Association Between Serum 25-Hydroxyvitamin D Level and Type of Coccidioidal Infection

Abstract

BACKGROUND

The clinical manifestations of coccidioidomycosis vary depending upon the extent of exposure and the immune status of the host. Recent studies have demonstrated an essential role for vitamin D in both innate and acquired immunity and serum levels strongly correlate with the development of upper respiratory tract infections, including tuberculosis. Despite similar pathophysiologic processes at play in the control of tuberculosis and invasive fungal infections, a possible association of low serum 25(OH) vitamin D levels had not previously been assessed in this patient group.

METHODS

We performed a case-control study examining serum 25(OH) vitamin D levels in three distinct groups with coccidioidomycosis compared to healthy uninfected controls.

RESULTS

Eighty-nine patients were included in this study (negative controls, 26; immune, 23; primary coccidioidal pneumonia, 22; disseminated/meningeal infection, 18). Serum 25(OH) vitamin D levels varied between groups with lowest levels seen in the group with disseminated/meningeal coccidioidomycosis (p=0.14).

CONCLUSIONS

We evaluated a diverse group of patients with varying forms of coccidioidomycosis and found no association of vitamin D with the acquisition, nor resolution, of coccidioidal infection. Vitamin D does not play a significant role in host susceptibility to coccidioidomycosis.

INTRODUCTION

Vitamin D has pleiotrophic effects on immunity, endothelial and mucosal function, and glucose metabolism. Additionally, vitamin D dependent modulation of monocyte-macrophage activity plays an important role in human innate immunity and T cell responsiveness with significant impacts on host susceptibility to infection [1]. In fact the effects on mucosal immunity are paramount to recognition and early defense against respiratory illnesses [2]. These in vitro findings have also been confirmed in recent clinical studies. Serum 25(OH) vitamin D levels have been found inversely associated with the development of upper respiratory tract infections [3], and low levels have been found to convey a higher risk of active pulmonary tuberculosis [4].

Similar to tuberculosis, coccidioidomycosis (caused by the dimorphic fungi Coccidioides immitis and Coccidioides posadasii) is acquired via respiratory inhalation and initial control is dependent upon innate immunity and macrophage activation. Additionally, granuloma formation is observed in both coccidioidomycosis and tuberculosis, further suggesting similar immunologic processes at play in the host response to these infection [5].

Black race and pregnancy are well known risk factors for those experiencing severe coccidioidal infections and interestingly these same groups are those most commonly deficient or insufficient in 25(OH) vitamin D [6]. Despite multiple reports detailing the association of low 25(OH) vitamin D levels predisposing to other respiratory infections, including both viral and mycobacterial etiologies, an association between vitamin D levels and fungal infections has not been previously examined. We sought to determine if serum vitamin D levels were a risk factor for the type of coccidioidal infection.

MATERIALS AND METHODS

A case-control study was designed to test whether a correlation between patient serum vitamin D level and type of coccidioidal infection could be found. All patients were enrolled at the University of California Davis Medical Center between September-October of 2010 and September-October of 2011 in an attempt to avoid seasonal variations of serum vitamin D levels with longer enrollment. Patients were excluded from the infection groups if they did not meet previously established criteria for the diagnosis of proven or probable coccidioidomycosis [7], if they had a known immunosuppressive condition or medication, or if they had a prior diagnosis of vitamin D deficiency or were taking vitamin D supplements. This study was approved by the Institutional Review Board of the University of California – Davis.

Negative controls were defined as patients with no clinical or serologic evidence of coccidioidal infection and were matched by zip-code to patients with evidence of disseminated coccidioidal infection to control for potential disease exposure. The past infection/immune group consisted of patients with a prior diagnosis of coccidioidal infection and who after 12 months from diagnosis exhibited no clinical or radiographic evidence of active coccidioidal infection. Those with primary coccidioidal pneumonia were defined as patients with clinical, radiographic and serologic evidence (positive for coccidioidal precipitin antibody (IgM)) of active and new coccidioidal infection. Those with disseminated/meningeal disease were defined as patients with clinical, radiographic, and serologic evidence of disseminated disease or those with recovery of Coccidioides spp. from a non-pulmonary site.

