Public Health Unit, Agrupamento de Centros de Saúde Grande Porto VIII-Espinho/Gaia, ARS Norte, Porto, Portugal.
Department of Community Medicine, Information and Health Decision Sciences (MEDCIDS), Faculty of Medicine, University of Porto, Porto, Portugal.
Public Health Rep. 2022 Nov-Dec;137(6):1178-1186. doi: 10.1177/00333549221114343. Epub 2022 Aug 20.
Information on the effectiveness of COVID-19 contact tracing is lacking. We proposed 2 measures for evaluating the effectiveness of contact tracing and applied them in a public health unit in northern Portugal.
This retrospective cohort study included the contacts of people with COVID-19 diagnosed July 1-September 15, 2020. We examined 2 measures: (1) number needed to quarantine (NNQ), as the number of quarantine person-days needed to prevent 1 potential infectious person-day; and (2) proportion of prevented infectious days by quarantine (PPID), as the number of potential infectious days prevented by quarantine divided by all infectious days. We assessed these measures by sociodemographic characteristics, types of contacts, and intervention timings (ie, time between diagnosis or symptom onset and intervention). We considered 3 scenarios for infectiousness periods: 10 days before to 10 days after symptom onset, 3 days before to 3 days after symptom onset, and 2 days before to 10 days after symptom onset.
We found an NNQ of 19.8-41.8 person-days and a PPID of 19.7%-38.2%, depending on the infectiousness period scenario. Effectiveness was higher among cohabitants and symptomatic contacts than among social or asymptomatic contacts. NNQ and PPID changed by intervention timings: the effectiveness of contact tracing decreased with time from diagnosis to quarantine of contacts and with time from symptom onset of the index case to contacts' quarantine.
These proposed measures of contact tracing effectiveness of communicable diseases can be important for decision making and prioritizing contact tracing when resources are scarce. They are also useful measures for communication with the general population, policy makers, and clinicians because they are easy to understand and use to assess the impact of health interventions.
关于 COVID-19 接触者追踪效果的信息有限。我们提出了 2 种评估接触者追踪效果的措施，并在葡萄牙北部的一个公共卫生部门进行了应用。
这项回顾性队列研究纳入了 2020 年 7 月 1 日至 9 月 15 日期间被诊断患有 COVID-19 的患者的接触者。我们检测了 2 种措施：（1）需要隔离的人数（NNQ），即预防 1 个潜在感染人日所需的隔离人日数；（2）通过隔离预防的感染日比例（PPID），即通过隔离预防的潜在感染日数除以所有感染日数。我们根据社会人口学特征、接触者类型和干预时机（即诊断或症状出现与干预之间的时间）评估了这些措施。我们考虑了 3 种感染期情景：症状出现前 10 天至后 10 天、症状出现前 3 天至后 3 天以及症状出现前 2 天至后 10 天。
我们发现，根据感染期情景，NNQ 为 19.8-41.8 人日，PPID 为 19.7%-38.2%。在共同居住者和有症状的接触者中，有效性高于社交接触者或无症状接触者。NNQ 和 PPID 随干预时机而变化：从接触者诊断到接触者隔离的时间以及从指数病例症状出现到接触者隔离的时间，接触者追踪的有效性会降低。
这些传染病接触者追踪效果的建议措施在资源有限时，可用于决策和优先考虑接触者追踪。对于与一般人群、政策制定者和临床医生的沟通，这些措施也是有用的，因为它们易于理解且可用于评估卫生干预措施的影响。
