Unchanged severity of influenza A(H1N1)pdm09 infection in children during first postpandemic season

Abstract

We conducted a nationwide hospital-based prospective study in Germany of influenza A(H1N1)pdm09 cases among children <15 years of age admitted to pediatric intensive care units and related deaths during the 2009-10 pandemic and the 2010-11 postpandemic influenza seasons. We identified 156 eligible patients: 112 in 2009-10 and 44 in 2010-11. Although a shift to younger patients occurred in 2010-11 (median age 3.2 vs. 5.3 years), infants <1 year of age remained the most affected. Underlying immunosuppression was a risk factor for hospital-acquired infections (p = 0.013), which accounted for 14% of cases. Myocarditis was predictive of death (p = 0.006). Of the 156 case-patients, 17% died; the difference between seasons was not significant (p = 0.473). Our findings stress the challenge of preventing severe postpandemic influenza infection in children and the need to prevent nosocomial transmission of influenza virus, especially in immunosuppressed children.

Figure 1

Overview of study participation and participant groups among severe pediatric cases with A(H1N1)pdm09, Germany, 2009–2011. PCIU, pediatric intensive care unit.

Figure 2

Distribution of 136 critically ill children with confirmed A(H1N1)pdm09, by date of disease onset, September 21, 2009–February 22, 2011, Germany. Only cases with available date of symptom onset are represented.

Figure 3

Proportion of critically ill children with A(H1N1)pdm09 by age group and season, Germany.

Figure 4

Age distribution of the 156 critically ill children with confirmed A(H1N1)pdm09, by season, Germany.