Deog-Yong Lee

BACKGROUND: In South Korea, norovirus outbreaks have been predominantly attributed to the GII.4 genotype; however, since mid-2024, strains harbouring the GII.17 genotype are being detected more frequently, raising concerns about a potential shift in the dominant circulating strain and resulting public health implications. AIM: We aimed to analyse the nt sequences of the gene encoding the viral protein 1 (VP1), the major capsid protein, of the GII.17 norovirus strains detected in South Korea in 2024, compare them with the corresponding nt sequences of the GII.17 Kawasaki 2014 lineage strains and evaluate whether GII.17 has the potential to replace the long-dominant GII.4 genotype. METHODS: We obtained 11 complete VP1 sequences from stool specimens collected across six regions in South Korea (Busan, Daejeon, Gangwon-do, Gyeongsangbuk-do, Incheon, Jeollanam-do) in 2024 and compared them with the VP1 sequence of the reference strain (GII.17 Kawasaki 2014) to identify genetic changes. RESULTS: Key amino acid substitutions (R299P, N378D and K388R) were identified in the P2 domain of the VP1, which is a major antigenic site. Notably, N378D corresponds to D374 in the GII.4 genotype, which is a position involved in histo-blood group antigen (HBGA) binding, and K388R, adjacent to other antigenic sites, may alter the surface charge of the capsid. CONCLUSION: The data provide molecular evidence that the emerging GII.17 strain in South Korea may evade the host immune surveillance machinery and exhibit altered receptor binding, underscoring the public health threat posed by this strain and the need for enhanced genomic surveillance and effective vaccine development.

Noroviruses are a leading cause of acute gastroenteritis worldwide, with a particularly high burden among children under five years of age. We analyzed nationwide surveillance data from EnterNet-Korea collected between 2019 and 2024—covering both the pre- and post-COVID-19 pandemic periods—to assess norovirus detection rates and genotype distribution. Noroviruses were detected by RT-qPCR, and dual genotyping of capsid (G) and polymerase (P) types was performed by sequencing the ORF1–2 junction region. Among the 67,159 specimens tested, 8.4% (n = 5652) were norovirus-positive, with the highest prevalence observed in children aged 0–5 years (19.9%). In this age group, genotyping was successful in 72.4% (2633/3635) of positive cases, identifying 30 distinct genotypes (GI: 9; GII: 21). The most common strains were GII.4[P31] (38.1%), GII.4[P16] (27.1%), and GII.2[P16] (10.4%), with substantial year-to-year variation. Notably, the emergence of GII.17[P17] in late 2024 indicates shifting genotype dynamics, underscoring the need for strengthened surveillance and reconsideration of vaccine strain selection. To our knowledge, this is the first nationwide dual-typing study in Korea encompassing the COVID-19 pandemic era. These findings provide essential baseline data for integration into global surveillance systems and inform future vaccine development and public health strategies.

The equine-like G3 rotavirus is a reassortant strain in which an animal-derived G3 genotype has recombined with a human-origin genetic backbone. Recently, this strain has spread across Asia and Europe. In this study, the VP7 and VP4 genes, along with the genomic backbone of 39 G3P[8] rotavirus strains detected in South Korean children with acute gastroenteritis between 2017 and May 2025, were analyzed. All strains harbored the equine-like G3 genotype for the VP7 gene, and segmental genotyping of VP7, VP4, and VP6 suggested that these strains possessed a DS-1-like genetic backbone (I2-R2-C2-M2-A2-N2-T2-E2-H2). All VP4 genes were confirmed as P[8]. Phylogenetic analysis revealed that these strains clustered with previously reported equine-like G3 strains from various regions, including East Asia. Although individual vaccination records were not available in the EnterNet surveillance data, the overall detection rate of rotavirus infection has declined following vaccine introduction. Nevertheless, equine-like G3P[8] strains have continued to appear sporadically in Korean children, underscoring the importance of ongoing genomic surveillance in the post-vaccine era. Overall, these findings indicate that equine-like G3P[8] strains with a DS-1-like backbone have been circulating for several years in the pediatric population in South Korea, offering important insights into vaccine effectiveness and the surveillance of reassortant rotaviruses.

