Outcome of influenza infections in outpatients after allogeneic hematopoietic stem cell transplantation

Background. Influenza can cause significant morbidity and mortality in patients after hematopoietic stem cell transplantation (HSCT). The diagnostic methods and antiviral treatment have scarcely been investigated.
Methods. We retrospectively identified influenza-infected patients with upper or lower respiratory tract infection (RTI) diagnosed by culture and polymerase chain reaction (PCR) testing between November 2007 and April 2008. Treatment with oseltamivir 75 mg twice daily and serial nasal swabs were performed at the discretion of the treating physician.
Results. We identified 21 influenza infections in 19 patients: 19 with upper RTI and 2 with lower RTI. At diagnosis, all 21 samples were positive for PCR with a median influenza load of 5.9 log₁₀ copies/mL. Culture was positive in 14 (67%) patients. Influenza A virus was diagnosed in 8 (38%) episodes and influenza B virus in 13 (62%) episodes. Two patients were sequentially infected by influenza A, followed by B after 38 and 47 days, respectively. Eighteen (86%) patients were treated with oseltamivir for 11 days (median, interquartile range [IQR]: 8–14). No progression to lower RTI or mortality occurred. Shedding persisted for 12 days (median, IQR: 8–13). Absolute lymphocyte count at diagnosis correlated inversely with shedding of the virus ( P <0.001).
Conclusions. Oseltamivir is well tolerated and may reduce mortality of influenza virus-infected patients after HSCT. PCR may help to optimize diagnosis and to monitor treatment strategies.