Bethesda, Md. — Invasive infections in children caused by community-acquired methicillin-resistant Staphylococcus aureus are on the rise.
Rates of severe infection have been rising as MRSA has become more common in the community. Recommendations from the American Academy of Pediatrics state that in areas where MRSA accounts for 10% or more of CA-MRSA isolates, initial empiric therapy of severe infections that could be due to S. aureus should include vancomycin. Naficillin should also be included because it’s superior to vancomycin for treating methicillin-sensitive S. aureus (MSSA).
Use of clindamycin should be based on local susceptibility. “You need to know the clindamycin susceptibility of CA-MRSA isolates in your area,” said Dr. Kaplan, head of the pediatric infectious disease section at Baylor College of Medicine and chief of the infectious disease service at Texas Children’s Hospital, both in Houston.
At Le Bonheur Children’s Medical Center in Memphis, the rate of acute osteoarticular infections increased from 2.6 to 6.0 per 1,000 admissions between 2000 and 2004. While the proportion of those infections caused by MSSA remained constant at 10%-13%, those caused by MRSA rose from 4% to 40%. Moreover, 71% of the patients with MRSA had subperiosteal abscesses, compared with 38% of those with MSSA, and surgical procedures were required in 91% with MRSA versus 62% with MSSA (J. Pediatr. Orthop. 2006;26:701-2). Similar findings have been reported elsewhere, Dr. Kaplan noted.
Recent studies have shown that osteomyelitis caused by PVL-positive S. aureus strains was associated with more severe local disease and a greater systemic inflammatory response, compared with osteomyelitis caused by S. aureus not containing that gene (Pediatrics 2006;117:433-40), and that PVL-positive isolates were associated with an increased likelihood of complications in children with osteomyelitis (Pediatr. Infect. Dis. J. 2005;24:284-5).
MRI appears to be the optimal method for detection of osteomyelitis resulting from community-acquired S. aureus.
In a retrospective study by Dr. Kaplan and his associates of 199 such children seen between August 2001 and December 2006, MRI had a sensitivity of 98% for diagnosing the infection, compared with a 53% sensitivity with bone scintigraphy. Of 36 patients who had both imaging studies done, results were discordant in 17 cases. In all of those, the MRI diagnosis proved to be the correct one (Pediatr. Radiol. 2008;38:841-7).
The study also showed that MRI – but not bone scan – allowed for visualization of extraosseous complications, including subperiosteal abscesses in 77 patients, pyomyositis in 43, septic arthritis in 31, and deep vein thrombosis in 12. “Clearly, MRI was superior to bone scan in detecting bone infection. In our institution, MRI is the first thing we use. It can help pick up other areas of concern,” Dr. Kaplan noted.
Some of these extraosseous complications also appear to be on the rise. At least two recent reports have documented cases of venous thrombophlebitis among children with invasive S. aureus infections. At Children’s Medical Center in Dallas, 10 of 35 children with confirmed osteomyelitis developed deep vein thrombosis during the acute infection, with evidence of dissemination in six (J. Pediatr. 2006;149:537-41).
And at Texas Children’s, Dr. Kaplan and his associates reported on 9 children seen between 1999 and 2004 who had venous thrombosis adjacent to the site of staphylococcal osteomyelitis. Seven patients had community-acquired infections caused by MRSA belonging to the same USA300 clonal group, and all 7 carried PVL genes. The USA300 clone may “have a unique propensity to cause [venous thrombosis] in association with osteomyelitis,” they concluded (Pediatrics 2006;117:1673-9).
Since then, they’ve seen about 40-50 children with osteomyelitis who developed thrombosis, despite not having genetic prothrombotic conditions. “We don’t understand what’s going on. There’s clearly something different about these community isolates, especially the USA300 strain,” Dr. Kaplan commented.
The USA300 MRSA genotype has also been implicated in septic arthritis. Among 44 isolates taken from 45 patients at Texas Children’s with septic arthritis caused by S. aureus, 16 were MRSA; of these, 13 were USA300 and 14 were PVL-positive. Infections caused by USA300 were more likely to be associated with a longer duration of fever, bacteremia, and a C-reactive protein level of 10 mg/dL or greater (Pediatr. Infect. Dis. J. 2009;28:1076-80).