Epidemiology and clinical profile of suspected diphtheria cases in the Governorate of Ibb, Yemen: a 6-year retrospective analysis (2020-2025)

Highlights

• •There were 721 suspected diphtheria cases over a 6-year period in Ibb Governorate.
• •The highest case count was among females, individuals aged 10-19 years, in autumn, and individuals with an unknown vaccination history.
• •The highest incidence rates were found among females, individuals aged 20-29 years, and in 2023.
• •Yarim and Ar Radmah districts had the highest diphtheria burden.
• •Deaths were most frequent among females, individuals aged <10 years, in 2022, and individuals with an unknown vaccination history.

Abstract

Objectives

This analysis aimed to evaluate the overall epidemiological situation of diphtheria in Ibb Governorate over 6 years (2020-2025).

Methods

This retrospective descriptive epidemiological study reviewed diphtheria cases recorded in the epidemiological surveillance database. The data were analyzed.

Results

Of the 721 suspected diphtheria cases, the highest case counts were among females (470; 65.2%), individuals aged 10-19 years (202; 28.0%), in autumn (235; 32.6%), and individuals with an unknown vaccination history (488; 67.7%). The cumulative incidence over 6 years was 21.5 cases per 100,000 inhabitants, with the highest rates observed among females (27.0), individuals aged 20-29 years (27.0), in 2023 (4.9), and in Yarim District (106.6). Additionally, the overall case fatality rate was 4.2% (30 deaths), with more deaths among females (17), individuals aged <10 years (18), and individuals with an unknown vaccination history (25).

Conclusion

The continued rise in diphtheria cases in the study area could pose a significant public health challenge, particularly given the fragile health system. Therefore, strengthening early detection, expanding vaccination coverage, improving healthcare services, and intensifying awareness campaigns are essential measures to control this epidemic.

Introduction

Diphtheria, caused by the bacterium Corynebacterium diphtheriae, is a highly contagious disease that is preventable through vaccination [1]. Furthermore, diphtheria continues to be a significant global health issue, particularly in densely populated settings that lack an effective health system and suffer from inefficient vaccination coverage. Unvaccinated individuals are more susceptible to diphtheria, and the risk is even higher among children aged <5 years. Without proper treatment, death occurs in 30% of cases due to complications from toxins produced by certain strains of diphtheria bacteria [2].

Furthermore, C. diphtheriae is commonly transmitted directly from an infected person to another via respiratory droplets or indirectly through contact with contaminated surfaces or sharing inanimate objects [3]. Weakness, swollen neck glands, a sore throat, and a mild fever are among the symptoms of diphtheria. Subsequently, a thick pseudomembrane develops in the throat or nose that can cover the tonsils and tissues of the throat and nose, thereby obscuring the ability to breathe and swallow [2,4].

Epidemiological indicators for diphtheria worldwide from 2010 to 2024 revealed significant variations in the total number of cases reported, which amounted to 166,280 [5]. Despite a notable decrease in diphtheria cases in 2010 (4603 cases), a sharp increase in diphtheria cases occurred in 2018, with 16,911 cases. The rise in diphtheria cases continued, reaching 22,989 in 2019, 407% higher than in 2015 (4535 cases) [6]. Despite a notable decrease in 2021 to 8659 reported cases, the curve rose dramatically to 24,782 reported cases in 2023, and 2024 saw an unprecedented epidemic surge of diphtheria, peaking at 25,146 cases reported to the World Health Organization [5]. These data were based on official reports from WHO member states without specifying whether all were laboratory-confirmed cases [5].

Previous studies have indicated the prevalence of diphtheria in Yemen, with 5701 documented cases and 330 deaths [7]. A report by Dureab et al. [8] revealed 1294 diphtheria cases with a 5.6% case fatality rate (73 deaths) recorded across Yemen. Of these 1294 cases, 441 (34%) were recorded in Ibb Governorate, which was identified as the most affected governorate, followed by Hodeida with 151 cases (12%), and Sana’a Governorate with 133 (10%). Recently, a WHO estimate indicated a 57% increase in diphtheria cases between 2022 and 2023, from 1283 to 1671 cases [9]. Recently, Hajjah Governorate recorded 1722 diphtheria cases [10] and Abyan Governorate 547 cases [11].

