key: cord-0726197-gvp58frm authors: Yazdani, Shahram; Heydari, Majid; Foroughi, Zeynab; Jabali, Hadi title: Factors Affecting COVID-19 Transmission and Modelling of Close Contact Tracing Strategies date: 2021-10-03 journal: Iran J Public Health DOI: 10.18502/ijph.v50i10.7516 sha: 87685d16976fd708169cd215b91d1f1c8cbcaaa8 doc_id: 726197 cord_uid: gvp58frm 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. Coronavirus disease 2019 (COVID- 19) was first identified in Dec 2019 in Wuhan, China, then spreads rapidly around the world. The COVID-19 primarily spreads between people during close contact, most often via small droplets produced by coughing, sneezing, and talking (1) . Therefore, the countries considered close contact tracing of COVID-19 cases as one of the first and most important measures to the control of the disease. Close contact tracing is a public health response to the outbreak of infectious diseases, especially in the early stages of the outbreak, when specific treatments are limited (2) . Contact tracing is an effective and efficient strategy for identifying potentially infected individuals before the onset of severe symptoms. It ensures rapid care of the patients, limits further transmission of the disease, and enables a better understanding of the transmission risk factors (2, 3) . According to the \WHO, close contact of a COVID-19 case is any person who had contact (within 1 meter) with a confirmed case during their symptomatic period, including 4 days before symptom onset (4) . In another definition by European Centre for Disease Prevention and Control (ECDC), close contact is any person who had contact with a COVID-19 case within a timeframe ranging from 48 h before the onset of symptoms to 14 days after the onset of symptoms (5). In close contacts, the COVID-19 transmission and exposure risk depends on many factors including route of disease transmission, patient characteristics, and environmental characteristics (6) . Viruses can be transmitted from person to person through direct or indirect contact, coarse or small droplets, or contaminated objects (7) . Determining the level of exposure in each contact (high-risk or low-risk exposure) is based on the associated risk of infection that in turn determines the type of monitoring and management of contacts (5). Therefore, in contact tracing, factors affecting transmission must be carefully considered and, an appropriate intervention strategy based on the evaluation of exposure risk should be selected. As well as, close contacts tracing is very costly and time-consuming when the disease is widespread in the community. Hence, having an accurate protocol for high-risk contacts tracing will be important. Therefore, the aim of this study was modeling of close contacts tracing protocol by considering the factors affecting the COVID-19 transmission in close contacts. We modeled the close contact tracing protocol based on factors affecting on COVID-19 transmission. The study was conducted in two general steps. In the first step, the factors affecting on COVID-19 transmission in close contact were identified by a rapid review of literature. This review was conducted on studies published between 2019 and 2020. The search strategy conducted using keywords "contact tracing", "close contact", "contact", "transmission", "exposure", "expose", "coronavirus", "COVID-19", "novel coronavirus", "2019-nCoV", "severe acute respiratory syndrome coronavirus 2"and "SARS-CoV-2" across electronic databases of Embase, PubMed, Scholar and Scopus. The inclusion criteria were those papers that pointed to the characteristics of close contacts, the pattern of transmission, and factors affecting COVID-19 transmission. Papers in languages other than English were excluded (except for papers with English abstracts that had useful information). Two assessors evaluated the papers independently. Disagreements between assessors were resolved by consensus or by the decision of a third independent assessor. Computer software for reference management) Endnote X9 (was used for organizing the papers. After removal of duplicate records, papers with non-relevant titles were excluded, and then, the abstract and the full text of papers were reviewed. Data analysis was done manually, and the results were categorized by content analysis method. In the second step, we built the COVID-19 contacts tracing protocol by formulating and scoring the identified factors. In this step, to determine the COVID-19 transmission risk at close contacts, we considered a specific score for influential factors based on their characteristics. Finally, the close contact transmission risk score calculates through the sum of these scores. The protocol was developed through two expert panels. The panel members (10 experts) consisted of various specialties, including public health experts, epidemiologists, physicians, and health policy specialists. In the first panel, the research team explained the goals of the study and provided their findings and initial scoring model to the members. Based on the literature review results in the first step and the opinion of experts, the factors were prioritized in terms of their importance and effects on disease transmission, and according to the situation of each factor in differ-ent conditions, scoring was done contractually (between 