduced in sepsis caused by pneumonia. However, for those with TLR6 variants, the risk of getting Legionnaires' disease is increased.

Prognosis

With treatment, most types of bacterial pneumonia will stabilize in 3–6 days. It often takes a few weeks before most symptoms resolve. X-ray finding typically clear within four weeks and mortality is low (less than 1%). In the elderly or people with other lung problems, recovery may take more than 12 weeks. In persons requiring hospitalization, mortality may be as high as 10%, and in those requiring intensive care it may reach 30–50%. Pneumonia is the most common hospital-acquired infection that causes death. Before the advent of antibiotics, mortality was typically 30% in those that were hospitalized. However, for those whose lung condition deteriorates within 72 hours, the problem is usually due to sepsis. If pneumonia deteriorates after 72 hours, it could be due to nosocomial infection or excerbation of other underlying co-morbidities. About 10% of those discharged from hospital are readmitted due to underlying co-morbidities such as heart, lung, or neurology disorders, or due to new onset of pneumonia.

Complications may occur in particular in the elderly and those with underlying health problems. This may include, among others: empyema, lung abscess, bronchiolitis obliterans, acute respiratory distress syndrome, sepsis, and worsening of underlying health problems.

Clinical prediction rules

Clinical prediction rules have been developed to more objectively predict outcomes of pneumonia. These rules are often used in deciding whether or not to hospitalize the person.

Pneumonia

CURB-65 score, which takes into account the severity of symptoms, any underlying diseases, and age

Awareness

Due to the relatively low awareness of the disease, 12 November was declared as the annual World Pneumonia Day, a day for concerned citizens and policy makers to take action against the disease, in 2009

Media contacts ,
Sana Jorge
Managing Editor
Journal of Clinicalimmunology And Allergy