Introduction

Stings caused by Hymenoptera – encompassing bees, wasps, and hornets – represent a significant global public health concern. In some countries such as Brazil, these incidents rank as the second leading cause of human envenomation after drug poisoning. Epidemiological data indicate a rising global trend in Hymenoptera sting cases; for instance, between 2013 and 2023, more than 206,000 cases were recorded in Brazil alone [1]. Although fatal outcomes are relatively uncommon, a comprehensive epidemiological study across Europe reported 1,691 sting-related deaths between 1994 and 2016, predominantly among middle-aged men [2].

In Iran, several studies have reported Hymenoptera stings with varying clinical outcomes. For example, Bemanian et al. documented 201 cases of sting-induced anaphylaxis in Gorgan [3]. Sedighi et al. reported a severe toxic reaction following multiple hornet stings in Kerman Province [4]. Dehghani et al. provided a comprehensive overview of venomous arthropods in Iran and neighboring regions [5]. These findings highlight the diversity of Hymenoptera species and the importance of region-specific epidemiological data.

The clinical spectrum of venom-induced reactions is broad, ranging from mild local manifestations such as pain, erythema, and swelling to severe systemic complications. Anaphylaxis constitutes the most severe outcome and is considered one of the most life-threatening allergic emergencies in adults. This reaction is typically mediated by an IgE-driven Type I hypersensitivity mechanism, whereby the immune system mounts an exaggerated response [6]. Furthermore, in cases of multiple stings, systemic toxic reactions [6] may occur due to the high volume of venom injected, potentially leading to acute renal failure, rhabdomyolysis, hepatic injury, and multi-organ dysfunction [7–9]. Delayed and unusual complications have also been documented, including hepatitis, Kounis syndrome (allergic myocardial infarction), and neurological or coagulation disorders [9,10]. Hymenoptera venom sensitization may be detectable in nearly 26% of adults, underscoring the critical role of a detailed clinical history in the initial risk assessment [11].

Global epidemiological studies have identified recurring patterns. A consistent male predominance among victims has been reported in studies from Brazil, Europe, and Iran, commonly attributed to greater male participation in outdoor occupational and recreational activities [1,2,8,11,12]. A pronounced seasonal trend has also been established, with peak incidence during warmer months such as summer and autumn [8,9]. Most stings occur in urban areas, with the head and neck representing the most frequently affected anatomical sites [8,12]. Additionally, environmental factors such as climate change, deforestation, and urbanization are altering insect behavior and increasing the frequency of human–insect encounters [1,10].

Despite the significance of the issue, epidemiological data detailing demographic characteristics, geographic distribution among sting victims remain limited—particularly in rural and semi-industrial regions of Iran. This gap is not unique to Iran; European authors have similarly highlighted the need for region-specific epidemiological data [2]. For example, a cross-sectional study in rural areas of Gorgan documented 201 cases of sting-induced anaphylaxis, emphasizing both the frequent systemic involvement and the critical role of rural healthcare infrastructure [11]. However, that study focused exclusively on the most severe reaction (anaphylaxis) and did not encompass the full clinical spectrum of sting-related complications. To date, no structured investigation has analyzed the clinical and demographic patterns of Hymenoptera sting victims in northwestern Iran. This study aims to address this knowledge gap by examining the demographic characteristics, anatomical sites of stings, seasonal distribution, clinical manifestations, and hospitalization-related factors among affected patients.

Materials and methods

Study design

This descriptive-analytical study was conducted from January 2021 to December 2024, in East Azerbaijan Province, northwestern Iran. Data were collected from medical records of patients with Hymenoptera sting incidents who presented to emergency departments and hospitals affiliated with Tabriz University of Medical Sciences in Maragheh, Osku, and Ajabshir Counties (Fig 1). The anonymized medical record data were accessed for research purposes between February 15 and April 20, 2025.

Download:

• PNG
  larger image
• TIFF
  original image

Fig 1. The map of study areas in East Azerbaijan, northwestern Iran.

Map created by the authors using ArcGIS Desktop (version 10.5; ESRI, Redlands, CA, USA). The base map was sourced from OpenStreetMap (https://www.openstreetmap.org), which is available under the Open Database License (ODbL). Map data is copyrighted by OpenStreetMap contributors.

https://doi.org/10.1371/journal.pone.0353652.g001

Results

Demographic characteristics

In this study, data from 225 patients presenting with a diagnosis of a Hymenoptera sting (bee, wasp, or hornet) were analyzed. Of these, 161 (71.6%) were male and 64 (28.4%) were female, indicating a male-to-female ratio of approximately 2.5 to 1.

