Seasonal variability of respiratory syncytial virus infection in the Top End of the Northern Territory (2012-2014)

Altered epidemiological patterns of Respiratory Syncytial Virus and influenza detections in a tropical Australian setting 2020 to 2023

BACKGROUND

We describe the recent temporal patterns of respiratory syncytial virus (RSV) and influenza virus detections in the Northern Territory (NT) of Australia, between 2020 and 2023.

METHODS

This retrospective analysis of patients presenting with respiratory diseases utilised a multiplex viral nucleic acid detection assay for RSV, influenza and SARS Cov2 (COVID-19) to determine the relative frequency of non-COVID-19 respiratory viral detections by age and month during the study period.

RESULTS

During this period of the NT COVID-19 epidemic, disruption of the usual annual wet season RSV outbreak patterns occurred, and the yearly influenza peak was absent for two annual cycles. Our data also reveals that 25% of RSV infections were occurring in patients greater than 40 years of age, compared to 32% of influenza infections presenting in the same period, documenting a greater burden of adult disease than previously documented in the NT.

CONCLUSIONS

Loss of non-COVID-19 viral seasonality and a substantial unrecognised RSV adult burden were noted. We will continue to monitor seasonality, and the RSV burden and this will help to target the populations benefiting from recently released RSV vaccine.

Burden of respiratory syncytial virus disease across the lifespan in Australia and New Zealand: a scoping review

OBJECTIVES

Respiratory syncytial virus (RSV) is the leading cause of acute lower respiratory tract infection in young children worldwide. RSV is increasingly associated with severe respiratory disease in people aged >65 years. The heterogeneous landscape of RSV in Australia and New Zealand makes generalisation of results from global studies to local contexts difficult. Given the changing landscape of RSV, we aimed to examine the existing literature on the burden of RSV disease and identify evidence gaps in Australia and New Zealand.

STUDY DESIGN

Scoping review.

METHODS

We designed a scoping review protocol and searched the Web of Science and Scopus databases for eligible peer-reviewed publications. Data from eligible studies were charted and summarised in tabular and narrative form.

RESULTS

Of the 153 eligible publications identified, 123 investigated RSV disease in a hospital setting and six in primary care. Only six studies reported the economic burden of disease, all of which estimated direct healthcare costs associated with treatment and/or hospitalisation; no studies quantified the indirect costs or costs to families.

CONCLUSIONS

In this scoping review, we describe the effect of RSV disease in several high-risk populations, including children and adults. An improved understanding of the RSV burden of disease, both in primary care settings and economically, within the local context will assist with the implementation of preventative strategies, including vaccination programmes. Future studies to determine the true burden of RSV-associated morbidity, mortality and economic burden across the entire patient journey and among different healthcare settings will help prioritise emerging RSV therapeutics.

Respiratory syncytial virus disease morbidity in Australian infants aged 0 to 6 months: a systematic review with narrative synthesis

BACKGROUND

A significant proportion of the global respiratory syncytial virus (RSV) associated morbidity is accounted for by infants aged 0 to 6 months, who are particularly vulnerable to severe disease. In 2015, 44% of global hospitalisations in infants in this age group were secondary to RSV. The objective of this systematic review is to appraise and synthesise the local evidence of RSV infection morbidity among Australian infants aged 0 to 6 months and to assess the implications for future immunisation strategies.

METHODS

Electronic databases (Medline, Embase, Pubmed and Global Health) were searched for full-text articles published between 2000 and 2023 in English language. Studies that examined markers of RSV disease morbidity in infants aged 0 to 6 months in Australia who had laboratory confirmed RSV infection were eligible for inclusion. The outcomes of interest were incidence, prevalence, testing rate, positivity rate, mortality, emergency department visits, community health visits, hospitalisation, intensive care unit admission, supplementary oxygen use, mechanical ventilation, risk factors for disease severity and monoclonal antibody use.

RESULTS

The database search identified 469 studies. After removal of duplicates and full-text review, 17 articles were eligible for inclusion. This review was reported according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses and Synthesis without meta-analysis guidelines.

CONCLUSIONS

Qualitative analysis of the included studies showed that Australian infants aged 0 to 6 months have higher rates of RSV testing, positivity and incidence; and more likely to develop severe disease that requires hospitalisation, intensive care unit admission or respiratory support, compared to children and adults of all ages. Aboriginal and Torres Strait Islander infants aged 0 to 6 months demonstrated higher rates of RSV infection and hospitalisation, compared to non-Indigenous infants. Age-related trends persisted in geographic areas with varying seasonal transmission of RSV, and during the SARS-CoV-2 pandemic. Passive immunisation strategies targeting infants in their first 6 months of life, either via vaccination of pregnant women or administration of long-acting monoclonal antibody during infancy, could effectively reduce RSV disease burden in Australia.

