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

Unseasonal respiratory syncytial virus epidemics during the COVID-19 pandemic: Relationship between climatic factors and epidemic strain switching

OBJECTIVES

The COVID-19 pandemic has altered respiratory syncytial virus (RSV) epidemic patterns. However, the influence of climatic and virological factors on RSV outbreaks remains unclear. We examined RSV incidence in Okinawa, Japan; Taiwan, China; and Florida, USA before and after the COVID-19 pandemic, focusing on the effects of population mobility and climate.

METHODS

We analysed correlations among RSV incidence, human mobility, and climate before and after the pandemic. Additionally, we conducted a phylogenetic analysis of the second variable region of RSV G proteins using viral genomes isolated from patients with acute respiratory tract infections in Okinawa.

RESULTS

Annual RSV epidemics in Okinawa were not correlated with post-pandemic human mobility. The temperature and humidity ranges at the onset of RSV epidemics differed between the pre- and post-pandemic periods, with decreased standard deviations. Genetic analysis of RSV strains from 2020 to 2022 revealed a cluster with low genetic diversity, which differed markedly from pre-2019 and 2023 prevalent strains.

CONCLUSION

Reduced human migration led to an RSV epidemic caused by an indigenous endemic strain, highlighting the natural relationship between epidemics and climatic factors. These findings could aid in developing effective prediction and control programs for RSV epidemics and optimising vaccine programs.

Interplay between climate, childhood mixing, and population-level susceptibility explains a sudden shift in RSV seasonality in Japan

Titrating the relative importance of endogenous and exogenous drivers for dynamical transitions in host-pathogen systems remains an important research frontier towards predicting future outbreaks and making public health decisions. In Japan, respiratory syncytial virus (RSV), a major childhood respiratory pathogen, displayed a sudden, dramatic shift in outbreak seasonality (from winter to fall) in 2016. This shift was not observed in any other countries. We use mathematical models to identify processes that could lead to this outcome. In line with previous analyses, we identify a robust quadratic relationship between mean specific humidity and transmission, with minimum transmission occurring at intermediate humidity. This drives semiannual patterns of seasonal transmission rates that peak in summer and winter. Under this transmission regime, a subtle increase in population-level susceptibility can cause a sudden shift in seasonality, where the degree of shift is primarily determined by the interval between the two peaks of seasonal transmission rate. We hypothesize that an increase in children attending childcare facilities may have contributed to the increase in susceptibility through increased contact rates with susceptible hosts. Our analysis underscores the power of studying infectious disease dynamics to titrate the roles of underlying drivers of dynamical transitions in ecology.

Epidemiological study of respiratory syncytial virus infection in adults during the pandemic of COVID-19

INTRODUCTION

While respiratory syncytial virus (RSV) is one of the most common pathogens in adults admitted to the ICU due to respiratory diseases, no reports regarding the occurrence rate of RSV infections in adults in Japan during the COVID-19 pandemic exist.

PATIENTS AND METHODS

We conducted this retrospective study to examine the exact occurrence rate of RSV infections in adults. We reviewed all patients (≥18 years) with any respiratory symptoms who received quantitative polymerase chain reaction (PCR) using nasopharyngeal samples for respiratory viruses by GeneLEAD at the Aichi Medical University Hospital between November 2022 and November 2023.

RESULTS

A total of 541 adult patients who underwent PCR test were enrolled in this study. RSV was identified in 18 cases (3.3 %); 8 (1.5 %) upper and 10 (1.8 %) lower respiratory tract infections. Influenza A and SARS-CoV-2 were found in 10 (1.8 %) and 61 (11.3 %), respectively. Patients with RSV infections and COVID-19 had more comorbidities than those with Influenza virus infections. As for RSV-associated with lower respiratory tract infection cases, 10 developed acute respiratory failure, resulting in 1 fatal case due to pneumonia and 1 died of septic shock due to ileus. The 30-, 90-day mortality rates were 1 (6 %) and 2 (11 %) respectively.

CONCLUSION

About 3 % of adults had RSV infections during the COVID-19 pandemic. The outcomes of RSV infections in adults were similar to those by COVID-19. Those with comorbidities should have a preventive method against RSV infections, the same as for COVID-19.

