Abstract
Since 2012, have we in Denmark observed an increase of invasive pneumococcal infections (IPD) due to Streptococcus pneumoniae serotype 24F. We here present epidemiological data on 24F IPD cases, and characterization of 48 24F clinical isolates based on clonal relationship, antimicrobial resistance (AMR) determinants and virulence factors. IPD surveillance data from (1999–2016) were used to calculate the incidence and age-distribution of serotype 24F IPD and the effect of pneumococcal conjugated vaccines (PCV). Characterization of forty-eight 24F isolates (14.7% of all 24F isolates from the period) was based on whole-genome sequencing analysis (WGS). The IPD cases of serotype 24F showed a significant increase (p < 0.05) for all age groups after the PCV-13 introduction in 2010. The majority of tested 24F isolates consisted of two MLST types, i.e. the ST72 and the ST162. Serotype 24F IPD increased in Denmark after the PCV-13 introduction in parallel with an increase of the ST162 clone. The genotypic penicillin binding protein (PBP) profile agreed with the phenotypical penicillin susceptibility. The virulence genes lytA, ply, piaA, piaB, piaC, rspB and the cpsA/wzg were detected in all 24F isolates, while the pspA and zmpC genes were absent.
Highlights
Streptococcus pneumoniae is a ubiquitous bacterium present in the commensal bacterial community in the human nasopharynx
The incidence of serotype 24F invasive pneumococcal disease (IPD) cases was low in the period from 1999–2007 (0.22 per 100.000, confidence interval (CI): 0.17–0.26) and 2008–2010 (0.19 per 100.000, CI: 0.09–0.30), while an increase in incidence (0.49 per 100.000, CI: 0.29–0.69) was observed in all age groups from 2011 to 2016
The increase in the Incidence Rate Ratio (IRR) of serotype 24F IPD varied with an IRR of 3.69 (CI: 1.30-10.53) in infants (P = 0.0083), 3.78 (CI: 1.73-8.32) in the age group from 5 to 64 years ((P < 0.001) and 1.74 (1.74 CI: 1.08–2.80) in the age group +65 (P = 0.025), the general mean incidence was very low
Summary
Streptococcus pneumoniae is a ubiquitous bacterium present in the commensal bacterial community in the human nasopharynx. It is responsible for non-invasive infections as well as invasive pneumococcal disease (IPD) with high morbidity and mortality especially among young children and the elderly[1]. The introduction of the pneumococcal conjugated vaccine (PCV) provided an effective protection against IPD in children. After the introduction of PCV13 in 2010 in France, serotype 24F, including other non-vaccine serotypes (10A, 12F and 15A), were responsible for approximately 39% of pneumococcal meningitis (PM) cases in children below 5 years of age from 2012 to 20148. Because the serotype 24F is an emerging non-pneumococcal vaccine serotype, which to our knowledge is not a part of any pneumococcal vaccine or as part of planned future pneumococcal vaccine. To monitor the epidemiology and susceptibility of serotype 24F, and to provide information to the international community that measures against serotype 24F are needed
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