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.