A surge in human metapneumovirus paediatric respiratory admissions in Western Australia following the reduction of SARS-CoV-2 non-pharmaceutical interventions.

AIM: Western Australian laboratory data demonstrated a decrease in human metapneumovirus (hMPV) detections through 2020 associated with SARS-CoV-2-related non-pharmaceutical interventions (NPIs), followed by a subsequent surge in metropolitan region in mid-2021. We aimed to assess the impact of the surge in hMPV on paediatric hospital admissions and the contribution of changes in testing. METHODS: All respiratory-coded admissions of children aged <16 years at a tertiary paediatric centre between 2017 and 2021 were matched with respiratory virus testing data. Patients were grouped by age at presentation and by ICD-10 AM codes into bronchiolitis, other acute lower respiratory infection (OALRI), wheeze and upper respiratory tract infection (URTI). For analysis, 2017-2019 was utilised as a baseline period. RESULTS: hMPV-positive admissions in 2021 were more than 2.8 times baseline. The largest increase in incidence was observed in the 1-4 years group (incidence rate ratio (IRR) 3.8; 95% confidence interval (CI): 2.5-5.9) and in OALRI clinical phenotype (IRR 2.8; 95% CI: 1.8-4.2). The proportion of respiratory-coded admissions tested for hMPV in 2021 doubled (32-66.2%, P < 0.001), with the greatest increase in wheeze (12-75% in 2021, P < 0.001). hMPV test percentage positivity in 2021 was higher than in the baseline period (7.6% vs. 10.1% in 2021, P = 0.004). CONCLUSION: The absence and subsequent surge underline the susceptibility of hMPV to NPIs. Increased hMPV-positive admissions in 2021 can be partially attributable to testing, but test-positivity remained high, consistent with a genuine increase. Continued comprehensive testing will help ascertain true burden of hMPV respiratory diseases.

Unusual 2020 respiratory syncytial virus bronchiolitis season in Western Australia: Not explained by weather.

OBJECTIVE: To describe and explore the relationship between weather and the unusual 2020 bronchiolitis season in Western Australia during the COVID-19 pandemic. METHODS: Correlation of meteorological data and presentations of infants with bronchiolitis through the ED of Perth Children's Hospital. RESULTS: The 2020 bronchiolitis epidemic showed a reversal of the usual seasonal pattern. There were no weather events to account for this phenomenon. CONCLUSIONS: The bronchiolitis outbreak showed no relationship to local weather patterns. State-mandated COVID-19 public health measures appear as the likely rationale.

Examining the interseasonal resurgence of respiratory syncytial virus in Western Australia.

BACKGROUND: Following 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. METHOD: At 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. RESULTS: RSV-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. INTERPRETATION: The 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.