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BackgroundFollowing a relative absence in winter 2020, a large resurgence of respiratory syncytial virus (RSV) detections occurred during the 2020/2021 summer in Western Australia. This seasonal shift was linked to SARS-CoV-2 public health measures. We examine the epidemiology and RSV testing of respiratory-coded admissions, and compare clinical phenotype of RSV-positive admissions between 2019 and 2020.MethodAt a single tertiary paediatric centre, International Classification of Diseases, 10th edition Australian Modification-coded respiratory admissions longer than 12 hours were combined with laboratory data from 1 January 2019 to 31 December 2020. Data were grouped into bronchiolitis, other acute lower respiratory infection (OALRI) and wheeze, to assess RSV testing practices. For RSV-positive admissions, demographics and clinical features were compared between 2019 and 2020.ResultsRSV-positive admissions peaked in early summer 2020, following an absent winter season. Testing was higher in 2020: bronchiolitis, 94.8% vs 89.2% (p=0.01); OALRI, 88.6% vs 82.6% (p=0.02); and wheeze, 62.8% vs 25.5% (p<0.001). The 2020 peak month, December, contributed almost 75% of RSV-positive admissions, 2.5 times the 2019 peak. The median age in 2020 was twice that observed in 2019 (16.4 vs 8.1 months, p<0.001). The proportion of RSV-positive OALRI admissions was greater in 2020 (32.6% vs 24.9%, p=0.01). There were no clinically meaningful differences in length of stay or disease severity.InterpretationThe 2020 RSV season was in summer, with a larger than expected peak. There was an increase in RSV-positive non-bronchiolitis admissions, consistent with infection in older RSV-naïve children. This resurgence raises concern for regions experiencing longer and more stringent SARS-CoV-2 public health measures.

Correspondence to Dr David Anthony Foley, Microbiology, PathWest Laboratory Medicine Western Australia, Perth, WA 6009, Australia; drdavidanthonyfoley@gmail.com An interseasonal resurgence of respiratory syncytial virus (RSV) was observed in Western Australia at the end of 2020. NPI, non-pharmaceutical intervention; OALRI, other acute lower respiratory tract infection; RSV, respiratory syncytial virus; WRS, wheeze responsive to salbutamol. Table 1 Comparison of RSV presentations in Western Australia in 2019 and 2020/21 seasons by clinical phenotype and rates per age group in Western Australia Metropolitan region Season 2019 2020/21 Duration (weeks) 28 14 Total admissions 398 563 Clinical phenotype N (% total) N (% total) P value Bronchiolitis 236 (59.3) 242 (43) <0.001 OALRI 94 (23.6) 167 (29.7) 0.04 Wheeze responsive to salbutamol 31 (7.8) 93 (16.5) <0.001 Other 37 (9.3) 61 (10.8) 0.4 Median age in months (IQR) 7.5 (2.2–22) 14.7 (4.4–24.8) <0.001 WA Metropolitan region N (% total) 332 (83.4) 519 (92.2) <0.001 Under 12 months N 194 210 Rate per 1000 7.8 8.4 0.46 95% CI 6.7–9 7.3–9.7 Between 12 and 24 months N 70 167 Rate per 1000 2.7 6.7 <0.001 95% CI 2.1 to 3.5 5.7 to 7.8 Between 24 and 48 months N 43 104 Rate per 1000 0.8 2.1 <0.001 95% CI 0.6 to 1.1 1.7 to 2.5 N, number; OALRI, other acute lower respiratory tract infection; RSV, respiratory syncytial virus; URTI, upper respiratory tract infection; WA, Western Australia.