Clinical epidemiology and predictors of outcome in children hospitalised with influenza A(H1N1)pdm09 in 2009: a prospective national study

Abstract

BackgroundThere are few large-scale, prospective studies of influenza A(H1N1)pdm09 in children that identify predictors of adverse outcomes.ObjectivesWe aimed to examine clinical epidemiology and predictors for adverse outcomes in children hospitalised with influenza A(H1N1)pdm09 in Australia.MethodsActive hospital surveillance in six tertiary paediatric referral centres (June–September, 2009). All children aged <15 years admitted with laboratory-confirmed influenza A(H1N1)pdm09 were studied.ResultsOf 601 children admitted with laboratory-confirmed influenza, 506 (84·2%) had influenza A(H1N1)pdm09. Half (51·0%) of children with influenza A(H1N1)pdm09 were previously healthy. Hospital stay was longer in children with pre-existing condition (mean 6·9 versus 4·9 days; P = 0·02) as was paediatric intensive care unit (PICU) stay (7·0 versus 2·3 days; P = 0·005). Rapid diagnosis decreased both antibiotic use and length of hospital and PICU stay. Fifty (9·9%) children were admitted to a PICU, 30 (5·9%) required mechanical ventilation and 5 (0·9%) died. Laboratory-proven bacterial co-infection and chronic lung disease were significant independent predictors of PICU admission (OR 6·89, 95% CI 3·15–15·06 and OR 3·58, 95% CI 1·41–9·07, respectively) and requirement for ventilation (OR 5·61, 95% CI 2·2–14·28 and OR 5·18, 95% CI 1·8–14·86, respectively). Chronic neurological disease was a predictor of admission to PICU (OR 2·30, 95% CI 1·14–4·61).ConclusionsDuring the 2009 pandemic, influenza was a major cause of hospitalisation in tertiary paediatric hospitals. Co-infection and underlying chronic disease increased risk of PICU admission and/or ventilation. Half the children admitted were previously healthy, supporting a role for universal influenza vaccination in children.

Influenza hospitalizations in Australian children

“…Infants aged 0-6 months represented the highest proportion (by 6-month age cohorts) of hospitalized children in our study; this age group is too young for influenza vaccination, but may be afforded protection from maternal vaccination [29,30]. Children hospitalized with influenza had a rate of complications comparable to adults, including pneumonia and seizures in 1/10, with ICU admission required in 1/12 children, similar to reports from seasonal and pandemic years [22,31,32]. Despite the median LOS being shorter than in adults, these findings confirm that influenza should not be regarded as a benign paediatric illness.…”

Vaccine‐preventable child deaths in New South Wales from 2005 to 2014: How much is preventable?

“…Another seven influenza deaths occurred in children over 6 months of age with no documented comorbidities and all influenza cases who died before arrival at hospital were previously healthy children under 5 years of age. Previously healthy young children with influenza have been shown to have high hospital admission rates and may be more likely to die before hospital admission or within 3 days of symptom onset, compared to those with underlying medical conditions . While influenza vaccination is recommended in Australia for all children between 6 months and 5 years of age, it is only funded under the NIP for those at higher risk and coverage is very low .…”

Epidemiology of Australian Influenza-Related Paediatric Intensive Care Unit Admissions, 1997-2013

“…Severe paediatric influenza-related illness occurs in Australia, even in years with low influenza activity. In this study we have only focused on ICU admissions, however it is estimated that between 10–30% of influenza-related hospitalisations result in an ICU admission, depending on the season [ 12 , 17 – 22 ]. Consistent with other reports of Australian paediatric influenza-related ICU admissions [ 9 – 13 ], we found a median length of stay of approximately 3 days and that half of the admissions required invasive respiratory support.…”

“…It has been estimated that fully vaccinated children are between 74–86% less likely to have an influenza-related hospital or ICU admission compared to unvaccinated children [ 10 , 29 , 30 ] and immunisation has been shown to reduce the burden of influenza in the community [ 13 , 31 , 32 ]. However influenza vaccination coverage among children in Australia remains low, even among individuals eligible for government-funded vaccination [ 6 , 11 , 12 , 29 ]. Vaccination history is not collected in the ANZPIC Registry, however given the low influenza vaccine coverage among Australian children [ 29 ], it is unlikely that many (if any) of our ICU cohort were vaccinated.…”