Factors associated with recurrent febrile seizures and electroencephalographic findings in children: a follow-up study in Vietnam

Introduction

Febrile seizures (FS) represent the most frequent type of seizure in childhood, affecting approximately 2–5% of children under 5 years of age worldwide, with higher prevalence rates observed in several Asian populations (1,2). FS are broadly categorized into simple febrile seizures (SFS), characterized by brief (<15 minutes), generalized, and non-recurrent episodes within 24 hours, and complex FS, which deviate from these parameters by virtue of prolonged duration, focal features, or recurrence during the same febrile episode (3). While the majority of FS cases are benign and self-limiting, a considerable proportion of children go on to experience recurrent febrile seizures (RFS), which may increase parental anxiety, lead to unnecessary interventions, and in a small subset, signal a heightened risk for epilepsy later in life (4,5).

Identifying factors associated with RFS is essential for early recognition of high-risk children and guiding parental counseling and follow-up planning.

Previous research has implicated several clinical, perinatal, and biochemical factors as being associated with recurrence, including younger age at first seizure, a positive family history of FS, seizure duration and type, delivery mode, and micronutrient deficiencies (6-9). However, results across studies have been inconsistent, particularly regarding the roles of seizure characteristics, perinatal factors such as cesarean delivery, and biochemical factors including iron and zinc deficiency (6,7,9). Data from Southeast Asia, including Vietnam, remain sparse.

Electroencephalography is not routinely indicated following a first FS episode, particularly when the seizure is simple. Nonetheless, electroencephalographic (EEG) may provide additional descriptive information in selected children with recurrent or complex FS, although its prognostic value remains uncertain (10-12). The prevalence and prognostic value of EEG abnormalities in RFS remain subjects of ongoing debate. While some studies suggest that EEG abnormalities may be associated with an increased risk of subsequent epilepsy or recurrence, others have reported limited or no prognostic value, particularly following SFS (10-12). This study aimed to investigate the clinical, perinatal, and biochemical factors associated with RFS in a Vietnamese pediatric cohort, and to assess interictal EEG abnormalities in children with RFS. We present this article in accordance with the STROBE reporting checklist (available at https://pm.amegroups.com/article/view/10.21037/pm-25-166/rc).

Methods

Study design and setting

This hospital-based follow-up study was conducted at Can Tho Children’s Hospital, Vietnam. Children aged 6–60 months presenting with FS were consecutively enrolled between March 2023 and March 2025, and all eligible children during the study period were considered for inclusion. Recurrence status was determined over 12 months of follow-up using outpatient visits, medical records review, and telephone follow-up. Only children with sufficient follow-up data were included in the recurrence analysis. Among the 198 enrolled children, 170 completed the 12-month follow-up and were included in the final analysis. The RFS group included 65 children with RFS (≥2 episodes), whereas the non-RFS group comprised 105 children with a single febrile seizure and no recurrence during 12 months of follow-up. The participant selection and follow-up process are shown in Figure 1.

Figure 1 Flow diagram of participant selection and follow-up in the study. RFS, recurrent febrile seizure.

Inclusion criteria

Children aged 6–60 months presenting with FS and fulfilling the American Academy of Pediatrics (AAP) 2011 (3) diagnostic criteria were eligible for inclusion. For the recurrence analysis, children were classified into the RFS group if they had ≥2 febrile seizure episodes, whereas children with a single febrile seizure and no recurrence during 12 months of follow-up were classified into the non-RFS group.

Exclusion criteria

Children were excluded if they had a history of afebrile seizures, central nervous system infection, seizures attributable to acute metabolic disturbances, toxic causes, or previously diagnosed epilepsy. Children with incomplete essential clinical information were also excluded.

