Bacteria are the most common causes of pneumonia. However, pneumonia can also be caused by viruses, fungi, and other agents. It is often impossible to identify the specific culprit.
Many bacteria are grouped into one of two large categories by the laboratory procedure used to look at them under a microscope. The procedure is known as Gram staining. Bacteria are stained with special dyes, then washed in a special solution. The color of the bacteria after washing determines whether they are Gram-negative or Gram-positive. Knowing which group the bacteria belong to helps determine the severity of the disease, and how to treat it. Different bacteria are treated with different drugs.
Gram-Positive Bacteria. These bacteria appear blue on the stain and are the most common organisms that cause pneumonia. They include:
Gram-Negative Bacteria. These bacteria stain pink. Gram-negative bacteria commonly cause infections in hospitalized or nursing home patients, children with cystic fibrosis, and people with chronic lung conditions.
Atypical pneumonias produce mild symptoms and a dry cough. Organisms that cause atypical pneumonias include:
A number of viruses can cause pneumonia, either directly or indirectly. They include:
The mouth contains a mixture of bacteria that is normally harmless. However, if this mixture reaches the lungs, it can cause a serious condition called aspiration pneumonia. This may happen after a head injury or general anesthesia, or when a patient takes drugs or alcohol. In such cases, the gag reflex doesn't work as well as it should, so bacteria can enter the airways. Unlike other organisms that are inhaled, bacteria that cause aspiration pneumonia do not need oxygen to live. These bacteria are called anaerobic bacteria.
Impaired immunity leaves patients vulnerable to serious, life-threatening pneumonias known as opportunistic pneumonias. They are caused by organisms that are harmless to people with healthy immune systems. Infecting organisms include:
In addition to AIDS, other conditions put patients at risk for opportunistic pneumonia. They include cancers, such as lymphoma and leukemia. Long-term use of corticosteroids and drugs known as immunosuppressants also increases the risk for these pneumonias.
Exposure to chemicals can also cause inflammation and pneumonia. Where you work and live can put you at higher risk for exposure to pneumonia-causing organisms.
Severe acute respiratory syndrome (SARS) is a contagious respiratory infection. The World Health Organization (WHO) officially identified SARS as a worldwide threat in 2003, and issued an unprecedented travel advisory. It wasn't clear at the time whether SARS would become a global pandemic or settle into a less aggressive pattern. The latter seems to have happened.
As of May 2005, there was no known SARS transmission anywhere in the world, according to the U.S. Centers for Disease Control and Prevention (CDC). The SARS outbreak is a dramatic example of how quickly world travel can spread a disease. According to reports from the CDC and WHO, more than 8,000 people became sick with SARS during the outbreak. Of that group, 774 died. The outbreak is also an example of how quickly a networked health monitoring system can respond to an emerging threat.
Causes And Risk Factors. SARS is a serious form of atypical pneumonia that causes acute respiratory distress and sometimes death. It is caused by a new member of the coronavirus family (the family that includes the virus that causes the common cold). The discovery of the SARS-related virus represents one of the fastest identifications of a new organism in history.
SARS is spread by droplet contact. When someone with SARS coughs or sneezes, infected droplets are sprayed into the air. Like other coronaviruses, the SARS virus may live on hands, tissues, and other surfaces for up to 6 hours in these droplets, and up to 3 hours after the droplets have dried.
While droplet transmission through close contact has been responsible for most cases of SARS, there is evidence that SARS might also spread by infected droplets carried on hands and other objects the droplets touch. Airborne transmission was a real possibility in some cases. The live virus was even found in the stool of people with SARS, where it has been shown to survive for up to 4 days. The virus may also be able to live for months or years when the temperature is below freezing.
The estimated incubation period is 2 - 10 days, although there have been documented cases where the start of illness was considerably faster or slower. People with active symptoms of illness are clearly contagious. It is not known, however, how early people begin to be contagious before symptoms appear, or how long they might be contagious after the symptoms have disappeared.
Prevention. The best way to prevent SARS is to avoid direct contact with people who have SARS until 10 days after their fever and other symptoms are gone. Reduce travel to locations where there is an uncontrolled SARS outbreak. The CDC has identified hand hygiene as the cornerstone of SARS prevention. Wash your hands often with soap and water, or use an alcohol-based instant hand sanitizer. Cover your mouth and nose when sneezing or coughing. Consider respiratory secretions infectious. Clean commonly touched surfaces with an Environmental Protection Agency (EPA)-approved disinfectant. In some situations, masks and goggles may help prevent the spread of airborne or droplet infection. Wear gloves when handling potentially infectious secretions.
Prognosis. The overall worldwide death rate from SARS at the end of the outbreaks was 14 - 15%, although it was up to 50% in infected people over age 65. Many more were sick enough to require breathing assistance from a machine (mechanical ventilation). Others needed to be treated in the intensive care unit (ICU).
Today, intensive public health policies are proving to be effective in controlling outbreaks. Many nations have stopped the epidemic within their own countries. All nations must be vigilant, however, to keep this disease under control.
Complications. Complications from pneumonia can include:
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