Modelled estimates of hospitalisations attributable to respiratory syncytial virus and influenza in Australia, 2009–2017

Abstract

Background Respiratory syncytial virus (RSV) and influenza are important causes of disease in children and adults. In Australia, information on the burden of RSV in adults is particularly limited. Methods We used time series analysis to estimate respiratory, acute respiratory infection, pneumonia and influenza, and bronchiolitis hospitalisations attributable to RSV and influenza in Australia during 2009 through 2017. RSV and influenza‐coded hospitalisations in <5‐year‐olds were used as proxies for relative weekly viral activity. Results From 2009 to 2017, the estimated all‐age average annual rates of respiratory hospitalisations attributable to RSV and seasonal influenza (excluding 2009) were 54.8 (95% confidence interval [CI]: 20.1, 88.8) and 87.8 (95% CI: 74.5, 97.7) per 100,000, respectively. The highest estimated average annual RSV‐attributable respiratory hospitalisation rate per 100,000 was 464.2 (95% CI: 285.9, 641.2) in <5‐year‐olds. For seasonal influenza, it was 521.6 (95% CI: 420.9, 600.0) in persons aged ≥75 years. In ≥75‐year‐olds, modelled estimates were approximately eight and two times the coded estimates for RSV and seasonal influenza, respectively. Conclusions RSV and influenza are major causes of hospitalisation in young children and older adults in Australia, with morbidity underestimated by hospital diagnosis codes.

Estimates of Seasonal Influenza Burden That Could Be Averted by Improved Influenza Vaccines in the Australian Population Aged Under 65 Years, 2015–2019

“…Our study used both modelled (influenza‐associated) and observed (influenza‐coded) hospitalisation estimates. Reliance on diagnosis codes only can underestimate influenza‐associated hospitalisations [2, 3]. This can occur because not all patients are tested for influenza and some positive test results are not recorded [2, 37].…”

“…It may be that as the accessibility, frequency and rapidity of testing have increased over time, ICD codes are now able to provide more sensitive estimates of influenza‐associated hospitalisations. On the other hand, including more diagnosis fields increases the risk of admissions with incidental infection being included [3].…”

“…We also analysed the effect on the calculated burden averted of using estimates for alternative aVE estimated for hospital admissions based on data from the Influenza Complications Alert Network (FluCAN) (Tables S2, S3 and S5) [16, 20, 44–46]. Additionally, results are presented for the burden averted using alternative published regression estimates of influenza‐associated hospitalisation categories: acute respiratory infections (ARI; ICD10‐AM J00–J22 and J44.0), and pneumonia and influenza (P&I; ICD‐10‐AM J09–J18) (Tables S4 and S5) [3].…”

“…For 2015 through 2017, we used published modelled estimates of age‐specific influenza‐associated respiratory hospitalisations in Australia [3]. Population rates of respiratory admissions attributable to influenza were estimated by regressing weekly respiratory hospitalisations on a proxy measure of the relative weekly incidence of seasonal influenza infection [3].…”

“…Seasonal influenza has been estimated to annually cause 290,000–650,000 respiratory deaths globally [1]. In Australia, influenza accounts for an estimated 1000 respiratory and 2800 all cause deaths [2] and 21,000 hospitalisations [3], annually.…”