From the Guidelines
Staphylococcus aureus is the most common bacterial cause of myositis, accounting for approximately 90% of pathogens causing pyomyositis. This is based on the most recent and highest quality study available, which was published in 2014 by the Infectious Diseases Society of America 1. The study highlights that community-acquired MRSA isolates are also a significant concern in this infection. Other possible etiologic agents include group A streptococci, Streptococcus pneumoniae, and gram-negative enteric bacteria.
Key Points
- Staphylococcus aureus is the primary cause of pyomyositis, a purulent infection of skeletal muscle that often leads to abscess formation 1.
- Community-acquired MRSA isolates are a significant concern in this infection, and empirical therapy with vancomycin is recommended 1.
- Other bacteria, such as group A streptococci and gram-negative enteric bacteria, can also cause myositis, particularly in patients with underlying conditions 1.
- Prompt administration of antibiotics with staphylococcal coverage, combined with surgical drainage of abscesses when present, is crucial for effective treatment 1.
Treatment Considerations
- Vancomycin is recommended for initial empirical therapy due to the prevalence of community-acquired MRSA in the United States 1.
- Other agents active against MRSA, such as linezolid, daptomycin, and ceftaroline, may also be effective, but clinical data are limited 1.
- Cefazolin or antistaphylococcal penicillin is recommended for definitive therapy of pyomyositis caused by MSSA 1.
From the Research
Bacterial Cause of Myositis
- The most common bacterial cause of myositis is Staphylococcus aureus, as reported in several studies 2, 3, 4, 5.
- According to a retrospective study published in 2021, Staphylococcal species accounted for 46% of all infections 2.
- Another study published in 2006 found that S. aureus was the cause of infection in 57.8% of children with pyomyositis or myositis 3.
- A study from 1986 also identified Staphylococcus aureus as the most common causative organism of pyomyositis 4.
- Additionally, a 2007 study noted that pyogenic myositis (pyomyositis) is usually caused by Staphylococcus aureus 5.
Prevalence and Characteristics
- The prevalence of Staphylococcus aureus as a cause of myositis has been increasing, particularly with the emergence of community-acquired methicillin-resistant Staphylococcus aureus (MRSA) 3.
- The mean age of patients with myositis can vary, with one study reporting a mean age of 48 years 2 and another reporting a mean age of 5.5 years in children 3.
- Common symptoms of myositis include muscle pain, subjective fever, and altered mental status 2, 3.