What is the severity of a Staphylococcus (Staph) aureus infection, particularly in high-risk populations such as the elderly, young children, and individuals with compromised immune systems or chronic medical conditions?

How Dangerous is Staphylococcus aureus Infection?

Staphylococcus aureus infections range from minor skin infections to life-threatening invasive disease with mortality rates of 15-30% for bacteremia, making it the leading cause of death from bloodstream infections worldwide with an estimated 300,000 deaths annually. 1

Mortality and Severity by Infection Type

Bacteremia and Invasive Infections

• S. aureus bacteremia carries a case fatality rate of 15-30%, with prolonged bacteremia (≥48 hours) associated with a 90-day mortality risk of 39%. 1
• S. aureus is the leading cause of death from bacteremia globally, responsible for approximately 300,000 deaths per year. 1
• Metastatic infection occurs in more than one-third of bacteremia cases, including endocarditis (≈12%), septic arthritis (7%), vertebral osteomyelitis (≈4%), and other deep-seated infections. 1

Infective Endocarditis

• In the United States, 34% of native valve endocarditis cases are due to S. aureus, with significantly higher mortality (20%) compared to other organisms (12%). 2
• Patients with S. aureus infective endocarditis experience embolic events in 60% of cases (versus 31% with other organisms) and central nervous system events in 20% (versus 13%). 2
• Prosthetic valve endocarditis with S. aureus treated with medical therapy alone has a mortality rate of 56%, compared to 23% with surgical debridement and valve replacement. 2
• Left-sided native valve endocarditis with S. aureus in injection drug users has a mortality rate of 20-30%, while right-sided disease has mortality <5%. 2

Skin and Soft Tissue Infections

• S. aureus SSTIs in 2019 were associated with an all-cause, age-standardized mortality rate of 0.5 globally. 3
• These infections range from superficial presentations to monomicrobial necrotizing fasciitis with systemic manifestations that can lead to serious complications or death. 3
• Superficial SSTIs may progress to invasive infections such as bacteremia and osteomyelitis. 4

High-Risk Populations with Increased Mortality

Immunocompromised Patients

• Persons with compromised immune systems from immunosuppressive therapies, HIV infection, organ transplantation, or splenectomy have more severe symptoms and higher hospitalization rates. 2
• Case-fatality rates among immunosuppressed persons are higher than the general population, with delays in recognition and treatment contributing to increased mortality. 2

Elderly Patients

• Older age (≥60 years) is a risk factor for severe disease. 2
• The modern higher rates of S. aureus infections reflect an older, less immunocompetent population with underlying degenerative conditions. 2

Pediatric Patients

• Children aged <10 years have the highest case-fatality rate among passively reported cases, despite frequently having asymptomatic or mild infections. 2
• In pediatric empyema cases, S. aureus accounted for 29-63% of cases, particularly evident in the first 6 months of life. 2

Patients with Comorbidities

• Risk factors for severe disease include intravascular devices, implantable cardiac devices, dialysis vascular catheters, recent surgical procedures, injection drug use, diabetes, and previous S. aureus infection. 1
• Hospital-acquired infective endocarditis has a mortality rate twice that of community-acquired disease, largely due to resistant staphylococcal species. 2

Methicillin-Resistant vs. Methicillin-Sensitive S. aureus

• Although mortality rates are lower with methicillin-sensitive S. aureus (MSSA), the rate of embolic events is even higher than with methicillin-resistant S. aureus (MRSA). 2
• MRSA infections are particularly significant because of their potential for unchecked spread within households and propensity for causing serious skin and pulmonary infections. 5
• Community-acquired MRSA is rapidly becoming rampant outside the hospital setting. 5

Complications and Treatment Challenges

Recurrent and Chronic Infections

• S. aureus infections are often chronic and highly recalcitrant to antibiotic treatment due to persister cells that are tolerant to antibiotics. 6
• Recurrence of SSTIs is common after initial successful treatment, and decolonization strategies have not been effective in reducing recurrence. 4

Co-infections

• Deaths attributed to co-infection with influenza and S. aureus, particularly MRSA, have increased, with the reason not fully established but possibly reflecting increasing prevalence of MRSA colonization with certain virulence factors. 2

Common Pitfalls and Clinical Considerations

• Many cases of severe or fatal disease occur in previously healthy children and young adults, not just high-risk populations. 2
• False-negative findings for intracardiac abscess on echocardiography are as high as 60%, even with high-quality 2D and 3D transesophageal imaging. 2
• All patients with S. aureus bacteremia should undergo transthoracic echocardiography, with transesophageal echocardiography for those at high risk for endocarditis. 1
• Source control is critical and may include removal of infected devices, drainage of abscesses, and surgical debridement. 1