Seroepidemiological study of coxsackievirus type A24 variant (CA24v) in Taiwan

In October 1985 and June 1986, for the first time, Taiwan experienced two outbreaks of acute hemorrhagic conjunctivitis (AHC) caused by a variant of coxsackievirus A24 (CA24v). Sera of virologically and clinically confirmed cases were studied together with the pre- and post-epidemic serum samples by the microneutralization method (cut-off titer, 1:8). The serum samples included 16 cases of virologically confirmed AHC and 18 cases of clinically diagnosed AHC which were collected during the period of January to July, 1987 (i.e., 7 to 21 months after the epidemic). In the same period of time, 374 serum samples were randomly collected as a post-epidemic control group. Meanwhile, 206 serum samples, which were randomly collected in 1980, were studied as a pre-epidemic control group. The results showed that in terms of CA24v neutralizing antibody (NTAb) positivity, a significant difference was found between the pre- and post-epidemic random sample groups (5.3% vs. 28.1%, P < 0.001) while no significant differences among the virologically confirmed, the clinically diagnosed and the post-epidemic random sample groups were noticed (31.3% vs. 28.1%; 44.4% vs. 28.1%, P > 0.05). For comparison, the enterovirus 70 (EV70) NTAb of the samples was studied simultaneously. The results showed that the positive rate and geometric mean titer of CA24v NTAb were lower than those of EV70 even in the post-epidemic serum samples collected shortly after the CA24v epidemic.