Respiratory viruses in hospitalized children with influenza-like illness during the h1n1 2009 pandemic in Sweden [corrected]

Abstract

Background: The swine-origin influenza A(H1N1)pdm09 pandemic of 2009 had a slower spread in Europe than expected. The human rhinovirus (HRV) has been suggested to have delayed the pandemic through viral interference. The importance of co-infections over time during the pandemic and in terms of severity of the disease needs to be assessed.

Objective: The aim of this study was to investigate respiratory viruses and specifically the presence of co-infections with influenza A(H1N1)pdm09 (H1N1) in hospitalized children during the H1N1 pandemic. A secondary aim was to investigate if co-infections were associated with severity of disease.

Methods: A retrospective study was performed on 502 children with influenza-like illness admitted to inpatient care at a pediatric hospital in Stockholm, Sweden during the 6 months spanning the H1N1 pandemic in 2009. Respiratory samples were analyzed for a panel of 16 viruses by real-time polymerase chain reaction.

Results: One or more viruses were detected in 61.6% of the samples. Of these, 85.4% were single infections and 14.6% co-infections (2-4 viruses). The number of co-infections increased throughout the study period. H1N1 was found in 83 (16.5%) children and of these 12 (14.5%) were co-infections. HRV and H1N1 circulated to a large extent at the same time and 6.0% of the H1N1-positive children were also positive for HRV. There was no correlation between co-infections and severity of disease in children with H1N1.

Conclusions: Viral co-infections were relatively common in H1N1 infected hospitalized children and need to be considered when estimating morbidity attributed to H1N1. Population-based longitudinal studies with repeated sampling are needed to improve the understanding of the importance of co-infections and viral interference.

Figure 1. Prevalence over time.

Total number of detected viruses among children with influenza-like illness at Astrid Lindgren Children’s Hospital, Karolinska University Hospital, Stockholm during the influenza A(H1N1)pdm09 pandemic. Included is also the number of PCR-negative children (neg, n = 193) as well as total number of sampled children (n = 502).

Figure 2. Co-infections over time.

Number of children with co-infections over time in (a) all children and (b) H1N1-positive children. H1N1-positive co-infected children divided into co-infection with HRV (H1N1/HRV) and co-infection with other viruses (H1N1/other).

Figure 3. Co-infections and age.

Comparison of number of co-infections according to age between children under 1 year (<1), children 1–6 years (1–6) and children over six years (>6) in (a) all children and (b) H1N1-positive children. H1N1-positive co-infected children divided into co-infection with HRV (H1N1/HRV) and co-infection with other viruses (H1N1/other).