Epidemiological Investigation of Adult Varicella in Five Foreign Workers

Abstract

Herein, we report five cases of adult varicella in foreign workers who were diagnosed at Kaga Medical Center between April 2016 and May 2019. We conducted epidemiological investigations of the sample by age distribution and monthly distribution of the onset for the five foreign cases, five cases of varicella in Japanese adults, and all cases of varicella and herpes zoster diagnosed during this period. All the five foreign workers who were diagnosed with adult varicella were Vietnamese, and their mean age was 22.6±0.8 years. The mean age of the five Japanese adults was 64.6±21.2 years, which indicates a wide variation. A total of 54 patients had varicella, of whom 41 (75%) were children below 10 years old. Among the patients who had zoster, 73 were Japanese, and 21 (28.8%) of them were in their 70s. The comparison of the distribution of varicella and herpes zoster cases by month of onset revealed that herpes zoster occurred throughout the year, most commonly in February and August. On the contrary, varicella was not found to occur during the summer, and it had a bimodal distribution peaking from March to May and November to January. The cases of adult varicella in foreign workers occurred in January, May, and November, coinciding with the varicella season in Japan. Moreover, four of the foreign workers developed varicella more than 3 weeks after arriving in Japan, indicating that they were likely exposed to the virus after entering the country. Conclusively, it is important that we enlighten clinicians with regard to the necessity of varicella vaccination for foreign workers who have no immunity against varicella zoster virus.