To characterize the prevalence and 48-week dynamics of enterovirus D68 (EV-D68) neutralizing antibodies among adult retail workers in Quebec City during the COVID-19 pandemic.
Approach:
Study Design and Population: Paired serum samples were obtained from 194 retail workers aged 18 years or older who were enrolled in a prospective SARS-CoV-2 cohort in Quebec City, Canada.
Sampling: Samples were collected 48 weeks apart, at visit 1 from June through October 2021 and at visit 5 from May through October 2022.
Neutralization Assay: Live microneutralization assays using the 2014 EV-D68 clade B1 strain US/MO/14/18949 measured antibodies that completely inhibited EV-D68–induced cytopathic effects. A neutralizing titer of at least 1:20 defined seropositivity.
Analysis: Geometric mean titers (GMTs) and geometric mean ratios (GMRs) were calculated. A change of at least 4-fold between visits defined a significant individual increase or decrease, and subgroup analyses examined sex, age, comorbidities, gathering exposure, and SARS-CoV-2 serologic status.
Key Findings:
EV-D68 neutralizing-antibody seropositivity exceeded 85% at both visits.
Overall GMT declined significantly from 69 at visit 1 to 59 at visit 5 (GMR, 0.85; 95% CI, 0.75–0.97; *P* = .0035).
Most participants—180 of 194 (93%)—maintained titers within a less than 4-fold range over 48 weeks.
Titers declined significantly among women and participants aged 40–59 years, whereas the decline among men was not statistically significant.
Significant within-group declines were also observed among participants with obesity or diabetes, those reporting fewer than 10 gatherings, and those with positive SARS-CoV-2 serology.
Six participants (3%) had an increase of at least 4-fold, with GMT rising from 21 to 593; this pattern was consistent with possible recent EV-D68 or other enterovirus exposure.
Eight participants (4%) had a decrease of at least 4-fold, with GMT declining from 129 to 13.
Interpretation:
The high seropositivity observed in this adult retail-worker cohort was consistent with substantial previous EV-D68 exposure. Although overall neutralizing-antibody levels declined over 48 weeks, most participants remained within a 4-fold titer range. The marked increases observed in 6 participants raise the possibility of EV-D68 or another enterovirus circulating in Quebec after nonpharmaceutical interventions were relaxed, but the small number of increases and potential cross-neutralization require cautious interpretation.
Limitations:
Cross-neutralization by antibodies against other nonpolio enteroviruses may have contributed to the high observed seropositivity.
Serum was tested only against a 2014 EV-D68 clade B1 strain, so the study could not distinguish antibodies generated by earlier B1 or B2 circulation from those induced by more recently circulating B3 and A2(D) strains.
Testing against only the B1 strain may not have captured the full breadth of neutralizing-antibody responses because titers can vary by EV-D68 subclade.
An antibody increase could reflect EV-D68 exposure or a cross-reactive response to another enterovirus.
Only 6 participants experienced a significant titer increase, requiring cautious interpretation of possible viral circulation.
Conclusion:
EV-D68 neutralizing antibodies were detected in more than 85% of participants, and titers declined overall during 48 weeks of follow-up while remaining within a 4-fold range for most individuals. Marked titer increases in a small subgroup were consistent with possible ongoing EV-D68 or other enterovirus circulation. Studies using contemporary viral strains in similar adult cohorts are needed to characterize cross-subclade immunity and strengthen adult EV-D68 serologic surveillance.