Study participants

Prior to study initiation, the required sample size was estimated for the primary objective using the formula for a single population proportion:

n=Z1−α2p(1−p)2d2[1]

Where Z1−a/2=1.96 for a 95% confidence level, p=0.329 based on the expected recurrence rate of 32.9% reported in a similar Asian pediatric cohort by Kumar et al. (7), and d=0.07 as the desired margin of error. Based on this calculation, the minimum required sample size was 173 participants. To account for an anticipated loss to follow-up of approximately 15% during the 12-month follow-up period, the target sample size was increased to at least 203 participants. During the recruitment period, 198 eligible children were enrolled. Of these, 28 children (14.1%) were lost to follow-up, resulting in a final analytical cohort of 170 children in Figure 1. This final sample size was close to the estimated minimum required for the primary objective, although the precision of some estimates may still have been limited.

Definitions

FS were defined according to the AAP 2011 (3) criteria and classified as simple or complex based on duration (<15 min), type (generalized/focal), and recurrence within 24 hours.

Iron and zinc deficiencies were defined based on World Health Organization (WHO) (13) guidelines: serum ferritin <12 ng/mL when C-reactive protein (CRP) <5 mg/L or <30 ng/mL when CRP ≥5 mg/L; and serum zinc <10.7 µmol/L.

Data collection

Demographic and clinical data included age at first seizure, sex, gestational age, delivery mode, peak temperature, fever duration before seizure, and etiology of fever. Seizure duration was categorized using the 15-minute threshold because this cutoff is clinically relevant in distinguishing simple from complex FS. Fever duration before seizure was categorized at 1 hour as a prespecified clinically pragmatic cutoff to reflect early seizure occurrence during febrile illness. Family history of FS or epilepsy and nutritional status were recorded. All participants underwent complete blood count and biochemical tests, including serum zinc, iron, and ferritin. These measurements were obtained at the time of initial clinical evaluation during the febrile seizure episode. The cut-off value for zinc deficiency was defined as <10.7 µmol/L, based on established research (14). Iron deficiency was defined as serum ferritin <12 ng/mL when C-reactive protein was <5 mg/L or <30 ng/mL when CRP was ≥5 mg/L, in accordance with World Health Organization guidelines (13). In addition, standard interictal EEG recordings were performed in all 65 children in the RFS group, using the international 10–20 electrode placement system. EEGs were acquired at least one week after the most recent seizure to avoid postictal abnormalities. Interpretation was performed by a pediatric neurologist blinded to the clinical and biochemical data.

Statistical analysis

Statistical analysis was performed using SPSS v25.0 (IBM Corp., Armonk, NY, USA). Continuous variables were summarized as means ± standard deviation or medians (IQRs) and compared using Student’s t-test or Mann-Whitney U-test, based on distribution. Categorical variables were analyzed with chi-squared or Fisher’s exact test. Variables with P<0.2 in univariate analysis, together with clinically relevant variables, were entered into a multivariable logistic regression model, provided that no problematic multicollinearity was detected (VIF <10 and tolerance >0.1), to identify factors associated with recurrence. Adjusted odds ratios (aORs) with 95% confidence intervals (CIs) were reported. Predicted probabilities generated from the multivariable logistic regression model were used to construct the receiver operating characteristic (ROC) curve. Model fit was evaluated using the Hosmer-Lemeshow test, with P>0.05 indicating good fit. A two-tailed P<0.05 was considered statistically significant.

Ethical considerations

The study was conducted in accordance with the Declaration of Helsinki and its subsequent amendments. The study protocol was approved by the Ethics Committee of Can Tho University of Medicine and Pharmacy (Approval No. 23.103.HV/PCT-HDDD). Written informed consent was obtained from parents or legal guardians of all participants.

Results

A total of 198 eligible children presenting with a first febrile seizure were initially enrolled during the study period. Over the 12-month follow-up period, 28 children were lost to follow-up, leaving 170 children for the final analysis, including 65 (38.2%) in the recurrence group and 105 (61.8%) in the non-RFS group. The mean age at first seizure was lower in the RFS group (22.09±9.93 months) than in the non-RFS group (25.71±10.90 months, P=0.03). Sex distribution did not differ significantly between groups; recurrence was observed in 42.1% of females and 35.1% of males, but this difference was not statistically significant (P=0.35).

