Abstract

Objective To estimate the incidence of laboratory-confirmed, invasive bacterial infections (IBIs) by week of age in infants over a 7-year period. Design Analysis of prospective national surveillance data for England. Setting National Health Service hospitals in England. Patients Infants aged <1 year who were hospitalised with IBI. Main outcome measures IBI incidence by week of age, incidence rate ratio (IRR) at 8, 12 and 16 weeks compared with the first week of life, and the main pathogens responsible for IBI. Results There were 22 075 IBI episodes between 2010/2011 and 2016/2017. The lowest annual cases were in 2011/2012 (n=2 799; incidence, 412/100 000 population), increasing year-on-year to 3 698 cases in 2016/2017 (incidence, 552/100 000 population). The incidence was highest in the first week of life and then declined rapidly. In 2016/2017, compared with the first week of life, weekly IBI incidence was 92% lower at 8 weeks (IRR 0.08; 95% CI 0.06 to 0.10) and 96% lower at 16 weeks of age (IRR 0.04; 95% CI 0.03 to 0.06). In 2016/2017, Escherichia coli was the most prevalent pathogen responsible for IBI (n=592, 16.0%), followed by group B Streptococci (n=493, 13.3%), Staphylococcus aureus (n=400, 10.8%) and Enterococci (n=304, 8.2%). The other pathogens were individually responsible for <5% of total cases. There were differences in age distribution of the pathogens with increasing age. Conclusion IBI incidence declines rapidly after the first week of life, such that infants have a very low risk of IBI by the time they are eligible for their routine immunisations from 8 weeks of age.