High rates of antimicrobial resistance (AMR) in adults with pneumococcal disease might require even higher valent pneumococcal conjugate vaccines (PCVs), according to a new study.

The report in Open Forum Infectious Diseases assessed AMR trends for Streptococcus pneumoniae isolates from adults with pneumococcal disease.

From January 2011 to February 2020, industry investigators evaluated 30-day nonduplicate S pneumoniae isolates from 290 U.S. hospitals utilizing the BD Insights Research Database from adults in inpatient and outpatient settings. The focus was on isolates that had more than one AMR result for invasive (i.e., blood, cerebrospinal fluid/neurologic) or noninvasive (i.e., respiratory or ear/nose/throat) pneumococcal disease samples. Within the study period, 34,039 S pneumoniae isolates were analyzed—61% from noninvasive sources and 39% from invasive sources.

The results indicated that 46.6% of the isolates were resistant to one or more drugs, and noninvasive isolates had higher rates of AMR than invasive isolates. The researchers reported that total S pneumoniae isolates had high rates of resistance to:

• Macrolides (37.7%)
• Penicillin (22.1%)
• Tetracyclines (16.1%).

Multivariate modeling identified a significant increasing trend in resistance to macrolides (+1.8%/year; P <.001), while significant decreasing trends were observed for penicillin (–1.6%/year; P <.001), extended-spectrum cephalosporins (ESCs; –0.35%/year; P <.001), and three or more drugs (–0.5%/year; P <.001).

“Despite decreasing trends for penicillin, ESCs, and resistance to ≥3 drugs, AMR rates are persistently high in S pneumoniae isolates among U.S. adults,” the authors wrote. “Increasing macrolide resistance suggests that efforts to address AMR in S pneumoniae may require antimicrobial stewardship efforts and higher valent pneumococcal conjugate vaccines.”

Background information in the article advised that—despite the availability of pneumococcal vaccines and antibiotics, which have led to substantial declines in pneumococcal disease—S pneumoniae “continues to exert a heavy burden on individuals and health care systems.”

In the United States, approximately 2 million pneumococcal infections occur annually, resulting in more than 6,000 deaths and costs of $4 billion. Pneumococcal infections can be either noninvasive (e.g., otitis media, sinusitis, and community-acquired pneumonia), or invasive pneumococcal disease (IPD), which occurs when pneumococcal bacteria enter a sterile site such as the bloodstream (bacteremia) or cerebrospinal fluid (meningitis).

In the U.S., more than 90% of IPD cases are in adults, with those aged 65 years and older having the highest rates of IPD and mortality.

“As with overall IPD cases in the United States, AMR in adult pneumococcal disease is driven largely by serotypes not covered by PCV13, and this trend is most pronounced in adults ≥65 years of age,” the researchers emphasized. “The introduction of PCV vaccines has been associated with significant reductions in pneumococcal disease and in S pneumoniae AMR, and hypothetical models support additional benefits with new PCVs recently approved for use in adults.”

The problem, however, is the low vaccination rates. The study reported that adult pneumococcal vaccination rates in the U.S. as of the 2018 National Health Interview Survey data were 23.3% for adults at increased risk of pneumococcal disease and 69.0% in adults aged 65 years or older.

“Both rates are far below the CDC 2020 Healthy People goals of 60% and 90%, respectively,” the authors noted. “Although pneumococcal vaccination is currently not recommended for low-risk adults aged 50–64, our results show that this age group had the most S pneumoniae isolates for both IPD (34.6%) and non-IPD (34.8%), suggesting that this population may also benefit from pneumococcal vaccination.”

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