ESSENTIALS OF DIAGNOSIS
Abrupt onset of sore throat and fever.
Throat red and edematous, with or without exudate; cervical nodes tender.
Centor criteria may be useful in guiding when a rapid antigen test or throat culture is indicated.
Group A beta-hemolytic streptococci (Streptococcus pyogenes) are the most common bacterial cause of pharyngitis. Transmission occurs by droplets of infected secretions. Group A streptococci producing erythrogenic toxin may cause scarlet fever in susceptible persons.
“Strep throat” is characterized by a sudden onset of fever, sore throat, pain on swallowing, tender cervical adenopathy, malaise, and nausea. The pharynx, soft palate, and tonsils are red and edematous. There may be a purulent exudate. The Centor clinical criteria for the diagnosis of streptococcal pharyngitis are temperature greater than 38°C, tender anterior cervical adenopathy, lack of a cough, and pharyngotonsillar exudate.
The rash of scarlet fever (also called scarletina) is diffusely erythematous and resembles a sunburn, and superimposed fine red papules give the skin a sandpaper consistency; it is most intense in the groin and axillas (eFigure 33–1). It blanches on pressure, may become petechial, and fades in 2–5 days, leaving a fine desquamation. The face is flushed, with circumoral pallor, and the tongue is coated with enlarged red papillae (strawberry tongue).
Scarlet fever. Skin lesions in the form of a blush from scarlet fever. The rash resembles a sunburn and is usually redder in the axillary and groin areas. (Public Health Image Library, CDC).
Leukocytosis with neutrophil predominance is common. Throat culture onto a single blood agar plate has a sensitivity of 80–90%. Rapid diagnostic tests based on detection of streptococcal antigen are slightly less sensitive than culture. Clinical criteria, such as the Centor criteria, are useful for identifying patients in whom a rapid antigen test or throat culture is indicated. Patients who meet two or more of these criteria merit further testing. When three of the four are present, laboratory sensitivity of rapid antigen testing exceeds 90%. When only one criterion is present, streptococcal pharyngitis is unlikely. In high-prevalence settings or if clinical suspicion for streptococcal pharyngitis is high, a negative antigen test or culture should be confirmed by a follow-up culture.
Suppurative complications include sinusitis, otitis media, mastoiditis, peritonsillar abscess, and cervical lymphadenitis.
Nonsuppurative complications are rheumatic fever and glomerulonephritis. Rheumatic fever may follow recurrent episodes of pharyngitis beginning 1–4 weeks after the onset of symptoms. Glomerulonephritis follows a single infection with a nephritogenic strain of streptococcus group A (eg, types 4, 12, 2, 49, and 60), more commonly on the skin than in the ...