The mean age of the patients was 30.99 ± 18.49 years, with an age range spanning from 1 to 82 years. An analysis of the age frequency distribution revealed a bimodal pattern. The first and largest peak of incidence was observed in the 0–9-year age group, accounting for 19.6% of cases. A second peak was noted in the 30–39 and 40–49-year age groups (16.9% and 16.4%, respectively) (Fig 2). The chi-square analysis revealed no statistically significant differences between age groups and gender in the context of Hymenoptera stings (χ² = 6.481, df = 7, p = 0.485).

Download:

• PNG
  larger image
• TIFF
  original image

Fig 2. Hymenoptera sting incidents by gender and age group in East Azerbaijan Province, Iran (2021-2024).

https://doi.org/10.1371/journal.pone.0353652.g002

Regarding occupational status, a highly significant association was observed between gender and occupation (χ² = 144.281, df = 6, p < 0.001). As shown in Table 1, there was a distinct gender-based distribution: female patients were predominantly housewives (65.6%), whereas male patients were distributed across various occupations, with the highest frequencies among self-employed individuals (30.4%), students (24.8%), farmers (15.5%), and manual workers (13.7%).

Download:

• PNG
  larger image
• TIFF
  original image

Table 1. Distribution of occupational categories, geographic location, and anatomical site by gender among patients with Hymenoptera stings in East Azerbaijan Province, Iran (2021-2024).

https://doi.org/10.1371/journal.pone.0353652.t001

Spatiotemporal distribution

The majority of sting incidents occurred in urban areas (53.3%, n = 120), followed by rural regions (43.6%, n = 98) and desert areas (3.1%, n = 7). Based on the Monte Carlo exact test (conducted due to sparse cell counts in desert categories), there was no statistically significant association between gender and the geographic location of the sting (χ² = 4.167, df = 2, p = 0.120). Although all 7 cases in desert areas involved male patients, the overall geographic distribution did not differ significantly between genders (Table 1).

The monthly trend of Hymenoptera sting incidents by gender is illustrated in Fig 3. Overall, males experienced a higher frequency of stings than females, with the most notable differences observed during the summer months, particularly June, July, and August.

Download:

• PNG
  larger image
• TIFF
  original image

Fig 3. Monthly Trend of Hymenoptera Sting Incidents by Gender in East Azerbaijan Province, Iran (2021-2024).

https://doi.org/10.1371/journal.pone.0353652.g003

Seasonal analysis showed that Hymenoptera stings were strongly influenced by the season. More than half of the cases (52.4%) occurred during the summer. Following summer were fall (26.7%), spring (18.7%), and winter (2.2%). No statistically significant association was found between gender and the season of sting occurrence (p = 0.323, χ² = 3.486). The seasonal pattern was similar for both genders, with the incidence peaking in the summer for both males (50.9%) and females (56.3%).

Factors associated with hospitalization

The demographic, epidemiological, and clinical characteristics of hospitalized and outpatient patients are compared in Table 2. A total of 63 patients (28.0%) were recorded as hospitalized, although most represented short-term admissions and were discharged within 6 hours; the remaining 162 patients (72.0%) were treated as outpatients. Among demographic and epidemiological variables, anatomical site (p = 0.016) and geographic location (p < 0.001) were significantly associated with hospitalization in univariate analysis. Notably, all 7 cases recorded in desert areas required hospitalization, compared to 29.6% in rural and 23.3% in urban areas. Other demographic factors, including gender (p = 0.105), age group (p = 0.129), and occupation (p = 0.338), did not significantly influence the rate of hospitalization.

Download:

• PNG
  larger image
• TIFF
  original image

Table 2. Comparison of demographic, epidemiological, and clinical characteristics between hospitalized and outpatient patients with Hymenoptera stings (n = 225).

https://doi.org/10.1371/journal.pone.0353652.t002

Clinical manifestations showed strong associations with hospital admission in univariate analysis. Pain was significantly more frequent among hospitalized patients than outpatients (47.6% vs. 3.7%, p < 0.001). Similarly, severe muscle pain (19.0% vs. 1.2%), local swelling/redness (27.0% vs. 2.5%), and itching (14.3% vs. 0.6%) were significantly more frequent in the hospitalized group (all p < 0.001). Furthermore, all patients who experienced numbness/muscle cramps or acute systemic symptoms were among those hospitalized (p < 0.001). Only 2.2% of cases had a documented history of underlying comorbidities, including chronic pulmonary disease, diabetes mellitus, and cardiovascular disease. The presence of comorbidities did not show a statistically significant relationship with the need for hospitalization (p = 0.621).

