Decreased Antibiotic Susceptibility of S pneumoniae Strains

Nasopharyngeal pneumococcal and acute otitis media isolates from children have exhibited reduced susceptibility to penicillin, third-generation cephalosporin, fluoroquinolone, and carbapenem antibiotics after the introduction of the 13-valent pneumococcal conjugate vaccine (PCV-13), according to results of a study published in Clinical Infectious Diseases.

Investigators believe resistance among Streptococcus pneumoniae strains in children has been increasing since 2013, as a result of serotypes not included in PCV-13. Pneumococcal resistance to penicillin was roughly 5% before 1989; this increased to approximately 20% before the introduction of the 7-valent PCV in 2000. Between 2000 and 2010, S pneumoniae strains that were nonsuspectible to penicillin increased to 30% to 50%. A similar phenomenon is occurring following the introduction of PCV-13.

Antibiotic susceptibility of S pneumoniae strains not contained in the PCV-13 were determined using isolates from children. Investigators collected 1201 nasopharyngeal isolates from 2006 to 2016 from 448 children, aged 6 to 36 months, who received care in a primary care setting. Testing for susceptibility to 16 different antibiotics of 10 classes was conducted.

The results showed that after the introduction of PCV-13, antibiotic susceptibility of pneumococci initially improved, significantly to penicillin. In 2013, however, susceptibility among pneumococcal strains began decreasing due to new serotypes not included in PCV-13. Minimum inhibitory concentrations demonstrated a significant decrease in the immediate post-PCV-13 period, with subsequent substantial increases from 2014 to 2016. Along with a reduced susceptibility to penicillin, the most recent isolates demonstrate reduced susceptibility to third-generation cephalosporins, fluoroquinolones, and carbapenems.

The strains evaluated in the came from a primary care setting, which is representative of a population that was consistent with the demographic of suburban communities in the United States. However, investigators acknowledged that, “pneumococcal antibiotic susceptibility patterns are dynamic and may show geographic and/or demographic variation in other settings.” Therefore, the results suggested the need for ongoing studies.  Investigators also did not investigate antibiotic consumption or assess antibiotic treatment failure. Finally, it is also possible that some patients sought care for acute otitis media at other facilities, meaning not every episode was captured.

The investigators concluded that, “beginning in 2013, a decrease in antibiotic susceptibility of pneumococci isolated from children in the primary-care setting occurred due to non-PCV-13 vaccine serotypes.” And, recent isolates show decreasing susceptibility to antibiotics commonly used to treat life-threatening, invasive pneumococcal diseases.

Reference

Kaur R, Pham M, Yu KOA, Pichichero ME. Rising pneumococcal antibiotic resistance in the post 13-valent pneumococcal conjugate vaccine era in pediatric isolates from a primary care setting [published online February 18 2020]. Clin Infect Dis. doi:10.1093/cid/ciaa157