Definition and Overview

Pneumonia is an acute medical disease that is characterized by the presence of an infection in the lung parenchyma. It is typically caused by bacteria or virus, and usually affects the alveoli, or the small air sacs in the lungs. The alveoli become filled with infected fluid, reducing lung capacity and decreasing oxygenation.

Pneumonia is generally classified into how the infection is acquired. Community-acquired pneumonia is the type that a patient develops in his usual environment. Healthcare-associated pneumonia, meanwhile, is pneumonia that an individual develops at a healthcare facility, such as a hospital. The organisms responsible for healthcare-associated pneumonia are more virulent than those associated with community-acquired pneumonia.

Pneumonia is one of the most frequently encountered medical conditions in the world, affecting 450 million patients every year, 150 million of which are children. Approximately 4 million people die of this disease each year, and it remains as one of the top ten leading causes of death per year worldwide. In children, it is the number one infectious cause of mortality across the globe. Although anyone can develop pneumonia, extremes of ages -- the very young and the very old -- are the ones that are usually severely affected. Developing nations are affected five times more than developed countries. Pneumonia is prevalent in sub-Saharan Africa and South Asia.

Cause of Condition

Pneumonia typically begins as an upper respiratory infection. Viruses and bacteria are usually responsible, but infection with parasites and fungi may also occur. These organisms typically enter the pulmonary system via the inhalation of airborne droplets that are contaminated with the organism. Some organisms may also infect a person's lungs through the bloodstream. Once they have entered the airways, the organisms invade the lung parenchyma and the alveoli. The body generates an immune response against these organisms, which result in the release of cytokines, inflammation, damage to the lungs and pulmonary consolidation.

The risk for the development of pneumonia increases in patients with certain medical conditions. These include individuals who are immunocompromised, those who have chronic obstructive pulmonary disease or COPD, and other chronic conditions, like diabetes and kidney disease. Patients who have been hospitalized for a long period, especially those who are intubated and are on respiratory support, also have a higher risk. Smoking and alcoholism, as well as exposure to certain farm animals and bird droppings, also increase the risk for pneumonia.

Bacterial infection is the most common cause of pneumonia. The most frequently encountered bacteria is Streptococcus pneumoniae, followed by Haemophilus influenza. Aspiration of gastric contents predisposes a person to infection with anaerobic organisms. For the viruses, the most commonly encountered viruses are respiratory syncytial virus, rhinovirus and influenza virus, especially during flu season. Fungal and parasitic infection usually occurs in those who are immunodeficient, and living in or traveling to areas where these organisms are endemic. For patients infected with HIV, infection with Pneumocystis jiroveci is common, and usually lethal.

Mixed infections with different organisms can occur in 15-45% of cases of pneumonia.

Key Symptoms

The most common symptom of pneumonia is productive cough. It is usually associated with the production of yellowish or greenish sputum, but blood-tinged sputum can also occur. This is typically associated with fever and chills. Some patients may also present with non-specific symptoms, such as fatigue and enlarged nodes in the neck. Chest pain, especially when taking deep breaths, can also occur. Difficulty of breathing or shortness of breath is also common, and usually manifested by an increased rate or pace of respiration and occurrence of wheezing. Patients, especially children, can present with chest indrawing or retractions, and even the use of accessory muscles of breathing, such as the neck muscles. In severe cases, patients may present with cyanosis or bluish skin color and decreased consciousness level, indicating poor oxygenation. Some patients, especially the elderly and the chronically ill, may present with atypical symptoms, such as abdominal pain or confusion.

Who to See and Types of Treatments Available

If you have symptoms of pneumonia, it is important to consult your doctor or a local health worker. The health care professional will conduct a physical examination and will request for laboratory tests. The usual laboratory examinations to diagnose pneumonia include a complete blood count, sputum studies to determine what organism is causing your disease, and a chest x-ray to check for the presence of lung infiltrates.

The majority of cases of mild pneumonia can be treated adequately at home. Patients are usually prescribed with antibiotics targeted against the offending organism. Patients start to feel better and notice an improvement in symptoms after about 2 or 3 days of treatment with oral antibiotics. Along with the antibiotics, you will need to rest for several days to allow your body to recover and successfully fight off the infection. You will also need to increase your fluid intake, avoid exposure to air pollution, and stop smoking. However, if the symptoms do not improve or even worsen, or if you have other serious medical conditions or diseases, you should consult your doctor immediately. In these cases, you may have to be admitted to a hospital for further management and given stronger intravenous medications for a longer period. Infants below two months who develop pneumonia also need to be hospitalized. Severe pneumonia is best managed by a pulmonary specialist.

In general, pneumonia typically resolves within a week of proper antibiotic treatment, although some symptoms may take several weeks before they completely disappear. For most cases of pneumonia, mortality is low; however, in hospitalized patients, mortality goes up to 10% and is even higher for patients admitted to intensive care units. Complications, such as pleural effusion, empyema, respiratory failure and sepsis, can occur in elderly patients and those with underlying diseases.

Pneumonia is a preventable disease that can result in unwanted, occasionally lethal, complications. Vaccination is recommended in order to prevent the development of pneumonia, or at least minimize the severity of the disease if it is acquired. Pneumococcal immunization is especially encouraged in populations at risk, such as people who are older than 65 years of age, those with chronic medical conditions, and smokers. For children, vaccination is an essential aspect of prevention and can help decrease child mortality.


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