Nocardiosis is an infection (typically of the lungs) caused by the gram-positive bacteria Nocardia.
Nocardia bacteria can infect the lungs when they are inhaled, and they can infect the skin when they enter the skin through a cut or scrape.
Symptoms depend on whether the bacteria infect the lungs (typically, causing a cough, fever, chills, chest pain, weakness, and loss of appetite) or the skin (abscesses, which may drain to the surface of the skin).
To diagnose nocardiosis, doctors examine a sample of infected tissue under a microscope or send the sample to a laboratory to be cultured.
Nocardiosis is treated with one or more antibiotics.
(See also Overview of Bacteria.)
Several species of Nocardia infect people. Nocardia asteroides usually causes lung and bodywide infections. Another species usually causes skin infections, particularly in people who live in tropical climates.
People become infected when
They inhale dust that contains Nocardia bacteria, resulting in a lung infection.
Soil or water that contains the bacteria enters the skin through a cut or scrape, resulting in a skin infection.
Nocardiosis rarely spreads from person to person.
Nocardia bacteria can spread to nearby tissue or through the bloodstream to infect any organ. They most commonly infect the brain, skin, kidneys, bone, or muscle. Abscesses (pockets of pus) may form in the infected organs.
Nocardiosis occurs worldwide in people of all ages. But it is more common among older people, especially men, and in people who have a weakened immune system. Any of the following conditions, which weaken the immune system, increases the risk of getting nocardiosis:
Having certain cancers (such as Hodgkin lymphoma)
Having an organ transplant
Taking high doses of corticosteroids or other medications that suppress the immune system
Having lung disease
Having advanced HIV/AIDS
Nocardiosis is considered an opportunistic infection because it occurs in people with a weakened immune system. However, about 20 to 30% of people with nocardiosis have no disorder or condition that increases the risk.
In the United States, an estimated 500 to 1,000 new cases of nocardiosis occur each year.
Symptoms of Nocardiosis
Symptoms of nocardiosis may be short-lived (acute) or become long-lasting (chronic).
Lung infection
If the lungs are infected, symptoms usually include cough, fever, chills, chest pain, weakness, loss of appetite, and weight loss.
Skin infection
If the skin is infected, abscesses often form in the skin or the tissues under the skin. The affected skin may be firm, red, warm, and tender to the touch. A lump that contains pus may form and spread under the skin or through the lymphatic vessels. Channels may form between the lump and the skin, and the pus may drain through them to the skin's surface.
Brain infection
In up to half of people with nocardiosis, the infection spreads to the brain, causing a collection of pus (abscess) to form. A brain abscess causes severe headaches and symptoms such as weakness, confusion, and seizures.
Diagnosis of Nocardiosis
Examination under a microscope or culture
Doctors may diagnose nocardiosis by identifying Nocardia bacteria in a sample of infected tissue examined under a microscope. Or they may send a sample of infected tissue to a laboratory where Nocardia bacteria, if present, can be grown (cultured) and identified. Doctors locate the infected tissue during a physical examination or on an x-ray or other imaging scan.
If Nocardia bacteria are identified, they are tested to see which antibiotics are effective (a process called susceptibility testing).
Treatment of Nocardiosis
Antibiotics
Abscesses typically must be cut open and drained and dead tissue surgically removed.
Prognosis for Nocardiosis
Without treatment, nocardiosis that involves the lungs or that has spread is usually fatal.
Even with appropriate antibiotic treatment, about 10% of people whose infection affects only the lungs die, and more than 50% of people with a weakened immune system whose infection has spread die.
Skin infections resolve in most people after treatment with antibiotics.
