The Persistence of Influenza Infection

Abstract

To the Editor: The report by Pinsky et al. (1) is interesting, but it raises some major questions. The finding of influenza virus in stool is not new (2). Of more interest is their statement regarding the prolonged shedding of influenza virus in the stool (for >2 months) and respiratory secretions (for >1.5 years). How frequently were respiratory samples collected and tested to confirm that the same virus was shed for these periods in these samples? Influenza virus, like most other acute respiratory viruses, typically does not cause long-term latent or persistent infections in humans. The authors need to exclude the possibility of frequent reinfection with contemporary circulating seasonal hemagglutinin 1 (H1) influenza viruses. However, they do not provide any data to this effect. Currently, with the wider availability and more stringent expectations of modern molecular techniques, such data might be obtained by collecting and sequencing several genes (ideally full genomes) from contemporary circulating seasonal H1 viruses and comparing them, phylogenetically, with the virus shed, contemporaneously, from the child, at monthly intervals, for example (if the child tolerates this testing). Even with this testing frequency, several influenza infection episodes may go undetected. Although the child’s virus, if it truly persists, may undergo some minor host-induced mutations, new infections with seasonal H1 viruses will likely demonstrate a greater, sudden sequence variability, which enables them to be relatively easily distinguished from the more minor, gradually accumulated mutations that can be seen in a persisting infection (3). Second, ribavirin is not recommended for treating influenza infection (4,5). Can the authors explain why this child was taking ribavirin for influenza infection, and how often was his condition treated with this drug during the 1.5 years when influenza H1 was shed? Was his treatment regimen eventually changed? Currently, the recommended treatment for influenza is with the neuraminidase inhibitors (oseltamivir, zanamivir), which have a much safer adverse effect profile, and their effectiveness has been shown to be cost-effective (5).