Evaluation of Rapid Antigen Detection Test for Group A Streptococci Pharyngitis among Children in an Out-Patient Clinic in Malaysia

One of the most common conditions encountered in the out-patient setting is acute pharyngitis. Group A Streptococcus (GAS) accounts for 15%-30% of cases of sore throat particularly in children under 15 years old. Rapid antigen testing (RADT) is an alternative diagnostic method to detect GAS pharyngitis. This study was done to evaluate the agreement between RADT whereby BIONEXIA® Strep A Plus (BioMérieux, France) kit was used and throat culture in the diagnosis of GAS pharyngitis in children presented with a sore throat. One hundred and ten children from a primary health care clinic with sore throat were included in this study. All children were evaluated based on McIsaac scoring and throat swab samples were taken for both throat culture and RADT testing. The prevalence of GAS pharyngitis by RADT in this study was 7.3% over one year. A higher incidence of GAS pharyngitis was noted in the school-aged children than the preschool-age children. There was no correlation between cough, lymph node enlargement, and tonsillar enlargement in predicting GAS pharyngitis. The sensitivity and specificity of RADT were 100% and 98%, respectively, when taking throat culture as a gold standard. A good agreement between RADT and throat culture was achieved (k=0.848). McIsaac scoring was noted to have good predictability for GAS pharyngitis with AUC=0.82. In conclusion, the rapid streptococcal antigen detection test showed excellent sensitivity and specificity and detecting GAS from the throat swab samples. Thus, it can be used to aid in the diagnosis of group A Streptococcal pharyngitis and could reduce the overuse of antibiotics. McIsaac score has also proven to be useful as a screening tool for bacterial pharyngitis.

In Vivo Secretion of β-Lactamase-Carrying Outer Membrane Vesicles as a Mechanism of β-Lactam Therapy Failure

Outer membrane vesicles carrying β-lactamase (βLOMVs) protect bacteria against β-lactam antibiotics under experimental conditions, but their protective role during a patient’s treatment leading to the therapy failure is unknown. We investigated the role of βLOMVs in amoxicillin therapy failure in a patient with group A Streptococcus pyogenes (GAS) pharyngotonsillitis. The patient’s throat culture was examined by standard microbiological procedures. Bacterial vesicles were analyzed for β-lactamase by immunoblot and the nitrocefin assay, and in vivo secretion of βLOMVs was detected by electron microscopy. These analyses demonstrated that the patient’s throat culture grew, besides amoxicillin-susceptible GAS, an amoxicillin-resistant nontypeable Haemophilus influenzae (NTHi), which secreted βLOMVs. Secretion and β-lactamase activity of NTHi βLOMVs were induced by amoxicillin concentrations reached in the tonsils during therapy. The presence of NTHi βLOMVs significantly increased the minimal inhibitory concentration of amoxicillin for GAS and thereby protected GAS against bactericidal concentrations of amoxicillin. NTHi βLOMVs were identified in the patient’s pharyngotonsillar swabs and saliva, demonstrating their secretion in vivo at the site of infection. We conclude that the pathogen protection via βLOMVs secreted by the flora colonizing the infection site represents a yet underestimated mechanism of β-lactam therapy failure that warrants attention in clinical studies.

The utility of rapid Group A streptococcus molecular testing compared with throat culture for the diagnosis of Group A streptococcal pharyngitis in a high-incidence rheumatic fever population.

Background: Group A Streptococcus (GAS) causes significant morbidity and mortality in New Zealand and is responsible for invasive disease and immune sequelae including acute Rheumatic Fever (ARF). Early treatment of GAS pharyngitis reduces the risk of ARF. In settings with a high-burden of GAS disease, a rapid GAS pharyngitis diagnostic test with a strong negative predictive value is needed to enable prompt and accurate treatment. Methods: This prospective study compares the Xpert® Xpress Strep A molecular test (Cepheid) to throat culture and a second molecular method, the BioGX Group A Streptococcus -OSR for BD MAX TM for the diagnosis of GAS pharyngitis. Throat swabs were collected from the emergency department and wards of Middlemore Hospital, New Zealand. The BioGX Group A Streptococcus - OSR for BD MAX TM , contributes to the composite gold-standard: throat culture or both molecular methods positive. Basic demographic, clinical and laboratory data was collected. Results: 205/214 swabs were suitable for analysis. 28/205 (13.7%) were GAS culture positive, 45/205 (22%) Xpert® Xpress Strep A positive and 38/205 (18.5%) BioGX positive. Compared to culture, the sensitivity, specificity, positive and negative predictive values of the Xpert® Xpress Strep A molecular test were 100%, 90.4%, 62.2% and 100%, respectively. Compared to the composite gold-standard, the sensitivity, specificity, PPV and NPV and were 100%, 95.8%, 84.4% and 100% respectively. 17 samples were Xpert® Xpress positive but culture-negative; 6 of these 17 swabs represent true positives with evidence of recent GAS infection. Ten samples were culture negative but both Xpert® Xpress and BioGX positive. Conclusion: The Xpert® Xpress Strep A molecular test is highly sensitive with a strong negative predictive value and rapid turnaround time. It can be safely introduced as a first line test for throat swabs in a high-incidence ARF population.

