Background: Human parechovirus type 3 (HPeV3) infection can cause sepsis-like syndrome and meningoencephalitis in neonates and young infants. Although maculopapular rash is a reported clinical manifestation of HPeV3 infection, the frequency and detailed characteristics of rash in neonates and young infants with HPeV3 infection are unknown. Methods: We retrospectively reviewed the clinical characteristics of neonates and young infants who received a diagnosis of HPeV3 infection on the basis of real-time polymerase chain reaction analysis of serum and/or cerebrospinal fluid specimens at the National Center for Child Health and Development in Tokyo between November 2010 and September 2011. Results: Fifteen neonates and young infants were diagnosed as having HPeV3 infection; median age was 33 days (range: 10–81 days). The most common clinical presentation on admission was fever (80%), the median duration of which was 3 days (range: 1–4 days). Five (33%) children required admission to the intensive care unit for close observation, and 2 (13%) required mechanical ventilation for cardiovascular instability. After hospitalization, all children developed rash, mainly on the extremities, at a mean of 3 days (range: 1–5 days) after fever onset. The most striking finding was that 80% (12/15) of patients developed a distinctive palmar–plantar erythematous rash, which disappeared after a median of 3 days (range: 2–7 days). All patients were discharged from hospital without serious sequelae. Conclusions: Palmar–plantar erythema in febrile neonates and young infants may be a diagnostic clue of HPeV3 infection.

Human parechovirus type 3 (HPeV3) is an emerging pathogen that causes sepsis and meningoencephalitis in young infants. To test the hypothesis that maternal antibodies can protect this population, we measured neutralizing antibody titers (NATs) to HPeV3 and other genotypes (HPeV1 and HPeV6) in 175 cord blood samples in Japan. The seropositivity rate (>1:32) for HPeV3 was 61%, similar to that for the other genotypes, but decreased significantly as maternal age increased (p<0.001). Furthermore, during the 2014 HPeV3 epidemic, prospective measurement of NATs to HPeV3 in 45 patients with severe diseases caused by HPeV3 infection showed low NATs (1:512) until age 6 months. All intravenous immunoglobulin samples tested elicited high NATs to HPeV3. Our findings indicate that maternal antibodies to HPeV3 may help protect young infants from severe diseases related to HPeV3 and that antibody supplementation may benefit these patients.