Ibb Governorate has become a safe area and is considered the second region in Yemen to host internally displaced individuals from various regions [12], as it hosted the highest percentage of displaced families relative to its population (9.5%) [13]. This influx exacerbates the epidemiological situation by creating unvaccinated communities and individuals within host communities, threatening to undermine local herd immunity and placing unprecedented pressure on the already fragile local health system. The report in Ibb Governorate between 2022 and 2023 stated that 73.1% of children received one dose of the diphtheria-tetanus-pertussis vaccine, 62.9% received two doses, and 55.7% received three doses [14].

Given the lack of recent epidemiological data on the burden of diphtheria in Ibb Governorate, this analysis is urgently needed to assess the epidemiological situation regarding the burden of diphtheria over the past 6 years (2020-2025). The results of this analysis help fill the knowledge gap regarding the burden of diphtheria in the study area during a period marked by significant challenges. Furthermore, this study provides comprehensive information on the epidemiological situation of diphtheria in the study area, which will contribute to the development of preventive strategies.

Methods

Study design and area

This retrospective descriptive epidemiological study was conducted based on epidemiological surveillance data on diphtheria cases in Ibb Governorate between 2020 and 2025. Ibb Governorate is an important Yemeni governorate, located in the central part of Yemen, 198 km from the capital, Sana’a. It is bordered to the north by Dhamar Governorate; to the south by Taiz Governorate; to the east by Al Dhale'e and Al Bayda' Governorates; and to the west by Al Hudaydah Governorate. It is the third most populous governorate and is administratively divided into 20 districts.

Data collection and analysis

This analysis relied on clinical data from diphtheria cases recorded in the database of the Ibb Governorate Health Office over a six-year period, from 2020 to 2025. The epidemiological surveillance department collected data from various health facilities (public and private) providing healthcare services to the residents of the districts within Ibb Governorate. The health facilities included 35 hospitals, 25 health centers, seven health units, 15 clinics, and 10 rapid response teams. Based on the WHO protocol [15], suspected cases of diphtheria were diagnosed based on clinical manifestations consisting of an upper respiratory tract infection characterized by laryngitis, pharyngitis, or tonsillitis, lymphadenopathy, and the presence of a pseudomembrane adhering to the tonsils, pharynx, or nose. The required data were exported electronically from the database to Excel. All data underwent thorough review and audit to ensure their quality and epidemiological accuracy. Furthermore, individual patient variables were matched to identify duplicate data, and in the event of duplicate entries, only the first record was included, and subsequent duplicate records were deleted. The extracted data included demographic and temporal variables, clinical symptoms, vaccination status, and mortality. This analysis included all suspected diphtheria cases that met the WHO clinical case definition (presentation with an adherent pseudomembrane) among individuals residing in Ibb Governorate during the study period. Records for individuals who did not meet the WHO clinical criteria, resided in other governorates, or had data recorded before or after the study period were excluded from this analysis.

The cumulative incidence of diphtheria was calculated by dividing the total number of cases by the average population over 6 years (denominator) and multiplying the result by 100,000 [16]. The cumulative incidence for a specific variable was calculated by dividing the number of reported cases for that variable by the corresponding population size and multiplying the result by 100,000. Furthermore, the annual incidence was calculated by dividing the number of reported cases in that year by the total population in that year, expressed per 100,000 person-years. Furthermore, the overall case fatality rate (CFR) due to diphtheria was determined by dividing the total number of deaths by the total number of cases and multiplying by 100. The CFR due to diphtheria for each variable was also calculated by dividing the number of deaths by the total number of cases and multiplying by 100.

The data were coded and entered into the Statistical Package for the Social Sciences (Version 26, IBM®, US), which was used to analyze the diphtheria case data. Descriptive statistics were used to summarize demographic characteristics, clinical manifestations, vaccination status, and mortality, which were presented in tables and graphs as frequencies and percentages. Differences among subgroups were assessed using the chi-square (χ²) test; P < 0.05 was considered statistically significant.

