Influenza related hospitalisations in Sydney, New South Wales, Australia
F Beard1, P McIntyre, H Gidding
1New South Wales Public Health Officer Training Program, New South Wales Department of Health, Sydney, New South Wales, Australia. Frank_Beard@health.qld.gov.au
Insights
Influenza causes significantly more hospitalizations in children than previously estimated. Even minimum burden estimates support routine influenza vaccination for children under two years old.
Area of Science:
- Pediatric infectious diseases
- Public health surveillance
- Vaccinology
Background:
- Routine influenza vaccination is recommended for children in the US, but accurate burden of illness data is needed globally.
- Existing data underestimate influenza's role in pediatric hospitalizations, complicated by concurrent respiratory syncytial virus (RSV) circulation.
- Previous studies on influenza-related hospitalizations in children yielded disparate results due to differing methodologies.
Purpose of the Study:
- To estimate the true burden of influenza-related hospitalizations in children using two established indirect methods.
- To compare these estimates with hospitalizations where influenza was the principal diagnosis.
- To inform global recommendations for pediatric influenza vaccination.
Main Methods:
- Retrospective population-based study of children (<18 years) in Sydney, Australia (1994-2001).
- Employed two methods comparing acute respiratory disease hospitalization rates during high influenza/low RSV periods versus low activity periods.
- Virological surveillance data defined influenza and RSV activity; estimates compared against principal discharge diagnosis codes.
Main Results:
- Influenza-attributable hospitalization rates were up to 11 times higher than those based on principal discharge diagnosis codes.
- The disparity varied by age group and estimation method used.
- This highlights significant underestimation in routinely reported data.
Conclusions:
- Estimating influenza-related morbidity via excess hospitalizations involves uncertainty, but minimum burden estimates are substantial.
- Even conservative estimates support considering routine influenza immunization for all children under two years of age.
- Principal discharge diagnosis codes, while underestimating burden, are widely available for informing public health policy.
Background:
Routine influenza vaccination for children aged 6-23 months has recently been recommended in the United States. Accurate assessment of influenza related burden of illness in children could support similar recommendations in other settings. However, routinely available data underestimate the role of influenza in causing hospitalisation, and indirect estimation methods face difficulties controlling for the concurrent circulation of respiratory syncytial virus (RSV). Recent studies from Hong Kong and the United States have used differing methods to estimate the true burden of influenza related hospitalisation, with disparate results.
Methods:
Retrospective population based study of children less than 18 years of age from Sydney, Australia, 1994 to 2001. Using two previously reported methods, estimates of annual hospitalisation rates attributable to influenza were derived by comparison of mean hospitalisation rates for acute respiratory disease during periods of high influenza activity and low RSV activity (defined using virological surveillance data) and periods where both influenza and RSV activity were low. These estimates were compared to rates of hospitalisation where influenza was recorded as the principal discharge diagnosis.
Results:
Hospitalisation rates attributable to influenza were up to 11 times higher, depending on the age group and method used, compared to rates calculated from principal discharge diagnosis codes.
Conclusions:
Although there remains considerable uncertainty in estimating influenza related morbidity by methods using excess hospitalisations, even minimum estimates of disease burden warrant consideration of routine influenza immunisation for all children less than 2 years of age. Such estimates, derived from principal discharge diagnosis codes, are available in most settings.
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