Discussion

This report provides an update on the epidemiology of coccidioidomycosis, histoplasmosis, and blastomycosis from 2019 surveillance data. Coccidioidomycosis, histoplasmosis, and blastomycosis are associated with substantial case numbers (21,425 cases total for all three diseases), morbidity (with approximately one half of histoplasmosis and blastomycosis patients hospitalized), and deaths (5% for histoplasmosis and 9% for blastomycosis). Continued surveillance in reporting states, expansion to other states, and collection of additional data elements would allow public health professionals to better understand year-to-year trends and changing epidemiology of coccidioidomycosis, histoplasmosis, and blastomycosis to identify populations at risk more effectively and to guide public health interventions.

The findings in this report confirm that coccidioidomycosis, histoplasmosis, and blastomycosis cause substantial illness in the United States, particularly coccidioidomycosis in terms of the number of cases reported (20,061). Although substantially fewer histoplasmosis and blastomycosis cases were reported, surveillance for these two diseases occurred in fewer states than for coccidioidomycosis. Even in states where histoplasmosis and blastomycosis are reportable, missed cases are likely because milder illnesses might be less commonly detected than mild coccidioidomycosis, in part because of the broader and less concentrated geographic distributions of histoplasmosis and blastomycosis than of coccidioidomycosis.^[37,38] In 2019, a total of 249 histoplasmosis and 147 blastomycosis cases resulted in hospitalization. These numbers are substantially lower than those reported in previous studies,^[39,40] which found that histoplasmosis and blastomycosis result in approximately 5,000 and 1,000 hospitalizations, respectively, each year in the United States according to administrative data, highlighting substantial discrepancies between sources of case reports. Although counts differed considerably, the high hospitalization and mortality rates for histoplasmosis and blastomycosis described in this report align with past surveillance reports.^[8,14,39] In-depth, state-level comparisons of surveillance and administrative hospitalization data are needed to evaluate potential gaps in reporting and accuracy of administrative coding data.

The acquisition of environmental diseases can be influenced by health disparities and is more likely to afflict vulnerable and minority populations.^[41] The data in this report confirm health disparities in the occurrence of these fungal diseases. AI/AN persons are more commonly affected by endemic mycoses, with blastomycosis incidence approximately six times as high and coccidioidomycosis incidence approximately four times as high as incidence in White persons. Asian and Native Hawaiian or other Pacific Islander persons had blastomycosis incidence approximately twice as high as White persons. Hispanic persons had coccidioidomycosis incidence rates almost three times as high as White persons. Incidence differences between other race and ethnicity categories for these three diseases were substantially smaller, although the relatively low proportion of data completeness for race and ethnicity suggests caution in interpreting these rates. Reasons for differences in reported incidences in endemic mycoses are not fully understood. The markedly higher coccidioidomycosis and blastomycosis rates for AI/AN persons might reflect in part greater population concentration in areas of higher incidence, although more specific exposures (e.g., occupational or recreational) might have a role. These disparities also might be related to chronic occupational, housing, and health care access discrimination. Disparities in insurance status or access to health care also might impede timely diagnosis and appropriate treatment.^[42,43] Understanding the associations of disease incidence and social vulnerabilities might help further explain the differences in reported incidences. Granularity in race and ethnicity data could identify populations at risk and help focus public health action; for example, persons of Hmong ancestry might be at higher risk for severe blastomycosis.^[27,44]

Coccidioidomycosis, histoplasmosis, and blastomycosis cases were more common in males, consistent with previous studies,^[8,14,30] although with substantial differences by pathogen, ranging from 52% of coccidioidomycosis infections to 70% of blastomycosis infections in males. Biologic differences and occupational exposure might explain why endemic mycoses occur more commonly in males. A recent study suggests that biologic differences might be a factor for higher rates and severity of coccidioidomycosis in males, raising the question of whether such factors also have a role in histoplasmosis and blastomycosis.^[45] The predominance of cases in males also might be related to occupational exposure, particularly for outdoor occupations traditionally held by males (e.g., construction, excavation, landscaping, hunting, or agricultural work);^[46] expanded surveillance could help in understanding the impact of these occupations.^[8,14,47] Although risk factors for hospitalization could not be determined because of the summary format of the data, other reports have identified males to be at increased risk for hospitalization related to histoplasmosis and coccidioidomycosis.^[14,48] Reports of hospitalization rates by sex for blastomycosis indicate conflicting results; further research is needed in this area.^[8,40]

Seasonal trends exhibited slight yet meaningful variations for all three fungal diseases throughout the year. Symptom onset date is rarely reported from states where coccidioidomycosis endemicity is high, and the use of laboratory report dates with associated lags might obscure seasonal trends. State-specific differences in how earliest event date is calculated as well as the incubation periods of coccidioidomycosis (7–21 days), histoplasmosis (14–28 days), and blastomycosis (median: 45 days) also might influence observed seasonality.^[37,38,49] Differences in peak coccidioidomycosis cases occurred in Arizona and California. A dual peak occurred in summer and autumn in Arizona, whereas California had only an autumn peak, which past surveillance reports also identified.^[30] A recent report suggested that wet winters accompanied by hot summers after dry years might increase the risk for coccidioidomycosis in California.^[50] Although exposure sources could not be ascertained, the spring peak in coccidioidomycosis cases reported from states where the disease is not known to be endemic is consistent with previous reports and likely stems from travelers spending the colder months in areas where Coccidioides is present and later returning to their permanent residence.^[9,30] Cases peaked in autumn for histoplasmosis and in winter for blastomycosis; however, increases were relatively small compared with other seasons. Studies suggest no seasonal variation with histoplasmosis hospitalizations whereas blastomycosis cases are more commonly reported in autumn and winter; however, certain disease presentations like pulmonary and disseminated disease might appear more often during different seasons of the year.^[39,51]

Previous studies have suggested that climate change could expand the geographic range of climate-sensitive fungi, especially Coccidioides, Histoplasma, and Blastomyces. Coccidioides is now detected as far north as Washington, and a predictive modeling study suggested that by the year 2100, the niche environment for Coccidioides could expand to dry western states including Montana, Nebraska, North Dakota, and South Dakota, which have not previously had locally acquired infections.^[4,11] Recent enhanced surveillance reports described a substantial number of histoplasmosis cases in Michigan, Minnesota, and Wisconsin, north of the previously defined area, suggesting northward expansion of hospitable habitats for Histoplasma.^[14] Dozens of blastomycosis cases have been reported in patients living outside of the disease's previously established endemic range in states such as Kansas, Nebraska, New York, Texas, and Vermont.^[52–54] Surveillance for coccidioidomycosis, histoplasmosis, and blastomycosis does not capture information from all states, which limits the understanding of the changes in geographic distribution of these diseases. Expanding surveillance to additional states would help create a more accurate picture of the geographic distribution and could provide standardized case data for further analysis with other data (e.g., weather, environment, or soil moisture) to monitor effects of climate change on disease risk.

Public health surveillance for these fungal diseases through NNDSS does not capture information related to exposures, occupation, disease presentation, antifungal treatment, hospitalization, or death. Efforts to improve public health surveillance by systematically collecting certain data elements would improve understanding of nationwide disease and treatment patterns, emerging populations at risk, and exposure sources.^[55] Certain state and local health departments are collecting such information through their local surveillance or cluster investigation efforts; specific message-mapping guides for coccidioidomycosis, histoplasmosis, and blastomycosis would allow additional valuable variables to be gathered through NNDSS.