Definition and research guide
This page combines a MeSH definition, publication statistics and selected research abstracts. It is a starting point for reading the literature, not a medical textbook or a systematic evidence review.
Content available: 4 complete abstracts (885 words), 10 references. Full article text is not stored or reproduced here; follow the PMID, DOI or PMC links to read the original sources and their access terms.
Definition
Identification of those persons (or animals) who have had such an association with an infected person, animal, or contaminated environment as to have had the opportunity to acquire the infection.
Definition: NLM Medical Subject Headings (MeSH) scope note (Public domain (U.S. National Library of Medicine); attribution requested). View the MeSH record.
Also known as: Tracing, Contact; Communicable Disease Contact Tracing; Contact Investigation; Investigation, Contact; Contact Screening; Screening, Contact; Infectious Disease Contact Tracing; Notification, Partner.
Where it fits in the MeSH classification
- Broader topics
- Epidemiologic Methods; Communicable Disease Control
Research landscape
PubMed indexes 6,939 records tagged with the MeSH heading “Contact Tracing” (counts retrieved 2026-10-29). 2,661 of them (38.3%) were published from 2020 onward, and the busiest period so far is 2020 onward with 2,661 records.
Reviews account for 598 records (8.6%) and meta-analyses for 45. Randomized controlled trials number 108 (1.6%) as a share of all records on the topic. Randomized trials make up only a small share of this literature, so much of what is known comes from laboratory, observational or descriptive work.
Show the data
| Period | Records |
|---|---|
| through 1999 | 966 |
| 2000-2009 | 1,432 |
| 2010-2019 | 1,880 |
| 2020 onward | 2,661 |
Publication-type chart data
| Type | Records | Share |
|---|---|---|
| Reviews | 598 | 8.6% |
| Meta-analyses | 45 | 0.6% |
| Randomized controlled trials | 108 | 1.6% |
Method: PubMed query "Contact Tracing"[MeSH Terms] with publication-type and date filters, retrieved 2026-10-29.
Reading the evidence in clinical research
Research methods determine how much a result can be trusted. Randomized trials guard against confounding, systematic reviews and meta-analyses combine many studies, and observational designs are valuable but can show only association. Reporting standards, trial registration and pre-specified outcomes reduce bias. When reading about a method, ask what problem it is designed to solve and which problems it does not solve.
Evidence from open-access studies
These open-access studies come from PubMed’s best-match results for this heading (papers whose main topic it is), ranked here by citation count, with one recent addition. Each abstract is reproduced in full under its recorded open licence so that you can read the authors’ own words. They illustrate the literature; they are not a systematic summary of it. Citation counts measure attention, not reliability or clinical benefit.
| Study / authors | Year | Source label / design | Europe PMC citations | Licence / source |
|---|---|---|---|---|
| Viral infection and transmission in a large, well-traced outbreak caused by the SARS-CoV-2 Delta variant | 2022 | Research article Design not recorded in structured metadata | 385 | cc by PMID 35075154 · DOI · PMC8786931 |
| Cross-reactive memory T cells associate with protection against SARS-CoV-2 infection in COVID-19 contacts | 2022 | Research article Design not recorded in structured metadata | 298 | cc by PMID 35013199 · DOI · PMC8748880 |
| COVID-19 Case Investigation and Contact Tracing in the US, 2020 | 2021 | Research article Design not recorded in structured metadata | 85 | cc by PMID 34081135 · DOI · PMC8176334 |
| Impact of temporal patterns in working contacts on epidemic spread | 2026 | Research article Design not recorded in structured metadata | 1 | cc by PMID 42542443 · DOI · PMC13428738 |
Viral infection and transmission in a large, well-traced outbreak caused by the SARS-CoV-2 Delta variant [1]
Abstract reading summary — source excerpts
- Opening excerpt
- The SARS-CoV-2 Delta variant has spread rapidly worldwide.
- Closing excerpt
- However, the transmission of minor iSNVs resulted in at least 3 of the 34 substitutions that were identified in the outbreak, highlighting the contribution of intra-host variants to population-level viral diversity during rapid spread.
