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Influenza infection in infants aged <6 months during the H1N1-09 pandemic: A hospital-based case series

Authors

  • Emilia E Esterman,

    1. Postgraduate Medical Program, Sydney Medical School, Westmead, New South Wales, Australia
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  • Monica M Lahra,

    1. WHO Collaborating Centre, Microbiology Department, SEALS, The Prince of Wales Hospital, Westmead, New South Wales, Australia
    2. Faculty of Medicine, School of Medical Sciences, The University of NSW, Westmead, New South Wales, Australia
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  • Yvonne A Zurynski,

    Corresponding author
    1. Discipline of Paediatrics and Child Health, Sydney Medical School, The University of Sydney, Westmead, New South Wales, Australia
    • Australian Paediatric Surveillance Unit, Westmead, New South Wales, Australia
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  • Robert Booy,

    1. Discipline of Paediatrics and Child Health, Sydney Medical School, The University of Sydney, Westmead, New South Wales, Australia
    2. National Centre for Immunisation Research and Surveillance, Westmead, New South Wales, Australia
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  • Elizabeth J Elliott

    1. Discipline of Paediatrics and Child Health, Sydney Medical School, The University of Sydney, Westmead, New South Wales, Australia
    2. Australian Paediatric Surveillance Unit, Westmead, New South Wales, Australia
    3. Department of Medicine, The Children's Hospital at Westmead, Westmead, New South Wales, Australia
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  • Conflict of interest: None declared.

Correspondence: A/Prof Yvonne Zurynski, Australian Paediatric Surveillance Unit, The Children's Hospital at Westmead, Locked Bag 4001, Westmead, NSW 2145, Australia. Fax: +02 98453082; email: yvonne.zurynski@health.nsw.gov.au

Abstract

Aims

To document risk factors, clinical features and outcomes in infants <6 months old admitted with laboratory-confirmed influenza to The Children's Hospital at Westmead during the H1N1-09 pandemic.

Methods

Prospective, hospital-based case series of infants admitted June–September 2009, identified by the Paediatric Active Enhanced Disease Surveillance system and supplemented by telephone interview post-discharge.

Results

Thirty-two infants <6 months old had influenza A: 18 H1N1-09, 11 H3N2 and three unknown subtypes. After discharge, 28 (88%) families were telephoned and provided additional information. Documented risk factors included close contact with young children (46%), living with a smoker (36%), intensive or special care at birth (25%), pre-existing illness (16%) and preterm birth (14%). The number of persons per household was double the state average. Only 14% of mothers were vaccinated against seasonal influenza. Infants commonly presented with cough (69%), coryza (69%), lethargy (38%), fever (31%), dyspnoea (31%) and vomiting (28%). Complications included pneumonia (22%), and bacterial (9%) and viral (6%) co-infection. Five infants (15%) required admission to intensive care, and one was mechanically ventilated. Sixteen (57%) had ongoing respiratory problems, and six (21%) presented to the Emergency Department within 6 months of discharge.

Conclusions

These novel data are clinically important. Rates of influenza in infants may be reduced by vaccinating close contacts and minimising exposure to infected contacts and cigarette smoke.

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