Streptococcal diagnostic testing and antibiotics prescribed for pediatric tonsillopharyngitis

Development of a fast and low-cost qPCR assay for diagnosis of acute gas pharyngitis

Background

Group A streptococci (GAS) are the most common bacterial cause of acute pharyngitis and account for 15–30 % of cases of acute pharyngitis in children and 5–10 % of cases in adults. In this study, a real-time quantitative PCR (qPCR) based GAS detection assay in pharyngeal swab specimens was developed.

Methods

The qPCR assay was compared with the gold standard bacterial culture and a rapid antigen detection test (RADT) to evaluate its clinical performance in 687 patients. The analytical sensitivity of the assay was 240 cfu/swab. Forty-five different potential cross-reacting organisms did not react with the test. Four different laboratories for the reproducibility studies were in 100 % (60/60) agreement for the contrived GAS positive and negative swab samples.

Results

The relative sensitivities of the RADT and the qPCR test were 55.9 and 100 %; and the relative specificities were 100 and 96.3 %, respectively. Duration of the total assay for 24 samples including pre-analytical processing and analysis changed between 42 and 55 min depending on the type of qPCR instrument used. A simple DNA extraction method and a low qPCR volume made the developed assay an economical alternative for the GAS detection.

Conclusion

We showed that the developed qPCR test is rapid, cheap, sensitive and specific and therefore can be used to replace both antigen detection and culture for diagnosis of acute GAS pharyngitis.

Performance of a rapid antigen-detection test and throat culture in community pediatric offices: implications for management of pharyngitis

OBJECTIVES

The goals were to establish performance characteristics of a rapid antigen-detection test and blood agar plate culture performed and interpreted in community pediatric offices and to assess the effect of the pretest likelihood of group A streptococcus pharyngitis on test performance (spectrum bias).

METHODS

Two throat swabs were collected from 1848 children 3 to 18 years of age who were evaluated for acute pharyngitis between November 15, 2004, and May 15, 2005, in 6 community pediatric offices. One swab was used to perform the rapid antigen-detection test and a blood agar plate culture in the office and the other was sent to our laboratory for blood agar plate culture. Clinical findings were used to calculate the McIsaac score for each patient. The sensitivities of the office tests were calculated, with the hospital laboratory culture results as the criterion standard.

RESULTS

Thirty percent of laboratory blood agar plate cultures yielded group A streptococcus (range among sites: 21%-36%). Rapid antigen-detection test sensitivity was 70% (range: 61%-80%). Office culture sensitivity was significantly greater, 81% (range: 71%-91%). Rapid antigen-detection test specificity was 98% (range: 98%-99.5%), and office culture specificity was 97% (range: 94%-99%), a difference that was not statistically significant. The sensitivity of a combined approach using the rapid antigen-detection test and back-up office culture was 85%. Among patients with McIsaac scores of >2, rapid antigen-detection test sensitivity was 78%, office culture sensitivity was 87%, and combined approach sensitivity was 91%. Positive diagnostic test results were significantly associated with McIsaac scores of >2.

CONCLUSIONS

The sensitivity of the office culture was significantly greater than the sensitivity of the rapid antigen-detection test, but neither test was highly sensitive. The sensitivities of each diagnostic modality and the recommended combined approach were best among patients with greater pretest likelihood of group A streptococcus pharyngitis.

Validity of using an electronic medical record for assessing quality of care in an outpatient setting

OBJECTIVE

We sought to evaluate the validity of retrieving data from a commercial, outpatient electronic medical record (EMR) to assess the management of pharyngitis, an important measure of quality of healthcare in pediatrics and a new measure for the Health Plan Employer Data and Information Set (HEDIS).

METHODS

For children ages 3-18 years, we electronically identified clinical encounters with diagnoses of pharyngitis using 3 different strategies (an EMR-based strategy, an administrative data-based strategy, and a reference strategy which used medical record review). By each strategy, we calculated the proportion of episodes of pharyngitis during 1 year for which management of pharyngitis adhered to published guidelines.

RESULTS

Among 479 total episodes of pharyngitis, 434 (91%) were from the EMR-based strategy and 281 (59%) from the administrative data-based strategy. Review of the records (the reference strategy) found that 391 of 479 (82%) were confirmed episodes of pharyngitis. A diagnostic test for group A streptococcus (GAS) was performed at 310 of 434 (71%) of episodes identified by the EMR-based strategy and at 214 of 281 (76%) of episodes by the administrative data-based strategy (P = 0.045). By the reference strategy, a diagnostic test was done in 301 of 391 (77%); more than at episodes found by the EMR-based strategy (71%, P < 0.001).

CONCLUSIONS

The EMR-based strategy resulted in a statistically different proportion of episodes having diagnostic testing for GAS compared with a reference strategy. Complete evaluations to validate strategies for extracting data from electronic databases are necessary before assuming that measures of quality of care will be the same regardless of the source of data.

Rapid Detection and Diagnosis of Group A Streptococcal Pharyngitis

This article reviews techniques of rapid testing and the effective diagnosis of streptococcal pharyngitis. Despite 50 years' study of streptococcal pharyngitis and 20 years' experience with rapid tests for its diagnosis, the subject continues to evolve. Rapid diagnostic tests have become more sensitive. Experts now consider not if but when they may replace throat cultures. Highly accurate rapid tests will still challenge clinicians to screen the right patients. The improvement of clinical diagnosis will require an understanding of the clinical spectrum of pharyngitis and questions relating to disease prevalence, test performance, and medical decision making. Implications for diagnostic strategies are discussed.