Univariate analysis (Table 1) showed no significant associations between recurrence and fever duration before seizure, peak temperature, or seizure duration. Although recurrence was more frequent in children with prolonged seizures (≥15 minutes) compared to shorter episodes (66.7% vs. 37.7%), the difference was not statistically significant (P=0.31). Likewise, preterm birth and family history of epilepsy showed no significant association with recurrence.

Several factors were strongly associated with recurrence. Although recurrence was more common in children with complex FS than simple ones (43.5% vs. 37.4%), the difference was not significant (OR: 0.78; 95% CI: 0.32–1.89; P=0.58). In contrast, a positive family history of FS was significantly associated with recurrence (55.7% vs. 28.4%; OR: 3.17; 95% CI: 1.65–6.10; P<0.001). Recurrence was more frequent among children delivered by cesarean section than among those without cesarean delivery (53.9% vs. 21.0%; P<0.001). Recurrence was also more frequent among children with iron deficiency than among those without iron deficiency (55.9% vs. 26.5%; P<0.001). Zinc deficiency was also significantly associated with recurrence (OR: 3.93; 95% CI: 1.91–8.05; P<0.001). Younger age at seizure onset was also associated with recurrence. Specifically, 72.3% of children in the recurrence group had their first seizure before 24 months, compared with 41.0% in the non-RFS group (OR: 3.77; 95% CI: 1.93–7.34; P<0.001).

Multivariate logistic regression (Table 2) identified five factors associated with recurrence: age at first seizure ≤24 months (aOR: 4.94; 95% CI: 1.96–12.4; P=0.001), family history of FS (aOR: 4.90; 95% CI: 1.96–12.25; P=0.001), cesarean delivery (aOR: 7.29; 95% CI: 2.90–18.3; P<0.001), iron deficiency (aOR: 5.92; 95% CI: 2.40–14.62; P<0.001), and zinc deficiency (aOR: 4.50; 95% CI: 1.76–11.61; P=0.002). Sex, preterm birth, and family history of epilepsy were not statistically significant in the final model; seizure type was not retained. Multicollinearity assessment showed no significant concern, with all VIF values <10 (range, 1.008–1.09) and tolerance >0.1 (range, 0.917–0.992), indicating low correlation among independent variables and supporting the stability of the logistic regression model (Figure S1). The ROC curve based on predicted probabilities from the multivariable logistic regression model showed an AUC of 0.871 (95% CI: 0.815–0.927) (Figure 2), demonstrating good discrimination between recurrent and non-RFS cases. The Hosmer-Lemeshow test yielded a P value of 0.06, indicating good model fit with no significant difference between observed and predicted probabilities. These findings indicate acceptable model fit and good discrimination within this cohort.

Figure 2 ROC curve for logistic model predicting febrile seizure recurrence: Multivariable logistic regression model for predicting febrile seizure recurrence (age at first seizure, iron deficiency, zinc deficiency, cesarean section, and family history). AUC, area under the curve; CI, confidence interval; ROC, receiver operating characteristic.

Neurophysiological evaluation (Table 3) was conducted in all 65 children with RFS. Abnormal interictal EEGs were observed in 8 children (12.3%), predominantly spike-wave discharges (10.8%), followed by generalized slowing (1.5%). Of these 8 children, 6 (75.0%) had complex FS and 2 (25.0%) had simple RFS. Among the 8 children with abnormal EEG findings, 6 had iron deficiency and 5 had zinc deficiency. No child in our cohort developed epilepsy during the one-year follow-up.

