Analysis of Adenovirus Detection Trends in the Republic of Korea (2023–2024)

Abstract

Objectives

This study aimed to assess the prevalence and serotype distribution of adenovirus in the Republic of Korea (ROK) by analyzing detection rates and identifying the predominant circulating serotypes.

Methods

Through the Korea Respiratory viruses Integrated Surveillance System, real-time polymerase chain reaction testing was performed on 33,688 respiratory specimens collected from symptomatic individuals in ROK between January 2023 and December 2024. Detection rates of adenovirus were analyzed, and selected positive samples—stratified by age group—were further examined via nucleotide sequencing to determine serotype distribution.

Results

The average adenovirus detection rates in 2023 and 2024 were 14.8% and 5.8%, respectively. A significant increase in detection rates was observed from summer to autumn in 2023, peaking at 42.4% during weeks 29 to 33, followed by a gradual decline. By 2024, detection rates decreased and remained below 10%. Age-stratified analysis revealed a higher detection rate among individuals aged 0–12 years, with the highest rate (27.5%) observed in the 0–6 years subgroup. Serotyping revealed serotype 3 as the most prevalent, accounting for 36.0% of cases, followed by serotypes 2, 1, and other subtypes. Significantly, serotype 3 predominated during the summer and autumn of 2023. Additionally, serotype 14, previously unreported in the community, was consistently detected throughout 2024.

Conclusions

This analysis suggests that the unusual increase in adenovirus detection during the summer of 2023 may have been driven by an outbreak of serotype 3 and highlights the importance for close monitoring for potential clinical changes following the identification of a new serotype, type 14. Accordingly, the national surveillance system will continue to operate to enhance our understanding of respiratory infectious disease trends and to support effective responses, providing data on pathogen detection patterns and characteristic analyses, including serotype identification.

Key messages

① What is known previously?

Adenovirus circulates year-round in the Republic of Korea without seasonal patterns, typically with detection rates below 10% and primarily affects infants and children. No significant variation in detection rates was observed between 2019 and 2022 prior to the coronavirus disease 2019 pandemic.

② What new information is presented?

In the summer of 2023, detection rates rose markedly among children aged 0–6 years and school-age children (7–12 years), with serotype 3 being the predominant strain during this period. Starting in April 2024, adenovirus serotype 14—previously unreported in the community—was consistently detected.

③ What are implications?

Continuous pathogen surveillance and subtype analysis are essential for identifying the emergence of new adenovirus subtypes. Additionally, clinical linkage studies are necessary to assess potential impacts on clinical symptoms.

Introduction

Adenovirus is a double-stranded DNA virus known as a major pathogen in humans and various animals. It causes a range of diseases, including respiratory infections, conjunctivitis, and gastrointestinal disorders. Since its initial discovery in 1953, 116 adenovirus serotypes have been identified; they exhibit diverse symptoms affecting respiratory and gastrointestinal systems. Thus, the virus has high genetic diversity and various transmission routes [1]. Adenoviruses causing respiratory diseases primarily lead to upper respiratory infections accompanied by such symptoms as high fever, cough, runny nose, and sore throat. In most cases, symptoms are mild, but adenovirus serotypes 1, 2, 3, 5, and 7 can cause severe illnesses in immunocompromised individuals, children, and older adults [2]. Type 3 predominantly causes acute respiratory infections in children and infants, whereas type 7 tends to occur more frequently in adults [3,4]. Various adenovirus serotypes have been reported, and the emergence of new serotypes in communities can significantly influence the epidemiological patterns of respiratory infections [5].

Adenovirus is designated as a level 4 sentinel surveillance pathogen, and the Korea Disease Control and Prevention Agency (KDCA) operates the Korea Respiratory Viruses Integrated Surveillance System (K-RISS). Respiratory specimens are collected from patients with respiratory symptoms at medical institutions participating in sentinel surveillance. Subsequently, pathogen identification and characterization analyses are performed to analyze the epidemiological patterns of various respiratory viruses, including adenovirus. The surveillance results are released weekly on the infectious disease portal of the KDCA website, and updates in sentinel surveillance newsletters and pathogen/vector monitoring information are included.

The study aim was to conduct genetic detection on respiratory specimens collected through the K-RISS sentinel surveillance system from January 2023 to December 2024 and analyze changes in adenovirus detection rates and serotypes to identify and share their epidemiological patterns and characteristics. The study findings provide important baseline data for predicting and preventing adenovirus epidemics.

Methods

1. Detection of Adenovirus Genes

A total of 33,688 respiratory specimens were examined in this study; specimens were collected from patients exhibiting respiratory symptoms identified through the K-RISS, which is operated by the KDCA, from January 2023 to December 2024. Specimens collected from medical institutions participating in surveillance were sent to local Public Health and Environment Research Institutes, where gene detection tests using polymerase chain reaction assays were conducted to confirm adenovirus positivity.

2. Analysis of Adenovirus Detection Rates

Based on the results of adenovirus gene detection tests, weekly detection rates for adenovirus were analyzed. To evaluate adenovirus infection distribution by age, detection rates were further analyzed across six age groups: 0–6 years, 7–12 years, 13–18 years, 19–49 years, 50–64 years, and ≥65 years.

3. Serotype Analysis of Adenovirus

Among adenovirus-positive specimens, suitable ones were selected considering age-specific incidence proportions and the availability of sufficient viral loads for analysis, after which a serotype analysis was performed. To identify serotypes, a sequence analysis was performed on a partial region (approximately 460 bp) of the adenovirus hexon gene, which encodes a viral capsid protein [6].

