Out-of-season increase of puerperal fever with group A Streptococcus infection: A case-control study, Netherlands, July to August 2018

We observed an increase in notifications of puerperal group A Streptococcus (GAS) infections in July and August 2018 throughout the Netherlands without evidence for common sources. General practitioners reported a simultaneous increase in impetigo. We hypothesised that the outbreak of puerperal GAS infections resulted from increased exposure via impetigo in the community. We conducted a case-control study to assess peripartum exposure to possible, non-invasive GAS infections using an online questionnaire. Confirmed cases were recruited through public health services while probable cases and controls were recruited through social media. We calculated odds ratios (OR) and 95% confidence intervals (95% CI) with logistic regression analysis. We enrolled 22 confirmed and 23 probable cases, and 2,400 controls. Contact with persons with impetigo were reported by 8% of cases and 2% of controls (OR: 3.26, 95% CI: 0.98-10.88) and contact with possible GAS infections (impetigo, pharyngitis or scarlet fever) by 28% and 9%, respectively (OR: 4.12, 95% CI: 1.95- 8.68). In multivariable analysis, contact with possible GAS infections remained an independent risk factor (aOR: 4.28, 95% CI: 2.02-9.09). We found an increased risk of puerperal fever after community contact with possible non-invasive GAS infections. Further study of this association is warranted.