- Interpretation limits
- Verbatim excerpts from the authors’ abstract; the closing excerpt may describe a finding, limitation or recommendation. Design, population, effect size and uncertainty have not been independently extracted or appraised. Read the complete abstract and linked paper before interpreting the findings.
Read complete abstract (147 words)
The SARS-CoV-2 Delta variant has spread rapidly worldwide. To provide data on its virological profile, we here report the first local transmission of Delta in mainland China. All 167 infections could be traced back to the first index case. Daily sequential PCR testing of quarantined individuals indicated that the viral loads of Delta infections, when they first become PCR-positive, were on average ~1000 times greater compared to lineage A/B infections during the first epidemic wave in China in early 2020, suggesting potentially faster viral replication and greater infectiousness of Delta during early infection. The estimated transmission bottleneck size of the Delta variant was generally narrow, with 1-3 virions in 29 donor-recipient transmission pairs. However, the transmission of minor iSNVs resulted in at least 3 of the 34 substitutions that were identified in the outbreak, highlighting the contribution of intra-host variants to population-level viral diversity during rapid spread.
Abstract reproduced from the open-access article under the recorded cc by licence; © the authors. PMID 35075154 · DOI · PMC8786931
Cross-reactive memory T cells associate with protection against SARS-CoV-2 infection in COVID-19 contacts [2]
Abstract reading summary — source excerpts
- Opening excerpt
- Cross-reactive immune responses to SARS-CoV-2 have been observed in pre-pandemic cohorts and proposed to contribute to host protection.
- Closing excerpt
- Our results are thus consistent with pre-existing non-spike cross-reactive memory T cells protecting SARS-CoV-2-naïve contacts from infection, thereby supporting the inclusion of non-spike antigens in second-generation vaccines.
- Interpretation limits
- Verbatim excerpts from the authors’ abstract; the closing excerpt may describe a finding, limitation or recommendation. Design, population, effect size and uncertainty have not been independently extracted or appraised. Read the complete abstract and linked paper before interpreting the findings.
Read complete abstract (158 words)
Cross-reactive immune responses to SARS-CoV-2 have been observed in pre-pandemic cohorts and proposed to contribute to host protection. Here we assess 52 COVID-19 household contacts to capture immune responses at the earliest timepoints after SARS-CoV-2 exposure. Using a dual cytokine FLISpot assay on peripheral blood mononuclear cells, we enumerate the frequency of T cells specific for spike, nucleocapsid, membrane, envelope and ORF1 SARS-CoV-2 epitopes that cross-react with human endemic coronaviruses. We observe higher frequencies of cross-reactive (p = 0.0139), and nucleocapsid-specific (p = 0.0355) IL-2-secreting memory T cells in contacts who remained PCR-negative despite exposure (n = 26), when compared with those who convert to PCR-positive (n = 26); no significant difference in the frequency of responses to spike is observed, hinting at a limited protective function of spike-cross-reactive T cells. Our results are thus consistent with pre-existing non-spike cross-reactive memory T cells protecting SARS-CoV-2-naïve contacts from infection, thereby supporting the inclusion of non-spike antigens in second-generation vaccines.
Abstract reproduced from the open-access article under the recorded cc by licence; © the authors. PMID 35013199 · DOI · PMC8748880
COVID-19 Case Investigation and Contact Tracing in the US, 2020 [3]
Abstract reading summary — source excerpts
- Opening excerpt
- ImportanceContact tracing is a multistep process to limit SARS-CoV-2 transmission.
- Closing excerpt
- These findings are relevant to decisions regarding the allocation of public health resources among the various prevention strategies and for the prioritization of case investigations and contact tracing efforts.
- Interpretation limits
- Verbatim excerpts from the authors’ abstract; the closing excerpt may describe a finding, limitation or recommendation. Design, population, effect size and uncertainty have not been independently extracted or appraised. Read the complete abstract and linked paper before interpreting the findings.
