10 and 11 Furthermore, a statistically significant association was found between viral co-detection and need for MV, a finding that, to the authors’ knowledge, was only observed in one previous study in children IN WHICH Torres et al. found viral co-detection with RSV as a predictor of death in a multivariable analysis in children admitted during the first pandemic wave in Argentina.17 Esper et

al. also found worse outcome in a mixed sample of both adults and children using RT-PCR.18 A minority of reports in pediatric patients mention the prevalence of viral co-detection, suggesting that tests for other viruses were not routinely performed in most situations.10, 19, 20, 21 and 22 Although some PS-341 mouse studies with other viruses, such as RSV, did not show worse prognosis when two or more viruses were detected, the authors believe that co-detection of influenza A(H1N1)pdm09 with other viruses could lead to more serious damage to the airways. This might be caused by immune response, since Esper et al. have shown that influenza titers were not altered by co-infection.18 and 23 The limited sensitivity of DFA for most of respiratory viruses is a limitation of the present study, as well as in the study of Torres et al., as tests for other viruses were performed with DFA in both studies; the prevalence of 15.5% observed

in the present study may be underestimated.24 The missing data in 17 patients for this predictor, together with the low sensitivity of DFA for viruses tested and PI3K inhibitor the inability of this PLEKHB2 test to detect other prevalent viruses (such as rRhinovirus) could bias the present results. The finding of 55.3% influenza A(H1N1)pdm09 detection with DFA compared with RT-PCR highlights the low sensitivity of

DFA, although most studies show sensitivities higher than that found in the present study.24 Nevertheless, only two studies in hospitalized pediatric population with influenza A(H1N1)pdm09 during the first pandemic wave in Argentina reported a higher prevalence of viral co-detection (19% and 25%).10 and 17 Another study in outpatients performed in Recife, Brazil, showed 78% of viral co-detection, but the detection of other viruses was performed by multiplex RT-PCR, which could, at least partially, explain the higher prevalence of co-detection.25 It is interesting that both studies with higher prevalence of co-detection than the present study were also performed in South America. It is also important to highlight the characteristics of pediatric deaths in the present patients, shown in Table 4, as they followed a similar pattern of risk factors found using need for MV as outcome. All but one patient had important CD, reinforcing the association between this risk factor with a worse outcome. The single patient who did not present such conditions was only 3 month-old and had co-detection of RSV. No association of early initiation of oseltamivir with lower incidence of respiratory complications was found.