7-90 in three identified categories). In other words, the situations of the factors in each category were compared in pairs in terms of transmission risk and each situation was scored according to its risk by the consensus of experts. The first session ended with the gathering of comments and feedback from the members after 8 hours. After applying the members' comments and modifying the scoring model, the second panel was held with the presence of all members that mentioned above, and after 4 h of discussion and testing the scoring system with several cases, the final protocol was approved by the members' consensus. From initially 6,168 studies, after removing duplicates and two-stage screening, 24 studies were eligible for the review. The results of the review showed that the risk of COVID-19 transmission from sentinel case to close contacts depends on three categories of factors: Characteristics of Contact Environment, Infectivity (Virus Shedding) of Sentinel Case, and Close Contacts Characteristics (Table 1) . (20) -Immunosuppression (11) The close contact transmission risk varies based on the factors' characteristics and conditions. In other words, the close contact transmission risk depends on the contact environment risk, infectivity (viral shedding) of sentinel case, and close contact risk. The following is the modeling of close contact transmission risk and tracing protocol. Several studies have suggested the effect of contact environment characteristics in the risk of the COVID-19 transmission in close contact (6, (8) (9) (10) (11) (12) (13) . Based on these characteristics, we determined the Contact Environment Risk Score (CERS). CERS depends on five factors: space volume of contact place, presence time of sentinel case, ventilation, mobility, and crowdedness. The space volume of contact place is an important factor in the COVID-19 transmission (10). According to Fig. 1 , that shows contact environment risk score (CERS: 7-30), the appropriate space volume considered for different contact place. The space volume is considered to be from less than 15 m 3 such as space of car, van, WC to more than 10,000 m 3 , such as department store, factories, and outdoor space. Contact duration in these spaces will create different risks of transmission. Therefore, we considered the presence time of sentinel case in contact from less than 5 min to more than 10 hours. By connecting contact duration with different volumes of space, we calculated the contact environment risk score from 7 to 21 (see Fig. 1 ). The different situations of the factors were compared in pairs with each other in terms of transmission risk, and then according to each situation risk (from low to high), scoring was done contractually between 7 to 21. In addition, poor ventilation, high mobility and crowdedness increased the CERS. Higher occupant density and increased indoor activity typically increase direct contact between individuals. High mobility in spaces with poor ventilation increases the risk of transmission (10) . If any of these characteristics were present, 3 points will be added to the CERS. Finally, the CERS graded between 7 and 30 considering the different situation of these five factors, according to Fig. 1 . The infectivity of the case or virus shedding rate is another factor that affects the COVID-19 transmission in close contact. Three factors affected on the infectivity of the sentinel cases: stage of infection (viral activity in the respiratory tract) (7, 9, 10, 15, 16, 18, 19) , droplet shedding (7, 10, 13, 20, 21) and observance of safety measures (20) . The disease stage determines the level of infectivity, viral activity, and viral shedding. Viral shedding begins before the appearance of the first symptoms, and viral loads decrease after symptom onset (17) . If we consider three phases for the disease, including Early Infection, Pulmonary Phase, and Hyper Inflammation Phase, the rate of viral activity and infectivity in the early phase will be high and decreases in the next two phases. Furthermore, the illness severity and the inflammatory response are low in the first phase, begin to increase in the second phase, and peak in the third phase (Fig. 2 . Section of disease stage). Currently, COVID-19 transmission through respiratory droplets has been accepted (10) . Infected droplets are spread by talking, coughing, or sneezing of an infected individual. Droplet shedding status is graded, from low to extremely high, through considering the mechanism of droplet shedding (approximately 600 drops per minute through talking,3000 drops per minute through coughing, and 40000 drops per minute through sneezing) and the frequency of droplet shedding (sporadic, occasional, and frequent). (Fig. 2) Observance of safety measures includes the use of face masks; covering coughs and sneezes with tissues can minimize the droplet shedding and risk of exposure. (Fig. 2 ) (20) . According to the levels of safety measures observance, a sentinel case can be cautious, observant, unobservant, or reckless. Depending on the stage of the disease and droplet shedding mechanism, the infectivity of the droplets will be different. So that, the infectivity of droplets in the pre-clinical period and the hyper inflammation Phase is low, which is moderate in the pulmonary phase and high in early infection (Fig. 2) . Based