Results

1. Adenovirus Detection Status

Among the 33,688 specimens collected from January 2023 to December 2024, a total of 3,388 were confirmed positive for adenovirus, resulting in an average detection rate of 10.1%. In 2023, the average adenovirus detection rate was 14.8%, with a sharp increase observed during summer and autumn (weeks 29–33), peaking at 42.4% in week 33 (Figure 1). Subsequently, detection rates gradually declined but remained above 10% until week 48. In 2024, the average detection rate decreased to 5.8%, with the highest detection rate of 10.1% observed in week 21. Otherwise, weekly detection rates remained below 10% (Table 1).

Figure 1. Distribution of adenovirus detection rate by week and age group.

Table 1. Monthly detection status of adenovirus during 2023–2024.

Year	No. of specimen	Detection rate (%)
		Total	Month
			1	2	3	4	5	6	7	8	9	10	11	12
2023	16,041	14.8	6.2	8.7	7.8	10.5	10.1	10.5	17.5	34.1	33.8	18.7	11.8	9.5
2024	17,647	5.8	7.2	5.3	6.8	8.3	7.7	6.2	5.0	3.3	4.5	4.0	4.6	5.1

2. Age-specific Adenovirus Detection Rates

The adenovirus detection rates by age group were 22.0% for ages 0–6 years, 9.5% for ages 7–12 years, 2.6% for ages 13–18 years, 2.1% for ages 19–49 years, 1.1% for ages 50–64 years, and 0.9% for ages ≥65 years. Notably, the average detection rate in the 0–6 years age group in 2023 was significantly higher at 27.5% compared to the overall average rate of 14.8% for the same year (Table 2). Detection rates rose sharply from week 29, reaching a peak of 61.6% in week 34 (Figure 1). The 7–12 years age group also exhibited its highest detection rate of 57.1% in week 33 of 2023 (Figure 1).

Table 2. Adenovirus detection rates in different age groups by year.

Year	Detection rate by age group (%)
	0–6	7–12	13–18	19–49	50–64	≥65
2023	27.5	14.1	3.6	2.9	1.4	0.9
2024	14.7	5.1	1.8	1.6	0.9	0.8
Total	22.0	9.5	2.6	2.1	1.1	0.9

3. Serotype Analysis

During 2023–2024, a total of 10 adenovirus serotypes were identified, with detection proportions as follows: type 3 (36.0%), type 2 (31.6%), type 1 (20.2%), and other serotypes (12.3%). Type 3 adenovirus was predominantly detected from July to November 2023, coinciding with an overall increase in adenovirus detections, whereas its detection remained low during other periods. Types 2 and 1 showed consistent monthly detections, except during periods when type 3 predominated. Type 14 was consistently detected from March 2024 onward, whereas types 5, 6, 8, 11, and 57 were sporadically identified (Figure 2).

Figure 2. Temporal variation in adenovirus serotype distribution.

Conclusions

Changes in social behaviors during the coronavirus disease 2019 (COVID-19) pandemic, such as wearing masks and practicing social distancing, not only influenced the control of COVID-19 transmission but also significantly reduced the incidence of various respiratory infections, including adenovirus. These altered patterns of respiratory pathogen prevalence continue to impact epidemiological trends of respiratory pathogens [7]. Distinct features in adenovirus detection patterns were also observed from pathogen surveillance results spanning 2023 to 2024. Unlike the period prior to COVID-19, during which adenovirus was typically detected at rates below 10% without notable seasonal outbreaks, the average detection rate in 2023 increased to 14.8%, peaking at an unusually high level (i.e., 42.4%) in week 33. In 2024, detection rates returned to patterns observed prior to the COVID-19 pandemic, again falling below 10%. This increase in detection rates was consistent with findings from the acute respiratory infection hospitalization surveillance conducted by the KDCA [7,8]. An analysis of age-specific detection rates indicated that the 0–12 years age group accounted for more than 85% of detections in both 2023 and 2024, with notably higher rates among children aged ≤6 years. Comparatively lower rates were observed for older adults aged ≥50 years (Figure 1). This age-specific detection trend may relate to naturally acquired immunity resulting from previous exposures, as demonstrated in multiple previous studies [9,10]. The unusually elevated detection rates observed in 2023 may also be attributed to increased infections among age groups with fewer pathogen exposures during the pandemic.

The serotype analysis revealed that serotype 3 predominated in 2023. In 2024, serotype 14, previously undetected in the Republic of Korea (ROK), emerged in March and continued to be detected thereafter. Serotypes 1 and 2 were consistently detected throughout both years. Notably, serotype 14, which was first detected in 2024, had previously caused outbreaks in the United States (2019), China (2010), and Japan (2025), with some reports of severe clinical presentations [11-13]. Therefore, clinical analyses evaluating the severity of adenovirus infections were required in the ROK for 2024, when serotype 14 was first detected. Careful monitoring for potential clinical changes should continue. Furthermore, as the serotype analysis in this study was based on specimens collected from mildly symptomatic patients visiting community-based sentinel surveillance medical institutions, expanded serotype analyses involving hospitalized patients at higher-level hospitals are necessary to further clarify associations between adenovirus serotypes and clinical severity.

Following the COVID-19 pandemic, sporadic outbreaks of various respiratory viruses have made epidemiological predictions more challenging. Consequently, national surveillance has become essential for effectively identifying and responding to respiratory disease outbreaks. Thus, the KDCA plans to continuously conduct detailed monitoring and characterization analyses of various respiratory viruses, including adenovirus, based on results obtained through the national integrated respiratory virus surveillance system. This approach should generate and provide essential scientific data to establish prevention and management policies that enable effective responses to future respiratory infection outbreaks.