Chest CT-detected pulmonary nodules across the COVID-19 pandemic in Guangzhou, China: a regression discontinuity-in-time study, 2013-2023.

Background: Chest computed tomography (CT) examinations became more frequent during and after the coronavirus disease 2019 (COVID-19) pandemic, increasing incidental pulmonary nodule detection and concern about surveillance burden and lung cancer risk. Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection can cause persistent focal pulmonary abnormalities that may resemble nodules on CT. Population-level evidence on changes in pulmonary nodule detection or progression after vaccination and widespread infection remains limited. We aimed to determine whether COVID-19 vaccination phases and the late-2022 SARS-CoV-2 infection wave were associated with abrupt changes in pulmonary nodule detection or CT-based progression. Methods: We conducted a retrospective cohort study using records from The First Affiliated Hospital of Guangzhou Medical University and the Guangzhou Cadre Health Management Center in Guangzhou, China. We analyzed 772,506 chest CT scans acquired from January 2013 to December 2023, including 627,164 inpatient scans, 46,411 hospital health-examination scans, and 98,931 cadre health-examination scans. Monthly pulmonary nodule detection and progression rates were calculated using 6-30 mm as the main nodule-size criterion and 0-30 mm as a secondary criterion. Regression discontinuity-in-time (RDiT) analyses examined four prespecified calendar time points: the first, second, and third COVID-19 vaccination phases in December 2020, June 2021, and September 2021, respectively, and the concentrated SARS-CoV-2 infection wave beginning in December 2022 after China's late-2022 policy restructuring. Results: The cohorts included 328,223 inpatients, 29,279 hospital health examinees, and 46,587 cadre health examinees. Median ages were 55 [interquartile range (IQR), 43-65], 46 (IQR, 36-54), and 50 (IQR, 43-57) years, respectively. Male proportions were 53.57%, 47.69%, and 66.81%. From 2013 to 2023, detection rates for 6-30 mm nodules increased from 25.85% to 31.19% in the inpatient cohort, from 12.11% to 21.64% in the hospital health-examination cohort, and from 18.38% to 29.49% in the cadre health-examination cohort. Nodules smaller than 6 mm accounted for an increasing share of detections over time. RDiT analyses showed no reproducible abrupt increase in 6-30 mm nodule detection around the three vaccination phases or the late-2022 SARS-CoV-2 infection wave. Detection P values ranged from 0.06 to 0.85, and progression P values, where estimable, ranged from 0.058 to 0.94. Secondary analyses using the 0-30 mm criterion and sex-specific inpatient analyses showed consistent patterns. Conclusions: In these Guangzhou cohorts, the gradual increase in pulmonary nodule detection from 2013 to 2023 primarily reflected greater ascertainment of nodules smaller than 6 mm. COVID-19 vaccination phases and the late-2022 SARS-CoV-2 infection wave were not accompanied by consistent abrupt increases in 6-30 mm nodule detection or progression.