Streptococcus is a genus of gram-positive, spherical bacteria that typically appear in chains. More than 50 recognized species are within this genus; however, only five cause human disease. Streptococci are subdivided into five main pathogenic groups commonly found in humans (A, B, C, D, and G). This subdivision is based on the antigenic differences of the carbohydrates in the bacterial cell wall. Group A Streptococcus (GAS) encompasses one species, Streptococcus pyogenes. Group B Streptococcus also encompasses one species, Streptococcus agalactiae. Groups C, D, and G each encompass several species.
Streptococcus pyogenes accounts for more than 90 percent of the diseases caused by streptococci and is the most common cause of bacterial pharyngitis. Streptococcal diseases are classified as either suppurative (i.e., primary infections) or nonsuppurative (i.e., complications that arise from primary streptococcal infections). The formation of pus is a common characteristic of suppurative diseases caused by Streptococcus pyogenes infection.
Suppurative diseases include:
- Streptococcal pharyngitis (strep throat)
- Puerperal fever
- Impetigo
- Cellulitis
- Erysipelas
Nonsuppurative diseases include:
- Scarlet fever
- Rheumatic fevers
- Acute glomerulonephritis
- Erythema nodosum
Streptococcal pharyngitis (strep throat) is a common childhood bacterial infection. Group A Streptococcus (GAS) is responsible for most cases, although other groups, such as C and G, may also cause disease. Strep throat affects all age groups but is most common in children ages 5 to 15 years. Strep throat has an incubation period of two to four days. Symptoms include:
- Abrupt onset of sore throat accompanied by fever
- Malaise
- Headache
People with strep throat may experience additional symptoms such as nausea, vomiting, and abdominal pain. Physical findings often reveal pharyngeal erythema, enlarged tonsils with exudate, and tender cervical lymphadenopathy.
Viral pharyngitis may mimic streptococcal pharyngitis, but unlike strep throat, viral pharyngitis will often be accompanied by cough, rhinorrhea, cervical lymphadenopathy, and pharyngeal exudates. The common cold, influenza, adenovirus, and mononucleosis infections may also present with signs and symptoms of pharyngitis.
