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 Overview of Bacteria Bacteria are microscopic, single-celled organisms. They are among the earliest known life forms on earth. There are thousands of different kinds of bacteria, and they live in every conceivable... read more .)
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 lung disease
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).
If the lungs are infected, symptoms usually include cough, fever, chills, chest pain, weakness, loss of appetite, and weight loss.
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 Overview of the Lymphatic System . Channels may form between the lump and the skin, and the pus may drain through them to the skin's surface.
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 Testing a Microorganism's Susceptibility and Sensitivity to Antimicrobial Drugs Infectious diseases are caused by microorganisms, such as bacteria, viruses, fungi, and parasites. Doctors suspect an infection based on the person's symptoms, physical examination results,... read more ).
Treatment of Nocardiosis
Nocardiosis is treated with one or more antibiotics for a long time. Trimethoprim/sulfamethoxazole is often used. If people have a weakened immune system or the infection has spread, they need to take a second antibiotic. Treatment is started before doctors get the test results. The antibiotics may later be adjusted based on the results of susceptibility testing.
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.