Discussion

Principal finding

This study identified a 38.2% recurrence rate of FS among children aged 6–60 months. Five factors associated with recurrence were identified: age at first seizure ≤24 months, positive family history of FS, cesarean delivery, iron deficiency, and zinc deficiency. Notably, abnormal interictal EEG findings were observed in 12.3% (n=8) of children with recurrent FS, particularly in those with complex seizures. Because EEG was performed only in children with RFS, no direct comparison of EEG abnormalities could be made with children who had a first febrile seizure without recurrence. Therefore, the EEG findings in this study should be interpreted within the RFS group only. Among the 8 children with abnormal EEG findings, 6 had iron deficiency and 5 had zinc deficiency. This descriptive pattern may warrant further investigation; however, given the very small number of abnormal EEG cases, it should be interpreted cautiously as an exploratory, hypothesis-generating observation rather than evidence of a confirmed association. No child in our cohort developed epilepsy during the one-year follow-up; however, this follow-up period may be insufficient to assess long-term epilepsy risk. These findings may help inform clinical follow-up and parental counseling, although their prognostic utility requires further validation.

Comparing with previous studies

The observed recurrence rate of 38.2% in our study aligns with previous findings, including Berg et al. (5) who reported 27.1%, and Kumar et al. (7) who found a 32.9% recurrence rate in North India. Others have found that there is a 15% to 70% risk of recurrence during the first two years after the initial febrile seizure (8). Consistent with prior evidence, we identified younger age at first seizure (≤24 months) as a significant factor associated with recurrence. In our cohort, 52.2% of children under 24 months experienced recurrence compared to 22.5% in older children (P<0.001). This parallels Kumar et al. (7), who reported a 41.3% recurrence rate in children with initial seizures before 18 months, and Berg et al. (5), who found recurrence rates of 44% in children younger than 18 months and 33% in older children. The increased susceptibility in younger children may be explained by delayed myelination and reduced inhibitory neurotransmission in the developing brain (9).

A positive family history of FS was also strongly associated with recurrence in our study (55.7% vs. 28.4%; P<0.001). This finding is consistent with previous studies by Kumar et al. (7), who reported a 45.5% recurrence rate in such cases, and Badda et al. (15), who identified a family history of FS as a significant factor associated with recurrence. Graves et al. (8) likewise reported that recurrence of FS was associated with a positive family history. In Vietnam, Minh et al. (16) similarly identified family history of FS as an important factor associated with complex FS, further supporting the role of genetic predisposition in seizure susceptibility. Genetic susceptibility has been linked to mutations in the SCN1A and GABRG2 genes (9). SCN1A encodes the alpha subunit of the voltage-gated sodium channel, and its mutations may lower the threshold for neuronal firing, increasing seizure risk. GABRG2 encodes the gamma-2 subunit of the GABA-A receptor, with mutations impairing inhibitory neurotransmission and contributing to neuronal hyperexcitability.

Recurrence was more frequent among children with iron deficiency than among those without iron deficiency (55.9% vs. 26.5%; P<0.001) and iron deficiency remained significant in multivariable analysis (aOR: 5.92; 95% CI: 2.40–14.62; P<0.001). These findings are supported by a meta-analysis by Kwak et al. (17), which reported that iron deficiency nearly doubled the risk of FS (OR: 1.98; 95% CI: 1.26–3.13; P=0.003). Similarly, Yahyaoui et al. (18) showed that children with FS had significantly lower serum iron and serum ferritin levels. Iron plays a critical role in GABA synthesis, dopamine metabolism, and myelination (19); its deficiency reduces GABA production and increases seizure susceptibility, also impairing mitochondrial energy production and antioxidant capacity (20).

Recurrence was more frequent among children with zinc deficiency than among those without zinc deficiency (49.5% vs. 20.0%), and multivariable analysis showed that zinc deficiency remained associated with recurrence (aOR: 4.50; 95% CI: 1.76–11.61; P=0.002). Our findings are consistent with Hosseini et al. (21), who reported significantly lower serum zinc levels in children with FS. Zinc modulates synaptic transmission via NMDA and GABA receptors (22), and its deficiency impairs inhibitory signaling, reducing seizure threshold.

