Molecular Epidemiology of Noninvasive and Invasive Group A Streptococcal Infections in Cape Town

Implementation of molecular diagnostic testing for group A streptococcal pharyngitis: considerations and challenges with a focus on point-of-care environments

INTRODUCTION

Rapid and accurate detection of group A streptococcus (GAS) pharyngitis allows for timely initiation of appropriate antibiotic treatment. This is important to prevent empiric antibiotic overuse while simultaneously lowering the risk of post-infection sequelae. Timely treatment may also reduce forward transmission, which could prevent cases of devastating invasive infections. The need for timely and accurate diagnosis of GAS pharyngitis has created an ideal environment for molecular diagnostic (MDx) testing. The high sensitivity of MDx tests mean no culture confirmation is required for negative results in most situations, and several MDx tests are approved for point-of-care (PoC) use. As such, MDx technology can lower the barriers to treatment in remote areas of high incidence, where resources are limited. We believe it is time for widespread adoption of MDx testing for GAS pharyngitis.

AREAS COVERED

Here, we highlight the advantages of MDx GAS pharyngitis testing and discuss challenges to implementation - as well as solutions to these challenges.

EXPERT OPINION

In the face of increased GAS-induced disease following the end of the COVID-19 pandemic, evidence supporting the clinical validity and cost-effectiveness of MDx testing for GAS pharyngitis continues to grow. Although hurdles to implementation exist, broad-based implementation of this technology is within practical reach.

A survey of antibiotic resistance patterns among Group A Streptococcus isolated from invasive and non-invasive infections in Cape Town, South Africa

Background

There is concern regarding the increasing resistance of Group A streptococcus (GAS) to routinely used antibiotics. GAS is a common cause of bacterial pharyngitis and more severe invasive infections such as septicaemia. Furthermore, GAS pharyngitis is the antecedent for serious conditions such as rheumatic fever and rheumatic heart disease. The study aimed to determine the antimicrobial susceptibility patterns of GAS cultured from patients with invasive and non-invasive infections from Cape Town, as part of the AFROStrep Registry.

Methods

Samples were provided by the AFROStrep Registry, a continental endeavour aiming to document Streptococcus pyogenes infection in Africa and create the first biorepository of its kind. Ninety-five GAS isolates (invasive, n = 40; non-invasive, n = 55) were evaluated for resistance to a panel of 20 antibiotics using the Sensititre® STP6F system with MICs interpreted by CLSI break points.

Results

Amongst all isolates, highest levels of resistance were observed with respect to tetracycline (8.33 %), followed by azithromycin (1.04 %) and erythromycin (1.04 %). No resistance to the remaining antibiotics was detected amongst all isolates. No differences with regard to MIC values were observed between isolates from invasive and non-invasive infections (p-value >0.05 for all antibiotics).

Conclusion

GAS remains susceptible to routine-antimicrobial agents used in our low-resourced setting. Eight percent of the GAS isolates were resistant to tetracycline, and we did not observe macrolide resistance as reported in high income countries. This is the first study to report on the antimicrobial patterns of GAS in South Africa. These results address a critical gap in the available data on GAS in Africa and specifically South Africa and, thus, aid in avoiding therapeutic failures.

State of the Art of Invasive Group A Streptococcus Infection in Children: A Scoping Review of the Literature with a Focus on Predictors of Invasive Infection

Currently, it remains unclear why some children develop invasive group A Streptococcus (iGAS) and how to manage this condition. Therefore, to explore available works in the literature, we performed a scoping review aiming to analyze the current literature on clinical presentation of different illnesses outcomes of iGAS, with a specific focus on predictors of invasive infection, including an assessment of the prodromal stages of the disease and the possible presence of previous non-invasive GAS infections in children that later developed iGAS.

METHODS

We conducted a systematic search on PubMed and SCOPUS of all pediatric studies reporting iGAS cases, following the Preferred Reporting Items for Systematic reviews and Meta-Analyses extension for Scoping Reviews (PRISMA-ScR) checklist. For those studies in which multivariable analysis investigating iGAS risk factors was performed, a second review was performed and reported in detail.

RESULTS

A total of 209 studies were included. Five studies investigated risk factors for iGAS, the most relevant being varicella infection, chronic underlying illness, presence of the speC gene in GAS strains, acetaminophen and ibuprofen use, children nonwhite, living in low-income households, exposure to varicella at home, persistent high fever, having more than one other child in the home, and new use of NSAIDs. Although we observed a progressive increase in the number of papers published on this topic, no trials investigating the benefits of clindamycin or intravenous immunoglobulins were found and low-to-middle-income countries were found to be poorly represented in the current literature.

