The DISTANCE study: Determining the impact of social distancing on trauma epidemiology during the COVID-19 epidemic-An interrupted time-series analysis

Abstract

Background: The large-scale social distancing efforts to reduce SARS-CoV-2 transmission have dramatically changed human behaviors associated with traumatic injuries. Trauma centers have reported decreases in trauma volume, paralleled by changes in injury mechanisms. We aimed to quantify changes in trauma epidemiology at an urban Level I trauma center in a county that instituted one of the earliest shelter-in-place orders to inform trauma care during future pandemic responses.

Methods: A single-center interrupted time-series analysis was performed to identify associations of shelter-in-place with trauma volume, injury mechanisms, and patient demographics in San Francisco, California. To control for short-term trends in trauma epidemiology, weekly level data were analyzed 6 months before shelter-in-place. To control for long-term trends, monthly level data were analyzed 5 years before shelter-in-place.

Results: Trauma volume decreased by 50% in the week following shelter-in-place (p < 0.01), followed by a linear increase each successive week (p < 0.01). Despite this, trauma volume for each month (March-June 2020) remained lower compared with corresponding months for all previous 5 years (2015-2019). Pediatric trauma volume showed similar trends with initial decreases (p = 0.02) followed by steady increases (p = 0.05). Reductions in trauma volumes were due entirely to changes in nonviolent injury mechanisms, while violence-related injury mechanisms remained unchanged (p < 0.01).

Conclusion: Although the shelter-in-place order was associated with an overall decline in trauma volume, violence-related injuries persisted. Delineating and addressing underlying factors driving persistent violence-related injuries during shelter-in-place orders should be a focus of public health efforts in preparation for future pandemic responses.

Level of evidence: Epidemiological study, level III.

Figure 1

Comparison of trauma volume before and after shelter-in-place. (A) Long-term ITSA for trauma volume at monthly intervals, showing overall decline in trauma team activations for the past 5 years. Pre–shelter-in-place monthly trend from January 2015–February 2020 of 2.8 fewer activations per month (p < 0.01), a level-shift of 26 fewer activations per month with the start of shelter-in-place (p = 0.01), and a nonsignificant rise from March to June less than expected compared with prior years (p = 0.08). (B) Short-term ITSA for volume at weekly intervals showing flat pre–shelter-in-place weekly trend (coefficient 0.06, p = 0.80), a level-shift of 28 fewer activations per week associated with the start of shelter-in-place (p < 0.01), and a post–shelter-in-place linear increase of 2 activations per week (p < 0.01). Lags specified for autocorrelation: 12 months in A, and 4 weeks in B. See Supplemental Tables 1 and 2 (http://links.lww.com/TA/B859) for complete ITSA model results.

Figure 2

Comparison of monthly trauma volume 2015 to 2019 versus 2020. Box and whiskers plots for 2015 to 2019 compared with 2020 values (diamonds) for January through June.

Figure 3

Comparison of pediatric trauma volume before and after shelter-in-place. (A) Long-term ITSA for pediatric trauma volume at monthly intervals, showing a slight decline over past 5 years. Pre–shelter-in-place trend from January 2015 to February 2020 was 0.14 fewer pediatric trauma team activations per month (p < 0.01), with a significant level shift associated with shelter-in-place of 7.0 fewer pediatric trauma team activations (p < 0.01), and increases from March to June not different from corresponding months in prior years (p = 0.72). (B) Short-term ITSA for pediatric trauma volume at weekly intervals demonstrated a decreasing pre–shelter-in-place 6 month trend (coefficient −0.10, p < 0.01), a level shift by one less pediatric trauma team activation per week associated with the first week of shelter-in-place (p < 0.14), post–shelter-in-place trend of 0.15 more trauma team activations per week (p < 0.09), and a slope change from pre– to post–shelter-in-place of 0.25 (p = 0.01). Lags specified for autocorrelation: 12 months in long-term ITSA and 4 weeks in short-term ITSA. See Supplemental Tables 3 and 4 (http://links.lww.com/TA/B859) for complete ITSA model results.

Figure 4

Comparison of monthly pediatric trauma volume 2015 to 2019 versus 2020. Box and whiskers plots for 2015 to 2019 compared with 2020 values (diamonds) for January through June.

Figure 5

Comparison of weekly violence-related vs. nonviolent injury mechanisms before and after shelter-in-place. ITSA model for violence-related versus nonviolent injury mechanisms at weekly intervals, lags specified for autocorrelation: 4 weeks. While pre–shelter-in-place trends for both violence-related and nonviolent injury mechanisms was stable, a large difference in level shift is notable in association with shelter-in-place for nonviolent injury mechanisms, but there was no level change in violence-related injury mechanisms (p < 0.01). After shelter-in-place, a gradual and significant increase in nonviolent injury mechanisms was noted (p < 0.01), but no significant change (slight upward trend) in violence-related injury mechanisms. See Supplemental Table 5B (http://links.lww.com/TA/B859) for complete ITSA model results.

Figure 6

Comparison of number of monthly homicides reported in San Francisco before and after shelter-in-place. (A) Box and whiskers plots of historical homicides reported by month 2016–2019 compared with 2020 values (diamonds). (B) ITSA model for homicides reported by month adjusting for historical variation, showing slight downtrend with seasonal monthly variation from 2016 to 2019, but with a significant level shift increase associated with shelter-in-place of 2.3 more homicides per month compared with historical levels (p = 0.01) and nonsignificant decrease after shelter-in-place (p = 0.15). Lags specified for autocorrelation: 12 months. See Supplemental Table 7 (http://links.lww.com/TA/B859) for complete ITSA model results.