Pneumonia
Pneumonia symptoms vary greatly, depending on any underlying conditions a person may have and the type of organism causing the infection:

Bacterial Agents in Pneumonia
Pneumonia in adults is most commonly caused by bacterial agents. It is a frequent respiratory infection in industrialized cities, lower socioeconomic groups or in cases of crowded living quarters. The incidence of bacterial pneumonia increases in winter and spring in temperate zones. Most infectious pneumonia is caused by bacteria and 60-80% of all bacterial pneumonia is caused by Streptococcus pneumoniae. These organisms are routinely found in the upper respiratory tract of healthy persons. It is when they are drawn into the lower respiratory tract of susceptible individuals that they cause infection. Pneumococci are spread by droplets or direct contact with an infected person. Bacterial pneumonia has an incubation period of 1-3 days. Antibiotic therapy with penicillin or erythromycin makes the patient non-infective and generally results in a rapid recovery.

One may develop bacterial pneumonia symptoms after having an upper respiratory infection such as a cold or the flu. Signs and symptoms of pneumonia, which are likely to come on suddenly, include shaking, chills, a high fever, sweating, chest pain (pleurisy), and a cough that produces thick, rust-colored, greenish or yellow phlegm. Older adults or patients of chronic illness may have fewer or milder symptoms. However, that does not mean pneumonia symptoms should be treated lightly. For people age 65 and older, or those with a chronic illness, pneumonia can be extremely serious. The tissue of part of a lobe of the lung, an entire lobe, or even most of the lung''''s five lobes becomes completely filled with liquid (this is called "consolidation"). The infection quickly spreads through the bloodstream and the whole body is invaded. The streptococcus pneumoniae is the most common cause of bacterial pneumonia. It is one form of pneumonia for which a vaccine is available.

   
Viruses and Pneumonia
Viruses, including the same viruses that cause influenza, are responsible for half of all cases of pneumonia. Pathogens include the Respiratory syncytial virus (RSV), parainfluenza, adenovirus, influenza, enterovirus, and rhinovirus. Viral pneumonia strikes primarily in the fall and winter and tends to be more serious in people with cardiovascular or lung disease. It usually starts with a dry cough, headache, fever, muscle pain, and fatigue. As the pneumonia progresses, a patient may become breathless and develop a cough that produces phlegm. With viral pneumonia, risks of developing a secondary bacterial pneumonia increase as well. Infection with the influenza virus may be severe and occasionally fatal. If the influenza virus destroys alveolar epithelial cells, plasma leaks from the capillary, filling the airspace. If enough alveoli are involved, patients drown in their own plasma. This is especially true of patients with increased pulmonary capillary pressure, because destruction of alveolar epithelial cells will lead to greater extravasation of plasma and more pulmonary edema than in otherwise healthy people. If the virus invades the lungs and multiplies, there are almost no physical signs of lung tissue becoming filled with fluid. Pneumonia finds many of its victims among those who have pre-existing heart or lung disease or are pregnant. In extreme cases, the patient has a desperate need for air and extreme breathlessness. Viral pneumonias may be complicated by an invasion of bacteria, with all the typical pneumonia symptoms of bacterial pneumonia.

Mycoplasmas
Because of its somewhat different pneumonia symptoms and physical signs, and because the course of the illness differed from classical pneumococcal pneumonia, mycoplasma pneumonia was once believed to be caused by one or more undiscovered viruses and was called "primary atypical pneumonia." Identified during World War II, mycoplasmas are the smallest free-living agents of disease in humankind, unclassified as to whether bacteria or viruses, but having characteristics of both. They generally cause a mild and widespread pneumonia. They affect all age groups, occurring most frequently in older children and young adults. The death rate is low, even in untreated cases. These tiny organisms cause symptoms similar to both bacterial and viral pneumonia, although the symptoms appear more gradually and are often milder. If a patient has been diagnosed with walking pneumonia, it is probably caused by a mycoplasma. One may not be sick enough to stay in bed, and many people with mycoplasma pneumonia never seek medical care. This type of pneumonia spreads easily in situations where people congregate and is common in child care centers and among school children and young adults. Although not caused by a bacteria, mycoplasma pneumonia responds well to treatment with antibiotics.

Chlamydia Trachomatis
This is a sexually transmitted disease that may also cause pneumonia and bronchitis. It usually is a subacute infection of early infancy producing a sudden cough and eosinophilia without fever that lasts from 1-3 weeks, but it may occur in adults too. It is transmitted to infants at birth from the cervix of an infected mother. Adults having chlamydial pneumonia are usually immunocompromised with the infection spreading from the eye (conjunctival) to the respiratory tract via the nasolacrimal duct. Pneumonia Symptoms

Diagnosis is by isolation of the organism and by finding antibodies in the blood. Erythromycin and tetracycline are effective therapies.

Eukaryotic Pneumonia
Pneumocystis carinii is an organism of mixed fungal and protozoal character that causes and acute, often fatal, respiratory infection in infants or immunocompromised patients. Pneumonia caused by a parasite, Pneumocystis carinii, is the most common opportunistic infection affecting Americans with AIDS. People whose immune systems are compromised by treatment with steroids, organ transplants or cancer also are at risk. The signs and symptoms of Pneumocystis carinii pneumonia (PCP) include a cough that doesn''''t go away, fever and trouble breathing. Symptoms are labored or difficult breathing, cyanosis and heavy infiltrates in the alveolar spaces. Diagnosis is by finding the organism in mucous smears or by biopsy of lung tissue. Treatment is by the use of trimethoprim-sulfanethoxazole or pentamidine isothionate. When treated, 60-90 % of patients survive. If untreated it is uniformly fatal.

Pneumonia and Fungi
Certain types of fungus also can cause pneumonia, especially Histoplasma capsulatum, which is common in the Mississippi and Ohio River valleys. Some people experience no symptoms at all after inhaling this fungus. Others develop symptoms of acute pneumonia, and still others may develop a chronic pneumonia that persists for months. The symptoms of bacterial pneumonia develop abruptly and may include chest pain, fever, shaking, chills, shortness of breath.