This cohort study, based on the design of a prior study in the United States, was conducted to elucidate the clinical features of primary human herpesvirus-6B (HHV-6B) infection.
Between June 2014 and May 2016, febrile children younger than 5 years who visited the emergency room (ER) and underwent blood examination were enrolled in this study.
Fifty-nine (12%) of the 491 patients were diagnosed with primary HHV-6B infection. The rates of both simple and complex febrile seizure were significantly higher in patients with primary HHV-6B infection than in those without (P < 0.001 and P = 0.008, respectively). The median age at primary HHV-6B infection was 15 months. Forty-seven (79.7%) of the 59 patients with primary HHV-6B infection were younger than 2-year-old. Clinical features were compared between HHV-6B–infected patients older and younger than 2 years. The frequency of apparent infection (exanthema subitum) was significantly higher in the younger patients (P = 0.01). The median leukocyte (P = 0.01) and lymphocyte (P < 0.001) counts in the patients older than 2 years were significantly lower than those in the younger patients.
Primary HHV-6B infection accounted for 12% of ER visits. Secondary febrile seizures, in particular the complex type, were considered to be a major contributor to the disease burden of primary HHV-6B infection. The timing of primary HHV-6B infection occurred at older ages than in past reports, and the frequency of inapparent infection was higher in older patients.
From the *Department of Pediatrics, Kariya Toyota General Hospital, Kariya, Aichi, Japan
†Department of Pediatrics, Fujita Health University School of Medicine, Toyoake, Japan
‡Department of Faculty of Clinical Engineering, Fujita Health University School of Health Sciences, Toyoake, Aichi, Japan.
Accepted for publication April 8, 2019.
This work was supported by a grant from the Ministry of Education, Culture, Sports, Science and Technology of Japan.
The authors have no conflicts of interest to disclose.
Address for correspondence: Fumihiko Hattori, MD, PhD, Department of Pediatrics, Kariya Toyota General Hospital, Kariya, Aichi 448–8505, Japan. E-mail: firstname.lastname@example.org.