Birgitta Versluijs

101 Good outcome of untreated RSV in pediatric HCT Discussion In this single center study, all HCT-recipients were routinely screened for RSV, while the absence of immunoprophylaxis or antiviral treatment allowed us to study the natural course of disease. The incidence of RSV was low (3%). Although most children acquired RSV pre-HCT, and received subsequent full myeloablative conditioning, none of them developed severe RSV-disease, despite not being treated. To our knowledge this is the first report on untreated RSV-infection early during HCT in children. Reported incidence of RSV in HCT-recipients varies between 1-17%, 8,9 de- pending largely on season, patients’ age and detection methods. Progression to LRTI occurs in 18-55%, 8,10 with risk factors for progression related to age, donor source, use of steroids, immune status and concomitant infections. 1,7,10,11 Our results are in line with these numbers, although LRTI was clinically less severe in our patients. RSV-related mortality of 10-45% has been reported. 8,10-14 Here, our results compare favor- able. Moreover, it is important to realize that in almost all pediatric studies, RSV-positive patients were treated with the antiviral drug ribavirin, 13 with anti-RSV monoclonal an- tibodies (palivizumab) or with non-specific intravenous immunoglobulins, 15 or with a combination. 12 Teusink et al. saw no change in the incidence of RSV-infection, nor in the course of disease in RSV-infected HCT-recipients after cost-saving restriction of the use of prophy- lactic palivizumab in their center, which made them change their preventive strategy. 16 One other study determined natural course of disease in untreated RSV-infection. In an outpatient care unit, 31 adult HCT-patients showed similar favourable course of RSV- infection detected at a median of 7 weeks after HCT, which was explained by some resto- ration of immunity. 17 These two studies underline our conclusions that prophylaxis nor treatment is routinely indicated for RSV in HCT. In healthy infants, there is supporting evidence for an important role of immune medi- ated pathology in RSV-disease. Upregulation of pro-inflammatory cytokines and chemo- kines and recruitment of neutrophils, results in a cascade of inflammation that can inhe- rently exert pathogenic as well as protective effects. 18 There is incomplete understanding of the immune response to RSV in an immune compromised host, and data suggest that morbidity and mortality are not correlated to the degree of immune suppression. 15 The absence of immunity may in fact aid to prevent neutrophil exerted epithelial damage upon RSV-infection. Likewise, we have shown that infection with respiratory viruses early during HCT does not directly progress to LRTI, but that symptoms only occur when there is some immune-recovery, with an important increased risk for allo-immune mediated lung syndromes. 7,19 6