Background: Hand, foot, and mouth disease (HFMD) in adults has rarely been reported in the literature, although its clinical significance is underestimated. This study was performed to systematically elucidate the epidemiological characteristics of adult HFMD. Methods: A total of 266 adult patients with HFMD were recruited. The control group comprised 40 healthy adults. Swabs and serum samples were collected. Enterovirus strains were tested by RT-PCR, and cytokine expression was examined using commercial kits. Socio-demographic data were collected through follow-up telephone calls. Daily meteorological data were obtained from the China Meteorological Data Sharing Service System. Socio-economic data were collected from the statistical bureau. Results: This study identified several unique spatiotemporal patterns in adult HFMD. Having a child recently diagnosed with HFMD was a risk factor for HFMD, whereas keeping pets was a protective factor against HFMD. The results of this study indicate the existence of subclinical carriers or misdiagnosed patients who might be the latent infectious source of HFMD. Further, this study also indicated that adults may act as the main infectious source of trans-regional spread of HFMD. Conclusions: This study revealed the potential hazards of adult HFMD and is a reminder of the vital clinical significance of further research into adult HFMD. Keywords: Adult HFMD; Epidemiological; Gut microbiome; Subcarrier.