A postinfluenza model of Staphylococcus aureus pneumonia

Infections caused by community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA) strains have spread throughout the United States [1, 2]. Although most of these infections involve the skin and soft tissues, the less frequent systemic ones, including sepsis, necrotizing fasciitis, osteomyelitis, and pneumonia, are often characterized by fulminant onset, rapid progression, and, in a subset of patients, a fatal outcome [3]. In the United States many of these infections have been due to the CA-MRSA strains USA300 or USA400. Among the invasive infections, necrotizing S. aureus pneumonia has emerged as one of the most lethal [4, 5]. Many of these pneumonias have been preceded by an influenza virus infection [6, 7]. This association of necrotizing bacterial pneumonia with antecedent influenza virus infection is well recognized. Recent studies have noted the importance of bacterial infections due to Streptococcus pneumoniae, Haemophilus influenzae, and S. aureus in the fatal cases associated with the 1918 influenza pandemic [8-10]. The increased influenza-associated mortality from coinfections with S. aureus among the pediatric age group resulted in a 2008 health advisory for the Centers for Disease Control and Prevention (CDCHAN-00268-2008-01-30-ADV-N) [11]. Although the association of influenza virus with S. pneumoniae respiratory infections has been investigated, few studies have investigated the association of influenza virus with S. aureus infections [12-14]. We have developed a murine model of postinfluenza S. aureus pneumonia to examine the factors associated with this life-threatening infection.