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Summary Table

Component	Details
Risk Factors	Age 5-15 years, winter/early spring season, close-contact settings (schools, military barracks), household exposure to confirmed Group A Streptococcus (GAS)
Etiology	Most cases are viral (rhinovirus, adenovirus, EBV, coxsackievirus). The critical testable cause is Group A beta-hemolytic Streptococcus (GAS), i.e., Streptococcus pyogenes
Patient Presentation	Sudden-onset severe sore throat, odynophagia, fever, headache, abdominal pain/nausea (especially in children). Notably absent: cough, rhinorrhea, conjunctivitis, hoarseness
Classic Physical Exam	Tonsillopharyngeal erythema with palatal petechiae, tonsillar exudates, tender anterior cervical lymphadenopathy, and a sandpaper-textured rash (if scarlet fever is present). Absence of cough is a strong clinical discriminator.
Key Diagnostic Results	Rapid Antigen Detection Test (RADT) positive for GAS. If RADT is negative in a child, confirm with throat culture (gold standard). Modified Centor score guides who gets tested.
Management	Penicillin V (oral, 10 days) or Amoxicillin (oral, 10 days). Penicillin-allergic patients receive cephalexin (if no anaphylaxis history) or azithromycin/clindamycin. A single IM dose of Benzathine penicillin G is an alternative for compliance concerns.
Keywords	"Sore throat without cough," "tonsillar exudates with anterior cervical lymphadenopathy," "palatal petechiae," "sandpaper rash," "child with sore throat and abdominal pain," "Jones criteria" (for the complication question)

1. Pathophysiology

Acute pharyngitis is inflammation of the pharynx and surrounding lymphoid tissue. The majority of cases (50-80% in adults, 30-40% in children) are caused by respiratory viruses and are self-limited. However, the diagnosis that matters on exams is GAS pharyngitis, caused by Streptococcus pyogenes, because untreated GAS carries the risk of suppurative complications (peritonsillar abscess, retropharyngeal abscess) and non-suppurative complications (acute rheumatic fever, post-streptococcal glomerulonephritis).

GAS is a gram-positive coccus that produces several virulence factors. M protein on the bacterial surface inhibits phagocytosis and is the primary virulence determinant. It is also the antigen responsible for molecular mimicry with cardiac myosin and valve tissue, which is the mechanism underlying acute rheumatic fever (ARF). The host immune response generates cross-reactive antibodies that attack the heart, joints, skin, and CNS. This is why antibiotic treatment of GAS pharyngitis is essential: the primary goal is prevention of ARF, not simply symptom relief.

The abrupt onset of fever, exudative pharyngitis, and tender anterior cervical nodes reflects the robust inflammatory response to GAS colonization of the pharyngeal mucosa. Palatal petechiae result from local capillary fragility due to streptococcal toxins. When GAS produces erythrogenic (pyrogenic) exotoxins, patients develop the diffuse erythematous sandpaper rash of scarlet fever, which typically spares the face (circumoral pallor), concentrates in skin folds (Pastia lines), and desquamates during recovery.

The reason the exam emphasizes the absence of cough, rhinorrhea, and conjunctivitis is because these symptoms point toward a viral etiology. GAS pharyngitis is a localized pharyngeal infection and does not produce upper respiratory catarrhal symptoms. This distinction is the foundation of clinical scoring systems.

2. Classification and Clinical Manifestation

Viral vs. Bacterial Pharyngitis

Feature	Viral Pharyngitis	GAS (Bacterial) Pharyngitis
Onset	Gradual	Sudden
Fever	Low-grade or absent	High (>38.3 C)
Cough / Rhinorrhea	Present	Absent
Conjunctivitis / Hoarseness	May be present	Absent
Tonsillar exudates	Variable (adenovirus can cause exudates)	Common
Palatal petechiae	Rare	Suggestive of GAS
Anterior cervical LAD	Less prominent	Tender, prominent
Rash	Variable (morbilliform)	Sandpaper texture (scarlet fever)
Age peak	All ages	5-15 years
Season	Year-round	Winter and early spring

Modified Centor Score (McIsaac Criteria)

This is the scoring system used to decide who to test and who to treat empirically.

Criterion	Points
Tonsillar exudates or swelling	+1
Tender anterior cervical lymphadenopathy	+1
Fever (history or measured >38 C)	+1
Absence of cough	+1
Age 3-14 years	+1
Age 15-44 years	0
Age 45 years or older	-1

Interpretation

Score	Recommended Action
0-1	No testing, no antibiotics (low probability of GAS)
2-3	Perform RADT (intermediate probability); treat only if positive
4-5	RADT or empiric antibiotics (high probability of GAS)

The exam tests whether you know that a low Centor score with cough and rhinorrhea means no testing is needed, and that you should not give antibiotics to every sore throat.

