Survey of infants hospitalized for respiratory syncytial virus disease in Tokyo, 2018

Abstract

Previously, in many regions of Japan, the respiratory syncytial virus (RSV) epidemic would begin each year in October to December and would end in March to May. In 2017, the epidemic started in July, and summer or early fall outbreaks were observed in Tokyo. The change in the RSV epidemic is likely climate related. Palivizumab, a monoclonal anti-RSV antibody, can be administered, intramuscularly, monthly throughout the epidemic period to infants expected to develop severe RSV diseases, such as acute bronchiolitis and pneumonia (high-risk infants). These are infants aged ≤6 months born at 29–36 weeks’ gestational age, infants aged ≤12 months born at 22–28 weeks’ gestational age; or infants with chronic lung disease (CLD), congenital heart disease (CHD), Down syndrome, or immunodeficiency aged ≤24 months at the beginning of the RSV epidemic. In the 2018 season, palivizumab was administered from August or September to March, depending on the discretion of the attending pediatrician at each hospital in Tokyo. As the epidemic season of RSV in Tokyo changed recently, this study aimed to investigate the relationship between hospitalization in high-risk infants and the introduction time of palivizumab. We conducted a survey of hospitalized patients aged <3 years with RSV disease from January 1 to December 31, 2018, in pediatric wards or pediatric intensive care units in 12 facilities in Tokyo and its suburbs. There were 900 patients aged <3 years with RSV disease. Of these, we collected respiratory treatment information for 552 patients and 473 received oxygen inhalation therapy: 407 (86.0%) via nasal cannula or mask, 58 (12.3%) with nasal high-flow therapy, 3 (0.6%) with nasal continuous positive airway pressure, and 5 (1.1%) with artificial ventilation. Of the 900 hospitalized patients, 22 (2%) were high-risk infants, for whom palivizumab is indicated, whereas 878 (98%) were not high-risk infants. Of the 606 non-high-risk infants whose clinical data were obtained, 578 (95%) were born at ≥36 weeks’ gestational age and 28 (5%) were aged >6 months and born at 29–35 weeks’ gestational age (n = 22) or aged >12 months and born at 22–28 weeks’ gestational age (n = 6). The detailed clinical data of 22 high-risk infants are shown in Table 1. The most predominant underlying condition was preterm birth with or without CLD, followed by Down syndrome. Seven patients with CLD or Down syndrome were hospitalized even over 1 year of age. The number of CHD cases was lower than that in previous Japanese reports, probably because this survey was conducted without pediatric cardiologists who mainly take care of the hospitalization of such patients. Based on the onset of the condition, these 22 high-risk infants were classified as developing the disease during and before palivizumab administration (n = 6, nos 1–6, and n = 16, nos 7–22, respectively). Of the 16 patients who developed RSV disease before palivizumab administration, 12 (75%, no. 7–18) did so after the epidemic began (July, August, and September), and four (25%, no. 19–22) did so before the epidemic began (May and June); two were preterm infants with a low age soon after discharge from the neonatal intensive care unit and two had CLD with preterm birth. Although there are survey reports on hospitalized patients due to RSV disease in 2007 and 2016, the results of the present study are significant because they are from the year the RSV epidemic changed. The present study also showed that 2% of the 900 patients hospitalized for RSV disease were high-risk infants, which is similar to the result reported from before the epidemic changed (13/438, or 3%, in Nagano prefecture). Only six high-risk infants were hospitalized during palivizumab administration (6/900, 0.7%), which was twofold lower than the number reported in Nagano (6/438, 1.4%). These data suggest that high-risk infants could avoid hospitalization for severe RSV disease if given palivizumab in this study. Notably, of the 16 patients who developed RSV disease before palivizumab administration, 12 did so just after the epidemic began. These 12 infants could have avoided hospitalization if palivizumab had been administered at the appropriate time, such as in June or early July. A limitation is that the survey was performed only in 12 facilities in Tokyo and its suburbs. However, the present study covered 900 patients with RSV disease; the numbers are larger than those in previous studies. Correspondence: Ichiro Morioka, MD PhD, Department of Pediatrics and Child Health, Nihon University School of Medicine, 30-1, Oyaguchi, Kami-cho, Itabashi-ku, Tokyo 173-8610, Japan. Email: [email protected] *These authors contributed equally. Received 19 March 2020; revised 16 May 2020; accepted 2 July 2020. doi: 10.1111/ped.14381