Distinct differences in clinical manifestation and viral laboratory parameters between children and adults with influenza A(H1N1)pdm09 infection--a retrospective comparative analysis.

During the influenza pandemic 2009 children and adults differed in the clinical course of the influenza disease. In following the question arose, if the case definitions used within the national and international organizations are an adequate tool for the clinical diagnosis of influenza in children as well as in adults. Therefore medical charts from 146 children and 229 adults were retrospectively analyzed. In addition, the initial viral loads of all 375 patients and the duration of virus shedding of a subset of 79 patients were also investigated. Children show a wider clinical spectrum including gastro enteric symptoms and also a different spectrum of laboratory parameters like elevated CRP-levels, leucocytosis, and higher viral loads. Further, children show significantly more often complications, for example, myositis that may be underdiagnosed. In patients receiving antiviral-therapy complications occurred significantly less often and the presence of symptoms was significantly shorter compared to the untreated group (2.3 days vs. 6.0 days). In summary, the differences in the clinical picture between children and adults should be taken into consideration for the clinical diagnosis of influenza and also for a future discussion on age specific influenza case definitions.