Special Presentations

Variant	Key Features
Scarlet Fever	GAS pharyngitis + diffuse sandpaper rash, circumoral pallor, strawberry tongue, Pastia lines, followed by desquamation
Peritonsillar Abscess (PTA)	Severe unilateral sore throat, "hot potato" (muffled) voice, uvular deviation away from affected side, trismus
EBV Infectious Mononucleosis	Pharyngitis + posterior cervical LAD + splenomegaly + atypical lymphocytes; ampicillin/amoxicillin causes a characteristic maculopapular rash
Herpangina (Coxsackievirus A)	Small vesicles/ulcers on the posterior oropharynx and soft palate; common in young children
Pharyngoconjunctival Fever (Adenovirus)	Pharyngitis + conjunctivitis + fever; can mimic GAS with exudates
Diphtheria	Grayish-white pseudomembrane that bleeds when removed, "bull neck" from cervical edema; unvaccinated patients

3. Diagnostic Workup

Summary Table

Test	Role	Sensitivity	Turnaround
Rapid Antigen Detection Test (RADT)	Best initial test in clinic	70-90% (high specificity >95%)	Minutes
Throat culture	Gold standard / confirmatory	90-95%	24-48 hours
Anti-Streptolysin O (ASO) / Anti-DNase B	NOT for acute diagnosis; used to confirm prior GAS infection when evaluating complications (ARF, PSGN)	N/A	N/A
Monospot (Heterophile antibody)	If EBV mononucleosis is suspected	~85% (lower in children <4 years)	Minutes

Diagnostic Approach

The decision to test depends on the Modified Centor Score. Patients scoring 0-1 require no testing because the pre-test probability of GAS is too low to justify further workup. For scores of 2 or higher, proceed with a RADT.

The RADT detects GAS carbohydrate antigens directly from a pharyngeal swab. It has high specificity (meaning a positive result reliably confirms GAS), but its sensitivity is imperfect. This creates the following algorithm:

In children and adolescents: If RADT is positive, treat. If RADT is negative, you must send a backup throat culture because a false-negative RADT could lead to missed GAS and subsequent risk of ARF. This is a high-yield testing point.

In adults: A negative RADT alone is generally sufficient to rule out GAS. Backup throat culture is not routinely recommended in adults because the incidence of ARF is extremely low in this population and the pre-test probability of GAS is lower.

Throat culture is performed on blood agar. GAS shows beta-hemolysis (complete clearing around colonies) and is sensitive to bacitracin (the classic board-style identification method). It is also PYR-positive and Lancefield Group A.

ASO titers should never be ordered to diagnose acute pharyngitis. They rise 1-5 weeks after infection and are used retrospectively when a patient presents with suspected ARF or PSGN weeks after the pharyngitis episode.

A critical exam point: do not perform a test of cure (repeat throat culture after treatment) in asymptomatic patients. It is unnecessary and may detect the carrier state, which does not require treatment.

4. Management and Treatment

Summary Table

Scenario	Drug	Dose (Adult)	Dose (Pediatric)	Duration
First-line	Penicillin V	500 mg PO BID or 250 mg PO QID	250 mg PO BID or TID (weight <27 kg)	10 days
First-line alternative	Amoxicillin	1000 mg PO once daily or 500 mg PO BID	50 mg/kg/day PO once daily (max 1000 mg) or divided BID	10 days
Compliance concern	Benzathine Penicillin G	1.2 million units IM x1	600,000 units IM x1 (weight <27 kg); 1.2 million units if >27 kg	Single dose
Penicillin allergy (no anaphylaxis)	Cephalexin	500 mg PO BID	20 mg/kg/dose PO BID (max 500 mg/dose)	10 days
Penicillin allergy (anaphylaxis history)	Azithromycin	500 mg day 1, then 250 mg days 2-5	12 mg/kg/day (max 500 mg) day 1, then 6 mg/kg/day days 2-5	5 days
Penicillin allergy (anaphylaxis history), alternative	Clindamycin	300 mg PO TID	7 mg/kg/dose PO TID (max 300 mg/dose)	10 days

Treatment Approach

The goal of antibiotic therapy for GAS pharyngitis is threefold: (1) prevent acute rheumatic fever, (2) reduce suppurative complications, and (3) decrease transmission. Antibiotics also shorten symptom duration by approximately 1-2 days if started within 48 hours of onset.

Penicillin V remains the drug of choice because GAS has never demonstrated penicillin resistance. This is a frequently tested fact. The full 10-day course is mandatory to achieve eradication; shorter courses lead to bacteriologic failure even if symptoms resolve. Amoxicillin is often preferred in pediatric practice because of better taste and availability as a once-daily suspension.

For patients where adherence to a 10-day oral course is uncertain, a single intramuscular injection of Benzathine Penicillin G achieves adequate bactericidal levels for approximately 3-4 weeks, ensuring eradication without relying on patient compliance.

