Relationship Between Valley Fever Occurrence and Satellite Assessment of Climate Response

English Abstract:

North America and particularly the southwestern region of the United States have been experiencing record warming and drought for the past 25 years (Cook et al., 2007; Herweijer et al., 2007; Mensing et al., 2007). In addition, Coccidioidomycosis or Valley Fever onset cases in the southwest have also increased since 1998 (Centers for Disease Control and Preventions, 2013). The California Department of Public Health annual reports show a significant increase of Valley Fever cases in southern California. Here we attempt to better understand the relationship between climate and the increased incidence of Valley Fever in the Antelope Valley region of southern California. Thirteen years of public health annual reports show a particular spike of Valley Fever cases in 2005, 2010, 2011 and 2012. To classify this relationship we have characterized the Antelope Valley land surface using multi-temporal Moderate Resolution Imaging Spectroradiometer (MODIS) NDVI 16-day composite data, Advanced Spacebourne Thermal Emission and Reflection Radiometer (ASTER) NDVI and Landsat NDVI composite imagery data. These satellite data were compared with climate variability data (surface temperature and precipitation) and Valley Fever onset statistics to correlate climate change to the increased Valley Fever cases. Results show a strong correlation between precipitation events and Valley Fever estimated onset, as well as a strong correlation between warmer years and increased registered cases. A correlation between hotter years and increased reported cases were prominent in results. Temperature increases in 2005, 2006, 2007, 2010 and 2012 show correlations between Valley Fever estimated onset and reported cases.NDVI values show a slight correlation between estimated onset and total cases. Substantial spikes in reported cases in 2005 and 2010 point to increased risk of onset for the months of August-December, indicating that August through December are particularly ‘at-risk’ months for contraction of Valley Fever. The methods used here can be used for other climate and human health hazard correlational studies for bacterial or fungal pathogens in arid soils.