Pneumonia basically consists of an inflammation of the lung, affecting primarily the alveoli. This inflammatory condition is typically caused by infection with viruses or bacteria, but in rare cases it can also be caused by other microorganisms, certain drugs or other conditions such as autoimmune diseases.
Pneumonia affects roughly 450 million people worldwide annually, i.e. 7 percent of the world’s population. It results in about 4 million deaths and remains a leading cause of death in developing countries among the very old, the very young or the chronically ill.
Signs and Symptoms of Pneumonia
Infectious pneumonia symptoms often include a productive cough, fever, chills, shortness of breath, an increased respiratory rate, and a sharp, stab-like chest pain when taking deep breaths. The elderly, meanwhile, may experience confusion as the most prominent sign. Children under age 5 usually experience symptoms such as fever, cough, as well as fast or difficult breathing.
Considering that fever occurs in many other common illnesses, it is not considered a very specific symptom of pneumonia. In those with severe disease or malnutrition fever may even be absent. Cough is also frequently absent in babies under two months old suffering from pneumonia. More severe signs and symptoms may include convulsions, decreased thirst, persistent vomiting, blue-tinged skin, extreme temperatures, or a decreased level of consciousness.
Pneumonia can be either bacterial or viral, but the symptoms are generally similar for both. Exceptions include pneumonia caused by Legionella, which may present abdominal pain, diarrhea, or confusion. Pneumonia caused by Streptococcus pneumonia may lead to rusty-colored sputum, while pneumonia caused by Klebsiella may display bloody sputum commonly described as “currant jelly.”
Common Causes of Pneumonia
As previously mentioned, pneumonia primarily stems from bacteria or viruses and is less commonly caused by fungi and parasites. Researchers have identified more than 100 strains of infectious agents, but only a few of those proved responsible for most cases. On the other hand, up to 45 percent of infections in children and 15 percent of infections in adults may have mixed infections with both viruses and bacteria. Despite thorough testing, roughly half of cases remain without an isolated causative agent.
Conditions and factors that increase the risk of developing pneumonia include immunodeficiency, sensitized lungs, smoking, alcoholism, chronic obstructive pulmonary disease, chronic kidney disease, and liver disease. An increased risk of pneumonia is also associated with acid-suppressing medications such as proton-pump inhibitors or H2 blockers. Old age also increases the risk of pneumonia.
Community-acquired pneumonia (CAP) has bacteria as the most common cause, with Streptococcus pneumoniae isolated in roughly half of cases. Other frequently isolated bacteria include Haemophilus influenzae, responsible for 20 percent of cases, Chlamydophila pneumonie, responsible for 13 percent of cases, and Mycoplasma pneumoniae, making up 3 percent of cases. Saphylococcus aureus, Moraxells catarrhalis, Legionella pneumophila and Gram-negative bacilli can also cause pneumonia.
Roughly a third of infections in adults and about 15 percent of pneumonia cases in children are caused by viruses. Frequently-involved agents include rhinoviruses, coronaviruses, influenza virus, adenovirus, respiratory syncytial virus (RSV), and parainfluenza. In rare cases, pneumonia may also be caused by herpes simplex virus, affecting groups such as newborns, cancer patients, transplant recipients, and people with considerable burns. People who underwent organ transplantation or those who are otherwise immuno-compromised are more vulnerable to cytomegalovirus pneumonia. Those with viral infections may also be secondarily infected with Streptococcus pneumoniae, Staphylococcus aureus, or Haemophilus influenzae, especially when they are also suffering from other health issues.
Predominant viruses typically vary depending on periods of the year. During flu season, for instance, influenza may account for more than half of all viral pneumonia cases. Outbreaks of other viruses may also occur occasionally.
While pneumonia caused by fungi is rather uncommon, it does occur more frequently in people with weakened immune systems due to immunosuppressant drugs, AIDS, or other medical conditions. Fungal pneumonia is primarily caused by Histoplasma capsulatum, blastomyces, Cryptococcus neoformans, Pneumocystis jiroveci and Coccidioides immitis. The latter half of the 20th century saw an increase in cases due to increasing travel and rates of immunosuppression. Histoplasmosis is the most common cause in the Mississippi River basin, while coccidioidomycosis is the most common in the Southwestern United States.
