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What types of pneumonia are there?

Bacterial pneumonia is caused by various bacteria. The Streptococcus pneumoniae is the most common bacterium that causes bacterial pneumonia. It usually occurs when the body is weakened in some way, such as illness, malnutrition, old age, or impaired immunity, and the bacteria are able to work their way into the lungs. Bacterial pneumonia can affect all ages, but those at greater risk include persons who abuse alcohol, persons who are debilitated, post-operative patients,

persons with respiratory diseases or viral infections, and persons who have weakened immune systems. The symptoms of bacterial pneumonia include shaking, chills, chattering teeth, severe chest pain, high temperature, heavy perspiring, rapid pulse, rapid breathing, bluish color to lips and nailbeds, confused mental state or delirium, cough that produces rust-colored or greenish mucus. Viral pneumonia is caused by various viruses, and is the cause of half of all cases of pneumonia. Early symptoms of viral pneumonia are the same as those of bacterial pneumonia, which may be followed by increasing breathlessness and a worsening of the cough. Viral pneumonias may make a person susceptible to bacterial pneumonia.

Mycoplasma pneumonia has somewhat different symptoms and physical signs. It is caused by mycoplasmas, the smallest free-living agents of disease in humankind, which have the characteristics of both bacteria or viruses, but which are not classified as either. They generally cause a mild, widespread pneumonia that affects all age groups. Symptoms include a severe cough that may produce some mucus. Mycoplasma pneumonia often affects younger people and may be associated with symptoms outside of the lungs (such as anemia and rashes), and neurological syndromes (such as meningitis, myelitis, and encephalitis). Severe forms of Mycoplasma pneumonia have been described in all age groups. Chlamydophila pneumonia occurs year round and accounts for 5-15% of all pneumonias. It is usually mild with a low mortality rate. In contrast, atypical pneumonia due to Legionella accounts for 2-6% of pneumonias and has a higher mortality rate. Elderly individuals, smokers, and people with chronic illnesses and weakened immune systems are at higher risk for this type of pneumonia. Contact with contaminated aerosol systems (like infected air conditioning systems) has also been associated with pneumonia due to Legionella.

Aspiration pneumonia is an inflammation of the lungs and bronchial tubes caused by inhaling foreign material, usually food, drink, vomit, or secretions from the mouth into the lungs. This may progress to form a collection of pus in the lungs (lung abscess). Aspiration of foreign material (often the stomach contents) into the lung can be a result of disorders that affect normal swallowing, disorders of the esophagus (esophageal stricture, gastroesophageal reflux), or decreased or absent gag reflex (in unconscious, or semi-conscious individuals). Old age, dental problems, use of sedative drugs, anesthesia, coma, and excessive alcohol consumption are also causal or contributing factors. The response of the lungs depends upon the characteristics and amount of the aspirated substance. The more acidic the material, the greater the degree of lung injury, although this may not necessary lead to pneumonia.

Atypical pneumonia refers to pneumonia caused by certain bacteria - namely, Legionella pneumophila, Mycoplasma pneumoniae, and Chlamydophila pneumoniae. While atypical pneumonias are commonly associated with milder forms of pneumonia, pneumonia due to Legionella, in particular, can be quite severe and lead to high mortality rates. Atypical pneumonia due to Mycoplasma and Chlamydophila usually cause milder forms of pneumonia and are characterized by a more drawn out course of symptoms unlike other forms of pneumonia which can come on more quickly with more severe early symptoms.

Cytomegalovirus (CMV) is a member of a group of herpes-type viruses that can cause an infection of the lungs in immune-suppressed persons. This infection is particularly common in solid organ transplant and bone marrow transplant recipients. Infection with CMV is very common. The majority of healthy adults have antibodies (an indication of previous infection) to CMV in their blood. Usually CMV produces no symptoms, but serious CMV infections can occur in people with impaired immunity, such as those with AIDS, organ transplant and bone marrow transplant recipients, and people receiving chemotherapy or other immunosuppressive treatments. CMV disease is a common complication of organ transplantation. CMV pneumonia occurs in 20% of bone marrow transplant recipients. CMV pneumonia is often present simultaneously with pneumocystis pneumonia. Decreased oxygen levels in the blood (hypoxemia) in association with CMV pneumonia often predicts a fatal outcome.

Hospital-acquired pneumonia is an infection of the lungs contracted during a hospital stay. Pneumonia is a very common illness. It is caused by many different organisms and can range in seriousness from mild to life-threatening. Hospital-acquired pneumonia tends to be more serious because defense mechanisms against infection are often impaired during a hospital stay, and the kinds of infecting organisms are more dangerous than those generally encountered in the community. Risk factors predisposing people to hospital-acquired pneumonia are alcoholism, older age, immunosuppression from medications or diseases, recent illness, and risk of aspiration.

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.

Legionnaire's disease is an acute respiratory infection caused by the bacterium Legionella pneumophila, which can cause a broad spectrum of disease from mild cough and fever to a serious pneumonia. The bacteria that cause Legionnaire's disease have been found in water delivery systems and can survive in the warm, moist, air conditioning systems of large buildings including hospitals. The infection is transmitted through the respiratory system. Person-to-person spread has not been proved. From the onset of symptoms, the condition typically worsens during the first 4 to 6 days, with improvement starting in another 4 to 5 days. Most infection occurs in middle-aged or older people, although it has been reported in children. Typically, the disease is less severe in children.

Pneumocystis carinii pneumonia is an infection of the lungs caused by the fungus Pneumocystis carinii. PCP is a pneumonia caused by the fungal organism Pneumocystis carinii, which is widespread in the environment, and is not a pathogen (does not cause illness) in healthy individuals. However, in individuals with weakened immune systems due to cancer, HIV/AIDS, solid organ and/or bone marrow transplantation, as well as individuals receiving chronic corticosteroids or other medications that affect the immune system, Pneumocystis carinii may lead to a lung infection. Individuals with advanced AIDS are of particular interest, since PCP was a relatively rare infection prior to the AIDS epidemic. Before the use of preventive antibiotics for PCP, up to 70% of individuals in the U.S. with advanced AIDS would develop PCP.

Pneumonia in an immunocompromised host describes a lung infection that occurs in a person whose infection-fighting mechanisms are significantly impaired. People who are immunocompromised have a defective immune response. Because of this, they are susceptible to infections by microorganisms that are present everywhere, but do not normally cause disease in healthy people. They are also more susceptible to the usual causes of pneumonia, which can affect anyone. Immunosuppression can be caused by HIV infection, leukemia, organ transplantation, bone marrow transplant, and medications to treat cancer.

Viral pneumonia is an inflammation (irritation and swelling) of the lungs caused by infection with a virus. Pneumonia is an infection of the lung that affects 1 out of 100 people annually. Viral pneumonia is caused by one of several viruses, including influenza, parainfluenza, adenovirus, rhinovirus, herpes simplex virus, respiratory syncytial virus, hantavirus, and cytomegalovirus. Most cases of viral pneumonia are mild and get better without treatment, but some cases are more serious and require hospitalization. People at risk for more serious viral pneumonia typically have impaired immune systems such as people with HIV, transplant patients, young children (especially those with heart defects), the elderly, and people taking medications to suppress their immune systems in the treatment of autoimmune disorders.

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