The Seasonality of Respiratory Syncytial Virus in Western Australia
Prior to Implementation of SARS-CoV-2 Non-Pharmaceutical Interventions
Abstract
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
incidence of RSV in WA was 6.3/10,000. The Northern region had the
highest incidence (15/10,000), more than 2.5 times the Metropolitan
region (IRR 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 Incidence 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 WA was consistent in timing and
intensity for the Metropolitan and Southern regions.