Most children presenting to the hospital with ARF lived in disadvantaged areas of Sydney. Pacific Islander and Aboriginal and Torres Strait Islander children were over-represented. Mitigation of RHD requires early identification of ARF and appropriate delivery of secondary prophylaxis.

Background: Severe complications of influenza in children are uncommon but may result in admission to hospital or an intensive care unit (ICU) and death. Methods: Active prospective surveillance using the Australian Paediatric Surveillance Unit with monthly reporting by pediatricians of national demographic and clinical data on children with <15 years of age hospitalized with severe complications of laboratory-confirmed influenza during ten influenza seasons 2008–2017. Results: Of 722 children notified, 613 had laboratory-confirmed influenza and at least one severe complication. Most (60%) were <5 years of age; 10% were <6 months, hence ineligible for vaccination. Almost half of all cases were admitted to ICU and 30 died. Most children were previously healthy: 40.3% had at least one underlying medical condition. Sixty-five different severe complications were reported; pneumonia was the most common, occurring in over half of all cases. Influenza A accounted for 68.6% hospitalizations; however, influenza B was more often associated with acute renal failure (P = 0.014), rhabdomyolysis (P = 0.019), myocarditis (P = 0.015), pericarditis (P = 0.013), and cardiomyopathy (P = 0.035). Children who died were more likely to be older (5–14 years), have underlying medical conditions, be admitted to ICU, and have encephalitis, acute renal failure, or myocarditis. Only 36.1% of all children reported received antiviral medications, and 8.5% were known to be vaccinated for seasonal influenza. Conclusions: Severe influenza complications cause morbidity and mortality in children, which may increase if coinfection with COVID-19 occurs in the 2020 season and beyond. Increased vaccination rates, even in healthy children, early diagnosis and timely antiviral treatment are needed to reduce severe complications and death.

The use of oseltamivir was well tolerated in hospitalized infants. Vomiting, one of the widely reported side effects of oseltamivir, was found to be more a presenting symptom of influenza than a side effect of oseltamivir. Based on pulse oximetry, oseltamivir-treated cases may have been more severe on presentation, but there was no significant difference in length of hospital stay.

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