Reconciling disparate estimates of viral genetic diversity during human influenza infections

Deep sequencing can measure viral genetic diversity within human influenza infections, but published studies disagree in their estimates of how much genetic diversity is typically present. One large-scale deep-sequencing study of human influenza reported high levels of shared viral genetic diversity among infected individuals in Hong Kong, but subsequent studies of other cohorts have reported little shared viral diversity. We re-analyze sequencing data from four studies of within-host genetic diversity encompassing more than 500 acute human influenza infections. We identify an anomaly in the Hong Kong data that provides a technical explanation for these discrepancies: read pairs from this study are often split between different biological samples, indicating that some reads are incorrectly assigned. These technical abnormalities explain the high levels of within-host variation and loose transmission bottlenecks reported by this study. Studies without these anomalies consistently report low levels of genetic diversity in acute human influenza infections.