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Article

Assessment of the Immune Response to Coxiella burnetii in Rural Areas of the Thessaly Region Following the Daniel Floods

by
Magdalini Christodoulou
1,
Ourania S. Kotsiou
2,*,
Konstantinos Tsaras
1,
Charalambos Billinis
3,
Konstantinos I. Gourgoulianis
4 and
Dimitrios Papagiannis
1,*
1
Public Health & Adults Immunization Laboratory, Department of Nursing, School of Health Sciences, University of Thessaly, 41110 Larissa, Greece
2
Laboratory of Human Pathophysiology, Department of Nursing, University of Thessaly, 41110 Larissa, Greece
3
Department of Microbiology and Parasitology, Faculty of Veterinary Science, University of Thessaly, 43100 Karditsa, Greece
4
Respiratory Medicine Department, School of Medicine, University of Thessaly, University Hospital of Larissa, 41500 Larissa, Greece
*
Authors to whom correspondence should be addressed.
Hygiene 2025, 5(3), 30; https://doi.org/10.3390/hygiene5030030
Submission received: 18 May 2025 / Revised: 4 July 2025 / Accepted: 9 July 2025 / Published: 13 July 2025
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Abstract

Background: In September 2023, Storm Daniel triggered catastrophic flooding across Thessaly, in central Greece, leading to the deaths of approximately 483,476 animals and heightening concerns about zoonotic diseases, particularly Q fever caused by Coxiella burnetii. Sofades, a municipality in the Karditsa region that is severely impacted by the floods, emerged as a critical area for evaluating the risk of zoonotic disease transmission. This study aimed to determine the seroprevalence status of Coxiella burnetii Phase 1 IgA antibodies among residents in the rural area of Sofades after the Daniel floods. Methods: Serum samples were obtained from a convenient sample of residents with livestock exposure between 1 March and 31 March 2024. Enzyme-linked immunosorbent assay (ELISA) was used to detect Coxiella burnetii Phase 1 IgA antibodies. Descriptive analyses summarized demographic data, and logistic regression was employed to examine the association between gender, age, and positive ELISA results. Results: The overall seroprevalence was 16.66%. Males had a significantly higher positivity rate (28.57%) than females (6.25%). Seropositivity was more frequent among individuals aged 41–80 years, with peak prevalence observed in the 61–80 age group. Conclusions: This cross-sectional study offers a snapshot of Coxiella burnetii exposure in a high-risk rural population post-flood. The slightly higher seroprevalence in Sofades (16.66%) compared to Karditsa (16.1%) suggests limited influence of environmental factors on transmission. Despite limitations in causal inference, the findings highlight the need for enhanced surveillance and targeted public health measures. Longitudinal studies are needed to assess the long-term impact of environmental disasters on Q fever dynamics.