Although geographic location and itching were significantly associated with hospitalization in univariate analysis, they were not included in the final multivariable logistic regression model. Geographic location was excluded because all desert-area cases were hospitalized, resulting in complete separation, while itching was excluded due to its low frequency and sparse cell distribution. A multivariable logistic regression analysis was performed to identify factors independently associated with hospitalization after Hymenoptera stings. The regression model was statistically significant (Omnibus χ²(8) = 124.175, p < 0.001), with a Nagelkerke R² of 0.611. The Hosmer–Lemeshow test was non-significant (χ²(8) = 7.677, p = 0.466), suggesting adequate model calibration. The model correctly classified 89.3% of cases.

In the multivariable model, pain, severe muscle pain, and local swelling/redness were independent predictors of hospitalization. Patients presenting with pain was strongly associated with increased odds of hospitalization compared with those without pain (OR = 40.43, 95% CI: 12.56–130.15, p < 0.001). Severe muscle pain was associated with 77.6 times higher odds of hospitalization (OR = 77.56, 95% CI: 12.97–463.89, p < 0.001), while local swelling/redness increased the odds of hospitalization by 16.1 times (OR = 16.05, 95% CI: 3.96–65.06, p < 0.001). Male gender showed a non-significant trend toward higher odds of hospitalization compared with female gender (OR = 3.06, 95% CI: 0.92–10.12, p = 0.067). Age and anatomical site were not independently associated with hospitalization (Table 3).

Download:

• PNG
  larger image
• TIFF
  original image

Table 3. Multivariable logistic regression analysis of factors associated with hospitalization among patients with Hymenoptera stings (N = 225).

https://doi.org/10.1371/journal.pone.0353652.t003

Discussion

Hymenoptera stings represent a frequent cause of medical attention worldwide, producing a spectrum of outcomes from localized inflammatory reactions to severe anaphylaxis and, in rare cases, fatal multi-organ dysfunction. Epidemiological profiles differ substantially between regions, reflecting ecological conditions, seasonal patterns, species distribution, and cultural or occupational exposures [12–14].

Globally, most reports point to young adults as the highest-risk group, reflecting their economic activity and outdoor exposure [8,12,14]. Against this backdrop, our study revealed a distinctive bimodal pattern, with peaks in childhood and middle age. This differs from findings in India [9], where a predominance in older adults (>45 years) was observed, and from several Brazilian studies that reported an earlier peak in the 20–29 age group [8,12]. These discrepancies likely stem from regional differences in workforce structure and population demographics. Overall, our findings support the consistently reported elevated risk among economically active adults [8,12,15].

Age is a critical determinant of clinical presentation and outcomes. While our study highlighted a significant peak in children under 10 years and adults aged 30–50, international research identifies unique risks at both ends of the age spectrum. For instance, studies in Brazil have shown that individuals over 60 years face a significantly higher risk of severe systemic outcomes and mortality due to pre-existing comorbidities and diminished physiological reserve [15–17]. Conversely, the clinical significance of pediatric cases is characterized by a high frequency of incidents but often lower severity. While some studies in Thailand suggested that age under 15 might have a protective value against severe anaphylaxis [7,17], other research emphasizes that children remain highly vulnerable due to their smaller body mass and inquisitive behaviors, which can lead to multiple stings [7,17,18]. In our cohort, the childhood peak (19.6%) likely reflects behavioral exposure during outdoor play. Recognizing these age-specific patterns is essential for clinical triage, as pediatric patients require vigilant monitoring for systemic reactions, even if the immediate risk of severe anaphylaxis is statistically lower than in older adults.

Occupational distributions differed markedly between male and female patients, suggesting potentially different exposure settings. While male cases were distributed among outdoor-oriented occupations such as self-employment (30.4%), farming (15.5%), and manual labor (13.7%), female patients were predominantly housewives (65.6%). This pattern is consistent with Yu et al. (2025), who reported that males are more frequently stung during work-related outdoor activities [19]. However, the high prevalence of stings among housewives in our cohort suggests that household and peri-domestic outdoor activities, such as gardening and routine chores around the home, may represent an important exposure route for women. Similar patterns have been reported in northern Iran and Brazil, where domestic or peri-domestic environments were identified as relevant settings for Hymenoptera exposure [3,8,11,15,17]. Furthermore, studies from Thailand and Sri Lanka reinforce the observation that individuals involved in agriculture and manual labor face the highest risk due to increased occupational exposure in outdoor environments where stinging insects are common [7,20]. These results indicate that preventive strategies in the region should be dual-focused: emphasizing the use of protective equipment for outdoor manual workers (predominantly males) and raising awareness about habitat management in domestic environments for housewives.

