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

Abstract 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 (log 10 copies/ml) of influenza A/H3N2 (6.94) was higher than influenza B (4.96) and HRV (5.58) (p  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.