Onychomadesis characteristics in cases of hand foot and mouth disease caused by coxsackie virus A6 in Ninghai county, Zhejiang

  Objective  To understand the epidemiologic characteristics of coxsachie virus A6 (Cox A6)-caused hand foot and mouth disease (HFMD) cases with onychomadesis in Ninghai county of Zhejiang province and provide evidence for the etiologic surveillance, diagnosis/treatment and prevention/control of HFMD.

  Methods  From 1 January 2018 to 31 December 2019, the surveillance data of HFMD cases were collected from hospitals in Ninghai. Follow up was conducted for the patients diagnosed with HFMD caused by Cox A6 for 24 consecutive weeks. The fluorescent reverse transcription-polymerase chain reaction (RT-PCR) was performed for the nucleic acid detection of enterovirus strains isolated. The full length of VP1 amplification, sequencing and phylogenetic analysis of Cox A6 strains were conducted.

  Results  A total of 412 patients with HFMD caused by Cox A6 were surveyed, in which 166 had different degrees of nail shedding, the incidence rate of onychomadesis was 40.29% (166/412), the average number of shed nails was 6.02, the earlier onychomadesis occurred, the more nails shed. The incidence rate was highest in thumbs (toes), followed by index fingers, middle fingers, ring fingers and little fingers ( trend χ²=117.39, P<0.001); The shortest onset time of onychomadesis was on day 7 and the longest was on day 116 after HFMD occurred. About 70% cases developed onychomadesis between day 15 and day 42 (3–6 week) after HFMD occurred. The degree of nail loss varied, and thumbs (toes) were mostly affected, Fingernail shedding mainly occurred in right hands and toenail shedding mainly occurred in right foots. The incidence rate of onychomadesis was higher in fingernails than in toenails ( χ²=103.61, P<0.001), the overall incidence of onychomadesis varied among four limbs（χ²=105.40, P<0.001）. Cox A6 positive rate was 91.67% (11/12) in shed nail samples by RT-PCR, but unshed and new nail samples were negative for Cox A6. The gene subtype of D3a.2 clade of the Cox A6 strains isolated from HFMD cases in Ninghai was consistent with the main circulating gene subtype in China.

  Conclusion  The incidence rate of onychomadesis in Cox A6-caused HFMD cases was 40%, the possible reason might be the direct invasion of Cox A6 virus to nail, but nail can regenerate. The gene subtypes of D3a.2 clad of the Cox A6 strains isolated from HFMD cases with onychomadesis in Ninghai was consistent with the main circulating gene subtype in China.