Urban-rural exposure patterns are strongly influenced by species ecology and local settlement structure. Africanized honeybees, for example, have increasingly colonized urban environments, as documented in Brazil, where Linard et al. [12] found that nearly 78% of stings occurred in cities due to nesting in walls and ornamental trees. In contrast, our study showed only a slight urban predominance (53.3%), suggesting a mixed exposure pattern rather than a clearly urban-centered distribution. Conversely, Xie et al. in China [13] reported that 85% of victims were rural residents, where dense wasp populations and occupational contact contributed to multiple severe stings. Taken together, these findings indicate that the urban-rural burden of Hymenoptera stings depends largely on species ecology, land use, and settlement characteristics.

Our study documented a summer peak (52.4%) with a secondary rise in autumn (26.7%). Bemanian et al. in Gorgan, Iran, also reported a summer predominance, citing Hymenoptera activity during flowering and increased human outdoor exposure [11]. By contrast, Himral et al. in Northern India found a peak in autumn (October–December), which they linked to intensified wasp foraging when food becomes scarce [9]. These observations demonstrate how climate, flowering cycles, and species-specific behavior shape seasonal sting incidence.

In our study, head and neck stings were most common (44.9%). Reports from other regions illustrate varied anatomical distributions. In Switzerland, Braun et al. [14] observed high rates of craniofacial and intraoral stings, considered particularly dangerous due to airway compromise. In Taiwan, Yu et al. [19] noted a predominance of limb involvement, likely due to exposed extremities during daily activities. Together, these data suggest that cultural habits, such as clothing coverage, and the defensive targeting of elevated body parts by Hymenoptera significantly influence sting localization [7,8,16,17,21]. Importantly, our findings revealed a highly significant gender-based disparity in the anatomical distribution of stings. While men predominantly suffered stings on the head and neck (51.6% vs. 28.1% in women), women experienced a significantly higher proportion of stings on their hands (35.9%) and legs (29.7% vs. 4.3% in men). This divergence may be partly influenced by common regional clothing patterns and gender-specific activities. In many public and outdoor settings in Iran, women commonly wear headscarves and long garments that cover the hair, neck, and torso. Such clothing may function as a physical barrier that reduces exposure of the head, neck, and upper body to insect contact. Conversely, areas that remain more exposed during household or agricultural tasks, such as the hands and lower limbs, may become more vulnerable to stings. For men, outdoor work with relatively greater exposure of the head, neck, and upper extremities may contribute to the higher frequency of craniofacial stings. This interpretation should be considered hypothesis-generating and warrants confirmation in future studies with more detailed exposure data [13]. This demonstrates that socio-cultural clothing norms, alongside gender-specific occupational and domestic roles, play a pivotal role in dictating the anatomical micro-environments of Hymenoptera envenomation.

Mechanistically, Hymenoptera venom elicits IgE-mediated hypersensitivity reactions, explaining the spectrum of local and systemic symptoms described worldwide [6]. Our study identified both local and systemic reactions, paralleling Bemanian et al. [11], who reported skin and respiratory involvement as dominant. However, Witharana et al. in Sri Lanka [20] found that even patients with over 100 stings usually developed only mild or moderate reactions, attributing this to species differences in venom potency. Such contrasts reinforce that host response, venom composition, and species ecology collectively determine clinical severity.

In our study, 28.0% of patients required hospitalization. The burden was far higher in China, where Xie et al. [13] reported frequent multi-organ dysfunction and a 5.1% mortality rate, attributed to multiple stings and delayed presentation averaging 10 hours. At the other extreme, Linard et al. in Brazil [12] noted that more than 80% of cases were mild, with deaths occurring only after treatment delays. These comparisons underscore that clinical severity reflects not only venom toxicity but also the number of stings and the timeliness of care.

