Antibiotic resistance rises among pneumococcus strains in kids

Dr. Kaur and colleagues report their analysis of pneumococcal resistance among nasopharyngeal and middle ear isolates (90% nasopharyngeal and 10% middle ear) collected between 2008 and 2016. They demonstrate the dominant role that nonvaccine serotypes play in carriage and acute otitis media (AOM) in children, and by extension potentially the entire spectrum of pneumococcal disease in the 13-valent pneumococcal conjugate vaccine (PCV13) era. Nonsusceptibility to beta-lactams was reported for one-third of isolates with the increase in the most recent reported years (2013-2016).

What are the implications for treatment of pneumococcal infections? For AOM, amoxicillin minimum inhibitory concentrations (MIC) were all less than 4 mcg/mL, which is the pharmacodynamic breakpoint for high-dose (90 mg/kg per day) AOM regimens; these data support continued use of high-dose amoxicillin for children with AOM that requires antimicrobial treatment. Resistance to macrolides (erythromycin and likely azithromycin) occurred in approximately one-third of isolates; however, in contrast to beta-lactams (amoxicillin), higher macrolide doses do not overcome resistance. Thus macrolide use for AOM appears limited to those with beta-lactam allergy and no better alternative drug, i.e., expect failure in one-third of AOM patients if macrolides are used. For ceftriaxone, no 2013-2016 isolate had a MIC over 0.5 mcg/mL, implying that ceftriaxone remains appropriate first-line therapy for serious pneumococcal disease and effective for pneumococcal AOM when oral drugs have failed or are not an option because of repeated emesis. Interestingly, trimethoprim/sulfamethoxazole (T/S) had lower resistance rates against the nonvaccine “bad boy” serogroup 35 (8%-15%), compared with cephalosporins (32%-57%). Perhaps we are back to the future and T/S will again have a role against pneumococcal AOM. Of note, no isolate was resistant to levofloxacin or linezolid. Linezolid or macrolide use alone must be considered with the caveat that nontypeable Haemophilus influenzae now likely surpasses pneumococcus as an AOM pathogen, and neither drug class is active against nontypeable H. influenzae.

What are the implications for prevention? This is one of many studies in the post-PCV era reporting serotype replacement with nonvaccine serotypes. But most prior studies reported reduced overall disease burden; in other words, the absolute number of pneumococcal infections was reduced, but residual AOM nonvaccine types dominated as the etiology. The current study, however, suggests that the overall number of AOM episodes may not be less because increases in AOM caused by nonvaccine serotypes may be offsetting declines in AOM caused by vaccine serotypes. This concept contrasts to multiple large epidemiologic studies demonstrating a decline in overall incidence of AOM office visits/episodes and several Israeli studies reporting a decline in pneumococcal AOM in children who warrant tympanocentesis. These new data are food for thought, but antibiotic resistance can vary regionally, so confirmation based on data from other regions seems warranted.

Next-generation vaccines will need to consider which serotypes are prevalent in pneumococcal disease, including AOM, as we continue into the PCV13 era. However, serotypes causing invasive pneumococcal disease and pneumonia would be higher priorities than AOM. Indeed, several candidate PCV vaccines are currently in clinical trials adding up to seven serotypes, including most of the newly emerging invasive disease serotypes. One downside to the newer PCVs is lack of serogroup 35, a prominent culprit in AOM resistance in the current report.

Stephen I. Pelton, MD, is professor of pediatrics and epidemiology at Boston University and senior attending physician at Boston Medical Center. Christopher J. Harrison, MD, is professor of pediatrics and pediatric infectious diseases at Children’s Mercy Hospital–Kansas City, Mo. Dr. Pelton has received honorarium from Merck Vaccines, Pfizer, and Sanofi for participation in advisory board meeting on pneumococcal vaccine and/or membership on the Data and Safety Monitoring Board. Boston Medical Center has received investigator-initiated research grants from Merck Vaccines and Pfizer.
Children’s Mercy Hospital – Kansas City Boston Medical Center has received funding from GlaxoSmithKline, Merck, and Pfizer for research vaccine studies, and from Pfizer and Merck for investigator-initiated research grants for in vitro pneumococcal investigations on which Dr. Harrison is an investigator.