title: Pitfalls in interpretation of CT-values of RT-PCR in children with acute respiratory tract infections.
abstract: The relation between viral load and disease severity in childhood acute respiratory tract infections (ARI) is not fully understood.
  
  
  
  To assess the clinical relevance of the relation between viral load, determined by cycle threshold (CT) value of real-time reverse transcription-polymerase chain reaction assays and disease severity in children with single- and multiple viral ARI.
  
  
  
  582 children with ARI were prospectively followed and tested for 15 viruses. Correlations were calculated between CT values and clinical parameters.
  
  
  
  In single viral ARI, statistically significant correlations were found between viral loads of Respiratory Syncytial Virus (RSV) and hospitalization and between viral loads of Human Coronavirus (HCoV) and a disease severity score. In multiple-viral ARI, statistically significant correlations between viral load and clinical parameters were found. In RSV-Rhinovirus (RV) multiple infections, a low viral load of RV was correlated with a high length of hospital stay and a high duration of extra oxygen use. The mean CT value for RV, HCoV and Parainfluenza virus was significantly lower in single- versus multiple infections.
  
  
  
  Although correlations between CT values and clinical parameters in patients with single and multiple viral infection were found, the clinical importance of these findings is limited because individual differences in host-, viral and laboratory factors complicate the interpretation of statistically significant findings. In multiple infections, viral load cannot be used to differentiate between disease causing virus and innocent bystanders.
authors.affiliation: Reinier de Graaf Hospital, Department of Pediatrics, PO Box 5011, 2600GA Delft, The Netherlands. Electronic address: Wishaupt@rdgg.nl.
authors.forename: Jérôme O
authors.initials: JO
authors.lastname: Wishaupt
authors.affiliation: Pieter van Foreest Institute for Education and Research, Medical Center Alkmaar, PO Box 501, 1800AM Alkmaar, The Netherlands.
authors.forename: Tjeerd van der
authors.initials: TV
authors.lastname: Ploeg
authors.affiliation: Reinier Haga Medisch Diagnostisch Centrum, PO Box 5011, 2600GA Delft, The Netherlands.
authors.forename: Leo C
authors.initials: LC
authors.lastname: Smeets
authors.affiliation: Radboud University Medical Center, Laboratory of Pediatric Infectious Diseases, Department of Pediatrics, PO Box 9101, 6500HB Nijmegen, The Netherlands.
authors.forename: Ronald de
authors.initials: R
authors.lastname: Groot
authors.affiliation: Groene Hart Ziekenhuis, Department of Pediatrics, PO Box 1098, 2800BB Gouda, The Netherlands; Ghent University Hospital, Department of Pediatrics, De Pintelaan 185, 9000 Gent, Belgium.
authors.forename: Florens G A
authors.initials: FG
authors.lastname: Versteegh
authors.affiliation: Franciscus Gasthuis en Vlietland, Department of Pediatrics, Postbus 10900, 3004BA Rotterdam, The Netherlands; Erasmus MC, University Medical Center Rotterdam, Department of Pediatric Infectious Diseases and Immunology, PO Box 2040, 3000CA Rotterdam, The Netherlands.
authors.forename: Nico G
authors.initials: NG
authors.lastname: Hartwig
mesh_terms: D002648:Child; D002675:Child, Preschool; D006801:Humans; D011446:Prospective Studies; D060888:Real-Time Polymerase Chain Reaction / Q000379:methods*; D012141:Respiratory Tract Infections / Q000473:pathology* / Q000821:virology*; D020133:Reverse Transcriptase Polymerase Chain Reaction / Q000379:methods*; D012720:Severity of Illness Index; D019562:Viral Load / Q000379:methods*; D014777:Virus Diseases / Q000473:pathology* / Q000821:virology*
keywords: Child; Cycle threshold value; Disease severity; Respiratory infection; Viral load