All that follows is from NOT ALL SORE THROAT IS STREP THROAT from the above resource.
Strep pharyngitis, commonly known as “strep throat” is a bacterial infection of the oropharynx caused by group A beta hemolytic streptococci (GAS), specifically S. pyogenes. This infection affects more than 500,000,000 people annually worldwide per year, ultimately resulting in a significant number of doctor’s visits, including to the ED (1). The classic clinical presentation of GAS pharyngitis includes sudden onset of sore throat, fever, and odynophagia. If untreated, complications of GAS pharyngitis include scarlet fever, rheumatic heart disease, post-streptococcal glomerulonephritis and peri-tonsillar abscess.
There are many clinical mimics of GAS pharyngitis which must be ruled out by the clinician prior to testing or treatment for GAS pharyngitis. Clinical mimics include acute retroviral syndrome, as the first presentation of acute HIV may be with pharyngitis with tonsillar exudate, lymphadenopathy, fevers, headache. Patients with acute HIV may appear to have many similar symptoms to those with GAS pharyngitis, but will tend to have more prolonged symptoms (>7 days), generalized lymphadenopathy (not just of the head and neck), and will often have GI symptoms (diarrhea, mouth sores) as well. In these patients, it is important to assess risk factors for HIV. Sexual history can also provide key information in the diagnosis of bacterial pharyngitis not due to GAS, such as gonococcal pharyngitis in patients who participate in receptive oral intercourse. Another common clinical mimic of GAS pharyngitis is infectious mononucleosis which also presents with fever, pharyngitis, and lymphadenopathy, and is most commonly due to infection with the Epstein Barr Virus. This can be difficult to differentiate from GAS infection clinically, however patients with infectious mononucleosis may also have palatal petechiae (+LR for infectious mononucleosis of 5.3), posterior cervical lymphadenopathy (+LR 3.1) and splenomegaly (2). Other important clinical mimics to consider include the infections of the deep neck space such as retropharyngeal abscess, Ludwig’s angina, and Lemierre’s syndrome.