1. Introduction

Coxiella burnetii, the causative agent of Q fever, is a highly infectious Gram-negative bacterium with significant global reach, posing a substantial public health threat [1]. This zoonotic disease, primarily transmitted to humans by inhaling contaminated aerosols from infected animals, is particularly concerning in agricultural regions [2]. The bacterium’s ability to persist in harsh environmental conditions for extended periods significantly impacts human health, especially in livestock-heavy environments [3].
Q fever presents a wide range of clinical manifestations in humans, from asymptomatic infection to severe, life-threatening complications. The disease typically presents in two forms: acute and chronic [4]. Acute Q fever develops 2–3 weeks post exposure and presents with flu-like symptoms such as high fever, fatigue, severe headaches, muscle pain, and respiratory issues [5]. A significant portion of acute cases, up to 30–50%, can progress to pneumonia, which may require hospitalization [6]. Hepatitis, characterized by elevated liver enzymes, can also develop. While most acute infections resolve spontaneously, they can be debilitating, especially in vulnerable populations like older adults or those with underlying health conditions [7].
Although less common, chronic Q fever can develop months or years after the initial infection, posing significant long-term health risks [8]. Individuals with pre-existing conditions, such as heart valve disease or vascular abnormalities, are particularly vulnerable [9]. Chronic Q fever typically manifests as endocarditis, severe inflammation of the heart’s inner lining that requires prolonged antibiotic treatment [10]. Other complications include chronic hepatitis, osteomyelitis, and vascular infections [11]. Chronic cases necessitate continuous medical surveillance due to the high risk of relapse, underscoring the need for long-term care [12].
Globally, the prevalence of Q fever varies widely, with significant under-reporting due to non-specific symptoms and diagnostic challenges [13]. In Greece, overall Q fever cases are relatively low, but regions like Thessaly show higher prevalence due to the region’s agricultural activity. Between 2012 and 2022, Thessaly accounted for 38.7% of all reported Q fever cases in Greece [14]. Specifically, our previous research revealed seroprevalence rates of 22.2% in Larissa and 16.1% in Karditsa, two of the most agriculturally active regions in Thessaly, highlighting the need for improved diagnosis and reporting to assess Q fever prevalence accurately [15].
Our earlier study also demonstrated that individuals working closely with livestock, including farmers, veterinarians, and slaughterhouse workers, face a significantly higher risk of infection [15]. Men show a higher seroprevalence compared to women. These occupational groups are predominantly located in rural areas like Thessaly, where frequent exposure to livestock increases the likelihood of infection with Coxiella burnetii [15].
In September 2023, Storm Daniel caused significant flooding in Thessaly, resulting in the loss of over 483,476 animals and extensive environmental disruption. Sofades, situated in the Karditsa region, was among the hardest-hit areas. Sofades was one of the most affected regions, making it a crucial location for studying post-disaster zoonotic disease transmission. Sofades covers an area of approximately 292.8 square kilometers and it is home to a population of around 15,000 to 20,000 people. The environmental devastation raised concerns about the heightened risk of zoonotic disease transmission, particularly Q fever, due to the disruption of livestock operations and the spread of contaminated animal waste into the environment. These conditions and prolonged exposure to contaminated aerosols likely increased the risk of human infection [16].
Previous studies, including our own research conducted under more stable environmental conditions in the same region, have indicated a lower seroprevalence rate of 12.5%. Comparing pre-flood and post-flood seroprevalence is essential for understanding how environmental disruptions can amplify the transmission of zoonotic diseases in livestock-dense rural regions like Sofades.
Coxiella burnetii is a highly resilient pathogen that is capable of surviving for extended periods in soil, dust, and water due to its spore-like form. Flooding can mobilize contaminated materials from animal farms, slaughterhouses, and wildlife habitats, facilitating the widespread dissemination of bacteria into new areas. This redistribution may increase the risk of exposure in previously unaffected regions. Furthermore, floods often lead to human displacement, extensive cleanup efforts, and agricultural disruptions—all of which can heighten direct or indirect contact with contaminated environments. Individuals involved in post-flood recovery activities may be exposed to aerosolized particles or contaminated floodwaters, thereby increasing their risk of infection.
In Greece, the diagnosis and surveillance of Q fever remain limited, as serological testing is not routinely available in hospitals or primary healthcare settings. Consequently, the disease is likely under-diagnosed and under-reported, particularly in asymptomatic or mild cases.
In the present study, we aimed to assess the immune status of residents in the municipality of Sofades six months after Storm Daniel.