Results

Incidence and incidence rate of diphtheria

A total of 721 suspected diphtheria cases were identified; patients ranged in age from <1 to 80 years (median = 19.0 years, interquartile range = 17.0 years). Higher case counts were observed among females (470; 65.2%), individuals aged 10-19 years (202; 28.0%), and individuals aged 20-29 years (187; 25.9%), as well as in 2023 (165; 22.9%). Additionally, the highest number of cases was reported in Yarim (281), whereas An Nadirah District recorded only three cases (Table 1).

Table 1.

Diphtheria cases and incidence rates in Ibb Governorate (2020-2025).

Variables		Number of cases (%)	Incidence per 100,000 inhabitants	χ²	P-value
Sex	Male	251 (34.8)	15.5	59.42	<0.001
	Female	470 (65.2)	27.0
Age group (years)	<10	167 (23.2)	17.4	45.18	<0.001
	10-19	202 (28.0)	25.8
	20-29	187 (25.9)	27.0
	30-39	96 (13.3)	20.1
	≥40	69 (9.6)	15.3
Years	2020	81 (11.2)	2.53	227.14	<0.001
	2021	69 (9.6)	2.12
	2022	94 (13.0)	2.83
	2023	165 (22.9)	4.86
	2024	151 (20.9)	4.37
	2025	161 (22.3)	4.57
Districts	Yarim	281 (39.0)	106.6	1104.85	<0.001
	Ar Radmah	73 (10.1)	62.7
	Al Qafr	50 (6.9)	31.1
	As Saddah	25 (3.5)	28.5
	Al Mashannah	35 (4.9)	21.1
	Rif Ibb	44 (6.1)	20.7
	Al Udayn	34 (4.7)	15.5
	Jiblah	26 (3.6)	14.6
	Al Dhihar	39 (5.4)	14.3
	Al Makhadir	20 (2.8)	11.8
	As Sabrah	13 (1.8)	11.8
	As Sayyani	20 (2.8)	11.6
	Dhi As Sufal	20 (2.8)	7.2
	Ba’dan	11 (1.5)	6.2
	Hubaish	10 (1.4)	6.2
	Hazm Al Udayn	7 (1.0)	5.3
	Mudhaykhirah	6 (0.8)	4.8
	An Nadirah	3 (0.4)	2.6
	Fara’ Al Udayn	4 (0.6)	2.6
	Ash Sha’ir	0 (0.0)	0.0

The cumulative incidence of diphtheria cases in Ibb Governorate over 6 years was 21.5 cases per 100,000 inhabitants. By sex, females exhibited a higher incidence rate than males (27.0 vs 15.5 cases per 100,000 inhabitants, respectively), with a significant difference (χ² = 59.42; P < 0.001). Furthermore, individuals aged 20-29 years had the highest incidence rate of diphtheria, at 27.0 cases per 100,000 inhabitants, and those aged ≥40 years had the lowest incidence rate (15.3), with a significant difference (χ² = 45.18; P < 0.001). Furthermore, the incidence of diphtheria was significantly higher in 2023 than in previous years. It more than doubled from 2.12 cases per 100,000 in 2021 to 4.86 cases per 100,000 in 2023 (Table 1).

In addition, the Yarim District recorded the highest incidence rate of diphtheria cases per 100,000 inhabitants at 106.6, followed by Ar Radmah District (62.7), Al Qafr District (31.1), and As Saddah District (28.5). Conversely, the lowest incidence rates were 4.8 cases per 100,000 individuals in Mudhaykhirah District and 2.6 per 100,000 in both An Nadirah and Fara’ Al Udayn districts, with a significant difference (χ² = 1104.85; P < 0.001) (Table 1).

Temporal trend of diphtheria cases

The highest weekly number of cases was 32 in week 39, followed by 27 in week 35 and 25 in week 44 (Figure 1a). Regarding diphtheria cases by month, the highest number was recorded in August, with 94 cases (13%), followed by September with 87 cases (12.1%), October with 84 cases (11.7%), and December with 67 cases (9.3%). In contrast, the lowest number was recorded in April (39 cases, 5.4%) (Figure 1b). In addition, the highest number of cases occurred in autumn (235, 32.6%), followed by summer (206, 28.6%), whereas the lowest number occurred in spring (125, 17.3%) (Figure 1c).

