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COVID-19 Case Investigation and Contact Tracing Efforts from Health Departments – United States, June 25-July 24, 2020

Our take —

In a study of US health departments from June to July 2020, higher COVID-19 caseloads per health department staff member correlated with poorer timeliness of COVID-19 case investigations and lower yield in the number of close contacts elicited from each COVID-19 case investigation. Given the inclusion of data from only 56 health departments and narrow data collection period, results may not reflect contact tracing performance outcomes of health departments not included in this study or at different stages of the SARS-CoV-2 pandemic.

Study design


Study population and setting

Between June 25 and July 31, 2020, investigators calculated COVID-19 contact tracing performance for 56 CDC-funded health departments in the United States. These indicators included average caseload per investigator (ratio of confirmed or probable COVID-19 cases to number of case investigators), average contact tracing load per investigator (ratio of elicited close contacts from case investigations to number of case investigators), case investigation timeliness (proportion of confirmed or probably COVID-19 cases contacted for a case interview within 24 hours of reporting to the health department), contact tracing timeliness (proportion of close contacts elicited from case investigations notified of exposure within 24 hours), and contact tracing yield (ratio of close contacts elicited from a case investigation to number of index COVID-19 cases interviewed). Contact tracing performance metrics were compared using the Spearman correlation coefficient (r).

Summary of Main Findings

During the reporting period of approximately one month, health departments reported a median caseload per investigator of 31 (range: 1–96 cases) and a median of 29 elicited close contacts requiring follow-up per investigator (range: 0.5–200). Among cases prioritized for interview, a median of 1.15 close contacts were elicited per case, and 42/53 (79%) health departments elicited fewer than two close contacts per case. A median of 57% of COVID-19 cases were interviewed within 24 hours of initial case reporting to the health department, and a median of 55% of close contacts were notified of their exposure within 24 hours of initial interview with the index case. Twelve (25%) health departments reported reaching fewer than 32% of elicited close contacts within a 24-hour period. Investigator caseload and case investigation timeliness (correlation coefficient: –0.68) and contact tracing yield (correlation coefficient: –0.60), respectively, were inversely correlated. Correlations were similar across health departments with different staffing models (i.e., allocating different staff members to case investigations and contact tracing, using the same staff members for case investigations and contact tracing, or a mix).

Study Strengths

The study used health system capacity metrics as indicators of contact tracing performance. Indicator correlations were also compared across health departments that allocated staff to case investigations and contact tracing efforts in different ways, which supports the consistency of reported correlations across different contact tracing models.


The study’s unit of analysis was the health department, rather than the individual case investigator or contact tracer; this prevented investigators from attributing contact tracing performance outcomes to unmeasured differences in staff member characteristics (e.g., individual caseload, training, years of experience) beyond the contextual factors (i.e., average caseload per investigator) reported in this study. Furthermore, the reported correlations in this study may be entirely spurious; these unadjusted estimates do not control or account for other factors, like SARS-CoV-2 incidence and laboratory capacity, that could confound the relationship between health department characteristics and contact tracing performance indicators. Because data from only 56 health departments were included in this study, the results may not be generalizable to health departments that did not participate. Similarly, because data were collected in a narrow timeframe (June–July, 2020), these results may not reflect contact tracing performance at different stages in the SARS-CoV-2 pandemic with varying health department staffing capacity and contact tracing demands.

Value added

This is among the first studies to correlate health workforce capacity and health systems indicators to performance outcomes of COVID-19 contact tracing efforts.

This review was posted on: 19 February 2021