Caroline Helwick

October 30, 2013

NEW ORLEANS — Methicillin-resistant Staphylococcus aureus (MRSA) is responsible for a growing number of acute musculoskeletal infections, according to new research.

"The spectrum of pediatric musculoskeletal S aureus infections is changing," said Eric Sarkissian, BS, a medical student at Drexel University College of Medicine in Philadelphia.

"Over the past decade, pediatric MRSA musculoskeletal infections have increased in frequency and resulted in significantly longer inpatient stays and other adverse outcomes," he noted.

Several small studies have suggested that the virulence and invasiveness of MRSA, compared with methicillin-sensitive S aureus (MSSA) infections, is increasing, Sarkissian said.

"The purpose of this study was to examine a decade of acute community-acquired MRSA and MSSA musculoskeletal infections at our institution with respect to clinical course and complexity of care," he said.

Sarkissian presented the results here at the American Academy of Pediatrics 2013 National Conference and Exhibition.

 
The spectrum of pediatric musculoskeletal S aureus infections is changing.
 

The researchers examined a consecutive series of patients presenting to the Children's Hospital of Philadelphia with culture-positive S aureus osteomyelitis, septic arthritis, or both from 2001 to 2010.

They compared hospital course, laboratory values, and surgical interventions in patients with MRSA or MSSA. To minimize bias caused by nosocomial infections, patients with postoperative and chronic infections were excluded from the analysis.

They identified 148 cases of acute musculoskeletal S aureus — 111 in patients with MSSA and 37 in patients with MRSA. According to the researchers, this is the largest known series of children and adolescents with culture-positive S aureus osteomyelitis, septic arthritis, or both.

Mean age was 9.0 years in the MSSA group and 7.7 years in the MRSA group. Approximately two thirds of each group was male, and three quarters of patients had infections of the lower extremity.

Over the study period, "the proportion of musculoskeletal infections caused by MRSA increased, from 11.8% in 2001 to 34.8% in 2009, which is a 3-fold rise," Sarkissian reported.

The increase was fairly steady. The incidence was 19.2% in 2003, 29.3% in 2005, and 24.4% in 2007.

"As MRSA infections rise, prompt recognition and aggressive treatment are critical to avoiding life-threatening complications and improving patient outcomes," he said.

MRSA patients had more complicated hospital stays than MSSA patients, as demonstrated by the significant difference in adverse outcomes.

Table. Significant Adverse Outcomes for Infections in Children

Outcome MRSA MSSA
Hospitalization, mean duration in days 13 8
Mean C-reactive protein at presentation (mg/L) 15 10
Surgical procedure required (%) 38 15
Infection-related complication (%) 24 6
Admission to intensive care unit (%) 16 3

 

Infection-related complications, which were more common in patients with MRSA, included deep vein thrombosis, septic emboli, septic shock, recurrent infection, and avascular necrosis.

"Our findings support concerns about the increased virulence of MRSA infections," Sarkissian said. "Optimizing patient outcomes will require increased vigilance from healthcare providers, early use of broad-spectrum antibiotics, and aggressive surgical management."

A similar study examined rates of S aureus infection in children residing in California from 1985 to 2009 (Emerg Infect Dis. 2013;19:10-20). The senior investigator of that study, Yvonne Maldonado, MD, from Stanford University School of Medicine in Palo Alto, California, was asked by Medscape Medical News to comment on the findings.

"Based on our data and others, including the current study, most of us recognize that MRSA is probably here to stay," she said.

Dr. Maldonado's team analyzed more than 140,000 records over 25 years. As such, it offered a "20,000-foot view" of trends, but was unable to "dig deep into each record." The study by Sarkissian's team was a more specific look at an inpatient population with osteomyelitis and septic arthritis.

Although these 2 perspectives provide different information, the conclusion is similar, Dr. Maldonado said. "We have seen around the country that MSSA is still prevalent, but MRSA rates have definitely risen; in fact, they have really taken off," she said. This might not reflect more cases, but a greater proportion that are resistant now, Dr. Maldonado added.

She noted that Sarkissian's team looked only at serious infections requiring hospitalization. "I suspect that pediatricians are still regularly treating many children as outpatients."

Dr. Maldonado explained that, "in our study, the percentage of cellulitis was very high, and while we think that MRSA is more likely to be invasive, we also see that the majority of disease is still not invasive. It's important to keep this in mind."

Treatment Implications

The fact that MRSA is accounting for a greater proportion of S aureus infections does have treatment implications, Dr. Maldonado told Medscape Medical News. "What needs to be done is probably already being done, which is no change in current practice for otherwise healthy children."

Many children can be treated topically or with incision and drainage of the abscess, but S aureus, in general, has become more resistant to clindamycin. This varies by region, of course, but in some places, resistance rates have reached 50%.

This means that patients who require hospitalization because of a bone or joint infection or positive blood culture need broad-spectrum coverage until the pathogen and sensitivities are known, Dr. Maldonado emphasized.

"Treatment with vancomycin plus clindamycin is a good start until you get the sensitivities back," she said. "Some people also recommend a third-generation cephalosporin. Although these generally do not provide optimal coverage for S aureus, they might cover other organisms."

She indicated that the rising MRSA trend might be abating, somewhat. "Since 2010, our data show a drop in MRSA. We don't know if that will continue, but we saw hospitalizations peak in 2009 and the trend coming down in 2010," she said. "We don't know what this means yet, but the rates are certainly not going up further, as far as we can tell."

Mr. Sarkissian and Dr. Maldonado have disclosed no relevant financial relationships.

American Academy of Pediatrics (AAP) 2013 National Conference and Exhibition. Presented October 26, 2013.

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