Read complete abstract (399 words)
ImportanceContact tracing is a multistep process to limit SARS-CoV-2 transmission. Gaps in the process result in missed opportunities to prevent COVID-19.ObjectiveTo quantify proportions of cases and their contacts reached by public health authorities and the amount of time needed to reach them and to compare the risk of a positive COVID-19 test result between contacts and the general public during 4-week assessment periods.Design, setting, and participantsThis cross-sectional study took place at 13 health departments and 1 Indian Health Service Unit in 11 states and 1 tribal nation. Participants included all individuals with laboratory-confirmed COVID-19 and their named contacts. Local COVID-19 surveillance data were used to determine the numbers of persons reported to have laboratory-confirmed COVID-19 who were interviewed and named contacts between June and October 2020.Main outcomes and measuresFor contacts, the numbers who were identified, notified of their exposure, and agreed to monitoring were calculated. The median time from index case specimen collection to contact notification was calculated, as were numbers of named contacts subsequently notified of their exposure and monitored. The prevalence of a positive SARS-CoV-2 test among named and tested contacts was compared with that jurisdiction's general population during the same 4 weeks.ResultsThe total number of cases reported was 74 185. Of these, 43 931 (59%) were interviewed, and 24 705 (33%) named any contacts. Among the 74 839 named contacts, 53 314 (71%) were notified of their exposure, and 34 345 (46%) agreed to monitoring. A mean of 0.7 contacts were reached by telephone by public health authorities, and only 0.5 contacts per case were monitored. In general, health departments reporting large case counts during the assessment (≥5000) conducted smaller proportions of case interviews and contact notifications. In 9 locations, the median time from specimen collection to contact notification was 6 days or less. In 6 of 8 locations with population comparison data, positive test prevalence was higher among named contacts than the general population.Conclusions and relevanceIn this cross-sectional study of US local COVID-19 surveillance data, testing named contacts was a high-yield activity for case finding. However, this assessment suggests that contact tracing had suboptimal impact on SARS-CoV-2 transmission, largely because 2 of 3 cases were either not reached for interview or named no contacts when interviewed. These findings are relevant to decisions regarding the allocation of public health resources among the various prevention strategies and for the prioritization of case investigations and contact tracing efforts.
Abstract reproduced from the open-access article under the recorded cc by licence; © the authors. PMID 34081135 · DOI · PMC8176334
Impact of temporal patterns in working contacts on epidemic spread [4]
Abstract reading summary — source excerpts
- Opening excerpt
- Most models for infectious disease spread simplify contact heterogeneity by assuming constant rates within a week.
- Closing excerpt
- We conclude that weekly contact dynamics should be explicitly incorporated into epidemic models to avoid systematic errors in reproduction number estimation.
- Interpretation limits
- Verbatim excerpts from the authors’ abstract; the closing excerpt may describe a finding, limitation or recommendation. Design, population, effect size and uncertainty have not been independently extracted or appraised. Read the complete abstract and linked paper before interpreting the findings.
Read complete abstract (181 words)
Most models for infectious disease spread simplify contact heterogeneity by assuming constant rates within a week. However, empirical studies show clear variation, such as reduced workplace contacts on weekends. In this work, we investigate the effects of daily variation in workplace contacts on the spread of respiratory infections using the individual-based framework GEMS (German Epidemic Micro-Simulation System) with a synthetic population of 5 million individuals. We compare the scenario with uniform daily contacts to the scenario with more contacts on workdays and fewer on weekends, keeping weekly totals constant. Simulations reveal that uniform contact rates yield higher prevalence for short latent periods (1-2 days) and lower prevalence for longer latencies (5-6 days). The effect diminishes for long infectious periods (≥ 7 days) but is more pronounced at lower basic reproduction numbers. Depending on the disease specification and the differences in weekday contacts, the impact of weekday heterogeneity can be very strong. These findings open new possibilities for weekday-dependent mitigation measures. We conclude that weekly contact dynamics should be explicitly incorporated into epidemic models to avoid systematic errors in reproduction number estimation.