For penicillin-allergic patients, the approach depends on allergy severity. A history of minor rash (non-anaphylactic) permits a first-generation cephalosporin such as cephalexin, since cross-reactivity with penicillin is approximately 1-2%. A history of anaphylaxis, angioedema, or urticaria to penicillin is a contraindication to all beta-lactams, and the patient should receive azithromycin or clindamycin. Note that macrolide resistance in GAS is increasing in some regions, making clindamycin a reasonable alternative.

Symptomatic management includes acetaminophen or NSAIDs for fever and pain. Corticosteroids (e.g., a single dose of dexamethasone) may be considered as adjunctive therapy in severe odynophagia, though this is not universally recommended and is more commonly tested in the context of peritonsillar abscess.

When NOT to treat: GAS carriers (asymptomatic individuals who test positive) do not need antibiotics. They are not at risk for ARF and are unlikely to transmit the organism. The exam may present a well child with a positive throat culture but no symptoms, and the correct answer is no treatment.

A patient can return to school or work 24 hours after initiating appropriate antibiotic therapy, as they are no longer considered contagious at that point.

5. Differential Diagnosis and Distractors

Differential	Why It Is Similar	Key Discriminator
Infectious Mononucleosis (EBV)	Exudative pharyngitis, fever, cervical lymphadenopathy in a teenager/young adult	Posterior cervical LAD (not anterior), hepatosplenomegaly, atypical lymphocytes on smear, positive heterophile antibody. Maculopapular rash after amoxicillin administration.
Peritonsillar Abscess	Severe sore throat, fever, tonsillar swelling, follows GAS pharyngitis	Unilateral swelling, trismus, uvular deviation, muffled "hot potato" voice. Requires drainage, not just antibiotics.
Retropharyngeal Abscess	Fever, sore throat, neck stiffness, odynophagia in a young child	Neck hyperextension, drooling, refusal to swallow, widened prevertebral space on lateral neck X-ray.
Epiglottitis	Acute sore throat, fever, drooling, dysphagia	Stridor, tripod positioning, "thumbprint sign" on lateral neck film. A true airway emergency. The pharynx itself looks relatively normal.
Herpangina	Sore throat, fever, oral lesions in a child	Vesicles and ulcers confined to the posterior oropharynx and soft palate. Caused by coxsackievirus. No exudates on tonsils.
Diphtheria	Pharyngitis, exudates/membranes, cervical lymphadenopathy	Gray pseudomembrane that bleeds on removal, "bull neck," unvaccinated individual, toxin-mediated myocarditis and neuropathy.
Gonococcal Pharyngitis	Pharyngitis with exudates in a sexually active patient	History of orogenital contact, often asymptomatic or mild. Diagnosed by NAAT of pharyngeal swab.
Ludwig Angina	Severe throat/mouth pain, fever, swelling	Bilateral submandibular (floor of mouth) swelling, tongue elevation, recent dental infection. Airway compromise risk.
Viral URI (Common Cold)	Sore throat, malaise	Cough, rhinorrhea, conjunctivitis dominate the picture. No tonsillar exudates, no high fever. Low Centor score. No testing or antibiotics needed.

6. Traps and High-Yield Pearls

The most common way students get questions on acute pharyngitis wrong is by overtreating viral pharyngitis or by failing to confirm GAS before prescribing antibiotics. The exam will present a patient with a sore throat plus cough, rhinorrhea, and low-grade fever (Modified Centor score of 0-1), and the correct answer is symptomatic care only with no testing and no antibiotics. Selecting "prescribe amoxicillin" in this scenario is the intended trap.

The second major trap involves the negative RADT in a child. When a pediatric patient has a negative rapid strep test, students often assume GAS is excluded. The correct next step is to send a throat culture because false-negative RADT results can miss true GAS infections, and the consequence of missing GAS in a child (rheumatic fever) is too high to accept. In adults, a negative RADT is sufficient.

Another tested concept: the exam may describe a teenager with exudative pharyngitis, fatigue, and lymphadenopathy who receives amoxicillin and develops a diffuse maculopapular rash. Students may select "penicillin allergy" as the answer, but the correct diagnosis is infectious mononucleosis. The rash is not a true drug allergy; it is a transient immune-mediated reaction triggered by aminopenicillins in the setting of EBV infection.

Finally, remember that the goal of treating GAS pharyngitis with antibiotics is prevention of acute rheumatic fever, not prevention of post-streptococcal glomerulonephritis. PSGN occurs regardless of antibiotic treatment. This distinction is tested directly. Also, antibiotic therapy can be initiated up to 9 days after symptom onset and still prevent ARF, so there is no need to rush treatment before confirming the diagnosis.

The core competency being tested across all pharyngitis questions is the ability to risk-stratify patients using clinical criteria, apply testing appropriately, and avoid unnecessary antibiotic use while still protecting children from preventable rheumatic heart disease.

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