Adults
A full spectrum of microorganisms is responsible for CAP in adults, and patients with certain risk factors are more susceptible to infections by certain groups of microorganisms. Identifying people at risk for infection by these organisms aids in appropriate treatment. Many less-common organisms can cause CAP in adults; these may be determined by identifying specific risk factors, or when treatment for more common causes fails. Risk factors
Some patients have an underlying problem which increases their risk of infection. Some risk factors are:

Obstruction - When part of the airway (bronchus) leading to the alveoli is obstructed, the lung cannot eliminate fluid; this can lead to pneumonia. One cause of obstruction, especially in young children, is inhalation of a foreign object such as a marble or toy. The object lodges in a small airway, and pneumonia develops in the obstructed area of the lung. Another cause of obstruction is lung cancer, which can block the flow of air. Lung disease - Patients with underlying lung disease are more likely to develop pneumonia. Diseases such as emphysema and habits such as smoking result in more frequent and more severe bouts of pneumonia. In children, recurrent pneumonia may indicate cystic fibrosis or pulmonary sequestration. Immune problems - Immune-deficient patients, such as those with HIV/AIDS, are more likely to develop pneumonia. Other immune problems that increase the risk of developing pneumonia range from severe childhood immune deficiencies, such as Wiskott–Aldrich syndrome, to the less severe common variable immunodeficiency.
Community-acquired pneumonia (CAP) refers to pneumonia (any of several lung diseases) contracted by a person outside of the healthcare system. In contrast, hospital-acquired pneumonia (HAP) is seen in patients who have recently visited a hospital or who live in long-term care facilities. CAP is common, affecting people of all ages, and its symptoms occur as a result of oxygen-absorbing areas of the lung (alveoli) filling with fluid. This inhibits lung function, causing dyspnea, fever, chest pains and cough. CAP, the most common type of pneumonia, is a leading cause of illness and death worldwide. Its causes include bacteria, viruses, fungi and parasites. CAP is diagnosed by assessing symptoms, performing a physical examination, by x-ray or by sputum examination. Patients with CAP sometimes require hospitalization, and it is treated primarily with antibiotics, antipyretics and cough medicine. Some forms of CAP can be prevented by vaccination and by abstaining from tobacco products. Signs and symptoms
Common symptoms
Coughing which produces greenish or yellow sputum
A high fever, accompanied by sweating, chills and shivering
Sharp, stabbing chest pains
Rapid, shallow, often painful breathing

Less-common symptoms
Coughing up blood (hemoptysis)
Headaches, including migraines
Loss of appetite
Excessive fatigue
Bluish skin (cyanosis)
Nausea
Vomiting
Diarrhea
Joint pain (arthralgia)
Muscle aches (myalgia)
Rapid heartbeat
Dizziness or lightheadedness

In the elderly
New or worsening confusion
Hypothermia
Poor coordination, which may lead to falls

In infants
Unusual sleepiness
Yellowing of the skin (jaundice)
Difficulty feeding

Complications
Major complications of CAP include:

Sepsis - A life-threatening reaction to infection. A common cause of sepsis is bacterial pneumonia, frequently the result of infection with streptococcus pneumoniae. Patients with sepsis require intensive care with blood pressure monitoring and support against hypotension.