Abstract reproduced from the open-access article under the recorded cc by licence; © the authors. PMID 42542443 · DOI · PMC13428738
Key reviews and meta-analyses
The most cited review-type papers among PubMed’s best-match results for this heading, listed with bibliographic details only. Follow the links for the full text and access terms.
- Research article Design and analysis of stepped wedge cluster randomized trials [5]
- Research article An evidence review of face masks against COVID-19 [6]
- Research article Contact investigation for tuberculosis: a systematic review and meta-analysis [7]
- Research article Tuberculosis and latent tuberculosis infection in close contacts of people with pulmonary tuberculosis in low-income and middle-income countries: a systematic review and meta-analysis [8]
- Research article Guidelines for the investigation of contacts of persons with infectious tuberculosis. Recommendations from the National Tuberculosis Controllers Association and CDC [9]
- Research article The risk of tuberculosis in children after close exposure: a systematic review and individual-participant meta-analysis [10]
References
- Li B, Deng A, Li K, Hu Y, Li Z, Shi Y, et al.. Viral infection and transmission in a large, well-traced outbreak caused by the SARS-CoV-2 Delta variant. . 2022. PMID 35075154 · DOI · PMC8786931
- Kundu R, Narean JS, Wang L, Fenn J, Pillay T, Fernandez ND, et al.. Cross-reactive memory T cells associate with protection against SARS-CoV-2 infection in COVID-19 contacts. . 2022. PMID 35013199 · DOI · PMC8748880
- Lash RR, Moonan PK, Byers BL, Bonacci RA, Bonner KE, Donahue M, et al.. COVID-19 Case Investigation and Contact Tracing in the US, 2020. . 2021. PMID 34081135 · DOI · PMC8176334
- Bryzgalov A, Ponge J, Suer J, Krueger T, Musundi B, Xu C, et al.. Impact of temporal patterns in working contacts on epidemic spread. . 2026. PMID 42542443 · DOI · PMC13428738
- Hussey MA, Hughes JP. Design and analysis of stepped wedge cluster randomized trials. Contemp Clin Trials. 2007. PMID 16829207 · DOI
- Howard J, Huang A, Li Z, Tufekci Z, Zdimal V, van der Westhuizen HM, et al.. An evidence review of face masks against COVID-19. Proc Natl Acad Sci U S A. 2021. PMID 33431650 · DOI · PMC7848583
- Fox GJ, Barry SE, Britton WJ, Marks GB. Contact investigation for tuberculosis: a systematic review and meta-analysis. Eur Respir J. 2013. PMID 22936710 · DOI · PMC3533588
- Morrison J, Pai M, Hopewell PC. Tuberculosis and latent tuberculosis infection in close contacts of people with pulmonary tuberculosis in low-income and middle-income countries: a systematic review and meta-analysis. Lancet Infect Dis. 2008. PMID 18450516 · DOI
- National Tuberculosis Controllers Association, Centers for Disease Control and Prevention (CDC). Guidelines for the investigation of contacts of persons with infectious tuberculosis. Recommendations from the National Tuberculosis Controllers Association and CDC. MMWR Recomm Rep. 2005. PMID 16357823
- Martinez L, Cords O, Horsburgh CR, Andrews JR, Pediatric TB Contact Studies Consortium. The risk of tuberculosis in children after close exposure: a systematic review and individual-participant meta-analysis. Lancet. 2020. PMID 32199484 · DOI · PMC7289654
About this article
- Sources
- NLM Medical Subject Headings (definition, synonyms); NCBI PubMed (counts, identifiers); Europe PMC (open-access abstracts and citation counts).
- Verification
- Every reference was resolved against PubMed on 2026-10-31; title, year and DOI matched.
- Review state
- automated source verified; no human expert review has been recorded yet.
- Version
- 1, last updated 2026-10-29.
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Evidence strength
EvidenceHelix's computed view of the study designs behind this topic: how common meta-analyses, randomized trials and reviews are, how recent the literature is, and a plain-language reading. It describes the design mix of the literature. It is not a quality appraisal of any study, and it is not medical advice.