Background. Scarce information exists about immunity to hand, foot, and mouth disease (HFMD) among household contacts of index cases in Vietnam and what that means for reducing ongoing HFMD transmission in the community. Methods. We analyzed neutralizing antibodies (NT) and the incidence of enterovirus (EVs) infection among household contacts of index cases in a province where HFMD remains endemic. Throat swab and 2 mL blood samples from household contacts were collected at enrollment, during and after 2 weeks follow-up. Results. The incidence of EV-A71 infection among household contacts was 40/84 (47.6%, 95% Cl: 36.9-58.3%), compared with 106/336 (31.5%, 95% Cl: 26.6-36.5%) for CV-A6 and 36/107 (33.6%, 95% Cl: 24.7-42.6%) for CV-A16. The incidence of CV-A6 infection was fairly constant across ages; in contrast, CV-A71 and CV-A16 had some variation across ages. At baseline, higher geometric mean titer (GMT) of EV-A71, CV-A6, and CV-A16 antibody titers was found for 25-34-year groups (range 216.3 to 305.0) compared to the other age groups. There was a statistically significant difference in GMT values of CV-A6 and CV-A16 between those who had an infection or did not have infection among households with an index case of these serotypes. Conclusions. Our results indicated that adults were becoming infected with HFMD and could be contributing to the transmission. There is, therefore, a need for considering the household setting as an additional target for intervention programs for HFMD.

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Aims: Norovirus (NoV), Hepatitis E virus (HEV) and Human Astrovirus (HAstV) are common human pathogenic viral agents in bivalve molluscs with frequent emergence of new variants, which pose various difficulties in fighting the epidemic. Therefore, this study aims to evaluate the molecular characteristics of viruses, thus proposing timely response measures and limiting unwanted consequences caused by food poisoning. Methods: A total of 120 samples (60 samples of oysters and 60 samples of clams) were collected at markets and supermarkets in Hanoi in 2016. The samples were analyzed for 3 indicators of Norovirus (NoV), Hepatitis E virus (HEV) and Human Astrovirus (HAstV) using Real-time RT-PCR technique. The samples that were positive for the virus were further analyzed for molecular characteristics through RT-Nested-PCR reaction, Sanger sequencing, and phylogenetic tree construction using MEGA 11 software. Results: For NoV GI, there are 5 detected genotypes: GI.2, GI.4, GI.5, GI.6 and GI.8 of which GI.5 genotype accounts for 56%. The number of genotypes of NoV GII detected is 9 types, including GII.3, GII.4, GII.6, GII.7, GII.13, GII.14, GII.17, GII.18, GII.21, with GII.3 accounting for the majority (54.8%). Three samples of HEV infection were detected, all belonging to the HEV-3 group. For HAstV, out of 6 positive samples, 4 strains of HAstV were sequenced, all belonging to HAstV-1, which is a common subtype of HAstV. Conclusion: The contamination of foodborne viruses in bivalve molluscs in Vietnam is relatively complicated with many genotypes circulating; in particular, there exist a number of genotypes capable of causing outbreaks in the community on a large scale such as NoV GII.4, NoV GII.7, HEV-3 and HAstV-1.