lung and airway disorders
Community Acquired Pneumonia
Causes of Community Acquired Pneumonia
Many organisms cause community-acquired pneumonia, including bacteria, viruses, fungi, and parasites. In most cases, the specific microorganism causing the pneumonia is not identified. However, doctors can usually predict which microorganisms are most likely to be causing the pneumonia based on the person’s age and other factors, such as whether the person also has other diseases. Community-acquired pneumonia can develop in people whose immune systems are normal (also called competent) or in people whose immune systems are impaired (also called immunocompromised people). However, when doctors use the term community-acquired pneumonia, they are generally referring to people whose immune systems are normal. Pneumonia in immunocompromised people is discussed separately. "Walking pneumonia" is a nonmedical term used to describe a mild case of community-acquired pneumonia that does not require bedrest or hospitalization. Some people even feel well enough to go to work and participate in other daily activities. The cause is often a viral lung infection or a bacterial infection withMycoplasma pneumoniaeorChlamydophila pneumoniae. The most common bacterial causes of community-acquired pneumonia are Streptococcus pneumoniae Haemophilus influenzae Chlamydophila pneumoniae Mycoplasma pneumoniae Streptococcal Infections (pneumococcus) causes about 150,000 hospitalizations in the United States each year. There are over 90 types of pneumococci, but most serious disease is caused by only a small number of types. Pneumococcal pneumonia can be very severe, particularly in young children and older people. Haemophilus influenzae Infections pneumonia may occur in adults but is more common among children. However, childhood infection has become much less common since children have been routinely vaccinated against Chlamydia and Other Nongonococcal Infections is the second most common cause of lung infections in healthy people aged 5 to 35 years. Chlamydia and Other Nongonococcal Infections causes infection very similar to that caused by Legionella Infections causes pneumonia and flu-like symptoms sometimes called Legionnaires’ disease. It accounts for about 1 to 8% of all pneumonias and about 4% of fatal pneumonias acquired in hospitals. Staphylococcus aureus Infections causes pneumonia that is resistant to some types of antibiotics. This bacteria is known as community-acquired methicillin-resistant Pseudomonas Infections is an especially common cause of pneumonia in people with Common viruses that can cause community-acquired pneumonia include SARS-CoV-2, the virus that causes Coronaviruses and Acute Respiratory Syndromes (MERS and SARS) None Respiratory Syncytial Virus (RSV) Infection and Human Metapneumovirus Infection (RSV) Adenoviruses Influenza (Flu) viruses Respiratory Syncytial Virus (RSV) Infection and Human Metapneumovirus Infection None Parainfluenza viruses Infectious Mononucleosis None Coxsackievirus (rarely) The virus that causes Chickenpox can also cause a lung infection. Fungal causes of community-acquired pneumonia include ( Histoplasmosis ) ( Coccidioidomycosis ) ( Blastomycosis ) and Parasites that cause community-acquired pneumonia in people who live in higher income countries include ( Toxocariasis ) ( Dog Heartworm Infection ) ( Fluke Infections of the Lungs ) Psittacosis (parrot fever) is a rare pneumonia caused byChlamydia psittaci,a bacterium present mainly in birds such as parrots, macaws, parakeets, and lovebirds. It is also present in other birds, such as pigeons, finches, chickens, and turkeys. Usually, people are infected by inhaling dust from the feathers or the waste of infected birds. The organism also may be transmitted by a bite from an infected bird and, rarely, from person to person in cough droplets. Psittacosis mainly occurs in bird fanciers or in people who work in pet shops or on poultry farms. About 1 to 3 weeks after being infected, a person develops a fever, chills, fatigue, and loss of appetite. A cough develops, which is initially dry but later brings up greenish sputum (thick or discolored mucus). Fever persists for 2 to 3 weeks and then slowly subsides. The disease may be mild or severe, depending on the person’s age and the extent of lung tissue involved. Blood tests to determine whether the person has a certain type of antibody, suggesting recent infection withChlamydia psittaci,are the most reliable method for confirming the diagnosis, but doctors usually suspect the infection in people who have a history of exposure to birds. Bird breeders and owners can protect themselves by avoiding dust from the feathers and cages of sick birds. Importers are required to treat susceptible birds with a 45-day course oftetracycline, which generally gets rid of the organism. People with psittacosis are treated withtetracyclinetaken by mouth for at least 10 days. Recovery may take a long time, especially in severe cases. The death rate may reach 30% in people with severe untreated psittacosis, although with appropriate treatment most people recover. 