Streptococcal Pharyngitis (‘Strep throat’)
Streptococci are a genus of gram-positive, spherical bacteria that appear in chains. There are over 30 recognized species within this genus. Streptococci cause an array of diseases in humans including pharyngitis, scarlet fever, impetigo, rheumatic fever, pneumonia, meningitis, otitis media, sinusitis, endometritis, and septicemia.
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 Streptococci (GAS) contain one species, Streptococcus pyogenes. Group B Streptococci contain one species, Streptococcus agalactiae. Groups C, D and G each contain several species.
Streptococcus pyogenes accounts for more than 90% of the disease caused by streptococci and are the most common cause of bacterial pharyngitis. Streptococcal disease is classified as either suppurative (primary infections) or nonsuppurative (complications from primary streptococcal infection). A common characteristic of suppurative diseases is the formation of pus. Suppurative diseases include pharyngitis (commonly referred to as "strep throat"), puerperal fever, impetigo, cellulites and erysipelas. Nonsuppurative diseases include scarlet fever, rheumatic fever, acute glomerulonephritis and erythema nodosum.
Streptococcal pharyngitis, or "strep throat," is a common bacterial infection found in childhood. Group A Streptococci (GAS) are responsible for the most streptococcal pharyngitis 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 between the ages of 5 to 15 years of age. Strep throat has an incubation period of 2-4 days. Classic symptoms include the abrupt onset of sore throat accompanied by fever, malaise and headache. Children 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 and rhinorrhea and cervical lymphadenopathy and pharyngeal exudates are usually absent in viral pharyngitis. The common cold, influenza, adenovirus and mononucleosis may also present with signs and symptoms pharyngitis.
Strep throat is spread by direct person-to-person contact via nasal and salivary secretions. Crowding is a significant risk factor that increases the likelihood of disease spread.
The diagnosis of strep throat is suspected based on symptoms and physical findings and confirmation is based on throat culture. Prompt and accurate treatment is paramount in order to prevent the occurrence of nonsuppurative disease such as acute rheumatic fever and post streptococcal acute glomerulonephritis that can occur following the acute infection. Culture results may take 2-3 days so physicians must either treat patients presumptively while awaiting culture results or, alternatively, withhold antibiotic therapy until the presence of Streptococcus pyogenes is confirmed with culture. PCR tests that detect GAS DNA have recently become available and may play a role in rapid antigen tests using throat swabs are highly specific for GAS and can confirm the diagnosis while the patient is in the doctor’s office.
Antibiotic treatment for Strep throat is recommended when children have the signs and symptoms consistent with Streptococcal pharyngitis and have a positive throat culture or rapid antigen test. Treatment can reduce the duration of symptoms and the likelihood of complications such as retropharyngeal abscess, but the primary purpose of treatment is to prevent rheumatic fever. Asymptomatic patients should not be tested and if they are tested, they should not be treated even if they test positive.
Shulman et al Clinical Infectious Diseases 2012, 55:86-102
Kits & Components
Dipstick immunoassay for the rapid qualitative detection of Group A Streptococcal antigen from throat swab specimens.
The QuickVue In-Line Strep A Test uses a unique in-line extraction to detect group A streptococcal antigen directly from patient throat swab specimens.
The QuickVue+ Strep A Test detects group A streptococcal antigen directly from throat swabs and beta-hemolytic colonies on blood agar plates.
The Sofia Strep A Fluorescent Immunoassay (FIA) uses advanced immunofluorescence-based lateral-flow technology to detect Group A Streptococcal antigens from...
The Sofia Strep A+ Fluorescent Immunoassay (FIA) uses advanced immunofluorescence-based lateral-flow technology to detect Group A Streptococcal antigens...
Quidel also offers these other Strep-related products:
The AmpliVue GAS Assay utilizes helicase-dependent amplification (HDA) of the DNase B (sdaB) sequence and a self-contained disposable amplification detection device that allows for manual evaluation of assay results.
The Solana GAS Assay is a rapid in vitro diagnostic test for the qualitative detection of Group A β-hemolytic Streptococcus (Streptococcus pyogenes) nucleic acids isolated from throat swab specimens obtained from patients with signs and symptoms of pharyngitis, such as sore throat.