2. Materials and Methods

2.1. Sample Collection

From the total number of 375 candidates who were invited to participate in the study, 90 of them accepted the invitation, and the response rate was 24%. Blood samples were collected from a convenient sample of 90 participants at private microbiological laboratories in Sofades, located in the Thessaly region, between March 1 and 31, 2024. This timeframe was chosen as it represents approximately six months after the severe flooding caused by Storm Daniel, which significantly impacted the area.
Participants had regular contact with livestock, aligning with the study’s focus on assessing Q fever seroprevalence in high-risk populations. Inclusion criteria consisted of adults aged 18 years or older who had direct exposure to livestock within the past six months and were residents of the area. Participants were asymptomatic for Q fever at the time of their visit to the laboratory.
Upon collection, blood samples were drawn using sterile venipuncture techniques into serum separator tubes. The samples were immediately refrigerated at 4 °C to preserve their integrity. Within 24 h, they were transported in temperature-controlled containers to the Public Health and Adult Immunization Laboratory at the University of Thessaly. During transportation, cold chain protocols were strictly maintained to ensure sample viability.
Upon arrival at the laboratory, samples were allowed to clot at room temperature for 30 min. The serum was then separated by centrifugation at 3000 rpm for 10 min. Aliquots of the serum were transferred into sterile, labeled cryovials and stored at −20 °C until further analysis could be conducted. This process ensured the preservation of antibody activity for accurate serological testing.
All participants provided written informed consent before inclusion in the study. Samples were anonymized to ensure confidentiality and compliance with ethical standards, and unique identification codes were assigned. Demographic data collected included gender, age, and place of residence, which were documented without personal identifiers.
The research protocol (protocol number 155/5/20/20.02.2023) received approval from the Ethics Committee of the University of Thessaly. The study was conducted according to the ethical principles outlined in the Declaration of Helsinki and adhered to national regulations for research on human subjects.

2.2. Laboratory Analysis

IgA antibodies play a role in the early immune response and are valuable in the diagnosis of Q fever. IgA typically appears within the first weeks of infection, making it useful for early detection, especially when IgM and IgG levels are still rising. IgM is usually the first antibody to appear, followed by IgA and then IgG. The simultaneous presence of IgA and IgM suggests a recent infection, while rising IgG levels over time indicate past exposure or convalescence. In cases of chronic Q fever, IgA levels may remain elevated, often in conjunction with very high IgG titers. While elevated IgA may reflect a prolonged immune response, the IgG profile is more commonly used to confirm chronic infection. Specifically, the presence of Phase 1 IgA antibodies may suggest progression toward or the presence of chronic Coxiella burnetii infection. In the present study, serum samples were analyzed using the SERION ELISA classic Coxiella burnetii Phase 1 IgA immunoassay (Institut Virion\Serion GmbH, Würzburg, Germany) to detect antibodies against Coxiella burnetii, the causative agent of Q fever. The assays were processed using the DYNEX DSX automated ELISA system (DYNEX Technologies, Chantilly, VA, USA), following the manufacturer’s instructions. Optical signal measurements were evaluated automatically using the SERION easy ANALYZE software (SERION Diagnostics Controlling Software: REVELATION DSX®, Chantilly, VA, USA). Quality control was ensured through the use of a certificate that included a standard curve and evaluation table for quantifying antibody concentrations in IU/mL or U/mL. According to the manufacturer’s instructions, antibody levels below 1 IU/mL were classified as negative, while levels at or above 1 IU/mL were considered positive for active infection. The testing was conducted at the Public Health and Adult Immunization Laboratory at the University of Thessaly.

2.3. Statistical Analysis

Descriptive statistics, including means, medians, and standard deviations, were calculated for age and ELISA values to summarize the data’s central tendencies and variability. Associations between variables were analyzed using Chi-square tests and Fisher’s exact tests for categorical data. In contrast, Mann–Whitney U and Kruskal–Wallis tests were employed for non-parametric comparisons of continuous variables across two or more groups, respectively. ANOVA was used when parametric assumptions were met to compare means between groups. Spearman’s rank correlation assessed the strength and direction of associations between continuous variables. Logistic regression was conducted to identify predictors of ELISA positivity, with gender and age as independent variables in the model. All statistical analyses were performed using SPSS version 25.0 (IBM Corp., Armonk, NY, USA). Additionally, the current seroprevalence findings from Sofades were compared with previous data collected under more stable environmental conditions in the same region to evaluate the impact of environmental disruption. A p-value of less than 0.05 was considered statistically significant for all tests.

