Determining the Role Soil Moisture Had on the 2017 Valley Fever Outbreak

Over the last century, droughts caused more deaths internationally than any other weather-related extreme event (floods, hurricanes, etc.). Droughts in the United States, however, are not generally thought of as public health threats, even though there are known associations between droughts and negative health outcomes. By better understanding the linkages between droughts and human health, we can help properly prepare public health agencies for drought-associated health impacts, which, in turn, can reduce health risks and save lives.

Coccidioidomycosis, also called Valley fever, is caused by the fungus Coccidioides spp., which is found in the soils of the southwestern United States, and regions of South America, Central America, and Mexico. People contract coccidioidomycosis by breathing in fungal spores that are carried in the air. Symptoms of this disease can be flu-like, which can persist for weeks or even months. The infection can, in rare cases, lead to pulmonary complications or spread from the lungs to other organs, leading to conditions of greater severity or death. Though inhalation of these spores does not always cause illness, those who do become ill are hospitalized in over 40% of cases, with 75% of patients unable to perform their normal daily activities for a median of 47 days.

Previous research has determined that changes in temperature and precipitation are related to the incidence of coccidioidomycosis in the southwestern United States. Coopersmith et al (2017) was the first to study the incidence of coccidioidomycosis as related to actual changes in soil moisture conditions. Their results found that there was higher incidence of coccidioidomycosis cases if the previous season’s soil moisture conditions were atypically dry. 

In 2017, a large outbreak of coccidioidomycosis took place in the southwestern United States. Previous outbreaks of coccidioidomycosis showed similar patterns across the Southwest. For the first time in 2017, the outbreak showed unique differences between California and Arizona. Recent drought in the region, and subsequent changes in the environment, likely caused the differences in the way the outbreak manifested. Applying the previous approach by Coopersmith et al. to the recent outbreak, this study aimed to understand the factors that control incidence of the disease. The ultimate goal of this task was to use these results to forecast and predict the next outbreak. 

For more information, please contact Amanda Sheffield (amanda.sheffield@noaa.gov).