Panton-Valentine leukocidin: a marker of severity for Staphylococcus aureus infection?

Until recently, Staphylococcus aureus– associated pulmonary infections have been indistinguishable with respect to the toxin-associated genes in the strains associated with each case. The recent emergence and worldwide spread of community acquired methicillin-resistant S. aureus (CA-MRSA) clones containing the genes encoding Panton-Valentine leuko-cidin (PVL) has led to an increase in the number of pulmonary lung infections associated with PVL-positive CA-MRSA and the recognition of more-specific clinical conditions. The diffusion of CA-MRSA within certain communities is now impressive. In Texas, for example, 76% of infections due to community-acquired S. aureus at Texas Children's Hospital (Houston) are caused by MRSA [1, 2]. In this issue of Clinical Infectious Diseases , Gonzalez et al. [3] compared the clinical characteristics of 92 children with invasive CA-MRSA infection with those of 68 children with invasive community-acquired methicillin-susceptible S. aureus (CA-MSSA) infection. The major difference between the 2 groups was the greater frequency of abnormal pulmonary imaging findings in the CA-MRSA group (67% of patients), compared with the CA-MSSA group (28% of patients) (). P p .00008 Overall, among 47 patients with CA-MRSA infections and abnormal pulmonary imaging findings, the primary diagnoses were pneumonia (21 patients [45%]), osteomyelitis (20 [43%]), deep-seated abscess (5 [11%]), and septic arthritis (1 [2%]). Patients with CA-MRSA and pneumonia were rarely bacteremic, in contrast to patients with osteomyelitis, among whom the frequency of metastatic pulmonary disease was accordingly higher. Cases of pneumonia associated with PVL-positive S. aureus strains have been described by Gillet et al. [4], and other cases have since been reported worldwide [5–11]. The clinical description of the cases reported by Gonzalez et al. [3] differs from the description reported by Gillet et al. [4]. Classic severe necrotizing pneumonia , which presents as a rapid extensive pneumonia evolving towards an acute respiratory distress syndrome with hemop-tysis (or blood secretions) and leukopenia, is reported in the study by Gonzalez and colleagues for only 3 patients. Pulmonary manifestations associated with PVL-positive MRSA clones were much more diverse in the Texas patients and included classic lobar pneumonia, pneumonia with pneu-matoceles, empyema, and septic emboli. No explanation can be given for these differences. The high incidence of CA-MRSA among the patients of Gonzalez and colleagues , in contrast to the low incidence of necrotizing pneumonia, suggests that specific host factors (which might be related to a specific host genotype) are associated with the development of the disease. S. aureus can access the lung …