This retrospective cohort study defined geographic distribution of endemic mycoses in older persons in the United States enrolled in Medicare and may help improve diagnostic or prevention measures for those at risk. These endemic mycoses were geographically distributed, but not all occurred in a traditionally mycosis-endemic area. Histoplasmosis was most common, although the highest state-based incidence rates were seen for coccidioidomycosis. As older persons in the United States continue to travel and participate in outdoor activities, exposure to these pathogens may increase. Moreover, increasing age and decreasing cell-mediated immunity as a result of transplantation, chemotherapy, or other immunosuppressive medications increase the risk for endemic mycoses (1,9
). Overall, most cases occurred in patients without known immunocompromising conditions.
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.
In conclusion, among this cohort of Medicare beneficiaries, histoplasmosis was the most common endemic mycosis. Geographic distribution among older persons in the United States for histoplasmosis, coccidioidomycosis, and blastomycosis is evident, although ≈10% of cases were identified for patients without evidence of claims or residence in traditionally mycosis-endemic areas. Knowledge of areas of increased incidence may improve diagnostic or prevention measures in older adults at risk for endemic mycoses, including those receiving immunosuppressive medications or with new environmental exposures.