S. aureus pneumonia rates in children have doubled over past decade

The rate of pneumonia in children caused by infection with Staphylococcus aureus bacteria has doubled over the past decade, according to a paper in the July issue of The Pediatric Infectious Disease Journal. The journal is published by Lippincott Williams & Wilkins, a part of Wolters Kluwer Health.

Led by Dr. Maria A. Carrillo-Marquez of Texas Children's Hospital, Houston, the study finds that most of these infections are caused by methicillin-resistant S. aureus (MRSA) and a particularly aggressive bacterial strain called USA300.

Rising Rate of S. aureus as Cause of Severe Pneumonia in Children
The researchers analyzed 117 children hospitalized with staph pneumonia at Texas Children's Hospital between 2001 and 2009. (The study excluded pneumonia occurring in children on mechanical ventilation.) The median age was under one year; most of the children were previously healthy. Nearly 60 percent required treatment in the intensive care unit, including mechanical ventilation in 30 percent.

Detailed analysis of the causative bacteria found that three-fourths of the infants were infected with MRSA—bacteria that have become resistant to the standard antibiotics used to treat staph infections. Once spread mainly in hospitals and other health care settings, MRSA increasingly occurs as a community-acquired infection. The remaining one-fourth of cases were caused by antibiotic-susceptible S. aureus.

Most of the children were infected with a strain of S. aureus called USA300, which has been linked to more aggressive infection. More than 90 percent of the children with MRSA had an antibiotic-resistant type of USA300. Children infected with USA300 strains were more likely to have complicated pneumonia requiring video-assisted surgery (VATS) for diagnosis and treatment.

In addition to S. aureus bacteria, some of the children were also infected with viruses—most often influenza virus. These children tended to have more severe pneumonia, with higher rates of ICU care and respiratory failure.

The children required an average of three weeks of treatment with antibiotics. At follow-up, more than 80 percent of the children were considered cured or improved. The rest had additional emergency room visits or hospital admissions. One child died, for a mortality rate of 0.85 percent.

The study is the largest of S. aureus pneumonia in children since the emergence of community-acquired MRSA. Rates of infection with MRSA appear higher in children with pneumonia compared to other types of staph infections.

The study also highlights the potential for severe infections caused by USA300, including antibiotic-resistant strains. In some cases, the bacteria were also resistant to clindamycin—a "second-line" antibiotic used to treat MRSA.

The study provides an important update on the "clinical characteristics, admission trends, and molecular epidemiology" of S. aureus pneumonia—at least at Texas Children's Hospital. The findings highlight some key clinical differences in children with pneumonia caused by MRSA or USA300 strains. Dr. Carrillo-Marquez and coauthors call for further studies to determine the best approach to treatment in children with S. aureus pneumonia, particularly when antibiotic-resistant or aggressive strains are present.