Pandemic (H1N1) 2009 influenza in Canadian pediatric cancer and hematopoietic stem cell transplant patients

Background The impact of pandemic H1N1 influenza (pH1N1) virus in pediatric cancer is uncertain. The objectives of this study were to characterize the clinical course of pH1N1 and identify factors associated with severe outcomes. Methods We conducted a Canadian multicenter retrospective review of children with cancer and stem cell transplant (SCT) recipients who were diagnosed with laboratory-confirmed pH1N1 infection between May 1, 2009 and January 31, 2010. Results We identified 100 (19 in wave 1 and 81 in wave 2) cases of pH1N1 infection. Median age was 8.7 years. 71% had a hematologic malignancy, and 20% received SCT. Median duration of fever and illness was 2 and 12.5 days, respectively. 51 (51.5%) were hospitalized for a median of 5 days, with no deaths and only 1 requiring admission to the intensive care unit. Radiologically confirmed pneumonia was diagnosed in 10 (10%). Interruption of chemotherapy or conditioning occurred in 43 patients. In multivariable analyses, age <5 years (relative to =10 years) and neutropenia were associated with hospitalization while neutropenia was associated with pneumonia. Despite oseltamivir use in 89%, viral shedding was prolonged (median, 46 days) and often persisted after symptom resolution. However, an extended treatment course (>5 days) correlated with shortened duration of viral shedding (P = 0.041). Conclusions pH1N1 infection in pediatric cancer and SCT patients infrequently caused complications but commonly interrupted cancer treatment. Persistent shedding of virus after illness resolution was common. Further research is needed to verify this finding as it could have implications for treatment guidelines and infection control practices.