Detection of the Onset of the Epidemic Period of Respiratory Syncytial Virus Infection in Japan

Abstract

Respiratory syncytial virus (RSV) is a leading cause of lower respiratory tract infection in young children worldwide. An annual epidemic of RSV infection generally begins around autumn, reaching a peak at the end of year in Japan, but in 2017 it started in early July and peaked in September. As the onset timing of RSV season varies, it is important to detect the beginning of an epidemic, to enable the implementation of preventive measures. However, there are currently no specified criteria or methods to determine the onset of RSV season in a timely manner. Therefore, we developed a model to detect the epidemic onset, based on data from the Infectious Diseases Weekly Report from 2012 to 2017. The 47 prefectures of Japan span 11 climate zones, which affect the timing of epidemic onset. Therefore, the onset of RSV season was assessed separately in each prefecture. Non-linear regression analysis was performed to generate a mathematical model of the annual epidemic cycle for each prefecture. A search index was used to determine the onset of RSV season, which was estimated using the number of RSV reports per week within an epidemic period (RSV-reports/w) and the number of reported cases included within an epidemic period relative to the total number of RSV reports (capture rate). A number of RSV-reports/w, which was used as a threshold (a number at onset line) to determine the condition of the onset of RSV season, was then estimated based on the search index. The mean number at the onset of RSV season for 47 prefectures was 29.7 reports/week (median 21.0, range 6.0–121.0 reports/ week). The model also showed that the onset of RSV season in 2017 was more than 1 month earlier than the previous year. In conclusion, the model detected epidemic cycles and their onset conditions in all prefectures, despite the 11 climate zones of Japan. The results are expected to contribute to infant medical care by allowing medical personnel to take preventive measures promptly at the beginning of the epidemic RSV season.

Shifts in the epidemic season of human respiratory syncytial virus associated with inbound overseas travelers and meteorological conditions in Japan, 2014–2017: An ecological study

“…We used the onset week of HRSV epidemic season in 46 prefectures for 4-year period estimated by Yamagami et al in the other paper [ 4 ]. They developed a new algorithm to estimate the start of the HRSV epidemic season based on the IDWR data, since NIID does not set the definition on the start of HRSV epidemic season in Japan.…”

“…In the following, Yamagami et al [ 4 ] define the parameters for A(x) denotes HRSV-reports/w (the number of HRSV reported per week); B(x) denotes capture rate (the number of HRSV reports included within onset-trough periods relative to the total number of HRSV reports in the dataset); Index(x) denotes the search index. The capture rate A(x) and HRSV-reports/w (B(x)) were converted into the same scale and summed; x is a percentile value ranging from 0 to 100 in integer units; s is the number of epidemic cycles in the dataset; Onset(x) is the ordinal number of each onset week within the dataset from 1 to x in integer units; Trough is the ordinal number of each trough-week within the dataset from 0 to x in integer units; k is the number of HRSV reports in a given week.…”

“…The HRSV epidemic season in Japan normally begins around October, peaks in December-January, and ends in March-April. However, a shift in the HRSV epidemic season to summer periods (from June-August) has been reported in Japan more recently [ 4 ]. Although many previous studies looked at the association between HRSV cases and meteorological conditions [ 3 , 5 – 11 ], there may well be other factors that determine the onset week of HRSV epidemic season.…”

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

“…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 1 . In 2017, the epidemic started in July, and summer or early fall outbreaks were observed in Tokyo 2 . The change in the RSV epidemic is likely climate related 3 .…”

The Working Group for Revision of “Guidelines for the Use of Palivizumab in Japan”: A Committee Report

“…Several methods have been reported to forecast the start of the epidemic season of RSV in Japan to plan an administration schedule, based on the results of epidemiological surveillance of infectious diseases for the last several years in each prefecture. (It should be noted that RSV infection has been classified through the sentinel site surveillance system as a category V infectious disease, after the amendment of the infectious disease control law in 2003) 6–8 …”