Human Metapneumovirus or Influenza A Upper Respiratory Tract Infection Associated with Increased Risk of Bacterial Superinfection in Allogeneic Hematopoietic Cell Transplant Recipients

Introduction Bacterial superinfection following moderate to severe respiratory viral infections (RVIs), especially influenza (Flu), is well described in immunocompetent hosts. The clinical impact of preceding RVIs on the development of bacterial superinfection in hematopoietic cell transplant (HCT) recipients may be significant although data are limited. Furthermore, the impact of upper respiratory tract infection (URTI) on this outcome has not been systematically evaluated. Objectives To investigate whether URTI due to specific respiratory viruses was associated with increased risk of developing bacteremia or bacterial pneumonia post-HCT. Methods In a longitudinal surveillance study of RVIs among allogeneic HCT recipients conducted from 2005-10, weekly post-HCT nasal washes were collected through day 100. Nasal and bronchoalveolar lavage samples were tested by multiplex PCR for respiratory syncytial virus, parainfluenza viruses (PIV)1–4, Flu A/B, human metapneumovirus (HMPV), adenovirus, rhinoviruses and coronaviruses. URTI was defined as having respiratory virus detected from nasal samples with respiratory symptoms. Bacteremia and bacterial pneumonia were defined as growth of significant bacteria (e.g., Coagulase-negative staphylococci was defined as insignificant bacteria) from blood and lower respiratory tract samples including bronchoalveolar lavage, respectively. Separate Cox proportional hazards models were used to examine associations between first URTI for individual viruses and the subsequent development of first bacteremia and/or bacterial pneumonia by 100 days post-HCT. Results We identified 471 HCT recipients (median age: 51 years, range 8 months-75 years). Number of patients for each first outcome event by 100 days post-HCT included the following: Gram-positive bacteremia (n=64), Gram-negative bacteremia (n=53), Gram-positive pneumonia (n=46), Gram-negative pneumonia (n=8), and either bacteremia or pneumonia (n=152). After adjusting for pre-transplant factors only and pre- and post-transplant factors, significant URTI variables for outcomes in both models were (1) Flu A for gram-positive bacteremia, (2) HMPV for gram-positive pneumonia, and (3) HMPV for bacteremia or bacterial pneumonia (Figure). The association between PIV URTI and development of bacteremia or pneumonia approached statistical significance. Conclusion In HCT recipients, URTIs due to Flu A and HMPV are significant risk factors for the development of gram-positive bacteremia and pneumonia, respectively. Further studies are needed to assess whether prevention or early diagnostic and treatment strategies for RVIs can reduce the risk of bacterial infection.