Increasing Incidence and Severity of Coccidioidomycosis at a Naval Air Station

Military Medicine, Aug 2008 by Lee, Rachel, Crum-Cianflone, Nancy

ABSTRACT Background: Increasing rates of coccidioidomycosis among the general population are being described. Given the large number of military personnel stationed and training in endemic areas, data regarding infection trends among military members would be informative. Methods: We performed a retrospective epidemiological study concerning the incidence and severity of clinical cases of coccidioidomycosis at a naval base located in an endemic area in California. Results: Eighty-two military beneficiaries at the base were diagnosed with coccidioidomycosis from January 2002 to December 2006. Among active duty personnel, the rate of coccidioidomycosis rose 10-fold during the 5-year study period: 29.88 to 313.71 cases per 100,000 person-years. The incidence of coccidioidal infections occurring in active duty members was higher than other military beneficiaries at the base. The median age of patients with a coccidioidal infection was 28 years, and 73% were male. Sixty-six had primary pulmonary disease and 14 had disseminated disease; data were unavailable for two cases. The number of disseminated cases increased significantly over time; by 2006, 30% of the diagnosed cases were disseminated disease. Among cases of dissemination, 43% occurred among Caucasian/non-Hispanics. Disseminated disease was associated with high complement fixation titers and a more recent year of diagnosis. Although the sample size was small, we found no differences in rates of disseminated disease by race, likely due to the large number of cases among Caucasians. Conclusions: Coccidioidomycosis incidence rates have significantly increased during the last 5 years among military beneficiaries. Active duty members were more likely to develop coccidioidomycosis than dependents or retirees, perhaps related to the number and intensity of exposures in this group.

INTRODUCTION

Coccidioidomycosis, known as "Valley Fever," is a common fungal infection which has gained notoriety over the past decade due to the increased incidence and severity-oftentimes despite treatment.1-3 It was first described in 1892, appearing in a soldier in Argentina and became more apparent as a significant public health concern during the 1930s and 1940s, particularly in the San Joaquin Valley in southern California, with the "dust bowl" migrations.4-6 Since then, coccidioidomycosis has become a well-described endemic mycotic infection in the lower Sonoran zone.7 It is estimated that 150,000 infections occur annually, and epidemiological studies show that ~40% develop symptomatic disease with protean manifestations ranging from mild pulmonary disease to more severe forms.6-8 Approximately 1 to 2% will develop disseminated disease, most frequently with involvement of the skin, bones, joints, and the meninges. The risk for dissemination appears to be increased in specific racial groups (especially African Americans and Filipinos), pregnant or postpartum women, elderly persons, and immunosuppressed individuals, such as those with AIDS or cancer, or those who are transplant recipients.9-12

Increasing numbers of infections have been reported in California and Arizona over the past 15 years,1,5,13,14 and coccidioidomycosis is now one of the most frequent causes of community-acquired pneumonia.15 These findings may be partly due to environmental factors, construction activities, migration of increasing numbers of people into endemic areas, and the rising number of immunocompromised hosts in these areas. Trends of coccidioidomycosis among specific populations, such as the military, have not been reported.

More than 350,000 military personnel are stationed at bases within endemic regions of the United States, including in California, Arizona, Nevada, New Mexico, Utah, and Texas; in addition, thousands more individuals conduct training exercises on temporary active duty order to these locations.16 Military exercises often create dusty conditions which may aerosolize the infectious arthroconidia, which when inhaled lead to infection. Numerous outbreaks and sporadic cases among military members have been reported.6,16-23 Active surveillance and documentation of incidence rates of the disease in the military setting have not been recently evaluated. Whether military personnel are experiencing increasing rates of infections, similar to reports in the general population, is unknown. Hence, we conducted an epidemiological evaluation to determine the incidence and predictors of coccidioidomycosis among military members at a naval base located in the San Joaquin Valley.

METHODS

A retrospective evaluation was conducted for coccidioidomycosis cases at the Naval Air Station Lemoore (NASL), which is located in Kings County in the central valley of California (Fig. 1). Cases were identified between January 1, 2002 and December 31, 2006 by recording patients presenting to the NASL internal medicine clinic with infection and by searching the laboratory's computerized database. A case was defined as a positive immunoglobulin M (IgM) and immunoglobulin G (IgG) enzyme-linked immunosorbent assay test, a positive immunodiffusion test, or a positive complement fixation (CF) of ≥ 1:2 in the setting of a clinical illness consistent with coccidioidomycosis. An isolated positive IgM without IgG seroconversion, a CF of ≤1:2, or no histopathological evidence of coccidioidomycosis were considered to have a false-positive IgM test and were not included in our study.