Figure 1.

Cumulative epidemiological weeks (Figure 1a), monthly (Figure 1b), and seasonal (Figure 1c) trends of diphtheria infection in Ibb Governorate (2020-2025).

Clinical profile, treatment, and outcome of diphtheria cases

These data showed that all patients had a pseudomembrane (100%). In addition, most patients had dysphagia (98.3%), pharyngitis/laryngitis (96.9%), and cervical lymphadenopathy (94.6%). More than three-quarters of patients had dyspnea (77.8%). Additionally, most patients (69.8%) were treated with antibiotics, and 22.2% were treated with both antibiotics and antitoxin. Antitoxin was used as a single treatment in only 52 patients (7.2%). Regarding treatment outcomes, 89.2% of patients recovered from diphtheria, 48 were referred to other hospitals, and 30 patients (4.2%) died from the disease (Table 2).

Table 2.

Clinical profile, treatment, and outcomes of patients with diphtheria in Ibb Governorate (2020-2025).

Variables		Frequency	Percentage (%)
Clinical features	Pharyngitis/laryngitis	713	96.9
	Presence of pseudomembrane	721	100
	Dysphagia	709	98.3
	Dyspnea	561	77.8
	Cervical lymphadenopathy	682	94.6
Treatment received	Antibiotic and antitoxin	160	22.2
	Antibiotic alone	503	69.8
	Antitoxin alone	52	7.2
	Unknown	6	0.8
Outcome	Recovered	643	89.2
	Referred	48	6.7
	Died	30	4.2

Vaccination status

Of the 721 patients with diphtheria, two-thirds (488; 67.7%) had an unknown vaccination history, slightly more than a quarter (185; 25.7%) were unvaccinated, and 48 (6.6%) had received one, two, or three or more vaccine doses. By sex, 71.3% of males had unknown vaccination status, whereas 27.9% of females were unvaccinated. The highest percentage with unknown vaccination status was among individuals aged ≥40 years (75.4%), whereas the highest percentage who were unvaccinated was among individuals aged 20-29 years (32.6%). In 2023 and 2024, 99.4% and 98.7% of patients, respectively, had unknown vaccination status. In 2025, 99.4% of patients were unvaccinated (Table 3).

Table 3.

Diphtheria burden by vaccination status in Ibb Governorate (2020-2025)

Variables		Unvaccinated No. (%)	1 dose No. (%)	2 doses No. (%)	≥3 doses No. (%)	Unknown No. (%)
Sex	Male	54 (21.5)	2 (0.8)	0 (0.0)	16 (6.4)	179 (71.3)
	Female	131 (27.9)	4 (0.9)	3 (0.6)	23 (4.9)	309 (65.7)
Age group (years)	<10	30 (18.0)	3 (1.8)	0 (0.0)	11 (6.6)	123 (73.7)
	10-19	52 (25.7)	2 (1.0)	1 (0.5)	16 (7.9)	131 (64.9)
	20-29	61 (32.6)	0 (0.0)	1 (0.5)	10 (5.3)	115 (61.5)
	30-39	26 (27.1)	1 (1.0)	1 (1.0)	1 (1.0)	67 (69.8)
	≥40	16 (23.2)	0 (0.0)	0 (0.0)	1 (1.4)	52 (75.4)
Years	2020	16 (19.8)	4 (4.9)	3 (3.7)	13 (16.0)	45 (55.6)
	2021	5 (7.2)	2 (2.9)	0 (0.0)	17 (24.6)	45 (65.2)
	2022	2 (2.1)	0 (0.0)	0 (0.0)	7 (7.4)	85 (90.4)
	2023	0 (0.0)	0 (0.0)	0 (0.0)	1 (0.6)	164 (99.4)
	2024	2 (1.3)	0 (0.0)	0 (0.0)	0 (0.0)	149 (98.7)
	2025	160 (99.4)	0 (0.0)	0 (0.0)	1 (0.6)	0 (0.0)

