Study Shows Antibiotic-Resistant Bacteria Responsible for Increase in Muscle Infections

Researchers in Houston, Texas have found two bacterial muscle infections common in tropical countries becoming more frequent occurrences along with the emergence of community-acquired methicillin-resistant Staphylococcus aureus (CA-MRSA), according to a study published in the Oct. 15 issue of Clinical Infectious Diseases, now available online.

Staphylococcus aureus, or staph, is a common bacterium found on the skin or in the nose of a quarter to a third of all people. Usually harmless, staph can cause skin infections such as pimples and boils and, less frequently, serious infections of surgical wounds or the bloodstream, and pneumonia. For years, infections caused by Staphylococcus aureus have been treated by inexpensive antibiotics in the penicillin and cephalosporin family.

Some years ago, strains resistant to these drugs, called methicillin-resistant Staphylococcus aureus (MRSA) appeared in hospitalized patients. Recently, however, newer forms of MRSA began to strike healthy people who have not been recently hospitalized or undergone invasive medical procedures. These community-acquired strains appear to be readily transmitted from person to person and can cause serious skin and soft tissue infections as well as invasive infections such as bone or joint infections or pneumonia. Failure by physicians to suspect this kind of drug-resistant staph can lead to treatment with the wrong antibiotic.

Pyomyositis is an acute bacterial infection of skeletal muscle that produces an abscess within the muscle. Myositis is also a muscle infection, but does not form an abscess. The study authors investigated the 45 cases of pyomyositis or myositis in otherwise healthy children who were hospitalized at Texas Children's Hospital from 2000 through 2005. Sixteen of these cases were caused by CA-MRSA and 10 by CA-MSSA (methicillin-susceptible Staphylococcus aureus).

The number of cases increased year by year, from four cases in the first year of the study to a high of 12 cases in the fifth year of the study. The authors also discovered that a specific strain of Staphylococcus aureus known as USA300 was associated with more severe disease. Similarly, staph that carried a group of genes known as PVL were also linked to a more severe illness.

"We're seeing an increasing number of muscle infections that is clearly associated with an increase in MRSA," said lead author Pia Pannaraj, MD. "Physicians need to be aware that this is a possibility and consider initial treatment with an antibiotic that covers MRSA, particularly if they live in a region where methicillin resistance is present."

Source: Infectious Diseases Society of America (IDSA)