3. Results

The demographic characteristics and ELISA test values for the whole population and comparisons among genders are presented in Table 1. Among the participants, 46.67% were male (n = 42) and 53.33% were female (n = 48), with a mean age of 65.85 years (range: 12–98 years). The overall mean ELISA value for Coxiella burnetii antibodies was 0.751 IU/mL.
Male participants had a slightly higher average age (68.07 ± 16.88 years) compared to females (63.91 ± 19.53 years). Similarly, the mean ELISA value for males (0.78 ± 0.27 IU/mL) was marginally higher than that for females (0.72 ± 0.22 IU/mL), though this difference was not statistically significant (p = 0.056).
Out of the total participants, 15/90 (16.66%) tested positive for Q fever antibodies, with a notable gender disparity. Among males, 28.57% tested positive, compared to only 6.25% of females (p = 0.012). Logistic regression analysis identified gender as a significant predictor of Q fever positivity, with males being 5.7 times more likely to test positive than females. This aligns with previous research linking male occupational roles, such as farming and livestock handling, to increased exposure risk.
A comparison of mean ELISA values and positive Q Fever cases by age group is presented in Figure 1, and ELISA crosstabulation by age is presented in Figure 2.
The stacked histogram shows the distribution of ELISA values stratified by gender, with males represented in blue and females in pink. The threshold for positive Q fever cases is ≥1.0 IU/mL. Males demonstrate higher representation in the positive range (≥1.0 IU/mL), while females show higher frequencies in the 0.6–1.0 IU/mL range. This pattern reflects the observed gender disparity in Q fever seropositivity, with males showing 28.6% positivity compared to 6.3% in females.
Figure 2 presents a comparison of the mean ELISA values (blue bars) and the numbers of positive Q fever cases (red line) across different age groups. The blue bars show standard deviations of 0.000, 0.248, 0.237, 0.252, and 0.220 for the age groups of 0–19, 20–40, 41–60, 61–80, and >80 years, respectively. The 61–80 age group exhibits the highest number of positive cases (eight) and elevated mean ELISA values, suggesting a peak in Q fever seropositivity and antibody levels among older adults. The 41–60 age group follows, with three positive cases and a slightly lower mean ELISA value. Younger age groups (<20 and 20–40) show no positive cases and low mean ELISA values, indicating reduced expo-sure or risk in these populations. The >80 age group demonstrates four positive cases, with a mean ELISA value comparable to that of other adult groups. These findings suggest an age-related trend, with middle-aged and older adults at greater risk for Q fever, likely due to environmental or occupational exposures.
Participants aged 41–80 exhibited the highest positivity rates for Q fever. Figure 3 presents the distribution of ELISA test results by age group for Q fever. In the 41–60 age group, 4 out of 23 individuals (17.39%) tested positive, while in the 61–80 age group, 7 out of 39 (17.95%) were positive. These results suggest greater exposure among middle-aged and older adults, likely due to agricultural work or flood recovery efforts. However, Spearman’s Rank Correlation analysis revealed no significant relationship between age and ELISA values (p = 0.785), indicating that age alone is not a predictor of antibody levels.
Figure 4 illustrates the distribution of ELISA values for Coxiella burnetii antibodies, stratified by gender and age group, using a boxplot.
A gender-specific analysis by age group was conducted. Statistical comparison of ELISA values between genders within each age group revealed significant differences only in the 41–60 year-old group. Specifically, males in this age group demonstrated higher mean ELISA values (0.804 ± 0.248 IU/mL, n = 10) compared to females (0.650 ± 0.196 IU/mL, n = 9; p < 0.05, Mann–Whitney U test). No significant gender differences were observed in other age groups: 20–40 years: males 0.635 ± 0.281 vs. females 0.638 ± 0.224 (p > 0.05); 61–80 years: males 0.811 ± 0.274 vs. females 0.744 ± 0.225 (p > 0.05); >80 years: males 0.787 ± 0.241 vs. females 0.756 ± 0.201 (p > 0.05) These findings suggest that gender-related occupational exposure differences may be most pronounced in middle-aged adults (see Table 2).

