Characterization of 2009 H1N1 pandemic influenza in a population of Dutch children with influenza-like signs and symptoms

Aim: To determine causative respiratory pathogens and describe epidemiological and clinical characteristics in a paediatric population with influenza-like illness during the 2009 H1N1-pandemic.

Methods: Observational study of 412 children visiting an outpatient clinic of a Dutch teaching hospital.

Results: From August to December 2009, 412 children were tested at the clinic; 32% proved H1N1-positive, confirmed by reverse-transcriptase-polymerase-chain-reaction (RT-PCR). Pathogens were detected in 65% of samples. Influenza A(H1N1) (n = 132), human rhinovirus (n = 55), respiratory syncytial virus (n = 45) and adenovirus (n = 34) were mostly identified. Co-infections were seen in 34 children (8.3%). Mean age was 6.8 and 4.2 years in H1N1-positive and H1N1-negative cases, respectively (p < 0.01). H1N1-positive outpatient children reported fever, cough and rhinorrhoea more frequently than their H1N1-negative counterparts. Of 72 hospitalized children, 31% proved H1N1-positive; all showed a relatively mild clinical illness. None of the children had been admitted to an intensive care unit or died. Oseltamivir treatment was initiated in 72 children and discontinued in 42 (63%) when RT-PCR results turned negative.

Conclusion: The 2009 H1N1-pandemic showed a mild clinical course in a Dutch paediatric outpatient clinic population. Respiratory pathogens were detected in the majority of children with influenza-like illness and influenza A(H1N1) virus was identified in one-third. Testing symptomatic children during an influenza pandemic has effectively limited the use of oseltamivir.