Recurrence was more frequent among children delivered by cesarean section than among those without cesarean delivery (53.9% vs. 21.0%; P<0.001), and cesarean delivery remained associated with recurrence in multivariable analysis (aOR: 7.29; 95% CI: 2.90–18.3; P<0.001). However, this finding should be interpreted with caution, as the observational follow-up design of our study does not permit causal inference. In contrast, Shen et al. (6) did not observe a similar association; this discrepancy may reflect differences in study population characteristics, healthcare practices, obstetric management, or approaches to confounding adjustment across studies. Rather than acting as a direct etiologic determinant, cesarean delivery may reflect underlying perinatal or obstetric vulnerability. Importantly, our study did not collect detailed data on the specific indications for cesarean section, and therefore we could not determine whether the observed association was attributable to cesarean delivery itself or to the clinical conditions leading to the procedure. Supporting this interpretation, Nguyen et al. (23) reported that the most common indications for primary cesarean section in Vietnam were non-reassuring fetal heart rate tracing (40%), labor arrest (31%), and maternal request (11%), suggesting that cesarean delivery often occurs in the setting of specific maternal or fetal conditions rather than as an isolated exposure. Therefore, the association observed in our study may be partly explained by unmeasured intrapartum factors. Although several biological hypotheses have been proposed in the literature, our data do not allow any mechanistic inference regarding the association between cesarean delivery and recurrence (24). Accordingly, cesarean section should be regarded as a potential associated factor for recurrence, and further prospective studies with detailed obstetric and perinatal data are needed to clarify whether this relationship is causal or primarily reflects underlying maternal-fetal conditions.

No significant associations were found between recurrence and sex, seizure type (simple vs. complex), family history of epilepsy, or seizure duration. These findings are consistent with previous studies, including Berg et al. (5).

Our model incorporated five factors associated with RFS–age at first seizure ≤24 months, iron deficiency, zinc deficiency, cesarean delivery, and family history of FS and showed good discrimination in this cohort (AUC =0.871). Although this AUC was higher than that reported by Shen et al. (6) (AUC =0.717), comparisons across studies should be interpreted cautiously because of differences in study populations, included variables, and analytic approaches.

EEG abnormalities were detected in 8 children with recurrent FS (12.3%), primarily spike-wave discharges (10.8%) and generalized slowing (1.5%). Abnormal EEGs were more frequent in children with complex RFS than in those with simple RFS (60.0% vs. 3.6%), aligning with Sownthariya et al. (25) who reported 82.5% abnormal EEGs in complex FS. Strzelecka et al. found abnormalities in 29.1% of children with FS and 40% in those with recurrent episodes (26). Although routine EEG is not recommended after SFS (3), our findings indicate that abnormal interictal EEG findings were identified in a small subset of children with RFS, particularly among those with complex features. Because EEG was performed only in the RFS group, these findings should be interpreted cautiously, and no direct comparison can be made with children without recurrence.

Among the 8 children with abnormal EEGs, most had iron deficiency and/or zinc deficiency. However, given the very small number of abnormal EEG cases, this finding should be interpreted cautiously as a descriptive, exploratory observation rather than evidence of a confirmed association. Although iron deficiency has been reported to impair oxygen delivery and neuronal metabolism (19,20), and zinc deficiency may influence synaptic signaling and ion channel regulation (27), the present data are insufficient to establish a mechanistic link with abnormal EEG patterns.

No child in our cohort developed epilepsy during the one-year follow-up. Therefore, the prognostic significance of abnormal EEG findings in this cohort remains uncertain. The relatively short follow-up period also limits conclusions regarding long-term epilepsy risk (28). Recent data from a pediatric referral cohort at Can Tho Children’s Hospital also showed that EEG abnormalities varied substantially according to age and clinical context, with a lower EEG yield in younger children and those presenting with febrile seizures, further supporting cautious interpretation of EEG findings in this population (29).