Recently, the norovirus GII.13[P16] strain, the source of which has not been identified, was detected in epidemiological investigation samples from four regions in South Korea. The norovirus GII.13 genotype is rare worldwide. In this case, the causative pathogen was not identified in the food, and the epidemiological characteristics of the transmission route could not be confirmed. The P2 domain of norovirus is a hypervariable region, and analyzing its sequence analysis is an important approach for identifying transmission routes and epidemiological relationships. Cluster analysis confirmed that the capsid region of the norovirus GII.13 strain detected in samples from the four regions showed some differences from that of the GII.13 strain reported in Germany. Additionally, the differences among the strains from the four regions in the capsid and the nucleotide sequence of the P2 domain were identical. Our findings suggest that the source of contamination in patients in the four regions was the same.

The norovirus GII.13 [P16] genotype, which is rarely detected and has unclear transmission routes, caused outbreaks in four Korean regions with no known infection source. By analyzing variations in the hypervariable P2 domain, identical sequences among patients were identified in this study, suggesting a common contamination source across the regions.

Objectives: On February 16, 2022, 12 cases of hepatitis E virus (HEV) infection were reported in a food manufacturing factory in Korea. The aim of this study was to identify additional cases and to determine the source of this HEV outbreak.Methods: This study was an in-depth investigation of 12 HEV immunoglobulin M (IgM)-positive cases and their demographic, clinical, and epidemiological characteristics. On-site specimens were collected from the environment and from humans, and a follow-up investigation was conducted 2 to 3 months after the outbreak.Results: Among 80 production workers in the factory, 12 (15.0%) had acute HEV infection, all of whom were asymptomatic. The follow-up investigation showed that 3 cases were HEV IgM-positive, while 6 were HEV IgG-positive. HEV genes were not detected in the HEV IgM-positive specimens. HEV genes were not detected in the food products or environmental specimens collected on-site. HEV was presumed to be the causative pathogen. However, it could not be confirmed that the source of infection was common consumption inside the factory.Conclusion: This was the first domestic case of an HEV infection outbreak in a food manufacturing factory in Korea. Our results provide information for the future control of outbreaks and for the preparation of measures to prevent domestic outbreaks of HEV infection.

The rotavirus vaccine is a live vaccine, and there is a possibility of infection by the virus strain used in the vaccine. We investigated the process of determining whether an infection was caused by the vaccine strain in a severe complex immunodeficiency (SCID) patient with rotavirus infection. The patient was vaccinated with RotaTeq prior to being diagnosed with SCID. The testing process was conducted in the following order: confirming rotavirus infection, determining its genotype, and confirming the vaccine strain. Rotavirus infection was confirmed through enzyme immunoassay and VP6 gene detection. G1 and P[8] were identified by multiplex polymerase chain reaction for the genotype, and G3 was further identified using a single primer. By detecting the fingerprint gene (WC3) of RotaTeq, it was confirmed that the detected virus was the vaccine strain. Genotypes G1 and P[8] were identified, and the infection was suspected of having been caused by rotavirus G1P[8]. G1P[8] is the most commonly detected genotype worldwide and is not included in the recombinant strains used in vaccines. Therefore, the infection was confirmed to have been caused by the vaccine strain by analyzing the genetic relationship between VP4 and VP7. Rotavirus infection by the vaccine strain can be identified through genotyping and fingerprint gene detection. However, genetic linkage analysis will also help to identify vaccine strains.

