Few data describing the incidence and geographic distribution of endemic mycoses in older persons in the United States are available. For infections such as histoplasmosis or blastomycosis, much of the information regarding geographic distribution of infection was described decades ago for younger adults (10,11). The most frequently cited study that describes areas of endemicity for histoplasmosis in the United States was published in 1969 by Edwards et al. (10). The study identified histoplasmosis endemicity on the basis of histoplasma skin testing, a diagnostic method of unknown sensitivity and probably poor specificity. The study population was military recruits; no older persons were included. In a recent report, Chu et al. described hospitalizations for endemic mycoses in adults and children by using 2002 Nationwide Inpatient Sample Data (12). Hospitalization rates for adults were described per region, but incidence rates, specifically for older patients, were not available. Moreover, outpatient cases were not captured; thus, rates were underestimated. Additional contemporary data regarding endemic mycoses among older persons in the United States are needed and would be helpful for identifying disease patterns and the geographic distribution of infection and for targeting areas for focused disease prevention. We describe the geographic distribution of endemic mycoses.

Studies estimating US incidence of histoplasmosis, coccidioidomycosis, or blastomycosis are limited, especially among older Americans. Our data suggest that the geographic distribution of these mycoses in older persons in the United States enrolled in Medicare is consistent with prior descriptions for younger patients (10,12); however, ≈10% of cases were identified in patients with primary residencies outside of mycosis-endemic regions. Our findings of increased incidence of histoplasmosis in the Southeast and Midwest were similar to prevalence estimates with use of skin testing among US Navy recruits (12). Our study expands on that early research by identifying cases of histoplasmosis, not antigen sensitivity, in an older population not described previously. Chu et al. reported a similar distribution of infection among children and adults with use of a similar case-finding method but evaluated only hospitalization data, potentially underestimating cases (12). Approximately 30% of our cases were identified only by outpatient physician claims.

Other studies have evaluated endemic mycoses in older adults but have not evaluated US geographic distribution (2,4). Leake et al. reported that coccidioidomycosis was more likely to develop in elderly persons who had recently moved to Arizona (2). Blair et al. compared clinical manifestations of coccidioidomycosis among older and younger patients and determined that immunosuppression, independent of age, was a predictor of widespread coccidioidomycosis (4). We used a sensitivity analysis and compared the complete cohort and a cohort that did not include patients who moved during the study but found that those who had recently moved did not affect regional incidence rates (data not shown). Of note, ≈10% of patients with an endemic mycosis had not lived or received medical services (based on available claims data) in a traditionally mycosis-endemic area, underscoring the need to consider these infections even in non–mycosis-endemic areas.

In our study population, concurrent conditions were common and, for the most part, similar in frequency among the endemic mycoses. COPD was the most common underlying disease for each endemic mycosis. Chu et al. found that immunosuppression, defined as hematologic or immunologic deficiency or transplantation, was more common in cases of histoplasmosis, when compared with the other endemic mycoses (12). Although we did not define immunosuppression as reported by Chu et al., solid malignancy was more frequent in cases of blastomycosis. In most cases, patients were without known immunocompromising conditions. Overall mortality rate for patients with endemic mycoses was low and similar to that seen by Chu et al. (12).

The use of Medicare 5% sample data enables national representative estimates of disease occurrence in older Americans, but several limitations deserve mention. The results described from 5% sample Medicare data may not be representative of the entire older American population and may not be valid for other populations outside the United States or for those with other insurance plans. There may be some degree of ascertainment bias because recognition of cases may vary by geographic region. The validity of our identification of presumed cases of endemic mycoses by using ICD-9 codes in claims data are uncertain. Few published data are available that evaluate the positive predictive value of codes for endemic mycoses, compared with other case ascertainment methods, but positive predictive values for opportunistic mycoses approach 70% (16–18). Our validation, with use of 2006–2007 Medicare Part D drug data for outpatients, suggests that our primary definition is reasonably specific for defining cases of coccidioidomycosis or blastomycosis.