Diphtheria CFR

The data showed that the total CFR related to diphtheria in Ibb Governorate was 4.2% (30 deaths) over the past 6 years. The CFR was higher among males than females (5.2% vs 3.6%, respectively). By age group, the highest CFR associated with diphtheria was recorded in patients aged <10 years (18 deaths; 10.8%), followed by patients aged 10-19 years (10 deaths; 5.0%) and only one death each among patients aged 20-29 and 30-39 years. The highest CFR was 11.7% in 2022, while the lowest rate was 0.6% in 2025. Furthermore, more than two-thirds of the deaths (24 deaths, 4.8%) were reported among patients who received antibiotics alone, and 6 deaths (3.8%) were recorded among patients who received antibiotics and antitoxin. Regarding vaccination status, most deaths (25, 5.1%) were documented among individuals with an unknown history of vaccination, and four deaths (2.2%) were reported among unvaccinated individuals (Table 4).

Table 4.

Diphtheria case fatality rate in Ibb Governorate (2020-2025).

Variables		Deaths	Case fatality rate (%)	χ2 (df)	P-value
Sex	Male	13	5.2	0.98 (1)	0.322
	Female	17	3.6
Age group (years)	<10	18	10.8	31.78 (4)	<0.001
	10-19	10	5.0
	20-29	1	0.5
	30-39	1	1.0
	≥40	0	0.0
Year of infection	2020	3	3.7	22.84 (5)	<0.001
	2021	1	1.4
	2022	11	11.7
	2023	7	4.2
	2024	7	4.6
	2025	1	0.6
Treatment received	Antibiotic and antitoxin	6	3.8	0.25 (1)	0.614
	Antibiotic alone	24	4.8
Vaccination status	Unvaccinated	4	2.2	4.41 (4)	0.353
	1 dose	0	0.0
	2 doses	0	0.0
	≥3 doses	1	2.6
	Unknown	25	5.1

Discussion

This analysis identified 721 suspected diphtheria cases over 6 years in Ibb Governorate. In this context, the diphtheria burden has been recorded in Ibb Governorate, with 441 cases [8], and across Yemen, with 2243 cases [17]. In addition, 747 diphtheria cases were recorded in Sada’a [18], 1722 cases in Hajjah [10], and 547 cases in Abyan [11]. The ongoing war in Yemen has led to the collapse of most health services across the country's governorates. Furthermore, logistical restrictions on the delivery of medical supplies have contributed to the spread of infectious diseases [19]. Studies indicate that these factors have played a key role in increasing diphtheria cases 11-fold [8,18].

The relationship between diphtheria incidence and seasonal variations and environmental conditions has been well documented [20]. The diphtheria cases peaked between weeks 35 and 44 during the study period, and the current finding aligns with a report by the WHO in Yemen [21]. Furthermore, the highest numbers of cases were observed in autumn and summer in this analysis, a finding that aligns with previous reports [7,22,23]. Conducting future longitudinal studies focusing on the impact of environmental and climatic factors on diphtheria epidemiological trends in Yemen is crucial for improving our understanding of diphtheria transmission dynamics.

Ibb Governorate recorded a six-year cumulative incidence of 21.5 cases per 100,000 inhabitants, and this finding is significantly lower than that reported in Hajjah Governorate at 73.12 cases per 100,000 inhabitants [10], Sada’a Governorate at 69.0 cases per 100,000 [18], and Abyan Governorate at 88.0 cases per 100,000 [11]. This incidence rate is higher than rates reported previously: 6.0-12.0 cases per 100,000 people in Hajjah [17]; 3.82 cases in Indonesia [24]; and 9.4-11.3 cases in Nigeria [25]. This variation may be attributed to political and economic conditions, internal migration to the study area, and the reporting system. Therefore, it is essential to improve healthcare and strengthen epidemiological surveillance systems to significantly reduce the spread of diphtheria pathogens in the study area.

In terms of sex, females demonstrated a significantly higher incidence rate of diphtheria than males, and these findings are consistent with previous findings in Yemen [17,18,26]. In contrast, these results contradict those of previous reports [8,22,23]. Previous studies have not shown that sex differences are a major factor in susceptibility to the disease [27,28]. The sex disparity likely reflects the sociocultural dynamics in Yemen that play a critical role in restricting girls' access to preventive healthcare services. Further epidemiological research is needed to investigate the contextual factors underlying this sex disparity.