The risk of polio importation and re-emergence persists since epidemic polio still occurs in some countries, and the resurgence of polio occurring almost 20 years after polio eradication was declared in Asia has been reported. We analyzed the results of acute flaccid paralysis (AFP) surveillance in Korea to assess the quality of AFP surveillance and understand the etiology of non-polio enterovirus (NPEV)-associated central nervous system diseases in a polio-free area. We investigated 637 AFP patients under 15 years of age whose cases were confirmed during 2012–2019 by virus isolation, real-time reverse transcription polymerase chain reaction, and VP1 gene sequencing. Among the 637 AFP cases, NPEV was detected in 213 (33.4%) patients, with the majority observed in EV-A71, with 54.9% of NPEV positives. EV-A71 has been shown to play a role as a major causative agent in most neurological diseases except for Guillain-Barré syndrome (GBS), acute disseminated encephalomyelitis (ADEM), and meningitis. This study provides information on the AFP surveillance situation in Korea and highlights the polio eradication stage in the monitoring and characterization of NPEV against the outbreak of neurological infectious diseases such as polio.

Hepatitis A, an acute type of hepatitis caused by the hepatitis A virus, occurs worldwide. Following the 2009 hepatitis A epidemic in South Korea, patient outbreak reports were collectively converted to an “all-patient report” in 2011, and national immunization programs were introduced for children in 2015. In this study, we aimed to analyze the changes and characteristics of hepatitis A antibody titers in South Korea following the epidemic. The results of hepatitis A antibody tests performed at clinical laboratories from 2009 to 2019 were analyzed based on year, age, region, sex, and medical institution. The average 2009–2018 positive anti-hepatitis A virus immunoglobulin G rate was 51.8%, but it increased (56.06%) in 2019. Significantly different antibody-positive rates were observed based on age: <10 years, 54.5%; 20–29 years, 19.5%; ≥50 years, almost 100%. The positive rate of individuals in their teens and 20s gradually increased, whereas that of those in their 30s and 40s gradually decreased. Males had higher antibody-positive rates than females, and samples from higher-level general hospitals exhibited higher antibody rates. The positive anti-hepatitis A virus immunoglobulin M rates gradually decreased after 2009 and were <1% after 2012. However, a high positive rate of 3.69% was observed in 2019 when there was an epidemic. Anti-hepatitis A virus immunoglobulin G-positive rates were similar throughout the year, but the anti-hepatitis A virus immunoglobulin M-positive rates increased from January, peaked in April, and decreased from July, exhibiting distinct seasonality. This is considered to be related to groundwater pollution during the spring drought season. The introduction of the “all-patient report” and national vaccination program for children has had an effective influence on hepatitis A management. However, for hepatitis A prevention, policy considerations for high-risk age groups with low antibody-positive rates will be necessary.

Contaminated salted shellfish were a suspected cause of the 2019 hepatitis A outbreak in Korea; however, no virus was detected in the shellfish by the virus detection tests used. In this study, we investigated the shortcomings of these detection tests for identifying hepatitis A virus in salted shellfish to serve as a guide for improvement of these tests. Salted shellfish were washed and desalted before collecting the mid‐guts for testing. For verification of the method, the mid‐guts were first inoculated with norovirus and then RT‐qPCR was performed to determine the presence of norovirus genes. The norovirus gene was amplified normally along with an internal positive control; however, when the nucleic acid was extracted to be concentrated, gene amplification was inhibited. Since NaCl was the suspected contaminant, RT‐qPCR was then performed on samples that had been desalinated for 2 days, and hepatitis A virus genes were successfully detected. Gene amplification enabled analyzing the relationship between patients in the outbreak and the distributed salted shellfish. To detect viral contamination in salted and fermented specimens such as salted shellfish, it is imperative to extract the mid‐gut intestinal tract and remove any PCR inhibitors (e.g., excess salt). In this study, desalting salted shellfish using sterile distilled water before harvesting the mid‐gut was effective in facilitating hepatitis A detection. Development of future test methods requires accurately determining the effect of PCR inhibitors through the incorporation of an IPC in genetic detection tests.