Original Article

Factors Affecting COVID-19 Transmission and Modelling of Close Contact Tracing Strategies



Background: Close contact tracing is an essential measure that countries are applying to combat the epidemic of COVID-19. The purpose of contact tracing is to rapidly identify potentially infected individuals and prevent further spread of the disease. In this study, based on the factors affecting the COVID-19 transmission, a scoring protocol is provided for close contact tracing.

Methods: First, the factors affecting the COVID-19 transmission in close contacts were identified by a rapid review of the literature. Data were gathered by searching the Embase, PubMed, Google Scholar, and Scopus databases. Then, by formulating and scoring the identified factors with two sessions of the expert panel, close contact transmission risk score determined, and a protocol for contacts tracing was designed.

Results: Close contact transmission risk depends on the contact environment characteristics, the infectivity (virus shedding) of the sentinel case, and contact characteristics. Based on these factors, the close contact transmission risk score and contact tracing protocol were prepared.  

Conclusion: The close contact transmission risk scores will provide the ability to contact classifications and developing specific tracing strategies for them. Given that there are not any specific treatments for COVID-19 and lack of universal vaccination, applying nonpharmaceutical measures such as contact tracing along with physical distancing is very crucial. Therefore, we recommended this model to the evaluation of exposure risk and contact tracing.

