Starting in October 2017, the Arizona Department of Health Services (ADHS) saw reports of coccidioidomycosis — Valley fever — climb. Cases usually rise in these months, but this rise was unusual.
| Cases reported | |
|---|---|
| October 2017–March 2018 | 4,827 |
| October 2016–March 2017 | 3,050 — so this was a 58.3% increase |
| October–March average, 2013–2017 | 3,211 — a 50.3% increase |
On provisional data, December 2017's rate of 17.2 cases per 100,000 people was the highest monthly rate in 5 years, above the previous peak of 14.2 per 100,000 in September 2015.
Monthly incidence of coccidioidomycosis in Arizona, April 2013–March 2018. CDC
What Valley fever is
- Cause: breathing in spores of the fungus Coccidioides, which lives in the soil of the southwestern United States.
- Symptoms: about 40% of infected people get sick, with fever, cough, fatigue, chest pain, shortness of breath or rash.
- Where: most reported U.S. cases are in Arizona, and there they peak in fall and winter.
Because cases are so common in Arizona and a positive lab result is so reliable a predictor, the state confirms a case on laboratory evidence alone: IgM or IgG antibodies against the fungus; culture, tissue or molecular evidence of Coccidioides; or a skin test that turns positive after the illness begins.
Who got sick, and where
The patients looked much like the year before:
| Oct 2017–Mar 2018 | Oct 2016–Mar 2017 | |
|---|---|---|
| Median age | 56 (IQR 39–69) | 57 (IQR 40–69) |
| Male | 50.5% | 51.2% |
About 90% of Arizona's reported cases are in its three most populous counties. The rise was steepest in Maricopa:
| County | Oct 2016–Mar 2017 | Oct 2017–Mar 2018 | Increase |
|---|---|---|---|
| Maricopa | 2,157 cases (52.0 per 100,000) | 3,674 (87.0 per 100,000) | — |
| Pima | 457 (45.1 per 100,000) | 601 (58.6 per 100,000) | 31.5% |
| Pinal | 254 (61.5 per 100,000) | 329 (76.9 per 100,000) | 29.5% |
Is it real, or a testing artifact?
One kind of test — an enzyme immunoassay (EIA) for IgM antibodies, used on its own — has been reported to be less specific than other methods in some circumstances. If more cases were being confirmed that way, the surge could be partly an artifact. The check:
| Period | Cases with a classifiable test | Positive by EIA IgM alone |
|---|---|---|
| Oct 2017–Mar 2018 | 4,638 | 602 (13.0%) |
| Oct 2016–Mar 2017 | 2,973 | 316 (10.6%) |
That slightly higher share is not enough to explain an increase this large, and there were no known changes in how doctors or laboratories reported cases.
Possible causes
The reasons are unknown. The authors point to several possibilities:
- Weather. Rain can help Coccidioides grow, and heat and drought that follow can help it spread. Preliminary data suggest that 2017 was unusually warm and dry in central Arizona.
- More people. During 2016–2017, Maricopa County gained more population than any other county in the United States.
- More dust. Increased home construction could have stirred up dust — and, with it, spores — while adding people susceptible to infection.
Finding out why Valley fever rises in areas where it is endemic is crucial, the authors say, both for prevention and for teaching doctors and the public how to diagnose and manage it properly.
Sources
Based on Bezold CP, Khan MA, Adame G, Brady S, Sunenshine R, Komatsu K, "Notes from the Field: Increase in Coccidioidomycosis — Arizona, October 2017–March 2018," MMWR volume 67, number 44, Centers for Disease Control and Prevention, with authors from CDC, the Arizona Department of Health Services and the Maricopa County Department of Public Health; a work of the United States government in the public domain. The report gives Maricopa County's rise as 70.5%, which does not match its own case counts (2,157 and 3,674), so that percentage is left out.
Licence: CC0 1.0 (public domain) · Adapted from www.cdc.gov
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