Vitamin D deficiency has been defined by the Institute of Medicine (IOM) as a 25 (OH) vitamin D level of ≤ 20 ng/ml. Vitamin D insufficiency has been defined as serum levels between 21 and 29 ng/ml[8]. Serum 25 (OH) vitamin D testing was performed by a centralized laboratory (ARUP, Salt Lake City, UT).

Chart abstraction was performed to identify demographic variables including age, sex, and ethnicity, the date of onset of symptoms, antifungal agents prescribed, and the type of coccidioidal infection.

Differences in demographic characteristics between patient groups were evaluated using analysis of variance (ANOVA) for age and Fisher’s exact test for gender and race. a Mean differences in 25(OH) Vitamin D levels across patient groups were tested with an analysis of variance (ANOVA). A chi-square test was used to evaluate the association between patient groups and vitamin D levels (deficient: < 20 ng/mL, insufficient: 21–29 ng/mL, normal: > 29 ng/mL). Data analysis was performed using R Version 2.11.1 and p-values less than 0.05 were considered to be statistically significant.

RESULTS

Eighty-nine patients were included in this study (negative controls, 26; immune, 23; primary coccidioidal pneumonia, 22; disseminated/meningeal infection, 18) (Figure 1). No statistically significant differences in baseline characteristics were found between negative controls, Coccidioides immune patients, those with primary coccidioidal pneumonia, or disseminated disease regarding age, sex, or ethnicity.

Figure 1.

Serum 25-OH vitamin D levels varied between groups with lowest levels seen in the group with disseminated/meningeal coccidioidomycosis (mean 20.1, range 6–40 ng/mL). However, these differences were not statistically significant ANOVA (F_3,85=1.86, P=0.14).

Interestingly both vitamin D deficiency and insufficiency were quite common among all patient groups. In the patient group with disseminated or meningeal coccidioidomycosis 10/18 (56%) were deficient in 25-OH vitamin D, while 6/18 (33%) were insufficient. Although we did not find a statistically significant association between patient group and vitamin D levels (χ₂=9.28, P=0.16), the patient group with disseminated or meningeal coccidioidomycosis had a higher proportion of patients that were deficient in 25-OH vitamin than the other patient groups (healthy controls: 10/26 (38%), immune: 6/23 (26%), and primary coccidioidal pneumonia: 5/22 (23%)).

DISCUSSION

Coccidioidomycosis remains a significant problem for those residing within endemic regions. Following inhalation of arthroconidia, the infectious form of Coccidioides spp., a myriad of clinical manifestations may present, yet 60% of all infections are subclinical [9]. Forty percent of patients manifest symptoms as a result of exposure to Coccidioides spp., with only 1–3% of all patients experiencing chronic or disseminated infection, often with disastrous consequences.

The immunogenetic and other host factors responsible for these differences in clinical sequalae and the type of coccidioidal infection remain poorly defined. Established risk factors for severe infection include depressed cell-mediated immunity through infection with the human immunodeficiency virus (HIV), or receipt of immunosuppressive medications [9], however other groups have been identified as being at significant risk for severe or disseminated coccidioidomycosis including African-Americans and pregnant women in the third trimester [10]. The reasons these groups are at high risk are poorly understood, however both share a predisposition to low serum vitamin D levels [6].

Similarly, despite widespread exposure to tuberculosis only 10% of patients develop clinical disease [11]. Numerous genetic factors have been implicated in the control of tuberculosis including the natural resistance-associated macrophage protein gene (NRAMP1), the major histocompatibility complex (MHC), serum 25(OH) vitamin D levels and single nucleotide polymorphisms within the vitamin D receptor genes [12].

