Pneumonia natural history

Editor(s)-in-Chief: C. Michael Gibson, M.S., M.D. [mailto:mgibson@perfuse.org] Phone:617-632-7753; Philip Marcus, M.D., M.P.H.[mailto:pmarcus192@aol.com]==References==

Complications
Sometimes pneumonia can lead to additional complications. Complications are more frequently associated with bacterial pneumonia than with viral pneumonia. The most important complications include:

Respiratory and circulatory failure
Because pneumonia affects the lungs, often people with pneumonia have difficulty breathing, and it may not be possible for them to breathe well enough to stay alive without support. Non-invasive breathing assistance may be helpful, such as with a bilevel positive airway pressure machine. In other cases, placement of an endotracheal tube (breathing tube) may be necessary, and a ventilator may be used to help the person breathe.

Pneumonia can also cause respiratory failure by triggering acute respiratory distress syndrome (ARDS), which results from a combination of infection and inflammatory response. The lungs quickly fill with fluid and become very stiff. This stiffness, combined with severe difficulties extracting oxygen due to the alveolar fluid, create a need for mechanical ventilation. Sepsis and septic shock are potential complications of pneumonia. Sepsis occurs when microorganisms enter the bloodstream and the immune systemresponds by secreting cytokines. Sepsis most often occurs with bacterial pneumonia; Streptococcus pneumoniae is the most common cause. Individuals with sepsis or septic shock need hospitalization in an intensive care unit. They often require intravenous fluids and medications to help keep their blood pressure from dropping too low. Sepsis can cause liver, kidney, and heart damage, among other problems, and it often causes death.

Pleural effusion, empyema, and abscess
Occasionally, microorganisms infecting the lung will cause fluid (a pleural effusion) to build up in the space that surrounds the lung (the pleural cavity). If the microorganisms themselves are present in the pleural cavity, the fluid collection is called an empyema. When pleural fluid is present in a person with pneumonia, the fluid can often be collected with a needle (thoracentesis) and examined. Depending on the results of this examination, complete drainage of the fluid may be necessary, often requiring a chest tube. In severe cases of empyema, surgery may be needed. If the fluid is not drained, the infection may persist, because antibiotics do not penetrate well into the pleural cavity.

Rarely, bacteria in the lung will form a pocket of infected fluid called an abscess. Lung abscesses can usually be seen with a chest x-ray or chest CT scan. Abscesses typically occur in aspiration pneumonia and often contain several types of bacteria. Antibiotics are usually adequate to treat a lung abscess, but sometimes the abscess must be drained by a surgeon or radiologist.

Prognosis and mortality
With treatment, most types of bacterial pneumonia can be cured within one to two weeks. Viral pneumonia may last longer, and mycoplasmal pneumonia may take four to six weeks to resolve completely. The eventual outcome of an episode of pneumonia depends on how ill the person is when he or she is first diagnosed.

In the United States, about one of every twenty people with pneumococcal pneumonia will die. In cases where the pneumonia progresses to blood poisoning (bacteremia), one of every five will die. The death rate (or mortality) also depends on the underlying cause of the pneumonia. Pneumonia caused by Mycoplasma, for instance, is associated with little mortality. However, about half of the people who develop methicillin-resistantStaphylococcus aureus (MRSA) pneumonia while on a ventilator will die. In regions of the world without advanced health care systems, pneumonia is even deadlier. Limited access to clinics and hospitals, limited access to x-rays, limited antibiotic choices, and inability to treat underlying conditions inevitably leads to higher rates of death from pneumonia.

Clinical prediction rules
Clinical prediction rules have been developed to more objectively prognosticate outcomes in pneumonia. These rules can be helpful in deciding whether or not to hospitalize the person.
 * Pneumonia severity index -online calculator
 * CURB-65 score, which takes into account the severity of symptoms, any underlying diseases, and age -online calculator