Objective

We describe cases of invasive group A Streptococcus (iGAS) in mothers or neonates and assess management according to national guidelines, which recommend administering antibiotics to both mother and neonate if either develops iGAS infection within 28 days of birth and investigation of clusters in maternity units.
Design

Cross‐sectional retrospective study.
Setting and population

Notified confirmed iGAS cases in either mothers or neonates with onset within 28 days of birth in London and the South East of England between 2010 and 2016
Method

Review of public health records of notified cases.
Main outcome measures

Incidence and onset time of iGAS in postpartum mothers and babies, proportion given prophylaxis, maternity unit clusters within 6 months.
Results

We identified 134 maternal and 21 neonatal confirmed iGAS infections. The incidence (in 100 000 person years) of iGAS in women within 28 days postpartum was 109 (95% CI 90–127) compared with 1.3 in other females aged 15–44. For neonates the incidence was 1.5 (95% CI 9–23). The median onset time was 2 days postpartum [interquartile range (IQR) 0–5 days] for mothers and 12 days (IQR 7–15 days) for neonates. All eligible mothers and most (109, 89%) eligible neonates received chemoprophylaxis. Of 20 clusters (59 cases of GAS and iGAS) in maternity units, two clusters involved possible transmission. However, in 6 of 15 clusters, GAS isolates were not saved for comparison even after relevant guidance was issued.
Conclusions

iGAS infection remains a potential postpartum risk. Prophylaxis among neonates and storage of isolates from maternity cases can be improved.