The current results showed a high number of diphtheria cases among individuals aged 10-19 years, and these results are consistent with previous studies in Yemen [7,8,17,18] and reports in some countries [23,29]. In contrast, individuals aged 20-29 years had the highest incidence rate of diphtheria, and these observations are consistent with the European Union report [22]. In this context, a global report indicated that the elevated burden of diphtheria was recorded in the age group ≤15 years, while the highest incidence rate was recorded in the age group ≥15 years [30]. The increase in diphtheria cases among adults and older age groups is attributed to declining immunity with age, lack of booster doses, and increased social exposure. Accordingly, adherence to the WHO recommendation to administer three additional booster doses (12-23 months, 4-7 years, and 9-15 years) is necessary to ensure long-term protection against diphtheria [31].

By year, 2023 saw the highest incidence of diphtheria, consistent with the WHO report [5], which indicated that the peak of diphtheria cases occurred in 2023 and 2024. Furthermore, other reports from Yemen [10] and Pakistan [29] also indicated that 2023 had the highest number of diphtheria cases. This increase may be attributed to the restrictions imposed by the coronavirus disease 2019 pandemic, which delayed the delivery of routine immunizations to various populations worldwide and directly impacted immunization schedules [[32], [33], [34]]. Therefore, to maintain routine immunization coverage even during pandemics, health authorities should implement a national vaccine security strategy to ensure vaccine supply chains and a rapid response in the event of outbreaks.

Furthermore, Yarim District was classified as the most affected area for diphtheria, followed by Ar Radmah District and Al Qafr District. Immediate intervention is needed to investigate the diphtheria outbreak and enhance epidemiological surveillance and case management in affected districts. These data revealed that all patients had a throat pseudomembrane, and most experienced dysphagia, pharyngitis/laryngitis, and cervical lymphadenopathy. These data are comparable to those reported in similar studies conducted in different countries [7,17,18]. Therefore, it is important to train healthcare professionals in the protocol for diagnosing diphtheria cases based on clinical manifestations to enable immediate therapeutic intervention, improve treatment success, and prevent transmission of the pathogen to others.

Furthermore, it is worth noting that a small percentage of patients received diphtheria antitoxin, which likely reflects a severe structural deficit and supply chain disruptions resulting from geopolitical constraints imposed on Yemen. In addition, more deaths were recorded among patients treated with antibiotics alone than among those receiving combination therapy. This situation is attributed to a combination of factors related to disease severity upon hospital admission and the unavailability of antitoxin during peak periods, rather than to the type of treatment itself. Therefore, the sustained availability of antitoxin and adherence to the combination therapy protocol (antibiotics and diphtheria antitoxin) are crucial for managing patients, particularly those who are critically ill, and reducing mortality.

According to vaccination status, the majority of diphtheria cases were recorded among individuals with an unknown history of vaccination and those who were unvaccinated. Our findings align with previous studies in Yemen [17,18]. Yemen's third-dose coverage for the diphtheria-tetanus-pertussis vaccine between 2017 and 2018 was under 80% [35], decreasing to 57% in 2020 and 42% in 2024 [2]. To control diphtheria, an effective immunization strategy should be adopted that focuses on evaluating vaccination coverage, identifying barriers, raising awareness, and encouraging vaccination in the community, with a particular emphasis on the most vulnerable groups. The sudden change in vaccination status from unknown to unvaccinated over time between 2023 and 2025 in this analysis may have resulted from administrative changes that affected the reporting system or the protocols for data entry and classification. This change cannot be interpreted as a true shift in population immunity. A robust surveillance system is therefore needed for reporting cases by case classification, especially vaccination status, and for supporting an immediate medical response.

Worldwide, the overall CFR related to diphtheria is 5-10%, reaching 20% among young children and the elderly [4]. The observed CFR of 4.2% is below the global range and below previously reported case fatality rates in Yemen, which range from 5.6% to 6.4% [7,8,17,18]. A higher CFR was recorded among males, and this finding is inconsistent with other reports [8,18]. In terms of age groups, patients aged <10 years had the highest CFR, which aligns with previous reports from Yemen [8,17]. Thus, establishing a robust epidemiological surveillance system that focuses on early case detection, accurate laboratory diagnosis, and immediate therapeutic intervention is a practical measure to reduce diphtheria mortality rates.