4. Discussion

The unprecedented Storm Daniel, which struck Thessaly from 5 to 7 September 2023, caused severe flooding and widespread environmental disruption. The findings of this study and previous studies underscore the potential impact of such environmental events on the prevalence of zoonotic diseases. In the present study, the observed seroprevalence in the rural area of Sofades was slightly higher (16.66%) compared to previous data from the Karditsa region under stable conditions (16.1%). This marginal difference suggests that despite the environmental devastation that it caused, the flooding may not have played a decisive role in altering Q fever transmission dynamics. These results are consistent with earlier research in the region, which reported similar seroprevalence rates among high-risk populations, even in the absence of extreme environmental disturbances [15].
Although the difference may seem marginal, it is not significant, despite the fact that Sofades is a smaller rural village that experienced more direct environmental disruption compared to the broader Karditsa region. The localized environmental damage, which included the loss of over 483,476 animals [17] along with the contamination of land and water sources, likely led to increased exposure to Coxiella burnetii [17].
We hypothesized that the dispersal of animal waste and other biological materials into the environment may have created conditions conducive to the airborne transmission of Coxiella burnetii, especially among individuals working with livestock or involved in post-flood cleanup efforts. The environmental contamination following Storm Daniel likely contributed to increased exposure to Coxiella burnetii. The combination of animal waste, stagnant water, and soil erosion formed ideal conditions for bacterial aerosolization. Notably, the resilience of Coxiella burnetii, which can remain viable in environmental dust for up to 24 months, highlights the potential for prolonged human exposure [18,19,20,21,22,23,24,25]. Similar patterns were observed during the Bizkaia cave outbreak in Spain—where goat feces were implicated in airborne transmission—and during the 2007–2010 Q fever outbreak in the Netherlands, where proximity to infected livestock farms was a major risk factor [18].
The observed gender disparity, with males showing significantly higher seroprevalence rates (26.19% vs. 4.35% in females), can be attributed to traditional gender roles in rural Thessaly. Male involvement in livestock farming, herding, and flood recovery activities likely increases their exposure. This pattern aligns with findings from the outbreak in the Netherlands, where occupational exposure was a primary driver of gender differences [26]. Likewise, studies have shown that increased rainfall and proximity to forests are associated with higher risks of zoonotic disease outbreaks [25]. Future public health initiatives should incorporate gender-sensitive strategies, acknowledging the socio-cultural context of the affected communities [27].
Age-related differences further reveal the heightened vulnerability of older adults (61–80 years: 17.9%; 41–60 years: 15.8%), likely due to cumulative exposure and occupational risk. These findings are consistent with the existing literature, which suggests that older individuals face a greater risk of infection due to cumulative exposure and their prevalence in high-risk occupations [28]. Interestingly, younger individuals also exhibited notable seroprevalence, suggesting that environmental factors during the flooding expanded exposure across demographics. These findings indicate that zoonotic risk is not confined to specific age groups or occupations, reinforcing the need for broad-based public health responses. In contrast, our previous study conducted under more stable conditions demonstrated a more distinct association between age and occupational exposure, with seroprevalence primarily confined to older, working-age adults [14,15,25].
Seasonal variations in seroprevalence, with higher rates during the dry season (20.5% vs. 13.8% in the rainy season), are consistent with global observations of Q fever patterns [29,30]. In Thessaly, dry conditions may facilitate aerosolization of Coxiella burnetii spores, increasing transmission risks. Q fever has been observed to exhibit seasonal trends globally, with varying patterns based on regional climatic conditions [29]. For instance, Q fever peaks in winter in Japan, whereas it mainly occurs in summer in Germany and in autumn in Cyprus [14]. These findings suggest that surveillance and mitigation efforts should be intensified during high-risk periods, particularly in regions prone to environmental disturbances.
The study also highlights the interconnectedness of zoonotic diseases, with parallels drawn to leptospirosis outbreaks in Thessaly following the same flooding event [25]. Both diseases underline the importance of integrated public health approaches addressing multiple zoonotic threats concurrently.
Contact with animals, especially livestock such as goats, represents a significant risk for Coxiella burnetii exposure [31,32]. In this study, all participants had some level of animal contact, which likely contributed to the overall seroprevalence rate of 16.66%. Goats are well-known carriers of Coxiella burnetii, and human exposure typically occurs via inhalation of contaminated aerosols during birthing processes or when handling infected materials [32].
While airborne transmission is the main route for Q fever, ticks may contribute to Coxiella burnetii transmission in specific settings. Ticks such as Ixodes ricinus and Dermacentor marginatus can ingest and excrete viable Coxiella burnetii, while Ixodes Ricinus is capable of transstadial transmission [33]. However, the role of ticks in Q fever epidemiology remains controversial, due to the difficulty of distinguishing Coxiella burnetii from similar Coxiella-like endosymbionts in ticks, and the generally low prevalence of the bacterium in ticks [34].
Previous longitudinal studies in Greece have reported similar findings. Specifically, among 5397 serum samples analyzed, 12.7% tested positive for acute Q fever. Of these positive cases, 64.4% were from male patients and 35.6% from females. However, the difference between genders was not statistically significant [15,35]. Our findings are consistent with these studies on disease seroprevalence, which identified livestock farming and animal contact as primary risk factors for Q fever exposure. Considering the post-flood conditions in Thessaly, the future implementation of stringent biosecurity measures in livestock farming is even more critical for preventing the spread of zoonotic diseases.
The findings of this study underscore the pressing requirement for targeted interventions to manage Q fever outbreaks, particularly in the aftermath of environmental disasters such as flooding. Public health initiatives should prioritize enhancing biosecurity measures in livestock farming, improving vector control, and promoting awareness regarding the risks of zoonotic diseases. Our observations regarding gender inequality and occupational exposure further underscore the necessity for gender-sensitive public health interventions and the consideration of socio-cultural factors. It is crucial to continuously monitor Q fever seroprevalence in flood-affected areas to detect and promptly respond to potential outbreaks [36]. While previous studies have highlighted the necessity for ongoing surveillance in high-risk areas [15,35], the additional environmental challenges presented by Storm Daniel emphasize the future need for even more comprehensive measures, including public health initiatives focused on environmental decontamination, gender-sensitive interventions, and improved biosecurity practices in livestock farming to prevent future outbreaks of zoonotic diseases such as Q fever.
Study Limitations and Additional Variables: While this study focused primarily on gender and age as predictive factors for *Coxiella burnetiid* seropositivity, several other variables could potentially influence antibody levels and infection risk. General health status, including chronic conditions such as hypertension, diabetes, cardiovascular disease, and immunocompromising conditions, may affect immune response and antibody production. Additionally, lifestyle factors such as smoking status, occupational safety practices, use of personal protective equipment during livestock handling, and specific types of animal contact (goats, sheep, cattle) could modify infection risk. Furthermore, environmental factors beyond flooding, such as proximity to livestock farms, duration of residence in the area, and seasonal variations in exposure, warrant consideration in future studies. The convenience sampling method employed in this study may have introduced selection bias, as participants who voluntarily attend private laboratories might differ systematically from the general population in terms of health awareness, socioeconomic status, or baseline health conditions. Future research should incorporate comprehensive health questionnaires to capture these additional variables and employ stratified sampling methods to ensure broader population representation. Longitudinal studies tracking participants over multiple seasons would provide valuable insights into the temporal dynamics of Coxiella burnetii transmission and the influence of various risk factors on seroconversion rates.

