An analysis today by the Centers for Disease Control and Prevention (CDC) of COVID-19 case investigation and contact tracing data from 56 US health departments shows that heavy investigator caseloads and an unengaged public may hinder the ability to locate and quarantine contacts in a timely manner.
The study, published in Morbidity and Mortality Weekly Report, used health department reports from Jun 25 to Jul 24, 2020, to determine the effectiveness of case investigation and contact tracing in mitigating the transmission of SARS-CoV-2, the virus that causes COVID-19, through rapid identification, testing, and quarantine of contacts.
Sixty-two of 64 health departments funded by the Epidemiology and Laboratory Capacity for Prevention and Control of Emerging Infectious Diseases Cooperative Agreement submitted data on average caseload per investigator, case investigation timeliness, and contact tracing timeliness and yield. Four health departments reported no COVID-19 cases, and two were excluded after submitting only partial data.
Among the 56 remaining health departments, researchers found wide variation in capacity and ability to conduct rapid, effective contact tracing and uncovered an inverse relationship between investigator caseload and timely interviewing of patients and number of contacts per case.
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Patients name few contacts
The median caseload per investigator was 31 (range, 1 to 196), and the median number of contacts assigned for follow-up per investigator was 29 (range, 0.5 to 200). On average, health department contact tracers interviewed 57% of COVID-19 patients within 24 hours after their case was reported (interquartile range [IQR], 27% to 82%).
Patients prioritized for an interview identified a median of only 1.15 contacts (IQR, 0.62 to 1.76), 55% of whom contact tracers notified within 24 hours of identification (IQR, 32% to 79%). But 12 health departments reported that less than 32% of contacts were contacted within 24 hours.
When contact tracers had heavier caseloads, the percentage of coronavirus patients interviewed within 24 hours of case report fell, as did the number of contacts identified per patient. Health departments with smaller average investigator caseloads interviewed more patients within 24 hours of report than those with larger caseloads. These trends were observed in health departments that assigned different, mostly different, or the same workers to be case investigators and contact tracers.
Of four health departments that interviewed more than 90% of patients within 24 hours, median investigator caseloads were fewer than 30 patients, while among four health departments with median investigator caseloads of more than 130 patients, less than 30% of interviews were conducted within that timeframe.
Because health departments weren’t given guidance on prioritization of patient interviews, they created their own practices, such as interviewing COVID-19 patients when their case was reported or prioritizing interviews based on whether patients had symptoms or underlying conditions, lived in congregate-care facilities, or worked in healthcare.
Public awareness, cooperation needed
The authors said that the low numbers of patient contacts identified might be linked to patient hesitance to engage in contact tracing efforts or to name people other than household contacts. “Strengthening awareness regarding state and local health department contact tracing efforts might improve community perception or willingness to provide more complete lists of contacts,” they wrote.
Delays in patient interviews and in reaching, testing, and quarantining contacts impairs the ability to slow coronavirus transmission, the researchers said. “The capacity to conduct timely contact tracing varied among health departments, largely driven by investigators’ caseloads,” they wrote. “Incomplete identification of contacts affects the ability to reduce transmission of SARS-CoV-2.”
The authors concluded that increasing staffing levels and improving community engagement in the contact tracing process could shorten the time to patient interviews and identification of more contacts. “Continued efforts to ensure notification of patients of their infection and contacts of their exposure are needed,” they wrote. “CDC recommends use of prioritization measures to reach populations at risk as well as use of innovative technologies to support this public health imperative.”