1200 - Risk of group A streptococcal Transmission Among the Pediatric Population in the Houston Area

Background: Disease due to group A Streptococcus (GAS) occurs frequently in children and usually manifests as pharyngitis or superficial skin infections.  However, invasive disease (iGAS) such as necrotizing fasciitis or streptococcal toxic shock syndrome is responsible for significant morbidity and mortality. National-level surveillance at the Centers for Disease Control and Prevention (CDC) estimates >10,000 cases and ~1,500 deaths due to iGAS occur annually in the US.  Much interest revolves around the ability to detect potential transmission events (PTEs) of GAS disease using surveillance data as such information may change recommendations for chemoprophylaxis of close contacts.  Studies by the CDC have shown a secondary attack rate from 66.1 to 102 /100,000, primarily occurring among older adults with co-morbidities.  However, previous studies were limited in that the GAS surveillance was limited to iGAS disease.

Methods: Retrospective study using a comprehensive GAS passive surveillance system.  GAS isolates and associated metadata were obtained from 2 hospital systems in the Texas Medical Center from 2017-2019. Molecular emm typing of GAS isolates was performed using the CDC protocol. PTEs were defined based on GAS disease isolates originating from the same zip code, occurring within 30 days of each other, and of the same emm type.

Results: A total of 1291 isolates were included in the study – 94 PTEs were identified representing 168 individual GAS isolates of which 74 were defined as index cases. The 4 most common GAS emm types identified among PTEs were emm1 (43/94, 45.7%), emm12 (30/94, 31.9%), emm4 (6/94, 6.4%), and emm6 (5/94, 5.3%).  Index cases most frequently resulted in a single PTE (n=74) with an average number of PTEs per index case of 1.3 (range 1 to 3 PTEs). From index cases, 10 GAS isolates were derived from invasive disease (10/74, 13.5%) and 6 from skin and soft tissue infections (SSTI; 6/74, 8.1%). A substantial proportion of PTEs resulted in iGAS (9/94, 9.5%) and SSTI (10/94, 10.6%).   
 

Conclusion: Using comprehensive local surveillance, we were able to identify several potential GAS transmission events. Further analysis – including whole genome sequencing on index and PTE isolates – is needed to better define transmission events.