Comparison of antimicrobial resistance and serotype patterns in Streptococcus pneumoniae from blood cultures and respiratory specimens in Canadian hospitals from the CANWARD study (2007-23).

OBJECTIVES

To compare the antimicrobial resistance and serotype patterns in Streptococcus pneumoniae collected from blood cultures and respiratory specimens in Canada from 2007 to 2023.

METHODS

S. pneumoniae isolates were submitted from Canadian hospitals as part of the ongoing national surveillance study, CANWARD. Antimicrobial susceptibility testing was performed by the CLSI broth microdilution method. Serotypes were determined using WGS and/or the Quellung method.

RESULTS

Of the 3111 S. pneumoniae isolates collected, 1103 (35.5%) were from blood cultures and 2008 (64.5%) were from respiratory specimens. The most common serotypes overall were 3, 19A, 22F and 11A. Serotypes 4, 5, 7F, 8, 12F, 14, 19A and 22F were more frequently identified (P ≤ 0.01) among blood culture isolates, while 6C, 7C, 11A, 19F, 21, 23A, 23B, 23F, 31, 34, 35B, 35F and non-typeable strains were more commonly recognized (P ≤ 0.03) among respiratory isolates. Susceptibility rates were significantly lower in respiratory isolates than blood culture isolates for penicillin, ceftriaxone, clarithromycin, clindamycin and doxycycline (P ≤ 0.03). Overall, 8.3% of isolates were MDR/XDR; rates increased over the course of the study (P = 0.004). MDR/XDR rates were higher in respiratory isolates (10.5%) than in blood culture isolates (5.8%) (P < 0.0001). Serotypes 19A (40.6%) and 15A (27.6%) were predominant in the MDR/XDR isolates.

CONCLUSIONS

S. pneumoniae from respiratory specimens demonstrated lower antimicrobial susceptibilities and higher MDR rates compared with isolates from blood cultures. Significant differences in the serotypes isolated from blood culture and respiratory specimens were observed. A greater proportion of isolates from blood cultures were serotypes covered by current pneumococcal vaccines.