In pharyngitis, only 5 to 10 percent of sore throats are caused by bacteria, with group A beta-hemolytic streptococci being the most common.
Other bacteria that occasionally cause pharyngitis include groups C and G streptococci, Neisseria gonorrhoeae, Mycoplasma pneumoniae, Chlamydia pneumoniae,and Arcanobacterium haemolyticus.
Pharyngitis caused by group A beta-hemolytic streptococci has an incubation period of two to five days and is most common in children five to 12 years of age. The illness is diagnosed most often in the winter and spring.
Group A beta-hemolytic streptococcal pharyngitis usually is an acute illness with sore throat and a temperature higher than 38.5°C (101.3°F). Constitutional symptoms include fever and chills, myalgias, headaches and nausea.
Patients with cough or coryza, are less likely to have streptococcal pharyngitis. A sandpaper-like rash on the trunk, which is sometimes linear on the groin and axilla (Pastia's lines), is consistent with scarlet fever.
Features of Streptococcal Tonsillopharyngitis
Features rarely associated with streptococ-cal tonsillopharyngitis–suggestive of other etiologies
- Sore throat (pain on swallowing)
- Patchy discrete
- Headache,Nausea, vomiting, abdominal pain (especially in children)
- Marked inflammation of throat and tonsils
- Tender, enlarged anterior cervical nodes
- Scarlet fever
2. Diagnostic Testing
- Laryngitis (stridor,croup)
- Nasal discharge (except in young children)
- Muscle aches/malaise
Throat culture is the gold standard for the diagnosis of streptococcal pharyngitis. The sensitivity of throat culture for group A beta-hemolytic streptococci is 90 percent. The specificity of throat culture is 99 percent.
A rapid antigen detection test (rapid strep test) can be completed in five to 10 minutes. This test has a specificity of greater than 95 percent but a sensitivity of only 76 to 87 percent.
A positive rapid antigen detection test may be considered definitive evidence for treatment of streptococcal pharyngitis. A confirmatory throat culture should follow a negative rapid antigen detection test when the diagnosis of group A beta-hemolytic streptococcal infection is strongly suspected.
Suppurative complications of streptococcal pharyngitis occur as infection spreads from pharyngeal mucosa to deeper tissues.
Penicillin is the drug of choice for streptococcal pharyngitis. This antibiotic has efficacy and safety, a narrow spectrum of activity and low cost. About 10 percent of patients are allergic to penicillin.
Alternatives to Penicillin
The cure rates for amoxicillin in children, given once daily for 10 days are similar to those for penicillin V. The absorption of amoxicillin is unaffected by the ingestion of food.
Amoxicillin is less expensive and has a narrower spectrum of antimicrobial activity than the once-daily antibiotics. Suspensions of this drug taste better than penicillin V suspensions, and chewable tablets are available. However, gastrointestinal side effects and skin rash may be more common with amoxicillin.
Erythromycin is recommended in patients with penicillin allergy. Because erythromycin estolate is hepatotoxic in adults, erythromycin ethylsuccinate may be used.
Erythromycin is absorbed better when it is given with food. But, some patients cannot tolerate the gastrointestinal side effects of erythromycin.
Azithromycin (Zithromax) allows once-daily dosing and a shorter treatment course of five-days. Azithromycin is associated with a low incidence of gastrointestinal side effects.
Cephalosporins have a broader spectrum of activity than penicillin V. Unlike penicillin, cephalosporins are resistant to degradation from beta-lactamase. First-generation agents such as cefadroxil (Duricef) and cephalexin (Keflex, Keftab) are preferable to second- or third-generation agents.
Cephalosporins are reserved for patients with relapse or recurrence of streptococcal pharyngitis.
Amoxicillin-clavulanate (Augmentin) is resistant to degradation from beta-lactamase produced by copathogens. Amoxicillin-clavulanate is often used to treat recurrent streptococcal pharyngitis. Its major adverse effect is diarrhea.
4. Management Issues
Treatment Failure and Reinfection.
Patients who do not comply with a course of penicillin should be offered intramuscular penicillin or a once-daily oral macrolide or cephalosporin. Patients with clinical failure should be treated with amoxicillin-clavulanate, a cephalosporin, or a macrolide.
Patients with streptococcal pharyngitis are considered contagious until they have been taking an antibiotic for 24 hours. Children should not go back to day-care or school until their temperature returns to normal and they have had at least 24 hours of antibiotic therapy.