Improving diagnostic testing and reducing overuse of antibiotics for children with pharyngitis: a useful role for the electronic medical record

BACKGROUND

Because of rising resistance to antibiotics, appropriate use of antibiotics is an important measure of quality of care. The purpose of this study was to use an electronic medical record (EMR) to assess use of diagnostic testing and of antibiotics for pharyngitis in a pediatric outpatient setting and to target areas for improvement.

METHODS

Using data retrieved from the EMR, we analyzed visits from March 1, 2001 to February 28, 2002 for children 3 to 18 years old diagnosed with pharyngitis. We determined the proportion of episodes with a diagnostic test for group A streptococci, the proportion for which a prescription for an antibiotic was dispensed and factors that predicted prescribing and testing.

RESULTS

Of 391 episodes of pharyngitis, a test was ordered for 303 (78%). Antibiotics were prescribed for 90 (23%); for 76 of 90 (84%) a test was ordered. Clinicians were less likely to order tests late in the week [relative risk (RR), 0.76; 95% confidence interval (CI), 0.66, 0.87)], more likely to order tests for patients with an exudate (RR 1.2; 95% CI 1.1, 1.3) and more likely to prescribe an antibiotic for patients with an exudate (RR 1.5; 95% CI 1.1, 2.1). When prescribing an antibiotic clinicians were less likely to order tests late in the week (RR 0.1; 95% CI 0.02, 0.5) and for patients diagnosed with scarlet fever (RR 0.07; 95% CI 0.01, 0.4).

CONCLUSION

Using data from the EMR, we could assess adherence to the guidelines for antibiotic use and identify areas to target for improving diagnostic testing and reducing overuse of antibiotics in our clinic.

Concordance of clinical findings and clinical judgment in the diagnosis of streptococcal pharyngitis

OBJECTIVE

It is uncertain how reliably clinicians apply clinical predictors of group A beta hemolytic streptococcal pharyngitis (GABHSP) to form a clinical impression, and how reliably this impression predicts culture results. The objective was to study clinician accuracy in diagnosing GABHSP.

METHODS

This was a prospective cohort study, conducted at an urgent care center of a major university. A convenience sample of 218 patients, aged 9-83 years, presenting with sore throat, was enrolled. Symptoms and signs of pharyngitis were documented on a standardized form; the likelihood of GABHSP was plotted on a visual analog scale; and throat culture was obtained. A comparison was then made between the clinical impression on presentation and the throat culture result.

RESULTS

Throat cultures were positive for GABHSP in 41 patients (19%). The probability of GABHSP was related to node size and tenderness, tonsillar exudate and hypertrophy, and pharyngeal erythema (p<0.05); but not throat soreness, degree of fever, or cough. A strong clinical impression of GABHSP (>50% on the visual analog scale) was associated with tonsillar exudate and hypertrophy, tender nodes, and pharyngeal erythema. Together, these four predictors had a sensitivity of 71%, a specificity of 77%, and a positive predictive value of 46%.

CONCLUSIONS

Clinicians in this study based their impression of GABHSP on the most reliable symptoms and signs. While a strong clinical suspicion of GABHSP predicted a greater probability of positive culture, the clinicians consistently overestimated the probability of GABHSP. Symptoms and signs predict GABHSP unreliably when used alone; they are helpful in modifying estimates of disease probability to facilitate optimal use of laboratory tests and antibiotics.

Multivariate predictive models for group A beta-hemolytic streptococcal pharyngitis in children

OBJECTIVES

To create predictive models for the clinical diagnosis of group A beta-hemolytic streptococcal (GABHS) pharyngitis in children.

METHODS

Patients aged 6 months to 18 years presenting to a pediatric ED with suspected GABHS pharyngitis were prospectively enrolled in the study. Clinicians recorded pertinent clinical information using a standardized form and obtained a throat swab to culture GABHS using a reference standard method. Twelve demographic and clinical features of patients with positive throat cultures were compared with the features of patients with negative throat cultures. Significantly different features were entered in a stepwise logistic regression analysis to create predictive models for the diagnosis.

RESULTS

Eighty-five patients (29%) were culture-positive and 212 (71%) were culture-negative for GABHS. Respective mean ages were 6.2 years and 6.1 years in the two groups. Univariate chi-square analysis of the 12 features identified six variables that were significantly associated with GABHS. All significant features were initially included in a stepwise logistic regression analysis. In model I, four independent variables were identified: moderate to severe presentation of tonsillar swelling, moderate to severe tenderness and enlargement of cervical lymph nodes, the presence of scarlatiniform rash, and the absence of moderate to severe coryza, yielding a 95% probability for GABHS. Excluding the rare scarlatiniform rash, the remaining variables were used in the second regression analysis. In model II, three independent variables were identified: moderate to severe tonsillar swelling, moderate to severe tenderness and enlargement of cervical lymph nodes, and absence of moderate to severe coryza, yielding a probability of 65% for the diagnosis. A probability of <15% was observed in the absence of scarlatiniform rash, the absence of moderate to severe tenderness and enlargement of cervical lymph nodes, and the presence of moderate to severe coryza.

CONCLUSIONS

In children with moderate to severe presentation of tonsillar swelling, tenderness and enlargement of cervical lymph nodes, and the absence of coryza, the probability of a positive throat culture is >65%. Conversely, in the absence of a moderate to severe presentation of tonsillar swelling, enlargement of cervical nodes, and the presence of coryza, the probability of a positive throat culture is <15%. If prospectively validated, these models could be integrated into a consistent treat, test, and no treatment/no testing approach to the clinical management of childhood pharyngitis.