5. Conclusions

This study highlights a notable increase in Q fever seroprevalence among residents of a rural Greek region following a large-scale flood event. Higher antibody levels were observed among older adults, males, and individuals with occupational exposure or animal contact. These findings suggest that both demographic factors and environmental conditions—particularly extreme weather events—may significantly influence Coxiella burnetii transmission. The temporal context of the study, following a September flood and coinciding with seasonal parturition of ruminants, further supports the hypothesis that seasonality and flooding act as synergistic drivers of infection. These results emphasize the need for targeted surveillance and preparedness in high-risk periods and areas. Future research should explore seasonal trends and the long-term impact of climate-related disasters on zoonotic disease emergence.

Author Contributions

Conceptualization, M.C. and D.P.; Methodology, M.C.; and D.P.; Software, M.C.; Validation, M.C., O.S.K., K.T., C.B., K.I.G., and D.P.; Formal Analysis, M.C., O.S.K., K.T., and D.P.; Investigation, M.C., and D.P.; Data Curation, M.C., O.S.K., and D.P.; Writing—Original Draft M.C., O.S.K., and D.P.; Writing—Review and Editing, M.C., O.S.K., K.T., C.B., K.I.G., and D.P.; Visualization, M.C., O.S.K., K.T., C.B., K.I.G., and D.P.; Supervision, D.P. All authors have read and agreed to the published version of the manuscript.

