The Effectiveness of Contact Tracing to Reduce Transmission of Infectious Diseases During Epidemic or Pandemic Response: Rapid Systematic Review.

backgroundContact tracing (CT), the process of identifying and managing contacts of infected cases, is one public health and social measure that may reduce the spread of infectious diseases. While previous systematic reviews of CT exist, a comprehensive review of both the effectiveness and potential unintended consequences has not been undertaken to our knowledge. Understanding effective CT strategies could help governments and health authorities prepare effectively for emergency epidemic or pandemic situations.

objectiveThis study aims to systematically review the evidence on the effectiveness of CT across infectious diseases with epidemic or pandemic potential. Effectiveness is measured in terms of impacts on disease transmission, health care use, mortality, or unintended consequences.

methodsWe searched 6 bibliographic databases (MEDLINE, Embase, Global Health, CINAHL Ultimate, Cochrane, and Scopus) between November 29 and December 3, 2024, with supplementary citation searching. We sought human studies comparing CT with interventions with no CT or other forms of CT, delivered in the community, in prespecified diseases of epidemic or pandemic potential. We included studies with any measure of disease transmission, related health care use, or unintended consequences of CT and prioritized studies with concurrent comparators. Screening, data extraction, and critical appraisal were performed in duplicate. Due to substantial heterogeneity, a narrative synthesis was performed. This review was informed by meetings with a patient and public involvement and engagement group.

resultsAfter deduplication, a total of 12,816 titles and abstracts were screened, with 198 records assessed for eligibility at full text. Five additional studies were found through supplementary searching. Finally, 88 reports (of 86 studies) were included, of which 57 reports (of 55 studies) were prioritized. Two main routes of transmission were represented: respiratory (tuberculosis [TB], 15 studies; COVID-19, 5 studies) and blood-borne or sexually transmitted infections (STIs; 35 studies, of which 13 were in HIV, and 22 were bacterial or parasitic infections). No evidence was found on vector-borne, direct contact, or food- or water-borne routes of transmission. Evidence was highly heterogeneous, and more than half of the studies had notable methodological limitations. While there was no difference between CT and comparator interventions for most outcomes, there was some evidence of reductions in disease prevalence in TB and for provider-initiated CT to be superior to patient-led approaches in STIs. Only 2 studies reported measures of unintended consequences.

conclusionsWe found inconsistent evidence for the effectiveness of CT, focused primarily on TB and on contrasts between provider-initiated CT and patient-led referral in STIs and HIV. High heterogeneity in study design precluded clear assertions regarding optimal strategies for CT, including with respect to relevant subgroups. Future work should consider generalizability of CT mechanisms across contexts, including by route of transmission and from the Global South, and a more thorough account of unintended consequences.