Invasive group B streptococcal infections in Western Australia, 2000–2018

Background: Neonatal and puerperal sepsis are major manifestations of invasive group B streptococcal (Streptococcus agalactiae; iGBS) infections. International data indicate the importance of iGBS infections among non-pregnant adults. Aims: To describe the burden of iGBS infections in Western Australia (WA) between 2000 and 2018 in terms of incidence, length of hospitalisation and all-cause 30- and 90-day mortality. Methods: This was a retrospective, population-based study using linked data from the state government-owned pathology provider, hospitalisations and death registrations. Children and adults with isolation of GBS in a normally sterile site or a hospital-based diagnosis of iGBS infection were included. Results: There were 2861 cases; just over a quarter (n = 768) were aged 0–1 year. Half of the cases were among females (1438 of 2861), and the median age was 39 years. Incidence increased over the study period, with an age- and sex-adjusted incidence rate ratio for year of 1.08 (95% confidence interval (CI) 1.06–1.09). The incidence in 2018 was 9.5 cases (95% CI 8.3–10.6 cases) per 100 000 population. The proportion of cases among those aged 0–1 year fell across the period, while the relative incidence in older age groups increased. The median length of hospital stay was 7 days (interquartile range 4–15 days), and mortality at 30 days was 3% (95 of 2861). Conclusions: iGBS cases increased across the period 2000–2018 in WA, with older adults making up a higher proportion of cases over time. Preventive efforts among older patients, including potentially through vaccination, may reverse this increase.