CONCLUSIONS

Our scoping review highlights important gaps regarding several aspects of iGAS in children, including prodromic presentation and optimal treatment strategies. There is also little representation of low-middle-income countries. The current literature does not allow the performance of systematic reviews or meta-analyses, but this work should inform healthcare professionals, policy makers, and funding agencies on which studies to prioritize on this topic.

Serum Immune Responses to Group A Streptococcal Antigens following Pharyngeal Acquisitions among Children in Cape Town, South Africa

There is limited information on the human immune response following infection with group A Streptococcus (Strep A). Animal studies have shown, in addition to the M protein, that shared Strep A antigens elicit protective immunity. This study aimed to investigate the kinetics of antibody responses against a panel of Strep A antigens in a cohort of school-aged children in Cape Town, South Africa. Participants provided serial throat cultures and serum samples at two-monthly follow-up visits. Strep A recovered were emm-typed, and serum samples were analyzed by enzyme-linked immunosorbent assay (ELISA) to assess immune responses to thirty-five Strep A antigens (10-shared and 25-M peptides). Serologic evaluations were performed on serial serum samples from 42 selected participants (from 256 enrolled) based on the number of follow-up visits, the frequency of visits, and throat culture results. Among these, there were 44 Strep A acquisitions, 36 of which were successfully emm-typed. Participants were grouped into three clinical event groups based on culture results and immune responses. A preceding infection was most convincingly represented by a Strep A-positive culture with an immune response to at least one shared antigen and M peptide (11 events) or a Strep A-negative culture with antibody responses to shared antigens and M peptides (9 events). More than a third of participants demonstrated no immune response despite a positive culture. This study provided important information regarding the complexity and variability of human immune responses following pharyngeal acquisition of Strep A, as well as demonstrating the immunogenicity of Strep A antigens currently under consideration as potential vaccine candidates. IMPORTANCE There is currently limited information regarding the human immune response to group A streptococcal throat infection. An understanding of the kinetics and specificity of antibody responses against a panel of Group A Streptococcus (GAS) antigens will serve to refine diagnostic approaches and contribute to vaccine efforts, which together will serve to reduce the burden of rheumatic heart disease, a major source of morbidity and mortality especially in the developing world. This study, utilizing an antibody-specific assay, uncovered three patterns of response profiles following GAS infection, among 256 children presenting with sore throat to local clinics. Overall, the response profiles were complex and variable. Of note, a preceding infection was most convincingly represented by a GAS-positive culture with an immune response to at least one shared antigen and M peptide. Also, more than a third of participants demonstrated no immune response despite a positive culture. All antigens tested were immunogenic, providing guidance for future vaccine development.

American Heart Association's Children's Strategically Focused Research Network Experience

The American Heart Association's Strategically Focused Children's Research Network started in July 2017 with 4 unique programs at Children's National Hospital in Washington, DC; Duke University in Durham, North Carolina; University of Utah in Salt Lake City, Utah; and Lurie Children's Hospital/Northwestern University in Chicago, Illinois. The overarching goal of the Children's National center was to develop evidence-based strategies to strengthen the health system response to rheumatic heart disease through synergistic basic, clinical, and population science research. The overall goals of the Duke center were to determine risk factors for obesity and response to treatment including those that might work on a larger scale in communities across the country. The integrating theme of the Utah center focused on leveraging big data-science approaches to improve the quality of care and outcomes for children with congenital heart defects, within the context of the patient and their family. The overarching hypothesis of the Northwestern center is that the early course of change in cardiovascular health, from birth onward, reflects factors that result in either subsequent development of cardiovascular risk or preservation of lifetime favorable cardiovascular health. All 4 centers exceeded the original goals of research productivity, fellow training, and collaboration. This article describes details of these accomplishments and highlights challenges, especially around the COVID-19 pandemic.

