Influenza epidemiology in patients admitted to sentinel Australian hospitals in 2017: the Influenza Complications Alert Network (FluCAN)

Abstract

The Influenza Complications Alert Network (FluCAN) is a sentinel-hospital-based surveillance program that operates at sites in all jurisdictions in Australia. This report summarises the epidemiology of hospitalisations with laboratory-confirmed influenza during the 2017 influenza season. In this observational surveillance system, cases were defined as patients admitted to any of the 17 sentinel hospitals with influenza confirmed by nucleic acid detection. Data are also collected on a frequency-matched control group of influenza-negative patients admitted with acute respiratory infection. During the period 3 April to 31 October 2017 (the 2017 influenza season), 4,359 patients were admitted with confirmed influenza to one of 17 FluCAN sentinel hospitals. Of these, 52% were elderly (≥65 years), 14% were children (<16 years), 6.5% were Aboriginal and Torres Strait Islander peoples, 1.6% were pregnant and 78% had chronic comorbidities. A significant proportion were due to influenza B (31%). Estimated vaccine coverage was 72% in the elderly (≥65 years), 50% in non-elderly adults with medical comorbidities and 24% in children (<16 years) with medical comorbidities. The estimated vaccine effectiveness (VE) in the target population was 23% (95% CI: 7%, 36%). There were a large number of hospital admissions detected with confirmed influenza in this national observational surveillance system in 2017, with case numbers more than twice that reported in 2016.

Perturbed CD8+ T cell immunity across universal influenza epitopes in the elderly

“…Most people experience mild to moderate influenza illness only once or twice in their lifetime, with symptoms ranging from fever, cough, sore throat, body aches, and fatigue. However, the risk of severe influenza illness, which often requires hospitalization and can result in death, is more pronounced in the elderly, with increased occurrence, higher hospitalization rates, and increased morbidity and mortality compared with younger adults . This is exemplified by the data obtained from 17 Australian major hospitals during the 2015 April–October influenza season, with the elderly (≥65 yr) accounting for 46% of all hospitalized influenza‐infected patients out of 2070 laboratory‐confirmed cases .…”

“…However, the risk of severe influenza illness, which often requires hospitalization and can result in death, is more pronounced in the elderly, with increased occurrence, higher hospitalization rates, and increased morbidity and mortality compared with younger adults . This is exemplified by the data obtained from 17 Australian major hospitals during the 2015 April–October influenza season, with the elderly (≥65 yr) accounting for 46% of all hospitalized influenza‐infected patients out of 2070 laboratory‐confirmed cases . Elderly individuals, particularly men, also preferentially succumbed to severe avian H7N9 influenza disease .…”

Opportunities to improve influenza vaccination rates in general medical inpatients

“…In recent influenza seasons in Australia, 91% of influenza‐related deaths were in people aged ≥65 years, and almost all influenza‐related deaths occurred in patients with chronic medical conditions . A 2018 Cochrane review identified that IIV reduces the risk of influenza in the elderly with number needed to treat being 30 .…”

“…The Australian National Immunisation Program (ANIP) recommends annual inactivated influenza vaccination (IIV) of the elderly (≥65 years), and younger patients with chronic conditions—those at high risk of severe influenza . However, under 80% of elderly Australians, and 60% of eligible younger adults received influenza vaccine annually . Recent data suggest that the ANIP prevents approximately 46% of influenza‐related hospital admissions, and increasing coverage in at‐risk groups could further reduce this by 14% .…”

“…However, under 80% of elderly Australians, and 60% of eligible younger adults received influenza vaccine annually . Recent data suggest that the ANIP prevents approximately 46% of influenza‐related hospital admissions, and increasing coverage in at‐risk groups could further reduce this by 14% . In patients with medical comorbidities, IIV is associated with reduced all‐cause mortality and hospitalisation during influenza season, including from pneumonia, cardiovascular and cerebrovascular events …”