Epidemiology and etiology of HFMD in Nanchang from 2019 to 2022
From 2019 to 2022, CVA6 and CVA16 were two major pathogens, accounting
for 34.0%-59.6% and 14.9%-31.4% EV-positive cases, respectively.
However, other un-serotyped enteroviruses (UEV) accounted for
13.7-%-33.2% EV-positive cases during 2019-2022. Overall, the UEV
accounted for a larger proportion in 2019 (33.2%) and 2021 (31.3%)
compared with that in 2020 (20.8%) and 2022 (13.7%). On the contrast,
proportion of CVA6-associated cases increased in 2020 (59.6%) and 2022
(57.0%) compared with that in 2019 (43.7%) and 2021 (34.0%)
(Supplementary Figure 2). This result indicated that the COVID-19
outbreaks and the associated measures had different levels of impact on
EVs. In geographical level, we analyzed and compared the positive rate
(Figure 3A-D) and serotype proportion (Figure 4) in different districts
and counties, in which their population densities were displayed in
Figure 3E. Overall, the EV-positive rate of the HFMD cases was high in
urban and suburb areas. In northwest areas AY and XJ, the positive rate
had a downtrend, while it was an uptrend in the suburb area NC from 2019
to 2022. During this period, Proportion of CVA6-infected cases
maintained in a low volatility in different areas apart from a very low
proportion in QSH but high proportion in DH and JX in 2022. This data
supports the predominance of CVA6 in Nanchang regions in the past few
years. As for CVA16, a relatively high volatility was observed in
outskirt areas like JX and AY. The 0% proportion of CVA16 in some areas
might be due to the COVID-19 intervention. In addition, UEV proportion
in QSH district was the highest reaching up to 60%.
Characterization
of UEV in Nanchang
As
the dominance of CVA6 becomes more pronounced in HFMD cases, the
proportion UEV tends to decline. However, there is an average 24% UEV
cases with unspecified serotypes during 2019-2022. The serotypes and
their proportion in UEV cases were determined using a nested RT-PCR, and
an expected PCR product (~389-bp) was obtained as shown
in 2% agarose gel electrophoresis (Figure 5A). A total of 46 UEV cases
were randomly selected during 2019-2022 for serotyping described above,
among them 6 serotypes were determined by sequencing and then online
blast in NCBI. Among them CVA4, CVA2, CVA5 and CVB3 were the major
agents accounting for 34.8%, 23.9%, 23.9% and 10.9%, respectively
(Figure 5B). And a partial 5’ UTR-based phylogenetic tree was
constructed for the representative strains of 6 serotypes CVA4, CVA2,
CVA5, CVB3, CVA9 and Echovirus 9 (ECHO9) (Figure 5C). After pairwise
sequence identity analysis, we found that the partial 5’UTR region was
conservative in CVB3 but hypervariable in CVA2, CVA4 and CVA5 (Figure
5D). According to the proportion of these serotypes in UEV, the
estimated proportions for CVA4, CVA2, CVA5, CVB3, CVA9 and ECHO9 in
EV-positive cases were 8.6%, 5.9%, 5.9%, 2.7%, 1.1% and 0.5%,
respectively. This result suggests that enhanced etiological
surveillance is essential, especially when the proportion of UEV rises.