Influenza and rhinovirus viral load and disease severity in upper respiratory tract infections

J Clin Virol. 2017 Jan:86:14-19. doi: 10.1016/j.jcv.2016.11.008. Epub 2016 Nov 22.


Background: 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.

Objectives: 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.

Study design: 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.

Results: Mean viral load (log10 copies/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.

Conclusion: When compared to ambulatory/ER patients, viral load was higher in hospitalized/ICU patients with influenza B, but not influenza A or HRV.

Keywords: Disease severity; Influenza A; Influenza B; RT-qPCR; Rhinovirus; Viral load.

MeSH terms

  • Adolescent
  • Adult
  • Age Factors
  • Aged
  • Aged, 80 and over
  • Child
  • Child, Preschool
  • Coinfection / microbiology
  • Coinfection / pathology
  • Coinfection / virology
  • Common Cold / complications
  • Common Cold / pathology*
  • Common Cold / virology
  • Female
  • Hospitalization
  • Humans
  • Infant
  • Infant, Newborn
  • Influenza, Human / complications
  • Influenza, Human / pathology*
  • Influenza, Human / virology
  • Male
  • Nasopharynx / microbiology
  • Nasopharynx / virology
  • Ontario
  • Orthomyxoviridae / isolation & purification*
  • Pneumococcal Infections / complications
  • Pneumococcal Infections / pathology
  • Real-Time Polymerase Chain Reaction
  • Respiratory Tract Infections / pathology*
  • Respiratory Tract Infections / virology*
  • Rhinovirus / isolation & purification*
  • Sex Factors
  • Streptococcus pneumoniae / isolation & purification
  • Viral Load*
  • Young Adult