Distribution of infection is worldwide, although mycetoma is reported as more common in tropical and subtropical areas of the USA, 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 (eg, 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 The incidence of infection due to any of the aerobic actinomycetes, although rare in the US, is probably much greater than thought because most infections go unreported.
MortalityNocardiosis presents most often as a lung infection. (80% of cases present as pulmonary, disseminated, or brain; 20% as cellulitis.) If the disease is left to disseminate (spread to the brain or CNS), mortality may be as high as 44%. 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.
10. Heymann DL. Control of Communicable Diseases Manual. 21th ed. APHA Press. 2022.