Detailed analysis of low temperature inactivation of respiratory syncytial virus

Our previous findings indicated that many respiratory syncytial virus (RSV) isolates are unstable at 4 °C compared to 20 °C. Some of the strains completely lose infectivity after 24 h at 4 °C. This study analyzed the inactivation process at 4 °C using a representative strain, RSV/Sendai/851/13. After 24 h of storage at 4 °C, the virus was completely inactivated but retained its ability to attach to and to be taken into host cells. It suggested a reduced fusion ability between the viral and cellular membranes. During storage at 4 °C, the RSV fusion (F) protein underwent a conformational change and was no longer recognized by pre-fusion form-specific antibodies. When the RSV/Sendai/851/13 strain was passaged at 4 °C, a variant with an amino acid substitution, I148T, in the F protein fusion peptide was selected. Also, an amino acid change in G protein demonstrating stability at low temperatures was obtained. These results show that the inactivation of RSV at 4 °C is due to the loss of membrane fusion activity in the F protein, which cannot maintain its pre-fusion state at 4 °C.

Nonlinear and Multidelayed Effects of Meteorological Drivers on Human Respiratory Syncytial Virus Infection in Japan

In this study, we aimed to characterize the nonlinear and multidelayed effects of multiple meteorological drivers on human respiratory syncytial virus (HRSV) infection epidemics in Japan. The prefecture-specific weekly time-series of the number of newly confirmed HRSV infection cases and multiple meteorological variables were collected for 47 Japanese prefectures from 1 January 2014 to 31 December 2019. We combined standard time-series generalized linear models with distributed lag nonlinear models to determine the exposure-lag-response association between the incidence relative risks (IRRs) of HRSV infection and its meteorological drivers. Pooling the 2-week cumulative estimates showed that overall high ambient temperatures (22.7 °C at the 75th percentile compared to 16.3 °C) and high relative humidity (76.4% at the 75th percentile compared to 70.4%) were associated with higher HRSV infection incidence (IRR for ambient temperature 1.068, 95% confidence interval [CI], 1.056-1.079; IRR for relative humidity 1.045, 95% CI, 1.032-1.059). Precipitation revealed a positive association trend, and for wind speed, clear evidence of a negative association was found. Our findings provide a basic picture of the seasonality of HRSV transmission and its nonlinear association with multiple meteorological drivers in the pre-HRSV-vaccination and pre-coronavirus disease 2019 (COVID-19) era in Japan.

Impact of meteorological and demographic factors on the influenza epidemic in Japan: a large observational database study

Factors affecting the start date of the influenza epidemic season and total number of infected persons per 1,000,000 population in 47 prefectures of Japan were evaluated. This retrospective observational study (September 2014-August 2019; N = 472,740-883,804) evaluated data from a Japanese health insurance claims database. Single and multiple regression analyses evaluated the time to start of the epidemic or total infected persons per 1,000,000 population with time to absolute humidity (AH) or number of days with AH (≤ 5.5, ≤ 6.0, ≤ 6.5, and ≤ 7.0), total visitors (first epidemic month or per day), and total population. For the 2014/15, 2015/16, and 2016/17 seasons, a weak-to-moderate positive correlation (R2: 0.042-0.417) was observed between time to start of the epidemic and time to first day with AH below the cutoff values. Except in the 2016/17 season (R2: 0.089), a moderate correlation was reported between time to start of the epidemic and the total population (R2: 0.212-0.401). For all seasons, multiple regression analysis showed negative R2 for time to start of the epidemic and total visitors and population density (positive for time to AH ≤ 7.0). The earlier the climate becomes suitable for virus transmission and the higher the human mobility (more visitors and higher population density), the earlier the epidemic season tends to begin.

Respiratory virus circulation in children after relaxation of COVID-19 restrictions in fall 2021 - a nationwide register study in Finland

BACKGROUND

Social restrictions interrupted the normal respiratory virus circulation in spring 2020. This report describes virus circulation in pediatric population before and after the restrictions ended in Finland in September 2021.

