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Case Study: Pharyngitis
Shira Doron, MD, Assistant Professor, Division of Infectious Diseases, Associate Hospital Epidemiologist, Antimicrobial Management ,Tufts Medical Center, Boston, MA
Kirthana Beaulac, PharmD, Clinical Pharmacy Specialist- Infectious Diseases and Antimicrobial Stewardship, Tufts Medical Center, Boston, MA
LL is a 12 year old female presenting to her pediatrician, complaining of sore throat and cough. She has had some hoarseness in her voice over the past few days and subjective sweats but no documented fever. She has a history of seasonal allergies in the fall, and takes loratidine only during that season. Upon review of systems, she complains of isolated throat pain, without any rhinorrhea, sinus pressure, or headache. Her mother has been taking her temperature at home, and they have fluctuated from 97.8oF- 99.2oF.
LL was given a prescription for ibuprofen, to help with the inflammation and subjective fevers. She was not given a prescription for antibiotics, but the pediatrician advised the patient and her mother that he would call in a prescription for amoxicillin if the culture returned positive. She was encouraged to drink plenty of fluids and rest. The culture returned negative after 48 hours and she symptomatically improved after 2 days.
Acute Group A Streptococcal Pharyngitis (GAS) is a common condition affecting mostly children and teenagers during the winter and early spring. While GAS is the most common bacterial cause of pharyngitis, acute pharyngitis is most commonly caused by viruses.1 GAS is the causative organism in 20-30% of cases of pharyngitis, but can increase to 35-50% depending on the population and season.2,3 Notably, the symptoms of viral and bacterial pharyngitis can be challenging to differentiate. However, LL’s cough and hoarseness without any abdominal symptoms, fever, headache, or rash suggest that a viral illness was more likely than GAS.1
Given the age of the patient, time of year, and clinical symptoms, testing for GAS pharyngitis was warranted. The gold standard for diagnosis of GAS pharyngitis is the culture of a throat swab on a sheep-blood agar plate.1 The results can be variable based on the technique by which the swab was obtained. The swab should be obtained from the surface of either of the tonsils and the posterior pharyngeal wall without touching other parts of the oral pharynx and mouth.4,5 Also, the culture must be incubated for at least 18-24 hours prior to interpreting results, and should not be read as negative until incubated for 48 hours.6
Another diagnostic alternative is the Rapid Strep Antigen Detection Test (RADT). This test can be performed easily in the outpatient setting and has a rapid turnaround time.1 In comparison to throat cultures, RADTs are over 95% specific but only 70-90% sensitive.7,8 Therefore, the Infectious Diseases Society of America recommends liberal testing and that a negative RADT result warrants further confirmatory testing with a throat culture. However, in a patient without overt signs of bacterial pharyngitis and a negative RADT, it is appropriate to treat as if the patient has viral pharyngitis while awaiting results of the culture, as the pre-test probability of GAS is low.1 The European Society of Clinical Microbiology and Infectious Diseases (ESCMID) recommends risk stratification and rapid testing of patients with high probability of GAS. In these clinical situations, the pre-test probability of a positive result is higher, and therefore, negative RADT results do not warrant further confirmatory culturing.9
It is estimated that 70% of patients complaining of sore throat receive antibiotics, while the vast majority do not have bacterial infections.10 Therefore, differentiating between viral and bacterial pharyngitis is critical to limiting the use of unnecessary antibiotics. It is common practice for many physicians to prescribe antibiotics and leave it to the patient’s discretion whether to fill the prescription or not, regardless of a negative RADT. In this situation, the patient is highly likely to fill the prescription and take the antibiotics with the hope of feeling better. Complicating the decision further is the fact that while GAS pharyngitis is a self-limiting condition, regardless of antibiotic administration,11 antibiotics are also given to prevent the development of long-term rheumatic complications. It should be noted, however, that antibiotics remain effective for prevention of these sequelae even if withheld up to 9 days after the initiation of symptoms.11 Therefore, waiting for the culture results to finalize before prescribing antibiotics may be an effective method for decreasing unnecessary antibiotic prescriptions.
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