Frequency of transmission, asymptomatic shedding, and airborne spread of Streptococcus pyogenes among schoolchildren exposed to scarlet fever: a longitudinal multi-cohort molecular epidemiology contact tracing study

Abstract

Background: Despite recommendations regarding prompt treatment of cases and enhanced hygiene measures, scarlet fever outbreaks increased in England between 2014-2018. Methods: We undertook a prospective, intensive contact tracing study in schools with consecutive scarlet fever cases to assess the impact of standard interventions on transmission of Streptococcus pyogenes between cases, classroom contacts, households, and classroom environments over 4 weeks using genome sequencing. Findings: Six classes, comprising 12 scarlet fever cases, 17 household contacts, and 278 classroom contacts were recruited. Prevalence of the outbreak strain in asymptomatic classroom contacts was high, increasing from 9.6% in week 1, to 26.9% in week 2, 23.9% in week 3, then 14.3% in week 4. Colonisation with non-outbreak strains was 0 - 7.5%. Genome sequencing showed clonality of isolates within each of six classes, confirming recent transmission accounted for high carriage. Of asymptomatic classroom contacts with S. pyogenes-positive throat swabs who were tested for transmissibility, 6/28 (21%) had positive cough plates and/or hand swabs, of whom three remained S. pyogenes-positive for 3 weeks. Only 1/60 surface swabs taken in 3 classrooms yielded S. pyogenes. In contrast, settle plates placed in elevated locations were S. pyogenes-positive in both classrooms tested. Interpretation: S. pyogenes transmission in schools is intense and may occur prior to, or in spite of reported treatment of cases, underlining a need for rapid case management. Despite guideline adherence, heavy shedding of S. pyogenes by small numbers of classroom contacts may perpetuate outbreaks, and airborne transmission has a plausible role in spread.

Transmission of SARS-CoV-2 by children to contacts in schools and households: a prospective cohort and environmental sampling study in London

“…The infrequency of transmission to other pupils contrasts with transmission frequency of other respiratory infections in schools, including group A streptococcus and influenza. [12][13][14] The result presumably reflects the multiple interventions in place during the pandemic period or the heterogeneity of infection in COVID-19, where most transmission is caused by a minority of infections. 24,25 Our study prospectively examined transmission from the same children to contacts in both schools and households; the secondary attack rate in households was higher than expected, and was in contrast to that seen in schools.…”

“…Forward contact tracing offers an opportunity to search actively for secondary infections in a controlled manner. Before the COVID-19 pandemic and the institution of several interventions to limit the spread of SARS-CoV-2, we did a scarlet fever forward contact tracing study 14 in schools and observed outbreak strains spread to over one quarter of classroom contacts, despite treatment and isolation of index cases, alongside evidence of pathogen dispersal into air. 14 We adapted our protocol to investigate transmission of SARS-CoV-2 by children in schools and…”

Time to negative throat culture following initiation of antibiotics for pharyngeal group AStreptococcus: a systematic review and meta-analysis to inform public health control measures

“…Without treatment, the secondary attack rate for pharyngitis and scarlet fever is estimated to be 25-35% within a family setting and 23-60% in educational settings [8][9][10]. Even with treatment of the index case, attack rates among contacts are high (26% among school contacts, 13% among household contacts) [5]. In classroom outbreaks, prevalence of the outbreak strain has been noted to increase rapidly among asymptomatic contacts, reaching 27% in week two [5].…”

“…Even with treatment of the index case, attack rates among contacts are high (26% among school contacts, 13% among household contacts) [5]. In classroom outbreaks, prevalence of the outbreak strain has been noted to increase rapidly among asymptomatic contacts, reaching 27% in week two [5]. Within households, the median time between primary and secondary cases is six days [11].…”

“…Outbreaks arise from both symptomatic and asymptomatic index cases and can occur in a range of settings including households, hospitals, and care homes [5][6][7]. Without treatment, the secondary attack rate for pharyngitis and scarlet fever is estimated to be 25-35% within a family setting and 23-60% in educational settings [8][9][10].…”