Global evidence points to a persistent gap in evidence-based management. In Switzerland, Braun et al. [14] reported widespread use of antihistamines (97%) and corticosteroids (80%), but epinephrine was given in only 12% of patients, even in severe cases. In our study, corticosteroids were the most frequently administered treatment (75.0%). This is highly consistent with global clinical practices reported in a systematic review by Liyanage et al., which found that the average rate of corticosteroid use in the emergency management of anaphylaxis and severe allergic reactions is approximately 68%, ranging up to 100% in some settings [22]. The high utilization rate in our cohort may reflect local clinical practice patterns aimed at managing inflammatory responses and potential airway edema, especially given the high frequency of head and neck stings observed in our patients. Improved clinical documentation, provider training, and standardized treatment protocols are essential to strengthen evidence-based management. In Iran, Bemanian et al. [3,11] described a similar, concerning underutilization of epinephrine, which they attributed to inadequate physician awareness and fear of adverse effects. By contrast, guideline adherence was stronger in Thailand, where Charoenwikkai et al. [7] documented epinephrine use in 77% of anaphylaxis cases. Together, these findings suggest that corticosteroids are frequently used in the acute management of Hymenoptera sting reactions, while previous studies have reported variable adherence to first-line epinephrine use in anaphylaxis. Standardized protocols and provider education may help improve evidence-based emergency care. The lower utilization of antihistamines (31.6%) compared to corticosteroids (75.0%) in our study suggests that clinical management was primarily focused on preventing severe inflammatory complications and airway compromise rather than the symptomatic relief of cutaneous reactions.

Although our retrospective data categorized stings into broad anatomical regions (e.g., head and neck) and did not specifically delineate intraoral stings within these records, it is clinically pertinent to emphasize the risk of such injuries. As highlighted in studies by Braun et al., intraoral stings [14], which often occur due to accidental ingestion of insects, represent a unique emergency scenario. Even if not explicitly captured in our current registry, clinicians should remain highly vigilant of this possibility when treating patients with head and neck stings. The anatomical vulnerability of the oropharynx means that even minor inflammatory responses in this region can progress rapidly to airway obstruction, necessitating close monitoring and early, aggressive intervention.

Taken together, the global evidence indicates that Hymenoptera sting epidemiology is shaped by ecological conditions, occupational exposure, and cultural practices, with consistent male predominance in most regions but important exceptions in specific contexts [9,19]. A strength of the present investigation is the inclusion of a broad clinical spectrum of sting victims across multiple years and settings, which enabled reliable assessment of seasonal and demographic patterns. Nonetheless, inherent limitations of retrospective design, the absence of species-level identification, and lack of follow-up data restrict the generalizability of the findings, as noted in other regional reports [2,12]. Clinically, previous studies have reported variable and sometimes suboptimal use of epinephrine in anaphylaxis management, highlighting the need for improved documentation, standardized emergency protocols, and provider training [7,11,14].

Limitations

Species-level identification of Hymenoptera was not consistently available in medical records because insects were generally identified based on patients’ descriptions rather than entomological confirmation, limiting species-specific analysis. Regarding the generalizability of our findings, this study focused on three major counties in East Azerbaijan province. While these areas provide a representative snapshot of the pediatric and adult populations in northwestern Iran due to their diverse urban and rural demographics, the results may not be directly generalizable to regions with significantly different climates, Hymenoptera species distributions (e.g., southern coastal areas), or different socio-cultural practices. Furthermore, the small number of patients requiring prolonged hospitalization (>24 hours, n = 4) limits the statistical power of subgroup analyses comparing clinical symptoms between short-term and long-term hospital stays.

Conclusion

Hymenoptera stings remain a significant public health concern with considerable variability in demographic, seasonal, and clinical patterns across regions. Our findings highlight a predominance among males, a bimodal age distribution, summer peaks, and frequent head and neck involvement, reflecting the interplay of ecological, occupational, and cultural factors. Preventive strategies should address both domestic and occupational exposure settings, including habitat management in residential areas, public awareness, and protective clothing for outdoor workers. Strengthening provider training and implementing standardized emergency treatment protocols may help improve evidence-based care, including the appropriate use of epinephrine in suspected anaphylaxis. Future research should adopt prospective multicenter designs, integrate entomological surveys, and evaluate preventive interventions tailored to high-risk populations.

Acknowledgments

The authors would like to extend their gratitude to all hospitals and healthcare facilities providing treatment services for Hymenoptera stings. We also acknowledge the support of the Health Deputy of Tabriz and Maragheh Universities of Medical Sciences, whose contributions were essential to the success of this study.