Antibiotic Resistant Bacteria

What is the problem and what is known about it so far?
Staphlococcus aureus (SA) is a class of bacteria that causes serious infections in the skin (boils) and sometimes in other places such as blood, bone and heart valves. Initially, most strains of SA were successfully treated with a number of antibiotics the most effective being methicillin. These strains were referred to as methicillin sensitive or MSSA. However, over the past 40 years many strains of SA have become resistant to methicillin and so are labeled methicillin resistant or MRSA. MRSA infections have mostly been found in hospitalized patients. Recently a new strain of MRSA, called community acquired methicillin resistant Staphylococcus aureus (CA-MRSA) has become a growing problem across the country in both the adult and child populations. Patients with CA-MRSA infections have no traditional risk factors for MRSA and are usually healthy individuals from the community.

Why did the researchers do this particular study?
The researchers wanted to determine if there had been an increase in the number of children admitted to their large hospital with CA-MRSA infections, and to compare the severity of illness from CA-MRSA infections to that from the methicillin sensitive strain (MSSA).

Who was studied?
239 children admitted to Memorial Hermann Children’s Hospital in Houston Texas from July 2000 to December 2003 who had a positive culture for S. aureus within 72 hours of admission.

How was the study done?
A retrospective chart review was completed on all patients aged 0-14 years who were admitted to the hospital. Patients were included in the study if they had a laboratory report of SA. Patients with any other chronic illnesses were not included in the study because they were more likely to have increased hospital visits. The remaining 239 patients were separated into those with MRSA infection and those with MSSA infection. These 2 groups were then compared to determine duration of bacteremia, types and severity of infections, number requiring surgical intervention, number of hospital days, and number of patients requiring intensive care.

What did the researchers find?
The researchers found that during the study period 67% of all SA infections could be attributed to CA-MRSA and that in each year CA-MRSA accounted for a higher percentage of identified SA infections. Patients who had CA-MRSA infection were significantly younger and more likely to be African American than those infected with MSSA. Patients with CA-MRSA also tended to have a longer duration of bacteremia and require many more surgical interventions. Abscesses and complicated pneumonias were seen much more frequently in patients with CA-MRSA. CA-MRSA strains were more likely to be resistant to erythromycin and fluoroquinolone antibiotics, but not clindamycin (5% in both groups).

What were the limitations of the study?
The patient population was drawn from a hospital in a large city, so these results may not apply to rural areas.

What are the implications of the study?
This study demonstrates that not only are CA-MRSA infections increasingly common but that the majority of SA infections in this community are due to CA-MRSA strains. Infections caused by CA-MRSA appear to be more severe and cause more severe complications. Standard therapy for presumed SA infection may no longer be adequate and physicians need to re-assess which antibiotics to begin in patients with suspected S. aureus infection.

Summarized by Scot Millay, College of Medicine, University of Vermont
from "Community associated Methicillin-resistant Staphylococcus aureus in Pediatric Patients." Ochoa, Theresa J et al. Emerging Infectious Disease. June 2005, Volume 11, Number 6, pages 966-968.