No Consistent Link Between Dust Storms and Valley Fever (Coccidioidomycosis)

Abstract

Dust storms, such as those associated with haboobs and strong regional winds, are frequently assumed to cause increases in cases of Valley fever (coccidioidomycosis). The disease is caused by inhaling arthroconidia of Coccidioides fungi that, after being disturbed from semi-desert subsoil, have become airborne. Fungal arthroconidia can be transported in low-wind conditions as well as in individual dust events, but there is no reliable evidence that all or most dust storms consistently lead to subsequent increases in coccidioidomycosis cases. Following a review of the relevant literature, this study examines the relationship between dust storms and coccidioidomycosis cases to determine if there is a consistent and general association between them. All recorded dust storms from 2006 to 2020 in and near the Phoenix area of Maricopa County, Arizona and the Bakersfield area of Kern County, California were used in a compositing analysis (superposed epoch analysis) of subsequent coccidioidomycosis cases in each area. Analyses of monthly and weekly disease case data showed no statistical differences in the patterns of coccidioidomycosis cases following dust storms versus non-dust storm conditions, for the entire data set as well as for seasonal subsets of the data. This study thoroughly analyzes post-dust storm coccidioidomycosis cases for a large set of dust storms, and it confirms and expands upon previous literature, including a recent study that measured airborne arthroconidia and found no consistent links connecting wind and dust conditions to increases in coccidioidomycosis.

Keywords: Valley fever; climate; coccidioidomycosis; disease; dust storms; haboobs; health; weather.

Figure 1

Panoramic photograph from a helicopter of an advancing haboob on 25 August 2015 in Phoenix, Arizona. The view is to the south, with Baseline Road running east‐west in the foreground and intersecting with Interstate 10 at bottom right. Winds in this storm gusted to almost 50 mph (80 km/hr) with visibility reduced to near 0 m in places (NCEI–National Centers for Environmental Information, 2021). Concentrations of Coccidioides arthroconidia across the area were lower for this dust storm day than on the clear days immediately before and after (Gade et al., 2020). Image credit: © Jerry Ferguson (https://imgur.com/04apBty), used with permission.

Figure 2

Total days per month with reported dust storms in the Bakersfield area of Kern County, CA and the Phoenix area of Maricopa County, AZ from 2006 to 2020.

Figure 3

Monthly coccidioidomycosis cases in Kern County, CA and Maricopa County, AZ and months with one or more dust storm days (y‐axis value is arbitrary), 2006–2020.

Figure 4

Weekly coccidioidomycosis cases in Maricopa County, AZ and weeks with one or more dust storm days (y‐axis value is arbitrary), 2006–2020.

Figure 5

Composite coccidioidomycosis cases for 0‐ to 12‐month lags (M + 0 to M + 12) for all months with and without dust storms in Kern County, CA (Kern DS and Kern non‐DS) and Maricopa County, AZ (Maricopa DS and Maricopa non‐DS), 2006–2020. Dust storm occurrence/non‐occurrence is in month M + 0 on the left, and each line denotes the average case count in subsequent months from left to right. Vertical bars indicate 95% confidence intervals (t‐distribution). Lag months zero to three (M + 0 to M + 3), in which any dust storm‐related case increases should be apparent, are shaded in gray.

Figure 6

Composite coccidioidomycosis cases as for Figure 5, for the summer months (June to September).

Figure 7

Composite coccidioidomycosis cases as for Figure 5, for the shoulder season and winter months (October to May).

Figure 8

Composite coccidioidomycosis cases for 0‐ to 52‐week lags (W + 0 to W + 52) for all weeks with and without dust storms in Maricopa County (Maricopa DS and Maricopa non‐DS), 2006–2020. Dust storm occurrence/non‐occurrence is in week W + 0 on the left, and each line denotes the average case count in subsequent weeks from left to right. Vertical bars indicate 95% confidence intervals (t‐distribution); those for Maricopa DS are colored darker for clarity. Lag weeks 0 to 12 (W + 0 to W + 12), in which any dust storm‐related case increases should be apparent, are shaded in gray.

Figure 9

Composite coccidioidomycosis cases as for Figure 8, for the summer weeks (June to September).

Figure 10

Composite coccidioidomycosis cases as for Figure 8, for the shoulder season and winter weeks (October to May).

Figure 11

An example small patch of desert landscape in Tucson, Arizona with creosote bush (Larrea tridentata), prickly pear cactus (Opuntia engelmannii; upper left), and animal burrows (center foreground), illustrating their focal nature. This site is untested for Coccidioides; fast cost‐effective methods to do so are still needed. Image credit: the author.