Molecular epidemiology and genetic diversity of human astrovirus in South Korea from 2002 to 2007.

The present study was conducted to survey the prevalence and genotypic distribution of human astrovirus (HAstV) circulating in South Korea. Of 160,027 patients with acute gastroenteritis, 2,057 (1.3%) were positive for HAstV antigen. We determined the genotypes of 187 HAstV strains collected from laboratories across the country. Genetic analysis revealed genotype 1 to be the most prevalent, accounting for 72.19% of the strains, followed by genotypes 8 (9.63%), 6 (6.95%), 4 (6.42%), 2 (3.21%) and 3 (1.60%). Our findings indicate that HAstV is less common but, even so, a potentially important viral agent of gastroenteritis in South Korea, with significant genetic diversity among circulating HAstV strains.

Changes in the intrafamilial transmission of hepatitis B virus after introduction of a hepatitis B vaccination programme in Korea.

Hepatitis B virus (HBV) infections are endemic in Korea. The aims of this study were to determine the prevalence of HBsAg positivity in Korea and to evaluate the changes in intrafamilial transmission after introduction of HBV vaccination in 1983. This study was based on the 2001 Korea National Health and Nutrition Examination Survey. A total of 2512 study subjects, aged 10-29 years, were selected from across Korea using a stratified multi-stage probability sampling design. To identify the changes in intrafamilial transmission after the introduction of the HBV vaccination programme, 1850 subjects with parental serological markers were selected. These subjects were then grouped into two birth cohorts (cohort 1: born before 1983; cohort 2: born after 1983). Appropriate sampling weights were used for all analyses. The weighted age-specific prevalence of HBsAg was 4.9% in participants in their 20s and 1.9% in adolescents; the combined weighted prevalence was 3.2%. Of subjects with HBsAg positivity in either parent, 17.5% were HBsAg-seropositive. Of subjects with two HBsAg-negative parents, 1.5% were HBsAg-seropositive. The HBsAg positivity rate of offspring with HBsAg-positive mothers was higher than those with HBsAg-positive fathers (27.3% vs. 4.8%, P<0.001). The weighted HBsAg positivity rate of offspring with HBsAg-negative mothers was 2.3% for cohort 1 and 0.4% for cohort 2 (P<0.01), and for those offspring with HBsAg-positive mothers it was also significantly decreased compared to cohorts 1 and 2 (40.2% vs. 16.4%, P<0.01). However, the weighted HBsAg positivity rate of offspring with HBsAg-positive mothers was still high. Our results showed that introduction of HBV vaccination has resulted in a decline in the overall HBsAg positivity rate and a reduction in intrafamilial transmission in Korea, but further preventive measures for maternal intrafamilial transmission are needed.

Detection of hepatitis A virus from clotting factors implicated as a source of HAV infection among haemophilia patients in Korea.

To investigate the causal relationship of blood clotting factors and hepatitis A virus (HAV) infection in haemophilia patients during 1998-1999 in Korea, we performed a 1:3 matched case-control study and molecular detection of HAV from clotting factors and patients. The epidemiological investigation showed that one lot of clotting factor VIII was related epidemiologically to patients with hepatitis A with an odds ratio of 35.0, or 38.4 when adjusted for the interval between injections. We examined 17 sera collected from seven patients and 124 lots of blood clotting factors (factor VIII and factor IV) by HAV reverse transcriptase-polymerase chain reaction (RT-PCR). HAV RNA was detected in five clotting factors and six sera. The HAV sequence of one of the factor VIII samples was identical to the sequences found in three patients' sera. Findings from the laboratory and epidemiological studies suggested that the clotting factor was causally related to HAV infection in three haemophilia patients.

A seroprevalence study of poliovirus antibody among primary schoolchildren in Korea.

We aimed to determine the seroprevalence of poliovirus antibody in Korea by using the cell culture neutralization method recommended by the WHO. A total of 500 sera collected from children at eight primary schools in Kyunggi province were used for this study. We found that 82.2% of children were positive for all three types of poliovirus and antibody-positive rates for types I, II and III were 94.4, 96.6 and 86.8% respectively, indicating that seropositive rates for types I and II were considerably higher than for type III (P<0.0001). This result implies that the type III component of the oral polio vaccine should be evaluated further. Although a greater number of children, including young infants, need to be tested for seroprevalence, this study still provides us with valuable information on the effectiveness of vaccination against polioviruses in Korea.

Genetic analysis of the VP1 region of human enterovirus 71 strains isolated in Korea during 2000.

We have isolated Human enterovirus 71 (EV71) from stool and CSF samples taken from patients with acute flaccid paralysis, herpangina, or hand, foot and mouth disease in 2000. Both the cell culture-neutralization test and RT-PCR were used to detect enteroviruses. Rhabdomyosarcoma (RD), HEP2c, and BGM cells were used for the isolation of viruses, and serotypes were determined by the neutralization test using EV71-specific antiserum. For genomic analysis, we amplified a 437-bp fragment of the 5'-noncoding region of the enterovirus genome and a 484-bp fragment of the VP3/VP1 region of EV71 by RT-PCR, with positive results. Products amplified using an EV71-specific primer pair were sequenced and compared with other isolates of EV71. Analysis of the nucleotide sequences of the amplified fragments showed that the EV71 isolates from patients were over 98% homologous and belonged to the genotype C.

PCR-RFLP based molecular typing of enteroviruses isolated from patients with aseptic meningitis in Korea.

We have evaluated PCR-RFLP as a practical method for rapid typing of enteroviruses causing aseptic meningitis in Korea. Through blind examination of 80 clinical isolates from patients with aseptic meningitis, we have compared the results of conventional serotyping with PCR-RFLP based genotyping, which was developed for this study. Among the 80 case isolates, which had been previously typed by routine neutralization test, only 42 cases (52.5%) were matched with typing by PCR-RFLP. The result clearly demonstrated that the enterovirus serotype does not coincide with the genotype. Therefore, the classification of enteroviruses by genotyping with PCR-RFLP, although rapid and simple, may be complicated by regional or seasonal differences. However, the PCR-RFLP method developed in this study is applicable to the epidemiological study of enteroviruses when regional or seasonal differences exist, and is useful in identifying the source of an infection.

Identification of human astrovirus infections from stool samples with diarrhea in Korea.

Human astrovirus (HAstV) infections were confirmed in 17 (1.5%) of 1153 children and adults with diarrhea, from different regions of Korea, by testing their stool samples by reverse transcription-polymerase chain reaction using primers targeted to partial ORF 1a. Genotypes of isolates were determined by sequencing the 289-bp PCR products. The predominant genotype was HAstV type 1, with intragenotypic variation of 0.7%. Unlike Norwalk-like viruses (NLVs), rotavirus and enteric adenovirus, no data on HAstV have been reported in association with diarrhea in Korea. The incidence of HAstV infection reported in this study indicates that HAstV is one of the viral agents causing gastroenteritis in Korea, and that a continuous molecular epidemiological study of HAstV infection is required.