Being the most susceptible population of handCfootCmouth disease, children under 3 years of age are more likely to be infected with enterovirus 71, and the immunity of children increases with increasing age. be infected with enterovirus 71, and the immunity of children increases with increasing age. Further cohort studies should be conducted, and measures for prevention and vaccination should be taken. Keywords: hand-foot-mouth disease, enterovirus 71, neutralizing antibodies, seroepidemiology 1. Introduction According to the updated surveillance summary of World Health Organization [1], an outbreak of hand-foot-mouth disease (HFMD) was recorded in China in 2014. In 2015, 2,014,999 cases of HFMD were reported in China. Zhang [2] reported that the incidence of HFMD in Guangdong increased, peaking twice each year from 2009 to 2012 (incidence range was from 9.75 10?5 to 32.08 10?5). Enterovirus 71 (EV71, species = 0.80) between the positive rate of EV71 neutralizing antibodies and morbidity within the same year. The status of EV71 neutralizing antibodies should be explored to determine HFMD morbidity and population immunity. By contrast, the seroepidemiological study of Rong [16] in Guangzhou revealed significant differences in seropositivity between the younger age group and the eldest group. The samples were obtained not only from children but also from adults aged 24C35 years. Therefore, investigation of the positive rate of EV71 neutralizing antibodies and the susceptibility to EV71 among children aged 1C5 years in Guangzhou is essential to provide the seroepidemiological information necessary for region disease control implementation and EV71 vaccination. 2. Materials and Methods All subjects provided their signed informed consent to inclusion prior to participation in the study. The study was conducted in accordance with Ropidoxuridine the 1964 Declaration of Ropidoxuridine Helsinki, and the protocol was approved by the Ethics Committee of Institutional Review Board of School of Public Health, Sun Yat-sen University. The ethical code is L2016[021]. Our study was conducted as a cross-sectional study via non-probabilistic sampling. We calculated the sample size as 119 with an estimated neutralizing antibody positive rate (abbreviation as p) of 59%, significance level of 0.05, and permissible error of 0.15 p. Considering the small sample number for each age group, we collected 197 samples between 2014 and 2015. All serum specimens and demographic characteristics of children in Guangzhou were collected from the blood sample database set up by Chinese National Science and Technique Major Project (2012ZX10004912). Child participants were divided into four groups: under 2 years old, between 2 and 3 years old, between 3 and 4 years old, and between 4 and 5 years old. As positive control, the EV71 positive serum was collected from child patients identified by Yuebei Hospital in Shaoguan City. Human rhabdomyoma (RD) cells were provided by Guangdong Centre for Diseases Control (CDC) and used for virus sub-cultivation and antibody neutralization test. EV71 (virus strain number 2014XN37281) was collected from HFMD cases, isolated, cultured, and sequencing identified by Guangzhou CDC. Virus titration was conducted via endpoint dilution assay. This assay was selected because of its higher sensitivity and cost-effectiveness compared with plaque assay [17,18]. Virus liquid was sequentially diluted by minimum essential medium (MEM) in gradient dilutions from Ropidoxuridine 10?1 to 10?10 and then cultured in 96-well culture plates (8 12 wells). Eight wells per vertical row in each culture plate were for one dilution level of virus liquid inoculated (50 L was added to each well). Each culture plate included one cultivating liquid group and one cell suspension group as controls. To prevent the infection from being trailed from non-neutralized virus wells to the cell culture suspension, all tips were changed for each new row. A 50% Tissue Culture Infective Dose (TCID50) was generated to measure the EV71 antibody titre, and mathematically calculated using the ReedCMuench method [19]. Observation Rabbit polyclonal to TIGD5 and recording lasted for 3 days. EV71 neutralizing antibody titre was determined by the absence of.