Throat culture screening for Beta-haemolytic streptococci among schoolboys in Saudi Arabia

Thistudy was designed to estimate the carrier rate of beta-haemolytic streptococci among 972 primary-school boys in a high-altitude area of Saudi Arabia, and its association with social class, crowding index and body mass index, and also to determine the seasonal variation of infection. A carrier rate of 13.1% for beta-haemolytic streptococci was detected. The carrier rate was significantly higher in spring than in winter. The association between streptococcal infection and social class, crowding index, or body mass index was statistically not significant. The low prevalence of streptococcal infection might be attributed to the high altitude but further studies are needed to determine whether this is the case

Effect of erythritol and xylitol on Streptococcus pyogenes causing peritonsillar abscesses

Polyols are effective against caries-causing streptococci but the effect on oropharynx-derived pyogenic streptococci is not well characterised. We aimed to study the effect of erythritol (ERY) and xylitol (XYL) against Streptococcus pyogenes isolated from peritonsillar abscesses (PTA). We used 31 clinical isolates and 5 throat culture collection strains. Inhibition of bacterial growth by polyols at 2.5%, 5% and 10% concentrations was studied and the results were scored. Amylase levels in PTA pus were compared to polyol effectivity scores (PES). Growth curves of four S. pyogenes isolates were analysed. Our study showed that XYL was more effective than ERY inhibiting 71–97% and 48–84% of isolates, respectively, depending of concentrations. 48% of clinical and all throat strains were inhibited by polyols in all concentrations (PES 3). PES was negative or zero in 26% of the isolates in the presence of ERY and in 19% of XYL. ERY enhanced the growth of S. pyogenes isolated from pus with high amylase levels. Polyols in all concentrations inhibited the growth in exponential phase. In conclusion, ERY and XYL are potent growth inhibitors of S. pyogenes isolated from PTA. Therefore, ERY and XYL may have potential in preventing PTA in the patients with frequent tonsillitis episodes.

Positive Rate of Tests for Group a Streptococcus and Viral Features in Children with Acute Pharyngitis

Group A streptococcus (GAS) is an important cause of acute pharyngitis. We investigated the positive rate of GAS tests and clinical viral features in children with acute pharyngitis. A retrospective review was conducted for patients <15 years old with both rapid antigen detection test (RADT) and throat culture results. Patients were excluded if they were diagnosed with influenza or had received antibiotics within two weeks before these tests. A total of 377 patients were eligible. The median age of patients was 3.5 years, and 45.4% of total patients were <3 years old. Among all patients, 68.7% had at least one viral feature, and 39% had more than two. The overall positiv rate for GAS was 11.4%. The GAS positive rate was significantly lower in patients <3 years old than in older patients (1.8% vs. 19.4%, p < 0.0001). The overall sensitivity and specificity of RADT were 75.0% (95% CI: 57.8–87.9) and 97.9% (95% CI: 95.8–99.2), respectively. The GAS positive rate was not significantly different between patients with and without viral features (12.4% vs. 9.3%, p = 0.4854). In patients aged 3–14 years, the GAS positive rate was not associated with the modified Centor score or the frequency of clinical viral features. Despite a low prevalence of GAS pharyngitis, testing for GAS was frequently performed in children <3 years old in this study. Appropriate use of laboratory testing for GAS pharyngitis and judicious prescription of antibiotics were imperative.

#6: High Diagnostic Accuracy of Automated Rapid Strep A Test Reduces Antibiotic Prescriptions for Children in the United Arab Emirates.

Background Diagnosis of Group A Streptococcus (GAS) pharyngitis in children is hindered by variable sensitivity of clinical criteria and rapid Strep A tests (SAT), resulting in reliance on throat cultures as the gold standard for diagnosis. Delays while awaiting culture reports result in unnecessary antibiotic prescriptions among children, contributing to the spread of antimicrobial resistance (AMR). Methods Diagnostic accuracy study of an automated SAT (A-SAT) in children up to 16 years of age presenting to an emergency room with signs and symptoms of pharyngitis between March and June 2019. Paired throat swabs for A-SAT and culture were collected. Sensitivity, specificity, positive predictive value (PPV) and negative predictive value (NPV) for A-SAT were calculated. Results Two hundred and ninety-one children were included in this study. 168 (57.7%) were boys and the mean age was 4.2 years. A-SAT was positive in 94 (32.3%) and throat culture was positive in 90 (30.9%) children. A-SAT and throat culture results showed a high level of consistency in our cohort. Only 6 (2%) children had inconsistent results, demonstrating that the A-SAT has a high sensitivity (98.9%), specificity (97.5%), PPV (94.7%) and NPV (99.5%) for the diagnosis of GAS pharyngitis in children. Only 92 (32%) children were prescribed antibiotics while the vast majority (68%) were not. Conclusions A-SAT is a quick and reliable test with diagnostic accuracy comparable to throat culture. Its widespread clinical use can help limit antibiotic prescriptions to children presenting with pharyngitis, thus limiting the spread of AMR.