The distribution of infection is worldwide, although mycetoma is reported to be more common in tropical and subtropical areas of the United States, Central and South America, and Australia. In the United States, Nocardia is the most commonly isolated of the aerobic actinomycetes.
At risk
Those with weakened immune systems (e.g., diabetes, cancer, HIV/AIDS, alcoholism, transplants, taking high doses of corticosteroids) are at the greatest risk of severe disease. Approximately 60% of nocardiosis cases are associated with being immunocompromised, and men are at three times greater risk than women.10 This statistic may be due to a more common risk among rural agricultural workers, usually men.
Incidence
In the United States, roughly 500–1,000 new cases of nocardiosis infection occur every year.11 Although rare in the US, the incidence of infection due to any of the aerobic actinomycetes is probably much greater than thought because most infections go unreported.
Mortality
Nocardiosis most often presents as a lung infection. Approximately 80% of cases present as pulmonary, disseminated, or brain; 20% as cellulitis. If the disease is left to disseminate, such as spread to the brain or CNS, mortality may be as high as 44%. The risk increases to 85% mortality among those with weakened immune systems.
Disseminated Rhodococcus infection among immunocompromised patients (those with HIV/AIDS) is also linked to high mortality.
