title: Influenza and rhinovirus viral load and disease severity in upper respiratory tract infections.
abstract: The role of viral load in respiratory viral infection is unclear. It is proposed that the viral load of some, but not all respiratory viruses correlate with disease severity.
  
  
  
  We aimed to determine if an association exists between viral loads among patients in ambulatory settings, compared to those requiring hospitalization/intensive care unit (ICU) admission with influenza A/H3N2, influenza B, or human rhinovirus (HRV); we also explored the impact of age, gender and co-detection of Streptococcus pneumoniae on patient setting. We hypothesized that hospitalized/ICU patients have higher respiratory virus viral loads compared to ambulatory (e.g. walk-in clinics, family practices)/ER patients.
  
  
  
  We quantified viral load by in-house real-time RT-PCR in 774 nasopharyngeal swabs with influenza A/H3N2, or B or HRV viruses from various patient settings in Ontario, Canada.
  
  
  
  Mean viral load (log10copies/ml) of influenza A/H3N2 (6.94) was higher than influenza B (4.96) and HRV (5.58) (p<0.0001). Influenza A/H3N2 viral loads were highest in infants and the elderly; however, increased A/H3N2 viral loads were not associated with hospitalization/ICU admission compared to swabs collected in ambulatory/ER settings. Influenza B viral loads were higher in patients in hospital/ICU settings compared to those in ambulatory settings (OR 1.28, 95% CI 1.11-1.47). HRV viral loads did not differ by age (p=0.67) or setting (p=0.54); there was no association between S. pneumoniae colonization and setting for any virus.
  
  
  
  When compared to ambulatory/ER patients, viral load was higher in hospitalized/ICU patients with influenza B, but not influenza A or HRV.
authors.affiliation: Public Health Ontario, Toronto, ON, Canada; Department of Laboratory Medicine and Pathobiology, University of Toronto, Toronto, ON, Canada. Electronic address: Andrea.granados@mail.utoronto.ca.
authors.forename: Andrea
authors.initials: A
authors.lastname: Granados
authors.affiliation: Public Health Ontario, Toronto, ON, Canada.
authors.forename: Adriana
authors.initials: A
authors.lastname: Peci
authors.affiliation: Department of Laboratory Medicine and Pathobiology, University of Toronto, Toronto, ON, Canada; Mount Sinai Hospital, Toronto, ON, Canada; Department of Medicine, University of Toronto, Toronto, ON, Canada.
authors.forename: Allison
authors.initials: A
authors.lastname: McGeer
authors.affiliation: Public Health Ontario, Toronto, ON, Canada; Department of Laboratory Medicine and Pathobiology, University of Toronto, Toronto, ON, Canada; The Hospital for Sick Children, Toronto, ON, Canada.
authors.forename: Jonathan B
authors.initials: JB
authors.lastname: Gubbay
mesh_terms: D000293:Adolescent; D000328:Adult; D000367:Age Factors; D000368:Aged; D000369:Aged, 80 and over; D002648:Child; D002675:Child, Preschool; D060085:Coinfection / Q000382:microbiology / Q000473:pathology / Q000821:virology; D003139:Common Cold / Q000150:complications / Q000473:pathology* / Q000821:virology; D005260:Female; D006760:Hospitalization; D006801:Humans; D007223:Infant; D007231:Infant, Newborn; D007251:Influenza, Human / Q000150:complications / Q000473:pathology* / Q000821:virology; D008297:Male; D009305:Nasopharynx / Q000382:microbiology / Q000821:virology; D009864:Ontario; D009975:Orthomyxoviridae / Q000302:isolation & purification*; D011008:Pneumococcal Infections / Q000150:complications / Q000473:pathology; D060888:Real-Time Polymerase Chain Reaction; D012141:Respiratory Tract Infections / Q000473:pathology* / Q000821:virology*; D012229:Rhinovirus / Q000302:isolation & purification*; D012737:Sex Factors; D013296:Streptococcus pneumoniae / Q000302:isolation & purification; D019562:Viral Load; D055815:Young Adult
keywords: Disease severity; Influenza A; Influenza B; RT-qPCR; Rhinovirus; Viral load