Approach Considerations
Rapid testing and throat culture
A throat culture remains the standard for diagnosis, though results can take as long as 48 hours. [8] Throat culture results are highly sensitive and specific for group A beta-hemolytic streptococci (GABHS), but results can vary according to technique, sampling, and culture media.
Most institutions and clinics have rapid testing, which is useful when immediate therapy is desired. Rapid testing can be highly reliable when used in conjunction with throat cultures. Several rapid diagnostic tests are available. Compared with throat culture, such tests are 70-90% sensitive and 95-100% specific.
Rapid screening followed by culture has become the standard in most institutions, especially in developed countries. In repeated investigations, rapid screening with throat culture backup for rapid screen–negative cases has continued to be the most proven strategy. This approach potentially minimizes unnecessary antibiotic administration by helping limit antibiotic use to cases with positive rapid screen findings or those with subsequent positive culture findings. [9]
This approach arises out of the somewhat low sensitivity and specificity of clinical screening. Although the categorization of clinical differentiators developed by the Infectious Diseases Society of America (IDSA) can assist in clinical management (see Presentation), rapid screening followed by culture remains the best combination when resources are available.
The IDSA added that testing for group A streptococcus usually is not recommended for the following: patients with sore throat and accompanying symptoms (eg, cough, rhinorrhea) that strongly suggest a viral etiology; children aged < 3 years, because acute rheumatic fever is extremely rare in this age group; and asymptomatic household contacts of patients with group A streptococcus pharyngitis. [10, 11, 12]
Testing for viral causes
If Epstein-Barr virus (EBV) is considered, obtain a complete blood count (CBC) to detect atypical cells in the white blood cell (WBC) differential, along with a Monospot test (or another rapid heterophile antibody test). EBV can also produce a subclinical hepatitis with a slightly elevation in aminotransferases.
Monospot findings are often negative in children younger than 6 years with EBV infections and in the first week of symptoms. In adolescents, Monospot testing detects approximately 90% of positive cases ultimately diagnosed with EBV-specific serologies.
Other viral pathogens usually do not call for further diagnostic testing, but viral cultures can be obtained. Viruses can be cultured in special media.
During viral outbreaks (eg, H1N1 influenza), if associated symptoms of the outbreak virus may initially include sore throat, one may opt to screen for streptococcal infection immediately or may elect to screen later, if symptoms persist, in order to rule out Streptococcus as the primary cause of the fever and sore throat.
Radiography
Imaging studies are usually not necessary unless a retropharyngeal, parapharyngeal, or peritonsillar abscess is suspected. In such cases, a plain lateral neck film can be used as an initial screening tool.
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Posterior pharynx with petechiae and exudates in a 12-year-old girl. Both the rapid antigen detection test and throat culture were positive for group A beta-hemolytic streptococci.
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Streptococcal pharyngitis. Note the redness and edema of the oropharynx and petechiae, or small red spots, on the soft palate caused by strep throat. Strep throat is caused by group A streptococcus bacteria. 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.
