Strep throat: Guidelines for diagnosis and treatment

Sore throat of viral origin is a common clinical presentation in the primary care setting. Findings in the National Ambulatory Care Survey indicate that acute pharyngitis is one of the top 20 reported diagnoses and represents 1.1% of primary care visits.¹ In fact, the Infectious Diseases Society of America (IDSA) has established clinical guidelines to help the clinician manage this common infection.² Infection with group A beta-hemolytic streptococci (GABHS) is the only common cause of acute pharyngotonsillitis that routinely requires antibiotic treatment,²³ While the highest rates of infection are in children aged 5 to 11 years, a study by Berkovitch and colleagues found that children as young as 3 months had documented GABHS pharyngitis.⁴  

Pathogenesis

The etiologic agent for streptococcal pharyngitis is the gram-positive organism Streptococcus pyogenes. The symptoms of strep throat, which most commonly occurs in the winter and early spring,² are preceded by a 24- to 72-hour incubation period. Transmission is by hand contact with nasal discharge;⁵ fomites and pets are not believed to be vectors of transmission. In addition to pharyngitis, GABHS are also responsible for the infectious skin lesions of impetigo and perianal streptococcal cellulitis. 

Clinical presentation

Symptoms of streptococcal infection often start with the sudden onset of sore throat, dysphagia, and fever. Children may also present with headache, nausea, vomiting, and abdominal pain. Findings on clinical presentation include pharyngeal erythema, tonsillar exudates, anterior cervical lymphadenitis, palatine petechiae, erythematous papillae of the tongue, and a sandpaper rash (scarlatiniform rash). Clinical findings are not diagnostic, although they can help to identify those patients in whom the probability of strep throat is high.

Signs and symptoms that help rule in streptococcal pharyngitis include tonsillar exudates and pharyngeal exudates; exposure to strep throat in the previous 2 weeks is also suspicious (see Table 1).⁶ Signs and symptoms that are suggestive of viral rather than bacterial etiology for sore throat include conjunctivitis, cough, hoarseness, coryza, anterior stomatitis, discrete ulcerative pharyngeal lesions, and the absence of fever.² An evidence-based patient encounter form, developed by McIsaac and colleagues for screening patients with symptoms of pharyngitis, utilizes the presence or absence of these signs and symptoms.⁷ The findings help the clinician to decide whether rapid antigen testing is indicated.  

Differential diagnosis

The list of organisms included in the differential diagnosis of pharyngitis is extensive. Many viruses—including rhinovirus, adenovirus, influenza, respiratory syncytial virus, coxsackievirus, echovirus, and herpesvirus (such as Epstein-Barr)—are implicated as etiologic agents of acute pharyngitis.² Up to 20% of pharyngitis may be associated with rhinovirus alone.⁸

Infectious mononucleosis is one of the more common differential diagnoses in the 15- to 30-year-old age group. Although the infection may be mild or subclinical, some cases can result in significant morbidity.⁹ The classical presentation of infectious mononucleosis is with fever, pharyngitis, tender cervical lymphadenopathy, and splenomegaly. A prodromal period of malaise, fatigue, headache, arthralgia, fever, chills, dysphagia, and anorexia lasting several days may precede the acute phase.⁸ A common finding is the development of a classic maculopapular rash in 90% of patients with mononucleosis who are treated with amoxicillin or ampicillin.¹⁰ This appears to be a hypersensitivity to the antibiotic that develops with the acute infection.  

Laboratory evaluation

Consider the clinical, historical, and epidemiologic evidence before deciding to perform microbiological tests to evaluate patients with symptoms of acute pharyngitis. Those who have signs and symptoms that are not suggestive of streptococcal infection do not require diagnostic tests. Diagnostic confirmation of strep throat is helpful in those patients whose presentation suggests it, however, because symptoms of bacterial and viral infections often overlap and because bacteriologic confirmation is necessary to resolve any uncertainty as to the etiology.