Cases in Medical Microbiology and Infectious Diseases. Melissa B. Miller
cold, croup, bronchiolitis, pneumonia
a COPD, chronic obstructive pulmonary disease.
b CF, cystic fibrosis.
c dsDNA, double-stranded DNA.
d ssRNA, single-stranded RNA.
e SARS-CoV, severe acute respiratory syndrome coronavirus.
f MERS-CoV, Middle East respiratory syndrome coronavirus.
CASE 7
The patient was a 5-year-old male who awoke on the day prior to evaluation with a sore throat and fever. His mother had him stay home from kindergarten and treated him symptomatically with Tylenol. He slept well but the next day awoke still complaining of sore throat and fever, as well as headache and abdominal pain. He was an only child and neither parent was ill.
On physical examination, he was noted to have a fever of 38.4°C. His physical examination was significant for a 2+ (on a scale of 1 to 4+) red anterior pharynx, tonsillar region, and soft palate. His anterior cervical lymph nodes at the angle of the mandible were slightly enlarged and tender. No skin lesions or rashes were seen. He did not have a cough, runny nose, or conjunctivitis. A rapid antigen test for group A streptococci (GAS) and a positive and negative control of the assay are seen in Fig. 7.1. When the results of the rapid antigen test were known, the patient was given a 10-day course of oral amoxicillin.
1 1. Based on his clinical presentation, what organism was most likely causing this patient’s infection? What does the rapid strep antigen test tell you?
2 2. Was antimicrobial therapy necessary in this patient? Explain.
3 3. This patient was at risk for two noninfectious sequelae. What are they? Briefly describe our current understanding of the pathogenesis of these two disease processes.
4 4. What antimicrobial resistance problems have been observed with this organism?
5 5. Sore throat associated with a maculopapular rash is frequently seen with this organism. What is this usually benign condition called? What virulence factor is believed to be responsible for production of this rash?
6 6. What is the current status of vaccine development for this organism?
CASE 7 CASE DISCUSSION
1. Based on a GAS clinical prediction scoring system developed at the University of Virginia and validated in both adults and children, this patient scored positive for all the criteria: temperature of >38°C, no cough, tender anterior cervical lymphadenopathy, tonsillar swelling and exudates, and age 3 to 14 years. Patients with this score are estimated to have a risk of ~50% of having GAS pharyngitis. Although not part of the prediction rule, abdominal pain, nausea, and vomiting are frequently seen in patients with GAS pharyngitis, though only abdominal pain was seen in this patient. What if the patient had presented with low-grade fever (<38°C), cough, sore throat without exudates, conjunctivitis, and coryza? Such a patient would have a score of 1 (positive only by virtue of age). Patients with a score of 1 have only a 5 to 10% risk of GAS pharyngitis. Viruses including rhinovirus, coronavirus, adenovirus, and influenza virus can all cause a syndrome of sore throat, cough, coryza, and conjunctivitis. This constellation of symptoms by and large is self-limited. Viral pharyngitis should be treated only symptomatically with analgesics and warm saltwater gargles.
A decision was made to confirm the clinical impression by determining if GAS was present. There are two ways to detect GAS: by direct detection of group A polysaccharide antigen in throat swabs, as was done in this case (Fig. 7.1), and by culture using a blood-containing agar plate. Direct antigen detection is accomplished by extracting the group A polysaccharide antigen from the throat swab and then performing an immunoassay on the extract. The test is very rapid, taking 10 to 15 minutes, and is highly specific (>95%), but when compared with culture it has a sensitivity of 80 to 90%, meaning that GAS will not be detected by this test in 10 to 20% of patients with GAS in their throats. The advantage of the “rapid strep test,” as it is called, is that a swab can be obtained in the office or clinic and a result can be obtained while the patient waits, i.e., a “real-time” microbiology test. For patients with a high pretest probability of disease, such as this patient, and a positive rapid GAS antigen test, antibiotics can be prescribed on the spot if that is the clinical decision that is reached. See answer 2 for further discussion of this issue.
Most guidelines no longer recommend performing culture in patients with negative rapid GAS antigen tests. For further explanation of why, see answer 2.
2. There are several benefits of antibiotics in the treatment of GAS pharyngitis. Of greatest significance is that treatment prevents nonsuppurative poststreptococcal sequelae (see answer to question 3 for further explanation). Further, if given early in the disease course (first 24 to 48 hours), they may also shorten the length of time the patient is symptomatic. Additionally, antibiotic therapy will prevent suppurative complications of GAS pharyngitis, such as peritonsillar and retropharyngeal abscesses, and decrease the infectivity of the infected individual. In school-age children, this is important so that they are less likely to infect their classmates and siblings, both at-risk populations. Because both suppurative and nonsuppurative poststreptococcal sequelae are now rare in the industrialized world, the importance of antimicrobial therapy in treatment of GAS is limited to the benefits of shortening disease course and decreasing transmissibility. This must be balanced with the risks of antimicrobial therapy. These include allergic reactions, especially since this infection is treated with penicillin; changes in the microbiota that may put the patient at risk for other infections; and increasing antimicrobial resistance among respiratory pathogens such as Streptococcus pneumoniae.
The problem is even more complex with patients who have a negative rapid GAS antigen test. Often, physician practice, especially in pediatrics, is to “back up” negative rapid GAS antigen tests with culture. There are at least four