Staphylococcal Infections

Author: Thomas Herchline, MD, Professor of Medicine, Wright State University Boonshoft School of Medicine; Medical Director, Public Health, Dayton and Montgomery County, Ohio
Contributor Information and Disclosures

Updated: Oct 20, 2010

Background

Staphylococcal infections are usually caused by the organismStaphylococcus aureus. However, the incidence of infections due toStaphylococcus epidermidis and other coagulase-negative staphylococci has been steadily increasing in recent years. This article focuses on S aureus but also discusses infections caused by coagulase-negative staphylococci when important differences exist.

Pathophysiology

S aureus is a gram-positive coccus that is both catalase- and coagulase-positive. Colonies are golden and strongly hemolytic on blood agar. They produce a range of toxins, including alpha-toxin, beta-toxin, gamma-toxin, delta-toxin, exfoliatin, enterotoxins, Panton-Valentine leukocidin (PVL), and toxic shock syndrome toxin–1 (TSST-1). The enterotoxins and TSST-1 are associated with toxic shock syndrome. PVL is associated with necrotic skin¹ and lung infections and has been shown to be a major virulence factor for pneumonia² and osteomyelitis.³ Coagulase-negative staphylococci, particularly S epidermidis, produce an exopolysaccharide (slime) that promotes foreign-body adherence and resistance to phagocytosis.

In a study of 42 Staphylococcus lugdunensis isolates, most isolates were able to form at least a weak biofilm, but the amount of biofilm formed by isolates was heterogeneous with poor correlation between clinical severity of disease and degree of biofilm formation.⁴

Frequency

United States

Up to 80% of people are eventually colonized with S aureus. Most are colonized only intermittently; 20-30% are persistently colonized. Colonization rates in health care workers, persons with diabetes, and patients on dialysisare higher than in the general population. The anterior nares are the predominant site of colonization in adults; carriage here has been associated with the development of bacteremia.⁵ Other potential sites of colonization include the throat,⁶ axilla, rectum, and perineum.

International

S aureus infection occurs worldwide. Pyomyositis due to S aureus is more prevalent in the tropics.

Mortality/Morbidity

Mortality due to staphylococcal infections varies widely. Untreated S aureus bacteremia carries a mortality rate that exceeds 80%. The mortality rate of staphylococcal toxic shock syndrome is 3-5%. Infections due to coagulase-negative staphylococci usually carry a very low mortality rate. Because these infections are commonly associated with prosthetic devices, the most serious complication is the need to remove the involved prosthesis, although prosthetic valve endocarditis may lead to death.

Race

Staphylococcal infections have no reported racial predilection.

Sex

The vaginal carriage rate of staphylococcal species is approximately 10% in premenopausal women. The rate is even higher during menses.

Age

Staphylococcal species colonize many neonates on the skin, perineum, umbilical stump, and GI tract. The staphylococcal colonization rate in adults is approximately 40% at any given time.

The mortality rate of S aureus bacteremia in elderly persons is markedly increased.⁷

Clinical

History

Common manifestations of staphylococcal infections include the following types of infections. The history obtained usually depends on the type of infection the organism causes.

• Skin infections (Many individuals who present with community-acquired skin infections are initially misdiagnosed with spider bites. These infections are often due to methicillin-resistant S aureus [MRSA].)
  • Folliculitis
  • Furuncles
  • Impetigo (bullous)
  • Wound infections
  • Scalded skin syndrome
• Soft-tissue infections (pyomyositis, septic bursitis, septic arthritis)
• Toxic shock syndrome
• Purpura fulminans⁸
• Endocarditis
• Osteomyelitis
• Pneumonia
• Food poisoning
• Infections related to prosthetic devices
  • Commonly associated with coagulase-negative staphylococci
  • Includes prosthetic joints and heart valves and vascular shunts, grafts, and catheters
• Urinary tract infection

Physical

• Skin and soft-tissue infections
  • Erythema
  • Warmth
  • Draining sinus tracts
  • Superficial abscesses
  • Bullous impetigo
• Toxic shock syndrome
  • Fever greater than 38.9°C
  • Diffuse erythroderma - Deep, red, "sunburned" appearance
  • Hypotension
  • Desquamation - Occurs 7-14 days after onset of illness, usually involves palms and soles
• Endocarditis
  • Regurgitant murmur
  • Petechiae or other cutaneous lesions
  • 
    

    

    Embolic lesions in patient with Staphylococcus aureus endocarditis.

  • 
    

    

    Close-up view of embolic lesions in patient with Staphylococcus aureusendocarditis.

  • Fever

Causes

Predisposing factors for staphylococcal infections include the following:

• Neutropenia or neutrophil dysfunction
• Diabetes
• Intravenous drug abuse
• Foreign bodies, including intravascular catheters
• Trauma

Colonization with S aureus is common. Skin-to-skin and skin-to-fomite contact are common routes of acquisition.⁹Isolates can be spread by coughing or sneezing.¹⁰ Evidence has also shown that S aureus can be spread during male homosexual sex.¹¹ Pets can also serve as household reservoirs.^1
2