Funding

This research received no external funding.

Institutional Review Board Statement

The study was conducted according to the ethical principles outlined in the Declaration of Helsinki, and adhered to national regulations for research on human subjects. The research protocol (protocol number 155/5/20/20.02.2023) received approval from the Ethics Committee of the University of Thessaly.

Informed Consent Statement

Informed consent was obtained from all subjects involved in the study.

Data Availability Statement

Data will be made available upon reasonable request.

Conflicts of Interest

The authors have no conflicts of interest to declare.

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Figure 1. Distribution of ELISA values by gender.
Figure 1. Distribution of ELISA values by gender.
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Figure 2. Comparison of mean ELISA values and positive Q fever cases by age group.
Figure 2. Comparison of mean ELISA values and positive Q fever cases by age group.
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Figure 3. Distribution of ELISA test results by age group for Q fever. Note: Figure 3 illustrates the distribution of ELISA test results by age group for Q fever, with positive results represented in red and negative results in blue. The age groups 61–80 and 41–60 exhibit the highest number of positive cases, corresponding to 7 and 4 individuals, respectively. The 61–80 group also has the largest overall count of participants, indicating significant representation. In contrast, the youngest (0–19) and second-youngest (20–40) age groups show no positive cases, highlighting lower exposure or risk in these demographics. The results emphasize a potential age-related trend, where middle-aged and older adults demonstrate higher positivity rates, likely due to increased exposure to Q fever risk factors such as agricultural or flood recovery activities.
Figure 3. Distribution of ELISA test results by age group for Q fever. Note: Figure 3 illustrates the distribution of ELISA test results by age group for Q fever, with positive results represented in red and negative results in blue. The age groups 61–80 and 41–60 exhibit the highest number of positive cases, corresponding to 7 and 4 individuals, respectively. The 61–80 group also has the largest overall count of participants, indicating significant representation. In contrast, the youngest (0–19) and second-youngest (20–40) age groups show no positive cases, highlighting lower exposure or risk in these demographics. The results emphasize a potential age-related trend, where middle-aged and older adults demonstrate higher positivity rates, likely due to increased exposure to Q fever risk factors such as agricultural or flood recovery activities.
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Figure 4. Boxplot of ELISA values by gender and age group. Note: The boxplots provide a visual representation of the median, interquartile range (IQR), and variability in ELISA values for each subgroup, highlighting differences and trends across genders and age categories. The analysis reveals that males tend to have higher median ELISA values compared to females, with greater variability and more prominent outliers in the male group. Among age groups, middle-aged (41–60 years) and older adults (61–80 years) exhibit broader interquartile ranges, indicating higher variability in antibody levels. Notably, males aged 61–80 show some of the highest ELISA values, aligning with higher Q fever positivity rates observed in this subgroup. In contrast, females across all age groups demonstrate relatively consistent ELISA values with fewer outliers. These patterns suggest that gender- and age-related differences in exposure, such as occupational roles or involvement in flood recovery, may influence ELISA values and Q fever risk. * Indicates statistical significance. In this case, used to highlight that in the 41–60 age group, males had significantly higher mean ELISA values than females (p < 0.05). For the other age groups, where the p-values are greater than 0.05, no asterisk appears, indicating that the differences were not statistically significant.
Figure 4. Boxplot of ELISA values by gender and age group. Note: The boxplots provide a visual representation of the median, interquartile range (IQR), and variability in ELISA values for each subgroup, highlighting differences and trends across genders and age categories. The analysis reveals that males tend to have higher median ELISA values compared to females, with greater variability and more prominent outliers in the male group. Among age groups, middle-aged (41–60 years) and older adults (61–80 years) exhibit broader interquartile ranges, indicating higher variability in antibody levels. Notably, males aged 61–80 show some of the highest ELISA values, aligning with higher Q fever positivity rates observed in this subgroup. In contrast, females across all age groups demonstrate relatively consistent ELISA values with fewer outliers. These patterns suggest that gender- and age-related differences in exposure, such as occupational roles or involvement in flood recovery, may influence ELISA values and Q fever risk. * Indicates statistical significance. In this case, used to highlight that in the 41–60 age group, males had significantly higher mean ELISA values than females (p < 0.05). For the other age groups, where the p-values are greater than 0.05, no asterisk appears, indicating that the differences were not statistically significant.
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Table 1. Demographic and ELISA test result values in the study group, and by gender, for Coxiella burnetii antibodies. Values are presented as mean ± standard deviation unless otherwise indicated.
Table 1. Demographic and ELISA test result values in the study group, and by gender, for Coxiella burnetii antibodies. Values are presented as mean ± standard deviation unless otherwise indicated.
Parameter Study Participants (N = 90)Men (n = 42)Women (n = 48)p-Value
Mean Age (years)65.85 ± 18.3668.07 ± 16.8863.91 ± 19.530.287
Mean ELISA values (IU/mL)0.751 ± 0.2460.78 ± 0.270.72 ± 0.220.056
ELISA Range (IU/mL)0.14–1.120.14–1.120.18–1.04
Positive ELISA Results, n (%)15 (16.6)12 (28.6)3 (6.3)0.012
Negative ELISA Results, n (%)75 (83.3)30 (71.4)45 (93.7)0.008
Table 2. Gender comparisons within each age group. The seroprevalence rate in Sofades (16.66%) was slightly higher than the 16.1% reported for the Karditsa prefecture under stable conditions in prior research.
Table 2. Gender comparisons within each age group. The seroprevalence rate in Sofades (16.66%) was slightly higher than the 16.1% reported for the Karditsa prefecture under stable conditions in prior research.
Age GroupMales (Mean ± SD)Females (Mean ± SD)Differencep-Value *
20–40 years0.635 ± 0.281 (n = 4)0.638 ± 0.224 (n = 6)−0.003p > 0.05
41–60 years0.804 ± 0.248 (n = 10)0.650 ± 0.196 (n = 9)+0.154p < 0.05
61–80 years0.811 ± 0.274 (n = 19)0.744 ± 0.225 (n = 20)+0.067p > 0.05
>80 years0.787 ± 0.241 (n = 9)0.756 ± 0.201 (n = 12)+0.031p > 0.05
* Indicates statistical significance. Specifically, the difference between the compared groups is statistically significant, usually at the threshold of p < 0.05.
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MDPI and ACS Style

