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

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.