The lungs can be affected by various parasites, including Toxoplasma gondii, Strongyloides stercoralis, Ascaris lumbricoides and Plasmodium malariae. Such parasites generally enter the body through direct contact with the skin, ingestion, or via an insect factor. Most parasite don’t specifically affect the lungs, but they do affect them secondarily to other sites. The Paragonimus westermani parasite is an exception to this rule. Some parasites, meanwhile, can stimulate a strong eosinophilic reaction, which in turn mat lead to eosinophilic pneumonia. When other infections such as malaria are involved, lung infection is mainly due to cytokine-induced systemic inflammation. Such infections in the developed world are usually seen in immigrants or people returning from travel. On a global scale, these infections are more common in immunodeficient individuals.
Idiopathic Interstitial Pneumonia
Non-infectious pneumonia is called idiopathic interstitial pneumonia, and consists of a class of diffuse lung diseases. This group includes diffuse alveolar damage, nonspecific interstitial pneumonia, organizing pneumonia, desquamative interstitial pneumonia, lymphocytic interstitial pneumonia, respiratory bronchiolitis interstitial lung disease, and the common interstitial pneumonia.
Pneumonia typically starts as an upper respiratory tract infection that later affects the lower respiratory tract as well. With viral pneumonia, viruses may take various routes to reach the lung. The respiratory syncytial virus, for instance, is typically contracted when touching contaminated objects and then touching one’s eyes or nose. Other viral infections are contracted by inhaling contaminated airborne droplets. Once the viruses enter the upper airway, they continue to invade the lungs where they enter the cells lining the airways, alveoli, or lung parenchyma. On the other hand, viruses such as measles and herpex ximplex may reach the lungs via the blood. Once the lungs are invaded, they may experience varying degrees of cell death. The inflammation primarily stems from white blood cells, mainly mononuclear cells. Many viruses not only damage the lungs, but also affect other organs and wreak havoc in other body functions. Viruses can also facilitate bacterial infections, making bacterial pneumonia a co-morbid condition.
With bacterial pneumonia, most bacteria enter the lungs through small aspirations of organisms in the throat or nose. About 50 percent of normal people have these small aspirations while sleeping. The throat contains bacteria at all times, but potentially infectious bacteria reside these only under certain conditions and at certain times. In more rare occasions, some bacteria may reach the lungs via contaminated airborne droplets. Bacteria can also spread via blood. Once bacteria reach the lungs, they may invade the spaces between cells and between alveoli.
Preventing and Managing Pneumonia
Preventive measures to avoid developing pneumonia include vaccination, environmental measures and proper treatment of other health issues. According to estimates, mortality among children could be reduced by as much as 400,000 if appropriate preventative measures were implemented globally. If proper treatment would be universally available, it is believed that childhood deaths could be reduced by another 600,000.
Vaccines prevent against certain bacterial and viral pneumonias, both in children and adults. Flu vaccines are slightly effective against influenza A and B. In the U.S., the Center for Disease Control and Prevention (CDC) recommends annual vaccination for every person 6 months and older.
Other preventive measures include smoking cessation, reducing indoor air pollution, properly treating underlying illnesses such as HIV/AIDS, malnutrition and diabetes mellitus, hand hygiene and others such.
Antibiotics proved better outcomes in individuals with bacterial pneumonia. The type of antibiotic will initially depend on the patient’s characteristics such as age, underlying health, and the location the infection was contracted. The UK recommends empiric treatment with amoxicillin as the first line of treatment for community-acquired pneumonia (CAP), giving doxycycline or clarithromycin as alternatives. In North America, the most common forms of CAP are the “atypical” ones, which lead to replacing amoxicillin with macrolides (azithromycin or erythromycin) as a first line of treatment in adults. Treatment traditionally lasts 7 to 10 days, but now more evidence indicates that shorter courses of 4 to 5 days can be just as effective.
For viral pneumonia, neuraminidase inhibitors may be used to treat the condition caused by influenza viruses (influenza A and B). Other types of viral CAP have no specific recommendations in terms of antiviral medications. Some experts advocate the use of antibiotics in viral pneumonia, claiming that it is impossible to rule out a complicating bacterial infection. The British Thoracic Society, meanwhile, recommends avoiding antibiotics in cases of mild disease. Corticosteroids are still controversial.
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