Epidemiology of invasive group A streptococcal infections in Norway 2010–2014: A retrospective cohort study

Genome sequence analysis of emm89 Streptococcus pyogenes strains causing infections in Scotland, 2010-2016

Purpose

Strains of type emm89 Streptococcus pyogenes have recently increased in frequency as a cause of human infections in several countries in Europe and North America. This increase has been molecular epidemiologically linked with the emergence of a new genetically distinct clone, designated clade 3. We sought to extend our understanding of this epidemic behavior by the genetic characterization of type emm89 strains responsible in recent years for an increased frequency of infections in Scotland.

Methodology

We sequenced the genomes of a retrospective cohort of 122 emm89 strains recovered from patients with invasive and noninvasive infections throughout Scotland during 2010 to 2016.

Results

All but one of the 122 emm89 infection isolates are of the recently emerged epidemic clade 3 clonal lineage. The Scotland isolates are closely related to and not genetically distinct from recent emm89 strains from England, they constitute a single genetic population.

Conclusions

The clade 3 clone causes virtually all-contemporary emm89 infections in Scotland. These findings add Scotland to a growing list of countries of Europe and North America where, by whole genome sequencing, emm89 clade 3 strains have been demonstrated to be the cause of an ongoing epidemic of invasive infections and to be genetically related due to descent from a recent common progenitor.

Burden of bloodstream infection in an area of Mid-Norway 2002-2013: a prospective population-based observational study

BACKGROUND

Studies from several countries indicate that the incidence and mortality of bloodstream infection (BSI) have been increasing over time.

METHODS

We studied the burden of disease and death related to BSI in a defined geographical area of Mid-Norway, where BSI episodes were prospectively recorded by the same microbiological department during 12 consecutive years. Death from BSI was defined as death within 30 days of BSI detection. Age and sex standardized incidence and mortality rates and case fatality rates were calculated.

RESULTS

Between 2002 and 2013, 1995 episodes of BSI in 1719 patients aged 16 to 99 years were included. The overall incidence of BSI was 215 per 100,000 person-years. The incidence increased exponentially with age, particularly in males. The incidence increased from 205 to 223 per 100,000 person-years from 2002-07 to 2008-13. Escherichia coli was the most frequently isolated infective agent, followed by Streptococcus pneumoniae and Staphylococcus aureus. The rate of S. pneumoniae BSI decreased over time in males (on average by 9.2% annually), but not in females. The total rate of BSI microbes with acquired resistance increased slightly over time, but did not exceed 2 episodes per 100,000 person-years. The mortality of BSI was 32 per 100,000 person-years, higher in males than in females (36 vs. 28 per 100,000 person-years) and was significantly higher in old age, particularly in males. The total BSI mortality was similar in the first and second halves of the study period, but the mortality of S. pneumoniae BSI decreased in males (15.0% annually). The crude case fatality decreased from the first to the second half of the study period (17.2% to 13.1%; p = 0.014). The rate of blood culture sampling increased more than twofold during the study period.

CONCLUSIONS

The mortality of BSI remained stable during 2002-2013. At the same time, BSI incidence increased and case fatality rate decreased, perhaps because an increased rate of blood culture sampling may have led to improved detection of milder BSI episodes. Very low, yet slightly increasing rates of microbes with acquired resistance were observed.