Although HAdV and classic HAstV usually cause a self-limiting short time watery diarrhea, they are frequent causes of acute diarrhea in children under five years of age [3, 20]. The real-time monitoring of HAdV and classic HAstV can help us to monitor the prevalence of those two pathogens in children with acute gastroenteritis, and play a guiding role in the prevention of major epidemics in Shanghai.
In the present study, the overall stool positivity rate for HAdV infection in this study was 3.47%, which is similar to what was reported in Brazil (3.9%), Bangladesh (4.82%), our previous studies (5.2%), but is much lower than in Northwest Ethiopia (32.0%) and Albania (23.2%) [18, 24, 32–34]. According to our continuous monitoring data, the detection rate of HAdV in children with acute diarrheas was relatively stable in Shanghai from 2010 to 2018 [14]. In addition with our previous study from 2010 to 2011 (1.9%), the detection rate of classic HAstV (5.22%) in Shanghai was also lower than the average global positive rate of 11.0% [14, 20]. This frequency was similar to that observed in other studies carried out in Thailand (2.6%), Asian Russia (2.8%), Brazil (3.9%), Lebanon (5.5%), Germen (5.0%) [35–39]. However, the detectable rate of classic HAstV in 2018 (7.87%) was significantly increased compared to the detection rate in 2017 (2.84%) in this study. Long-term monitoring is needed to determine the reason for this increase. Furthermore, gender was not found to play a role in HAdV and classic HAstV infections in our study. This conclusion is consistent with the findings describing data in Tanzania and Northwest Ethiopia [24, 40]. Moreover, we found that only one child aged 5 years in 2018 was co-infected with HAdV and classical HAstV.
Although a small number of positive samples of HAdV and classic HAstV were reported in this study, description of seasonality of those two viruses infection were also analyzed. HAdV and classic HAstV infections had a tendency to occur in oscillatory fluctuations. The highest rates of HAdV infection was observed in July both in 2017 and 2018, which was similar to Tianjin from 2008 to 2009 and Thailand from 2011 to 2017 [8, 41]. However, in our previous study on inpatients with acute diarrhea from 2006 to 2011, HAdV infection was more frequent during the winter months [27]. Besides, the seasonal pattern of HAdV infection was not observed in our previous study on outpatients from 2012 to 2016 [36]. All those data indicate that seasonal pattern of HAdV infection was not obvious and consistent in Shanghai. A longer time-series analysis is needed to describe the discrepancies in HAdV prevalence drawn from the acquired data of inpatients and outpatients ≤ 5 years of age. The same phenomenon was also found in Thailand and Indian [8, 42]. Similar to several other studies conducted in Germany, Spain, Northern Italy and our previous study, classic HAstV infection was also frequent during the cold-weather period in Shanghai [14, 26, 39, 43].
According to our data, a higher HAdV (82.14%, 23/28) and classic HAstV (66.67%, 28/42) positive component ratios were both identified in children ≤ 3 years which were in line with the findings of other studies [19, 27, 32]. In this study, both of HAdV (13.33%, 6/45) and classic HAstV (6.67%, 3/42) infection were most frequently detected in children of 37 to 48 months old. This finding suggest that herd immunity to HAdV and classic HAstV may be developed gradually in children after 4 years old in Shanghai. However, the neutralizing antibody production and duration of herd immunity and the epidemiological pattern to HAdV and classical HAstV still need to be determined.
The molecular characterization of HAdV through phylogenetic analysis revealed a genetic diversity in the analyzed samples in this study. A total of seven HAdV genotypes including five non-enteric HAdV genotypes were found in children with acute diarrhea from 2017 to 2018. Our survey of HAdV genotypes in children with acute diarrhea indicated that enteric HAdV including HAdV-F40 and -F41 accounted for 64.29% (18/28), being considered as the most remarkable pathogens associated with acute diarrhea in Shanghai. However, HAdV-F40 was found in only one child. This finding coincides with previous reports from our previous studies, Bangladesh and Japan [14, 32, 44]. One reason for the predominance of HAdV-F41 over HAdV-F40 is an antigenic drift of HAdV-F41. Meanwhile, some studies have discovered that the GTC1 and GTC2 subdivisions trigged by the build-up of amino acid mutations in the HVRs (hexon hypervariable regions) of hexon may allow the HAdV-F41 to escape from the host immune response and cause an increased HAdV-F41 infection in the individuals [45–47].
In this study, non-enteric HAdV including HAdV-A31, -B3, -C1, -C2, -C5, might play an important role in causing acute diarrhea in children, although they primarily caused conjunctiva and the upper and lower respiratory tracts infections [13]. Interestingly, non-enteric HAdV-C2 and HAdV-B3 unexpectedly exceeded HAdV-F40 and became the second and third leading genotype in diarrhea children. In addition, different from our previous studies during 2012 to 2016, the detection rate of HAdV-C2 exceeded HAdV-A31 and became the second prevalent genotype from 2017 to 2018 [39]. All those results suggested that the genotypes of non-enteric HAdV in diarrhea children were in a dynamic change in Shanghai. Our investigation showed that continuous surveillance of HAdV in diarrhea children in Shanghai is very important.
For classic HAstV, HAstV-1 is the most prevalent genotype detected worldwide whereas HAstV-2 to -8 are less [7, 23]. According to the phylogenetic tree analysis of classic HAstV, only two genotypes including HAstV-1 and HAstV-5 were identified in Shanghai from 2017 to 2018. HAstV-1 (95.24%) was the absolute predominant genotype detected in children with diarrhea which is consistent with our previous study from 2008 to 2011 as well as with other reports conducted in Japan, Switzerland, Asian Russia, Korea, German and Brazil [36, 37, 39, 48–51]. HAstV-5 was only detected in two samples in early 2018. To our knowledge, this was the first time to report the appearance of HAstV-5 in Shanghai. Nevertheless, long-term monitoring data on HAstV-5 are needed to derive the epidemic characteristics of this genotype.