McIsaac Score Research Articles

Evaluation of a Streptococcal Pharyngitis Score in Southern Taiwan

Group A streptococcus (GAS) pharyngitis can cause serious complications such as rheumatic heart disease. The McIsaac sore throat score is a clinical prediction score used to improve the detection rate of GAS pharyngitis. We evaluated the validity of the McIsaac sore throat score in Southern Taiwan and compared our findings to those of other studies. We retrospectively analyzed chart records from children aged 3 to 15 years old who complained of fever and sore throat. They had throat cultures collected at the outpatient pediatric clinic of Fooyin University Hospital, located in Pingtung County, Taiwan during the period between January 2007 and January 2010. Clinical characteristics were reviewed, and sore throat score was analyzed. A total of 342 throat cultures met the inclusion criteria of sore throat and fever. The positive rate of GAS was 4.1%. Culture-positive cases were associated with higher odds for a skin rash [adjusted odds ratio (AOR): 14.66, 95% confidence interval (CI): 4.63-46.40, p<0.001), lower odds for cough (AOR: 0.19, 95% CI: 0.04-0.85, p=0.030) and having a runny nose (AOR: 0.22, 95% CI: 0.05-0.99, p=0.048). The most common physical sign was scarlet fever rash (AOR: 57.35, 95% CI: 15.45-212.98, p<0.001). A McIsaac score of 5 had a sensitivity of 71%, specificity of 70%, and a positive predictive value of only 9.3%. Pediatric streptococcal pharyngitis in Southern Taiwan is uncommon. Diagnosis of GAS pharyngitis based on the McIsaac sore throat score is unreliable among pediatric patients with febrile pharyngitis in Southern Taiwan.

Performance of a Rapid Antigen-Detection Test and Throat Culture in Community Pediatric Offices: Implications for Management of Pharyngitis

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). 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. 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. 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.

Relationship Between the Clinical Likelihood of Group A Streptococcal Pharyngitis and the Sensitivity of a Rapid Antigen-Detection Test in a Pediatric Practice

The sensitivity of a rapid antigen-detection test (RADT) for group A streptococcal (GAS) pharyngitis is critical to whether the test is cost-effective and to whether a confirmatory throat culture is needed. We evaluated a second-generation RADT to determine if its sensitivity varies across the broad clinical spectrum of patients tested for GAS in pediatric outpatient practice. We used laboratory logbooks from a single pediatric clinic to identify 1184 consecutive patient visits at which an RADT was performed. In a blinded chart review, we calculated McIsaac scores to separately estimate the pretest clinical likelihood of GAS pharyngitis for visits at which the RADT result was positive (n = 384) and for visits at which the result proved to be false-negative (n = 65). Positive RADT results were assumed to be true positives, and test sensitivity was estimated by dividing the number of positive results by the sum of positives and false-negatives. As the clinical likelihood of GAS increased, there were stepwise increases in RADT sensitivity (from 0.67 to 0.88). Sensitivity was low (0.73; 95% confidence interval [CI]: 0.62-0.86) in patients clinically unlikely to have GAS (McIsaac score < or =2) and high (0.94; 95% CI: 0.89-0.99) in patients <15 years old who had tonsillar exudate and no cough. False-negative RADT results were associated with lighter growth of GAS than found on specimens obtained from a random sample of clinic patients who had only primary throat cultures ordered. For pediatric patients who are clinically unlikely to have GAS pharyngitis, as indicated by a McIsaac score < or =2, the sensitivity of a second-generation RADT may drop below thresholds reported for cost-effectiveness. For children who have tonsillar exudate and no cough, the test may be sensitive enough to meet current pediatric practice guidelines for stand-alone testing.