Christodoulou, M.; Kotsiou, O.S.; Tsaras, K.; Billinis, C.; Gourgoulianis, K.I.; Papagiannis, D. Assessment of the Immune Response to Coxiella burnetii in Rural Areas of the Thessaly Region Following the Daniel Floods. Hygiene 2025, 5, 30. https://doi.org/10.3390/hygiene5030030

AMA Style

Christodoulou M, Kotsiou OS, Tsaras K, Billinis C, Gourgoulianis KI, Papagiannis D. Assessment of the Immune Response to Coxiella burnetii in Rural Areas of the Thessaly Region Following the Daniel Floods. Hygiene. 2025; 5(3):30. https://doi.org/10.3390/hygiene5030030

Chicago/Turabian Style

Christodoulou, Magdalini, Ourania S. Kotsiou, Konstantinos Tsaras, Charalambos Billinis, Konstantinos I. Gourgoulianis, and Dimitrios Papagiannis. 2025. "Assessment of the Immune Response to Coxiella burnetii in Rural Areas of the Thessaly Region Following the Daniel Floods" Hygiene 5, no. 3: 30. https://doi.org/10.3390/hygiene5030030

APA Style

Christodoulou, M., Kotsiou, O. S., Tsaras, K., Billinis, C., Gourgoulianis, K. I., & Papagiannis, D. (2025). Assessment of the Immune Response to Coxiella burnetii in Rural Areas of the Thessaly Region Following the Daniel Floods. Hygiene, 5(3), 30. https://doi.org/10.3390/hygiene5030030

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