Valley Fever Epidemiology: Outbreak Response Plan

Introduction to Valley Fever

According to the Centers for Disease Control and Prevention (CDC, 2018a), coccidioidomycosis, also known as Valley Fever, is an infection caused by the fungus Coccidioides. The fungus is commonly found in the soil of the Southwestern United States and Mexico. When people breathe in the spores of the fungus, which can hang in dusty air, they can develop Valley Fever. People who already have weakened immune systems are most likely at risk for developing the disease (Woods et al., 2000). Those with healthier immune systems tend to recover within a few weeks, though sometimes it can take months to heal completely, and antifungal medication may be provided for treatment.

The purpose of this paper is to discuss why several patients testing positive for coccidioidomycosis represents an epidemiological problem, what approach an epidemiologist would take to address the issue, and how to develop an outbreak response plan. The paper describes how descriptive and analytical epidemiology can be used to provide a response plan for the disease.

Why Valley Fever Is an Epidemiological Problem

Epidemiology is a field in medicine that deals with the incidence, distribution, and potential control of diseases. Valley Fever is a problem for the field of epidemiology because the rate of incidence is so high and control of the disease is so difficult given the manner in which it is contracted. According to the CDC (2018b), there were 14,364 cases of Valley Fever reported in 2017, and "most of these cases were in people who live in Arizona or California, [where] rates of Valley Fever are typically highest among people age 60 and older." It is estimated, moreover, that Valley Fever is responsible for approximately 30% of all pneumonia-related cases in the region each year, though researchers have argued that the actual rate may be even higher since testing rates are so low and infrequent (Valdivia et al., 2006).

Additionally, as McCotter et al. (2019) note, "the incidence of reported coccidioidomycosis in the past two decades has increased greatly; monitoring its changing epidemiology is essential for understanding its burden on patients and the healthcare system and for identifying opportunities for prevention and education" (p. 958). Valley Fever is difficult to diagnose and treat, and because of the high rate of incidence and distribution, its impact on health and the healthcare system, the potential control of Valley Fever poses a genuine problem for the field. Prevention, as always, is the best medicine — and that applies in the case of Valley Fever no less than in any other situation.

Epidemiological Approach and Surveillance Methods

The epidemiological approach for addressing the issue of Valley Fever is to examine trends, the overall burden of disease, and the geographical risk associated with the spread of coccidioidomycosis. As the disease has recently appeared in Washington State, a fresh look at these elements must be undertaken. Cairns et al. (2000) linked an outbreak in Washington State to a group of travelers returning from Mexico; however, this has not been an isolated case. Litvintseva et al. (2014) showed that although epidemiologic data "suggested that Coccidioides might have been acquired from the local environment, all 3 case-patients [in Washington State] had traveled to endemic regions several years prior to infection; therefore, the possibility of reactivation of latent infection could not be excluded" (p. e1). Litvintseva et al. (2014) also collected soil samples showing that the fungus was indeed present in Washington State soil. The researchers argued that it was possible that Coccidioides "has been present in WA for an extended time, but because of low human population density in eastern WA, sporadic distribution of the pathogen, and lack of awareness among physicians, human cases of coccidioidomycosis have not been previously recognized in WA" (Litvintseva et al., 2014, p. e2). To understand the true scope of the fungus, a proper epidemiological approach is therefore necessary.

Surveillance is a top priority in any epidemiological approach. Laboratory tests are used to confirm cases, and the incidence of the disease is recorded, monitored, and analyzed. Severity, seasonality, geographical associations, and related factors are all examined during surveillance. Interviews with infected individuals can be helpful in obtaining additional information about their habits, practices, and recent travels, providing a clearer picture of where patients had been prior to infection and where they might have acquired it.

As Thacker, Parrish, and Trowbridge (1988) note, epidemiological surveillance is defined as "the systematic collection, analysis and dissemination of health data for the planning, implementation and evaluation of public health programmes" (p. 11). Factors for evaluating surveillance methods should include: (1) sensitivity, (2) specificity, (3) representativeness, (4) timeliness, (5) simplicity, (6) flexibility, and (7) acceptability.

The purpose of surveillance is to assist in establishing either prevention or control of the disease. In the case of controlling or preventing coccidioidomycosis, a flexible surveillance method should be implemented so that regional data can be compared with random-sample data and new population groups can be added — as may be necessary in the northwestern portion of the United States, following evidence of coccidioidomycosis in that region.

Descriptive and Analytic Epidemiology Applied

Descriptive epidemiology refers to the examination of patterns as they pertain to the occurrence and incidence of disease. Its focus is on the who, what, when, where, why, and how. The purpose of descriptive epidemiology is to provide context for determining how a public health response should be developed and implemented. Those who practice public health typically conduct a descriptive epidemiological study in their region in order to construct a hypothesis for future analysis. One of the most famous epidemiological cases is that of the cholera outbreak in London and the work of John Snow in identifying the who, what, where, when, and why — ultimately leading to the identification of the outbreak's source and its bacterial cause.

Analytic epidemiology differs in that it focuses more on the complexities of the disease, such as associated risks, causes, and exposure. One of the main ways this is achieved is by comparing groups. If descriptive epidemiology is useful for developing hypotheses about a disease, analytic epidemiology is useful for testing those hypotheses. For this study, the descriptive epidemiological approach would examine who was infected, when, and where. A hypothesis would then be constructed about why and how the individual was infected. That hypothesis would be tested using analytical epidemiology through a randomized controlled trial or an observational study.

In this case, both descriptive and analytical epidemiology would be useful, especially given that the spread — or at least the discovery — of the disease in Washington State in recent years suggests that more is unknown about it than previously understood, and a new hypothesis is required. Since a new hypothesis is required, a new test is also required; thus both approaches should prove valuable.

References

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