Relapse is rare but does occur even after a full course of treatment. Prognosis
Published estimates of the case fatality rate for blastomycosis have varied from 4% to 78%. A 2020 meta-analysis of published studies found an overall mortality rate of 6.6%. This rose to 37% for immunocompromised patients and 75% for patients with ARDS. A 2021 analysis of 20 years of disease surveillance data from the five US states where blastomycosis is reportable found an overall mortality rate of 8% and a hospitalization rate of 57%. These numbers may be affected by the under-reporting of mild cases. Epidemiology
Incidence in most endemic areas is about 0.5 per 100,000 population, with occasional local areas attaining as high as 12 per 100,000. Most Canadian data fit this picture. In Ontario, Canada, considering both endemic and non-endemic areas, the overall incidence is around 0.3 cases per 100,000; northern Ontario, mostly endemic, has 2.44 per 100,000. Manitoba is calculated at 0.62 cases per 100,000. Remarkably higher incidence was shown for the Kenora, Ontario region: 117 per 100,000 overall, with aboriginal reserve communities experiencing 404.9 per 100,000. In the United States, the incidence of blastomycosis is similarly high in hyperendemic areas. For example, the city of Eagle River, Vilas County, Wisconsin, which has an incidence rate of 101.3 per 100,000; the county as a whole has been shown in two successive studies to have an incidence of about 40 cases per 100,000.
In 1952, the first documented case outside North or Central America, in Tunisia, was reported. The 1950s also saw the first introduction of antifungal drugs including amphotericin B. Before 1950, the fatality rate for disseminated blastomycosis was 92%, and treatment options were limited to iodide compounds, radiation therapy, and surgery. The first azole antifungal drug, ketoconazole, was developed in the 1970s and approved in the United States in 1981.Prior to 2013, the only species known to cause blastomycosis was B. dermatitidis. Since that time, genomic analysis has identified multiple other Blastomyces species causing blastomycosis, including B. gilchristii (2013), B. helicus (reassigned from the genus Emmonsia in 2017), B. percursus (2017), and B. emzantsi (2020). Other animals
Blastomycosis affects a broad range of mammals. As with humans, most animals that become infected were formerly healthy and immunocompetent. Dogs are frequently affected; blastomycosis is eight to ten times more common in dogs than in humans. Sporting and hound breeds are at the greatest risk. Cats and horses can also be infected. Cats with feline immunodeficiency virus are particularly at risk. However, the overall risk of blastomycosis in cats is 28 to 100 times lower than in dogs. Cases of blastomycosis have also been reported in captive lions and tigers, in a wild North American black bear, and in marine mammals such as the Atlantic bottlenose dolphin.The nonspecific symptoms that make blastomycosis difficult to diagnose in humans also complicate veterinary diagnosis. Cats in particular are often only diagnosed after death.Dogs and humans frequently acquire blastomycosis from the same exposure event.