Children with methicillin-resistant Staphylococcus aureus infections are more likely to show abnormal pulmonary imaging than those with methicillin-susceptible S. aureus infections.
The presence of genes encoding for Panton-Valentine leukocidin (PVL), which is much more common in methicillin-resistant S. aureus (MRSA), may be a factor in MRSA-associated pulmonary complications, said Blanca Gonzalez, M.D., and her colleagues.
The gene has been associated with severe necrotizing pneumonia and osteomyelitis, said Dr. Gonzalez of the Texas Children's Hospital, Houston, and her associates (Clin. Infect. Dis. 2005;41:583–90).
The investigators examined pulmonary complications in 70 pediatric patients with MRSA and 43 with methicillin-susceptible S. aureus (MSSA). Pulmonary complications were much more common in the MRSA group than the MSSA group (67% vs. 28%). Two patients with MRSA died, as did one with MSSA.
Of the 47 MRSA patients with abnormal pulmonary imaging, 21 (45%) received a primary diagnosis of pneumonia. Four of these had bacteremia; 14 had empyema; 3 had uncomplicated pneumonia with bacteremia; and 4 had lung abscess. A total of 20 patients (43%) received a primary diagnosis of osteomyelitis; most (85%) had bacteremia. Imaging showed atelectasis in four; eight had pneumonia (three with effusions); and four had pneumatoceles. Six patients had septic emboli, and the rest had multifocal air space disease or interstitial disease.
Patients with a primary diagnosis of pneumonia were significantly younger than those with other invasive MRSA disease (3.5 years vs. 10 years). Again, patients with MSSA who had a primary diagnosis of pneumonia also were significantly younger than those with other invasive disease (7 months vs. 12 years). Only 10 patients with MSSA had pulmonary complications: 2 had a primary diagnosis of pneumonia and also had loculated empyema, 6 had bone or joint infections, and 2 had endocarditis.
Isolates from 103 children were tested for genes encoding for PVL. All but one of the MRSA isolates was positive for PVL, compared with only 2 (26%) of the MSSA isolates. Among the 80 PVL-positive isolates, 51 came from children with abnormal chest radiographs, compared with 2 of 23 PVL-negative isolates.
In an accompanying editorial, Jerome Etienne, M.D., argued for routine testing for PVL.
“Regardless of the localization of the infection, the presence of PVL appears to be associated with increased severity, ranging from cutaneous infection requiring surgical drainage to severe chronic osteomyelitis and deadly necrotizing pneumonia,” said Dr. Etienne of the National Reference Center of Staphylococcus, Lyon, France. “With the increased prevalence of community-acquired MRSA, which usually contain the genes encoding PVL, it is important that clinical laboratories test for detection of this toxin in routine S. aureus isolates” (Clin. Infect. Dis. 2005;41:591–93).