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Antibiotic resistance rises among pneumococcus strains in kids

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What are the implications for treatment

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.


 

FROM CLINICAL INFECTIOUS DISEASES

Antibiotic resistance in strains of Streptococcus pneumoniae has been rising since 2013 because of changing susceptibility profiles, based on data from 1,201 isolates collected from 448 children in primary care settings.

“New strains expressing capsular serotypes not included in the 13-valent pneumococcal conjugate vaccine are emerging to cause disease, and strains that acquire antibiotic resistance are increasing in frequency due to their survival of the fittest advantage,” wrote Ravinder Kaur, PhD, of Rochester (N.Y.) General Hospital Research Institute, and colleagues.

Similar Darwinian principles occurred after the introduction of PCV-7, the study authors added.

In a prospective cohort study published in Clinical Infectious Diseases, the researchers reviewed 1,201 isolates collected from the nasopharynx during healthy periods, and from the nasopharynx and middle ear fluid (MEF) during episodes of acute otitis media, in children aged 6-36 months who were seen in primary care settings.

The isolates were collected during 2006-2016 to reflect the pre- and post-PCV13 era. Children received PCV-7 from 2006 until April 2010, and received PCV-13 after April 2010.

Overall, the number of acute otitis media (AOM) cases caused by S. pneumoniae was not significantly different between the PCV-7 and PCV-13 eras, nor was the frequency of pneumococci identified in the nasopharynx during healthy visits and visits at the start of an AOM infection.

The researchers examined susceptibility using minimum inhibitory concentrations (MIC). During healthy visits, the MIC50 of isolated pneumococci was low (no greater than 0.06 mcg/mL) for all four beta-lactam drugs tested. And it didn’t change significantly over the study years.

In contrast, among the nasopharyngeal and MEF isolates during AOM, the MIC50 to penicillin, amoxicillin, ceftriaxone, and meropenem during 2013-2016 rose significantly, the investigators said.

A change in antibiotic susceptibility within a subtype also contributed to the development of PCV-13 resistance.

The study authors identified three serotypes that affected the changes in susceptibility in their study population. Serotypes 35B and 35F increased their beta-lactam resistance during 2013-2016, and serotype 11A had a higher MIC to quinolones and became more prevalent during 2013-2016. Those three serotypes accounted for most of the change in antibiotic susceptibility, the researchers said.

In addition, “the frequency of strains resistant to penicillin and amoxicillin decreased with the introduction of PCV-13, but rebounded to levels similar to those before PCV-13 introduction by 2015-2016,” the investigators noted.

The study findings were limited by several factors, including the homogeneous study population and potential lack of generalizability to other settings. In addition, the researchers did not study antibiotic consumption or antibiotic treatment failure, and they could not account for potential AOM cases that may have been treated in settings other than primary care.

However, the investigators said the results support the need for additional studies and attention to the development of the next generation of PCVs, the PCV-15 and PCV-20. Both include serotypes 22F and 33F, but neither includes 35B or 35F. The PCV-20 also includes 11A and 15B.

The study was supported in part by the National Institutes of Health and Sanofi Pasteur. Some isolates collected during the 2010-2013 time period were part of a study supported by Pfizer. The researchers had no relevant financial conflicts to disclose.

SOURCE: Kaur R et al. Clin Inf Dis. 2020 Feb 18. doi: 10.1093/cid/ciaa157.

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