METHODS

We used data from the Finnish Infectious Disease Register. Nationwide influenza A and B, rhinovirus, SARS-coronavirus-2 (SARS-Cov-2) and RSV (respiratory syncytial virus) findings from January 2018 to December 2021. Age stratified (0-4, 5-9, and 10-14 years) weekly incidences per 100,000 children were calculated.

RESULTS

School and day-care closures interrupted completely the circulation of all other respiratory viruses than rhinovirus in spring 2020. After restrictions were relaxed in September 2021, SARS-Cov-2 detections increased majorly. We observed high RSV season in atypically early. SARS-Cov-2 was detected in older children whereas RSV season peaked especially among children aged under five. Influenza seemed to return to normal circulation.

CONCLUSIONS

In conclusion we report that the ending of social restrictions in September 2021 led to an increase in SARS-Cov-2 detections and high epidemic peaks of RSV and parainfluenza in atypical timing in children. Our results highlight the importance of continuous pathogen surveillance during pandemic, as atypical surges of non-COVID-19 respiratory viruses were observed. This article is protected by copyright. All rights reserved.

The Effect of International Travel Arrivals on the New HIV Infections in 15-49 Years Aged Group Among 109 Countries or Territories From 2000 to 2018

OBJECTIVE

The prevalent international travel may have an impact on new HIV infections, but related studies were lacking. We aimed to explore the association between international travel arrivals and new HIV infections in 15-49 years aged group from 2000 to 2018, to make tailored implications for HIV prevention.

METHODS

We obtained the data of new HIV infections from the Joint United Nations Programme on HIV/AIDS and international travel arrivals from the World Bank. Correlation analysis was used to explore the relation briefly. Log-linear models were built to analyze the association between international travel arrivals and new HIV infections.

RESULTS

International travel arrivals were positively correlated with new HIV infections (correlation coefficients: 0.916, p < 0.001). After controlling population density, the median age of the total population (years), socio-demographic index (SDI), travel-related mandatory HIV testing, HIV-related restrictions, and antiretroviral therapy coverage, there were 6.61% (95% CI: 5.73, 7.50; p < 0.001) percentage changes in new HIV infections of 15-49 years aged group associated with a 1 million increase in international travel arrivals.

CONCLUSIONS

Higher international travel arrivals were correlated with new HIV infections in 15-49 years aged group. Therefore, multipronged structural and effective strategies and management should be implemented and strengthened.

Decreased human respiratory syncytial virus activity during the COVID-19 pandemic in Japan: an ecological time-series analysis

BACKGROUND

Non-pharmaceutical interventions (NPIs), such as sanitary measures and travel restrictions, aimed at controlling the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), may affect the transmission dynamics of human respiratory syncytial virus (HRSV). We aimed to quantify the contribution of the sales of hand hygiene products and the number of international and domestic airline passenger arrivals on HRSV epidemic in Japan.

METHODS

The monthly number of HRSV cases per sentinel site (HRSV activity) in 2020 was compared with the average of the corresponding period in the previous 6 years (from January 2014 to December 2020) using a monthly paired t-test. A generalized linear gamma regression model was used to regress the time-series of the monthly HRSV activity against NPI indicators, including sale of hand hygiene products and the number of domestic and international airline passengers, while controlling for meteorological conditions (monthly average temperature and relative humidity) and seasonal variations between years (2014-2020).

RESULTS

The average number of monthly HRSV case notifications in 2020 decreased by approximately 85% (p < 0.001) compared to those in the preceding 6 years (2014-2019). For every average ¥1 billion (approximately £680,000/$9,000,000) spent on hand hygiene products during the current month and 1 month before there was a 0.29% (p = 0.003) decrease in HRSV infections. An increase of average 1000 domestic and international airline passenger arrivals during the previous 1-2 months was associated with a 3.8 × 10^- 4% (p < 0.001) and 1.2 × 10^- 3% (p < 0.001) increase in the monthly number of HRSV infections, respectively.

CONCLUSIONS

This study suggests that there is an association between the decrease in the monthly number of HRSV cases and improved hygiene and sanitary measures and travel restrictions for COVID-19 in Japan, indicating that these public health interventions can contribute to the suppression of HRSV activity. These findings may help in public health policy and decision making.