The findings showed that, with only one exception, the observed deaths occurred among individuals who were either unvaccinated or had an unknown vaccination status, and this finding is consistent with previous studies [8,17,23] that documented diphtheria-related deaths among unvaccinated individuals. Therefore, heads of households should take responsibility for protecting their family members from preventable infectious diseases and ensuring their regular vaccination to promote herd immunity and maintain public health.

Importance and limitations of this study

The significance of this analysis lies in its valuable contribution to the epidemiological literature and its provision of comprehensive and spatially and temporally accurate epidemiological documentation. Furthermore, this analysis established a robust database reflecting the precise geographic distribution of the outbreak. These data are crucial for policymakers in developing prevention strategies to improve health promotion. Assessing the distribution of diphtheria cases based on vaccination status provides a crucial epidemiological advantage in revealing the precise relationship between vaccination and disease outbreaks. Determining treatment outcomes also offers precise and impartial measures of the efficacy of the protocols used. Notwithstanding the significance of this analysis, this study has some limitations. This analysis depends on data recorded in government databases, which may affect the accuracy and quality of the data due to underreporting in some cases or differences in reporting systems between regions. Consequently, these findings may not accurately represent the actual number of cases or the overall epidemiological issues in the study area. A large proportion of patients had unknown vaccination status, which limits causal conclusions about vaccination. Additionally, the sharp change in vaccination status (from 'unknown' to 'unvaccinated') between 2023 and 2025 hinders the analysis of time trends in the study area, as it appears to be a reporting artifact in the surveillance system. Owing to a lack of data, this study was unable to identify some factors that may have contributed to the increased diphtheria rate in the study area. The diagnosis was based solely on clinical manifestations and was not confirmed by laboratory tests, which may have led to an increased number of cases due to confusion with other similar diseases.

Conclusion

The continued rise in diphtheria cases in the study area presents a major obstacle to the health system's ability to promote public health. The highest number of cases was recorded among females and individuals aged 10-29 years, and during the autumn season. Furthermore, Yarim District was classified as a high-burden district, necessitating immediate investigation to determine the underlying causes of this increase and a prompt response with appropriate treatment. The majority of cases and deaths occurred among individuals with an unknown vaccination history or who were unvaccinated, emphasizing the need to increase immunization coverage in all areas and intensify awareness campaigns. Most deaths occurred among patients who received antibiotics alone, highlighting the importance of adhering to the combination treatment protocol to ensure improved clinical outcomes and reduced mortality rates. Strengthening the capacity of healthcare staff to accurately diagnose diphtheria cases based on clinical manifestations, along with enhancing confirmatory laboratory diagnostic capabilities, will contribute to the prompt treatment of patients and reduce the epidemic burden. Furthermore, improving epidemiological surveillance and prompt reporting in health facilities across all districts is essential for managing new cases before outbreaks occur. Additionally, decision-makers in health institutions should build partnerships with global health organizations to ensure a continuous and adequate vaccine supply to all regions to combat and control this outbreak.

CRediT authorship contribution statement

Wadee Abdullah Al-Shehari: Writing – review & editing, Writing – original draft, Formal analysis, Data curation, Conceptualization. Eglal Ahmed Qasem: Writing – review & editing, Methodology, Formal analysis, Data curation. Wadhah Hassan Edrees: Writing – review & editing, Writing – original draft, Supervision, Conceptualization. Motea Ahmed Aboras: Writing – review & editing, Resources, Formal analysis, Data curation. Abdulrahman Abdullah Humaid: Writing – review & editing, Resources, Methodology, Formal analysis. Qais Yusuf Abdullah: Writing – review & editing, Resources, Investigation, Formal analysis. Ahmed Mohammed Al-Haddad: Writing – review & editing, Supervision, Resources, Methodology.

Declaration of competing interest

The authors have no competing interests to declare.