Novel H1N1 Influenza in Hematopoietic Stem Cell Transplantation Recipients: Two Centers’ Experiences

Respiratory virus infections, such as influenza A, cause significant morbidity in hematopoietic stem cell transplantation (HSCT) recipients. The clinical characteristics and impact of infection with the novel H1N1 virus in this patient population is not yet well defined, however. HSCT recipients diagnosed with proven or probable H1N1 during the 2009 pandemic were identified and charts were retrospectively reviewed with analysis of clinical descriptions, risk factors, diagnosis, treatments, and outcomes. Twenty-seven patients from two medical centers were identified. Fever and cough were the most common presenting symptoms. The incidence of influenza lower respiratory tract infection (LRTI) was 52% (14/27). Compared with patients with LRTI, those with influenza upper respiratory tract infection (URTI) were more likely to have a classic influenza-like syndrome. Compared to patients with URTI, those with LRTI were started on antiviral therapy significantly later after symptom onset (3.0 days vs 6.58 days after onset of symptoms; P = .03; 95% confidence interval [CI], 0.29-6.8). Overall influenza-related 30-day mortality was 22% (6/27), and that in patients with LRTI was 43% (6/14). Chronic steroid use (≥20 mg/day of prednisone equivalent) at the time of presentation was associated with LRTI (P = .006) and mortality (P = .003) on univariate analysis. Five cases were hospital-acquired. In this first season of the novel H1N1 pandemic, infection in HSCT often presented as an atypical severe illness with a high incidence of LRTI and high mortality.

Key Words: 2009 Influenza virus, Immunocompromised, Lower respiratory tract infection