Multiple versus single virus respiratory infections: viral load and clinical disease severity in hospitalized children

BACKGROUND Molecular testing for viral pathogens has resulted in increasing detection of multiple viruses in respiratory secretions of ill children. The clinical impact of multiple virus infections on clinical presentation and outcome is unclear. OBJECTIVES To compare clinical characteristics and viral load between children with multiple virus versus single virus illnesses. PATIENTS/METHODS Eight hundred and ninety-three residual nasal wash samples from children treated for respiratory illness at Children's Hospital, Seattle, from September 2003 to September 2004 were evaluated by quantitative PCR for respiratory syncytial virus (RSV), human metapneumovirus (hMPV), influenza (Flu), parainfluenza, adenoviruses, and coronaviruses (CoV). Illness severity and patient characteristics were abstracted from medical charts. RESULTS Coinfections were identified in 103 (18%) of 566 virus-positive samples. Adenovirus was most commonly detected in coinfections (52%), followed by CoV (50%). Illnesses with a single virus had increased risk of oxygen requirement (P = 0·02), extended hospital stays (P = 0·002), and admissions to the inpatient (P = 0·02) or intensive care units (P = 0·04). For Adv and PIV-1, multiple virus illnesses had a significantly lower viral load (log(10) copies/ml) than single virus illnesses (4·2 versus 5·6, P = 0·007 and 4·2 versus 6·9, P < 0·001, respectively). RSV, Flu-A, PIV-3, and hMPV viral loads were consistently high whether or not another virus was detected. CONCLUSIONS Illnesses with multiple virus detections were correlated with less severe disease. The relationship between viral load and multiple virus infections was virus specific, and this may serve as a way to differentiate viruses in multiple virus infections.