Group A Streptococcus Infections: Their Mechanisms, Epidemiology, and Current Scope of Vaccines

Group A streptococci (GAS) are gram-positive, cocci-shaped bacteria that cause a wide variety of infections and are a cause of significant health burden, particularly in lower- and middle-income nations. The GAS genome contains a number of virulence factors such as the M-protein, hyaluronic acid, C5a peptidase, etc. Despite its significant health burden across the globe, a proper vaccine against GAS infections is not yet available. Various candidates for an effective GAS vaccine are currently being researched. These are based on various parts of the streptococcal genome. These include candidates based on the N-terminal region of the M protein, the conserved C-terminal region of the M protein, and other parts of the streptococcal genome. The development of a vaccine against GAS infections is hampered by certain challenges, such as extensive genetic heterogeneity and high protein sequence variation. This review paper sheds light on the various virulence factors of GAS, their epidemiology, the different vaccine candidates currently being researched, and the challenges associated with M-protein and non-M-protein-based vaccines. This review also sheds light on the current scenario regarding the status of vaccine development against GAS-related infections.

A Review of Streptococcus pyogenes: Public Health Risk Factors, Prevention and Control

Streptococcus pyogenes, (colloquially named "group A streptococcus" (GAS)), is a pathogen of public health significance, infecting 18.1 million people worldwide and resulting in 500,000 deaths each year. This review identified published articles on the risk factors and public health prevention and control strategies for mitigating GAS diseases. The pathogen causing GAS diseases is commonly transmitted via respiratory droplets, touching skin sores caused by GAS or through contact with contaminated material or equipment. Foodborne transmission is also possible, although there is need for further research to quantify this route of infection. It was found that GAS diseases are highly prevalent in developing countries, and among indigenous populations and low socioeconomic areas in developed countries. Children, the immunocompromised and the elderly are at the greatest risk of S. pyogenes infections and the associated sequelae, with transmission rates being higher in schools, kindergartens, hospitals and residential care homes. This was attributed to overcrowding and the higher level of social contact in these settings. Prevention and control measures should target the improvement of living conditions, and personal and hand hygiene. Adherence to infection prevention and control practices should be emphasized in high-risk settings. Resource distribution by governments, especially in developed countries, should also be considered.

Systematic Review and Meta-analysis of the Prevalence of Group A Streptococcal emm Clusters in Africa To Inform Vaccine Development

Low vaccine coverage is of grave public health concern, particularly in developing countries where epidemiological data are often absent. To inform vaccine development for group A Streptococcus (GAS), we report on the epidemiology of the M protein emm clusters from GAS infections in Africa, where GAS-related illnesses and their sequelae, including rheumatic fever and rheumatic heart disease, are of a high burden. This first report of emm clusters across the continent indicates a high probably of coverage by the M protein-based vaccine currently undergoing testing were an emm-cluster based approach to be used.

An emm-cluster based system was proposed as a standard typing scheme to facilitate and enhance future studies of group A Streptococcus (GAS) epidemiological surveillance, M protein function, and vaccine development strategies. We provide an evidence-based distribution of GAS emm clusters in Africa and assess the potential coverage of the new 30-valent vaccine in terms of an emm cluster-based approach. Two reviewers independently assessed studies retrieved from a comprehensive search and extracted relevant data. Meta-analyses were performed (random-effects model) to aggregate emm cluster prevalence estimates. Eight studies (n = 1,595 isolates) revealed the predominant emm clusters as E6 (18%; 95% confidence interval [CI], 12.6% to 24.0%), followed by E3 (14%; 95% CI, 11.2% to 17.4%) and E4 (13%; 95% CI, 9.5% to 16.0%). There was negligible variation in emm clusters with regard to regions, age, and socioeconomic status across the continent. Considering an emm cluster-based vaccine strategy, which assumes cross-protection within clusters, the 30-valent vaccine currently in clinical development would provide hypothetical coverage to 80.3% of isolates in Africa. This systematic review indicates the most predominant GAS emm cluster in Africa is E6 followed by E3, E4, and D4. The current 30-valent vaccine would provide considerable coverage across the diversity of emm cluster types in Africa. Future efforts could be directed toward estimating the overall potential coverage of the new 30-valent vaccine based on cross-opsonization studies with representative panels of GAS isolates from populations at highest risk for GAS diseases.

IMPORTANCE Low vaccine coverage is of grave public health concern, particularly in developing countries where epidemiological data are often absent. To inform vaccine development for group A Streptococcus (GAS), we report on the epidemiology of the M protein emm clusters from GAS infections in Africa, where GAS-related illnesses and their sequelae, including rheumatic fever and rheumatic heart disease, are of a high burden. This first report of emm clusters across the continent indicates a high probably of coverage by the M protein-based vaccine currently undergoing testing were an emm-cluster based approach to be used.