1. Harapan H, Itoh N, Yufika A, et al (2020). Coronavirus disease 2019 (COVID-19): A literature review. J Infect Public Health, 13(5), 667-673.
2. Keeling MJ, Hollingsworth TD, Read JM (2020). Efficacy of contact tracing for the containment of the 2019 novel coronavirus (COVID-19). J Epidemiol Community Health, 74(10), 861-866.
3. Burke RM, Midgley CM, Dratch A, et al (2020). Active monitoring of persons exposed to patients with confirmed COVID-19 United States, January–February 2020. MMWR Morb Mortal Wkly Rep, 69(9):245-246.
4. World Health Organization (‎2020)‎. The first few X cases and contacts (‎FFX)‎ investigation protocol for coronavirus disease 2019 (‎COVID-19)‎, 23 February 2020, version 2.2. World Health Organization. https://apps.who.int/iris/handle/10665/332023
5. European Centre for Disease Prevention and Control (2020). Contact tracing: Public health management of persons, including healthcare workers, having had contact with COVID-19 cases in the European Union-second update. ECDC, Stockholm.
6. Park O, Park YJ, Park SY, et al (2020). Contact transmission of Covid-19 in South Korea: Novel investigation techniques for tracing contacts. Osong Public Health Res Perspect, 11(1):60-63.
7. Peng X, Xu X, Li Y, et al (2020). Transmission routes of 2019-nCoV and controls in dental practice. Int J Oral Sci, 12(1): 1-6.
8. Canova V, Lederer SH, Piso RJ, et al (2020). Transmission risk of SARS-CoV-2 to healthcare workers–observational results of a primary care hospital contact tracing. Swiss Med Wkly, 150:w20257.
9. Wu WS, Li YG, Wei ZF, et al (2020). Investigation and analysis on characteristics of a cluster of COVID-19 associated with exposure in a department store in Tianjin. Zhonghua Liu Xing Bing Xue Za Zhi, 41(4):489-493.
10. Dietz L, Horve PF, Coil DA, et al (2020). 2019 novel coronavirus (COVID-19) pandemic: built environment considerations to reduce transmission. Msystems, 5(2), e00245-20.
11. Al-Tawfiq JA, Rodriguez-Morales AJ (2020). Super-spreading events and contribution to transmission of MERS, SARS, and SARS-CoV-2 (COVID-19). J Hosp Infect, 105(2), 111-112.
12. Ghinai I, McPherson TD, Hunter JC, et al (2020). First known person-to-person transmission of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) in the USA. The Lancet, 395(10230), 1137-1144.
13. Morawska L, Cao J (2020). Airborne transmission of SARS-CoV-2: The world should face the reality. Environment International, 139, 105730.
14. Wang D, Zhou M, Nie X, et al (2020). Epidemiological characteristics and transmission model of Corona Virus Disease 2019 in China. J Infect, 80(5): e25–e27.
15. Bai Y, Yao L, Wei T, et al (2020). Presumed asymptomatic carrier transmission of COVID-19. JAMA, 323(14), 1406-1407.
16. Wei WE, Li Z, Chiew CJ, et al (2020). Presymptomatic transmission of SARS-CoV-2 Singapore, january 23–march 16, 2020. MMWR Morb Mortal Wkly Rep, 69(14):411-415.
17. He X, Lau EH, Wu P, et al (2020). Temporal dynamics in viral shedding and transmissibility of COVID-19. Nat Med, 26(5), 672-675.
18. Tuite AR, Fisman DN, Greer AL (2020). Mathematical modelling of COVID-19 transmission and mitigation strategies in the population of Ontario, Canada. CMAJ, 192(19), E497-E505.
19. Jeong EK, Park O, Park YJ, et al (2020). Coronavirus disease-19: summary of 2,370 contact investigations of the first 30 cases in the Republic of Korea. Osong Public Health Res Perspect, 11(2): 81–84.
20. Hamid S, Mir MY, Rohela GK (2020). Novel coronavirus disease (COVID-19): a pandemic (epidemiology, pathogenesis and potential therapeutics). New Microbes New Infect, 35: 100679.
21. Rothan HA, Byrareddy SN (2020). The epidemiology and pathogenesis of coronavirus disease (COVID-19) outbreak. J Autoimmun, 109:102433.
22. Zhang Z, Zhang L, Wang Y (2020). COVID‐19 indirect contact transmission through the oral mucosa must not be ignored. J Oral Pathol Med, 49(5):450-451.
23. Singh A, Shaikh A, Singh R, et al (2020). COVID-19: From bench to bed side. Diabetes Metab Syndr, 14(4): 277-281.
24. Wang J, Feng H, Zhang S, et al (2020). SARS-CoV-2 RNA detection of hospital isolation wards hygiene monitoring during the Coronavirus Disease 2019 outbreak in a Chinese hospital. Int J Infect Dis, 94:103-106.
25. Guo ZD, Wang ZY, Zhang SF, et al (2020). Aerosol and surface distribution of severe acute respiratory syndrome coronavirus 2 in hospital wards, Wuhan, China, 2020. Emerg Infect Dis, 26(7):1583-1591.
26. Cai J, Sun W, Huang J, et al (2020). Indirect virus transmission in cluster of COVID-19 cases, Wenzhou, China, 2020. Emerg Infect Dis, 26(6):1343-1345.
27. Abeler J, Bäcker M, Buermeyer U, et al (2020). COVID-19 contact tracing and data protection can go together. JMIR Mhealth Uhealth, 8(4): e19359.
28. Palatnik A, McIntosh JJ (2020). Protecting labor and delivery personnel from COVID-19 during the second stage of labor. Am J Perinatol, 37(08): 854-856.
29. Wong SCY, Kwong RS, Wu TC, et al (2020). Risk of nosocomial transmission of coronavirus disease 2019: an experience in a general ward setting in Hong Kong. J Hosp Infect, 105(2): 119-127.
30. Verbeek JH, Rajamaki B, Ijaz S, et al (2016). Personal protective equipment for preventing highly infectious diseases due to exposure to contaminated body fluids in healthcare staff. Cochrane Database Syst Rev, 4:CD011621.
31. World Health Organization (2020). Modes of transmission of virus causing COVID-19: implications for IPC precaution recommendations: scientific brief, 29 March 2020 (No. WHO/2019-nCoV/Sci_Brief/Transmission_modes/2020.2). World Health Organization.
32. Salathé M, Althaus CL, Neher R, et al (2020). COVID-19 epidemic in Switzerland: on the importance of testing, contact tracing and isolation. Swiss Med Wkly, 150:w20225.
33. European Centre for Disease Prevention and Control (2020). Resource estimation for contact tracing, quarantine and monitoring activities for COVID-19 cases in the EU/EEA. ECDC, Stockholm.
34. Hellewell J, Abbott S, Gimma A, et al (2020). Feasibility of controlling COVID-19 outbreaks by isolation of cases and contacts. Lancet Glob Health, 8(4), e488-e496.
35. Cheng HY, Jian SW, Liu DP, et al (2020). Contact tracing assessment of COVID-19 transmission dynamics in Taiwan and risk at different exposure periods before and after symptom onset. JAMA Intern Med, 180(9): 1156-1163.
IssueVol 50 No 10 (2021) QRcode
SectionOriginal Article(s)
COVID-19 Transmission Close contact tracing Protocol

Rights and permissions
Creative Commons License This work is licensed under a Creative Commons Attribution-NonCommercial 4.0 International License.
How to Cite
Yazdani S, Heydari M, Foroughi Z, Jabali H. Factors Affecting COVID-19 Transmission and Modelling of Close Contact Tracing Strategies. Iran J Public Health. 2021;50(10):2121-2131.