The seasonality of respiratory syncytial virus in Western Australia prior to implementation of SARS‐CoV‐2 non‐pharmaceutical interventions

Background

Respiratory syncytial virus (RSV) seasonality is dependent on the local climate. We assessed the stability of RSV seasonality prior to the SARS-CoV-2 pandemic in Western Australia (WA), a state spanning temperate and tropical regions.

Method

RSV laboratory testing data were collected from January 2012 to December 2019. WA was divided into three regions determined by population density and climate: Metropolitan, Northern and Southern. Season threshold was calculated per region at 1.2% annual cases, with onset the first of ≥2 weeks above this threshold and offset as the last week before ≥2 weeks below.

Results

The detection rate of RSV in WA was 6.3/10,000. The Northern region had the highest detection rate (15/10,000), more than 2.5 times the Metropolitan region (detection rate ratio 2.7; 95% CI, 2.6-2.9). Test percentage positive was similar in the Metropolitan (8.6%) and Southern (8.7%) regions, with the lowest in the Northern region (8.1%). RSV seasons in the Metropolitan and Southern regions occurred annually, with a single peak and had consistent timing and intensity. The Northern tropical region did not experience a distinct season. Proportion of RSV A to RSV B in the Northern region differed from the Metropolitan region in 5 of the 8 years studied.

Conclusions

Detection rate of RSV in WA is high, especially in the Northern region, where climate, an expanded at-risk population and increased testing may have contributed to greater numbers. Before the SARS-CoV-2 pandemic, RSV seasonality in WA was consistent in timing and intensity for the Metropolitan and Southern regions.

Off-season RSV epidemics in Australia after easing of COVID-19 restrictions

Human respiratory syncytial virus (RSV) is an important cause of acute respiratory infection with the most severe disease in the young and elderly. Non-pharmaceutical interventions and travel restrictions for controlling COVID-19 have impacted the circulation of most respiratory viruses including RSV globally, particularly in Australia, where during 2020 the normal winter epidemics were notably absent. However, in late 2020, unprecedented widespread RSV outbreaks occurred, beginning in spring, and extending into summer across two widely separated regions of the Australian continent, New South Wales (NSW) and Australian Capital Territory (ACT) in the east, and Western Australia. Through genomic sequencing we reveal a major reduction in RSV genetic diversity following COVID-19 emergence with two genetically distinct RSV-A clades circulating cryptically, likely localised for several months prior to an epidemic surge in cases upon relaxation of COVID-19 control measures. The NSW/ACT clade subsequently spread to the neighbouring state of Victoria and to cause extensive outbreaks and hospitalisations in early 2021. These findings highlight the need for continued surveillance and sequencing of RSV and other respiratory viruses during and after the COVID-19 pandemic, as mitigation measures may disrupt seasonal patterns, causing larger or more severe outbreaks.

Non-pharmaceutical interventions for COVID-19 also reduced incidence of respiratory pathogens such as respiratory syncytial virus (RSV). Here, the authors report the resurgence of RSV in Australia following lifting of some of the restrictions and describe reduction in genetic diversity in circulating clades.

Respiratory viral infections in hospitalised paediatric patients in the tropics

AIM

Respiratory viruses are a huge disease burden globally. An understanding of the seasonal trends and the ability to predict peak periods of respiratory virus disease incidence is useful for clinical care.

METHODS

This is a retrospective analysis of paediatric hospitalizations of laboratory-confirmed viral respiratory tract infections in KK Women's and Children's Hospital, Singapore, from 1 January 2011 to 31 December 2016. Standard direct immunofluorescence was used to detect respiratory syncytial virus (RSV), influenza A and B viruses, parainfluenza 1, 2 and 3 viruses, metapneumovirus and adenovirus.

RESULTS

A total of 97 840 specimens were analysed with a positive detection rate of 23.8%. RSV made up the largest proportion (42% of the total positive results), predominating between May to September. Influenza A had two peaks, June to July and December to January. Type 3 was the most common parainfluenza virus and showed annually recurring peaks. In contrast, parainfluenza 1 and 2, metapneumovirus and adenovirus had a biennial pattern. The test of seasonality detected identifiable seasonality for RSV and parainfluenza 3 virus.