Limitations

This study has several limitations. Because this was an observational follow-up study, the reported associations should not be interpreted as evidence of causality. First, the one-year follow-up period may not capture late recurrences or long-term outcomes, such as the development of epilepsy. Future studies with longer follow-up are needed to better assess long-term neurological outcomes. Second, this was a single-center study, which may limit the generalizability of the findings. Multi-center studies involving more diverse populations would strengthen external validity. Important maternal, obstetric, intrapartum, and socioeconomic confounders were not available, which may have particularly affected interpretation of the association between cesarean delivery and recurrence. Third, family history data were collected retrospectively and may therefore be subject to recall bias; the use of objective data sources, such as medical records, would improve data accuracy. In addition, EEGs were interpreted by a single clinician, which may have introduced observer bias; involving multiple raters or applying automated analysis methods could enhance reliability. Although this study focused on iron and zinc deficiencies, other potentially relevant micronutrients, such as vitamin D and magnesium, were not assessed. A broader biochemical evaluation may provide a more comprehensive understanding of the relationship between nutritional deficiencies and febrile seizure recurrence. Moreover, although an a priori sample size estimation was performed for the primary objective, the final sample size remained modest and the number of recurrence events was limited, which may have reduced the precision of the estimated associations, as reflected by the wide CIs for several variables. Some non-significant findings may therefore reflect insufficient statistical power (Type II error) rather than a true absence of association. Finally, some continuous variables were categorized to improve clinical interpretability, but this approach may have resulted in some loss of information compared with analyses using continuous measures.

Clinical implications

This study emphasizes the value of early risk identification in children prone to RFS. Timely recognition may help guide parental counseling and follow-up planning. Beyond clinical risks, RFS can cause significant parental anxiety, potentially leading to overprotection and the “vulnerable child syndrome”. Therefore, education and reassurance are essential components of holistic pediatric care in managing RFS.

Conclusions

Abnormal interictal EEG findings were identified in a subset of children with RFS, particularly among those with complex features. Because EEG was performed only in the RFS group, these findings should be interpreted as descriptive observations rather than evidence of broader prognostic significance. Early recognition of the identified clinical and biochemical factors associated with recurrence may help inform follow-up planning and parental counseling. Longitudinal studies with extended follow-up are needed to clarify the long-term neurological significance of EEG abnormalities and to validate these associations in more diverse pediatric populations.

Acknowledgments

The authors express their sincere gratitude to the Can Tho University of Medicine and Pharmacy and Can Tho Children’s Hospital for their administrative and logistical support throughout the study. We also thank the participating children and their parents for their cooperation and trust.

Footnote

Reporting Checklist: The authors have completed the STROBE reporting checklist. Available at https://pm.amegroups.com/article/view/10.21037/pm-25-166/rc

Data Sharing Statement: Available at https://pm.amegroups.com/article/view/10.21037/pm-25-166/dss

Peer Review File: Available at https://pm.amegroups.com/article/view/10.21037/pm-25-166/prf

Funding: None.

Conflicts of Interest: All authors have completed the ICMJE uniform disclosure form (available at https://pm.amegroups.com/article/view/10.21037/pm-25-166/coif). The authors have no conflicts of interest to declare.

Ethical Statement: The authors are accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved. The study was conducted in accordance with the Declaration of Helsinki and its subsequent amendments. The study was approved by the Ethics Committee of Can Tho University of Medicine and Pharmacy (Approval No. 23.103.HV/PCT-HDDD). Written informed consent was obtained from the parents or legal guardians of all participants.

Open Access Statement: This is an Open Access article distributed in accordance with the Creative Commons Attribution-NonCommercial-NoDerivs 4.0 International License (CC BY-NC-ND 4.0), which permits the non-commercial replication and distribution of the article with the strict proviso that no changes or edits are made and the original work is properly cited (including links to both the formal publication through the relevant DOI and the license). See: https://creativecommons.org/licenses/by-nc-nd/4.0/.

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