Although the genetic risk factors for coccidioidomycosis are less well defined, MHC differences have been implicated in small studies [13], but serum vitamin D levels had not been examined prior to our study. We chose to evaluate serum (25) OH vitamin D levels in a comparative study of four distinct groups of patients with coccidioidomycosis. While we did not find significant differences, in the future when the immunopathogenesis of coccidioidomycosis is better defined, it is plausible that specific genetic subgroups may benefit from vitamin D therapy.

Our results showed no statistically significant differences in mean Vitamin D levels across subgroups and no significant association between subgroups and deficiency categories. Certainly, the lack of significance does not imply that no differences exist among these groups; only that we could not reject the null hypothesis of no differences in this pilot study. Nevertheless, the data are suggestive as patients with disseminated/meningeal infection had lower mean Vitamin D levels than found in the other infection groups but the differences among the groups were not large relative to the within-group variation. With 18–26 patients per group, our sample size was modest, but large differences would have been evident and prior studies of serum 25(OH) vitamin D levels in tuberculosis have shown statistically significant differences at similar sample sizes [14]. A larger study would be necessary to provide sufficient power to detect differences of the magnitude observed in our study.

Recently others have performed a similar study attempting to show a correlation between vitamin D and coccidioidomycosis, however vitamin D levels in patients with coccidioidal infection in their study (mean = 25.0 ng/mL) were significantly higher than their control group (22.6 ng/mL) [15]. Although methodologic issues prevented further analysis in their study, the vitamin D levels they observed in coccidioidomycosis patients corroborate our findings.

Vitamin D has a myriad of effects on both innate and acquired immunity including the induction of reactive nitrogen and oxygen species [16], suppression of matrix metalloproteinase enzymes implicated in pulmonary cavity formation [17], upregulation of the antimicrobial peptides including defensins [2, 18] and cathelicidin [19], and effective macrophage-monocyte interactions – all factors that are likely to play a significant role in the mucosal immunity to Coccidioides spp. In a recently completed double-blind randomized trial high-dose vitamin D was prescribed as an adjunctive agent in the treatment of pulmonary tuberculosis [20]. In this study vitamin D did not significantly affect the time to sputum conversion in the whole study population, but it did significantly hasten sputum culture conversion in participants with the tt genotype of the TaqI vitamin D receptor polymorphism. Given the similar immunologic processes responsible for effective control of both tuberculosis and coccidioidomycosis, this finding provides support that the potential role for vitamin D therapy as an adjunctive option during antifungal treatment should be evaluated in specific subgroups.

Important differences from tuberculosis exist in this study given the importance of environmental factors (precipitation, temperature, and wind patterns) on the epidemiology of coccidioidomycosis and that person-to-person transmission of Coccidioides spp. does not occur. In fact, as few as 10 arthroconidia have been found lethal in mouse models [21] and it is thus possible that despite the numerous effects of vitamin D on host immunity, infection cannot be prevented following exposure due to the very low ID₅₀ of Coccidioides spp. Instead serum vitamin D levels may contribute to long-term outcomes following infection - thus the lower vitamin D levels observed in patients with disseminated/meningeal infection. However the evaluation of serum vitamin D levels in patients with chronic/disseminated infection is problematic as these patients often lead sedentary lifestyles with low sun exposure secondary to the debilitating sequalae of their prior coccidioidal infection. Similar populations have been shown to have low serum 25(OH) vitamin D levels [22] thus causality in this subgroup is difficult to prove in the absence of a longitudinal study.

In conclusion we have evaluated the potential role of 25(OH) vitamin D as a risk factor for infection with Coccidioides spp. Although hypovitaminosis D cannot be added to the list of known risk factors for coccidioidomycosis at this time, further investigation of the immunomodulatory effects of vitamin D in fungal infections and the potential benefit in specific patient genotypes should be undertaken.