CONCLUSIONS

In conclusion, respiratory viruses have different and overlapping seasonality in tropical Singapore. Respiratory virus testing for patients admitted for acute respiratory infection is useful to target antiviral therapies and appropriate infection control practices.

Respiratory syncytial virus-associated hospitalisations in Australia, 2006-2015

OBJECTIVE

To estimate rates of respiratory syncytial virus (RSV)-associated hospitalisation across the age spectrum, and to identify groups at particular risk of serious RSV-associated disease.

DESIGN, SETTING AND PARTICIPANTS

Retrospective review of National Hospital Morbidity Database data for all RSV-associated hospitalisations in Australia, 2006-2015.

MAIN OUTCOMES AND MEASURES

RSV-coded hospitalisation rates by age, sex, Indigenous status, jurisdiction, and seasonality (month and year); hospital length of stay; in-hospital deaths.

RESULTS

During 2006-2015, there were 63 814 hospitalisations with an RSV-specific principal diagnostic code; 60 551 (94.9%) were of children under 5 years of age. The hospitalisation rate for children under 5 years was 418 per 100 000 population; for children under 6 months of age it was 2224 per 100 000 population; the highest rate was for infants aged 0-2 months (2778 per 100 000 population). RSV-coded hospitalisation rates were higher for adults aged 65 or more than for people aged 5-64 years (incidence rate ratio [IRR], 6.6; 95% CI, 6.2-7.1), and were also higher for Indigenous Australians than other Australians (IRR, 3.3; 95% CI, 3.2-3.5). A total of 138 in-hospital deaths were recorded, including 82 of adults aged 65 years or more (59%).

CONCLUSIONS

Prevention strategies targeting infants, such as maternal or early infant vaccination, would probably have the greatest impact in reducing RSV disease rates. Further characterisation of RSV disease epidemiology, particularly in older adults and Indigenous Australians, is needed to inform health care strategies.

Evolution of Human Respiratory Syncytial Virus (RSV) over Multiple Seasons in New South Wales, Australia

There is an ongoing global pandemic of human respiratory syncytial virus (RSV) infection that results in substantial annual morbidity and mortality. In Australia, RSV is a major cause of acute lower respiratory tract infections (ALRI). Nevertheless, little is known about the extent and origins of the genetic diversity of RSV in Australia, nor the factors that shape this diversity. We have conducted a genome-scale analysis of RSV infections in New South Wales (NSW). RSV genomes were successfully sequenced for 144 specimens collected between 2010⁻2016. Of these, 64 belonged to the RSVA and 80 to the RSVB subtype. Phylogenetic analysis revealed a wide diversity of RSV lineages within NSW and that both subtypes evolved rapidly in a strongly clock-like manner, with mean rates of approximately 6⁻8 × 10^-4 nucleotide substitutions per site per year. There was only weak evidence for geographic clustering of sequences, indicative of fluid patterns of transmission within the infected population and no evidence of any clustering by patient age such that viruses in the same lineages circulate through the entire host population. Importantly, we show that both subtypes circulated concurrently in NSW with multiple introductions into the Australian population in each year and only limited evidence for multi-year persistence.

Meteorological factors and respiratory syncytial virus seasonality in subtropical Australia

Evidence is emerging regarding the influence of meteorological factors on seasonal respiratory syncytial virus outbreaks. Data however, are limited for subtropical regions, especially in the southern hemisphere. We examined whether meteorological data (daily minimum and maximum temperatures, rainfall, relative humidity, dew point, daily global solar exposure) and tourist numbers were associated with the incidence of RSV in children aged <5 years for the Gold Coast region of South-East Queensland, Australia (latitude 28.0°S). RSV cases between 1 July 2007 and 30 June 2016 were identified from the Pathology Queensland Gold Coast Laboratory database. Time-series methods were used to identify seasonal patterns. RSV activity peaked in mid-to-late autumn (April–May), tapering in winter (June–August). While most meteorological variables measured were associated with RSV incidence, rainfall (ρ = 0.40, 95% confidence interval (CI) 0.32–0.48) and humidity (ρ = 0.38, 95% CI 0.29–0.46) 8 weeks earlier had the nearest temporal relationship. Tourist numbers were not correlated with RSV activity. Identifying meteorological conditions associated with seasonal RSV epidemics can improve understanding of virus transmission and assist planning for their impact upon the health sector, including timing of passive RSV immunoprophylaxis for high-risk infants and future public health interventions, such as maternal immunisation with RSV vaccines.