Staphylococcus aureus α-Toxin Response Distinguishes Respiratory Virus-Methicillin-Resistant S. aureus Coinfection in Children.

<bold>Background: </bold> Development of methicillin-resistant Staphylococcus aureus (MRSA) pneumonia after a respiratory viral infection is frequently fatal in children. In mice, S. aureus α-toxin directly injures pneumocytes and increases mortality, whereas α-toxin blockade mitigates disease. The role of α-toxin in pediatric staphylococcal-viral coinfection is unclear.<bold>Methods: </bold> We enrolled children across 34 North American pediatric intensive care units with acute respiratory failure and suspected influenza virus infection. Serial serum anti-α-toxin antibody titers and functional α-toxin neutralization capacity were compared across children coinfected with MRSA or methicillin-susceptible S. aureus (MSSA) and control children infected with influenza virus only. MRSA isolates were tested for α-toxin production and lethality in a murine pneumonia model.<bold>Results: </bold> Influenza virus was identified in 22 of 25 children with MRSA coinfection (9 died) and 22 patients with MSSA coinfection (all survived). Initial α-toxin-specific antibody titers were similar, compared with those in the 13 controls. In patients with serial samples, only MRSA-coinfected patients showed time-dependent increases in anti-α-toxin titer and functional neutralization capacity. MRSA α-toxin production from patient isolates correlated with initial serologic titers and with mortality in murine pneumonia.<bold>Conclusions: </bold> These data implicate α-toxin as a relevant antigen in severe pediatric MRSA pneumonia associated with respiratory viral infection, supporting a potential role for toxin-neutralizing therapy. [ABSTRACT FROM AUTHOR]