Group A streptococcal infection pathophysiology

Group A streptococcal infection Microchapters
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Pathophysiology

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]

Overview

The group A streptococcus bacterium (Streptococcus pyogenes, or GAS) is a form of Streptococcus bacteria responsible for most cases of streptococcal illness. Other types (B, C, D, and G) may also cause infection.

Pathophysiology & Etiology

Streptococcus pyogenes or group A streptococcus.

These bacteria are spread through direct contact with mucus from the nose or throat of persons who are infected or through contact with infected wounds or sores on the skin. Ill persons, such as those who have strep throat or skin infections, are most likely to spread the infection. Persons who carry the bacteria but have no symptoms are much less contagious. Treating an infected person with an antibiotic for 24 hours or longer generally eliminates their ability to spread the bacteria. However, it is important to complete the entire course of antibiotics as prescribed. It is not likely that household items like plates, cups, or toys spread these bacteria.

Types of infection

Infections are largely categorized by the location of infection:

• bacteremia -- bloodstream
• impetigo, cellulitis, and erysipelas -- skin and underlying tissues
• focal infections -- limited to a particular site. Bacteremia can be associated with these infections, but it is not always present. Treatment depends on the specific clinical findings. Types include:
  • pneumonia -- pulmonary alveolus
  • tonsillitis -- tonsils
  • septic arthritis -- joints
  • osteomyelitis -- bones
  • peritonitis -- peritoneum
  • meningitis -- meninges
• necrotizing fasciitis -- skin, fascia and muscle
• scarlet fever -- upper body
• sinusitis - nose.
• strep throat -- pharynx
• toxic shock syndrome -- multiple systems

(Note that some of these diseases can be caused by other infectious agents as well.)

Severe streptococcal infections

Some strains of group A streptococci (GAS) cause severe infection. Those at greatest risk include children with chickenpox; persons with suppressed immune systems; burn victims; elderly persons with cellulitis, diabetes, blood vessel disease, or cancer; and persons taking steroid treatments or chemotherapy. Intravenous drug users also are at high risk. GAS is an important cause of puerperal fever world-wide, causing serious infection and, if not promptly diagnosed and treated, death in newly delivered mothers. Severe GAS disease may also occur in healthy persons with no known risk factors.

All severe GAS infections may lead to shock, multisystem organ failure, and death. Early recognition and treatment are critical. Diagnostic tests include blood counts and urinalysis as well as cultures of blood or fluid from a wound site. The antibiotic of choice is penicillin, to which GAS is particularly susceptible and has never been found to be resistant. Erythromycin and clindamycin are other treatment options, though resistance to these antibiotics exists.

Why does invasive group A streptococcal disease occur?

Invasive GAS infections occur when the bacteria get past the defenses of the person who is infected. This may occur when a person has sores or other breaks in the skin that allow the bacteria to get into the tissue, or when the person’s ability to fight off the infection is decreased because of chronic illness or an illness that affects the immune system. Also, some virulent strains of GAS are more likely to cause severe disease than others.