on these characteristics and by pairwise comparison of situations in terms of transmission risk, we determined the Infectivity Score of Sentinel Case (ISSC: 0-30). In Fig. 3 , ISSC is calculated for unobservant sentinel cases. Add additional 5 scores for reckless cases. Subtract 2 scores for observant cases. Subtract 5 scores for cautious cases. Transmission risk in close contact depends on three factors: contact experience, protective behavior, and immune system performance. The contacts experience can be direct or indirect, through the particles transferred from animate or inanimate objects, or particles transferred through the air (7, 8, 12, 13, (23) (24) (25) (26) . COVID-19 transmission can occur by direct contact with sentinel case or indirect contact with surfaces or objects used on the sentinel case (31) . In direct contact, where there is skin-to-skin contact between two persons, three types of contact can occur, including intimate contact, causal contact or accidental contact. In indirect contact, where there is contact with an inanimate object that may serve as a vehicle for transmission of pathogen, depending on the contact frequency, frequent contact with shared objects or occasional contact with shared objects will occur. The contact experience can also be through airborne particles (7, 13, 25, 26, 31) . Particles transferred through the air can be large droplets, small droplet, or airborne. Confrontation with large droplets, where large droplets of 50-100 μm that travel face to face up to 2 meters, can be pro-longed near confrontation or short near confrontation. In addition, contact experience with small droplets, where small droplets of 10-50 μm travel face to face to within the room, can be considered in two forms of prolonged distant confrontation or short distant confrontation. Protective behaviors such as the use of personal protective equipment and wearing respiratory protection can reduce the risk of transmission in close contact (12, 20, 24, (28) (29) (30) . Protective behaviors can be categorized into strict protection (e.g. use of N95, surgical, of FFP1 masks, latex gloves, disinfecting hands and working surfaces), ordinary protection (use of dust masks, polyvinyl gloves and washing hands frequently), or loose protection (following basic health recommendations). Immune system performance is another influential factor in close contact transmission. People with weak immune systems or Immunosuppression were considered as a high-risk group (11, 20) . We considered three states for the immune system: mild immunosuppression (chronic conditions: heart disease, lung disease, lupus, diabetes & malnutrition), moderate immunosuppression (in steroids, cancer), and Severe Immunosuppression (in chemotherapy, HIV/AIDS), to determine the risk of transmission in different situations. Based on the described characteristics and by pairwise comparison of different situations in terms of transmission risk, we determined the Close Contact Risk Score (CCRS: 0-30) according to Fig. 4 . Since there is no definitive treatment or universal vaccination against COVID-19, the close contact tracing is one of the most famous solutions to control its outbreak (2, 3) . This approach is necessary to minimize the damage to population health and maintain economic and social activities during the pandemic (32) . Generally, key steps of contact tracing include contact identification, listing and follow-up (5). Contacts tracing in the early stages of an epidemic with the limited number of patients is most effective and efficient (5). However, when the transmission has widespread in the community, it will be costly and time-consuming (33) in this regard, Keeling et al referred to the high burden and optimism of tracing all close contacts within 2 weeks (2). In addition, Hellewell et al referring to the large volume of contact tracing to control the disease outbreak, Suggested that a 3 months effective contact tracing and case isolation could prevent a new outbreak (34) . Therefore, this study aimed to present an efficient and effective protocol for close contact tracing through detecting factors affecting COVID-19 transmission. By reviewing existed literatures on COVID-19 contact tracing different influential factors in transmission risk detected and categorized, and were organized into three general categories then a comprehensive model provides by conducting expert panels. The results of the study introduced three factors that are influential in close contact transmission risk, including the characteristics of the contact environment, the infectivity of the patient, and the contact characteristics. The contact environment risks depend on space volume of contact place, presence time of sentinel case, poor ventilation, high mobility, and crowdedness. The risk of infectivity of patients determine by stage of infection, droplet shedding, and observance of safety measures. Finally, the contact characteristics risk is associated with contact experience, protective behavior, and immune system performance. Until now, no study has been published that calculated all these factors in a single model. For example, Covid-19 were examined transmissibility and evaluated the disease transmission risk, the results showed high transmissibility risk before and immediately after symptom onset (35) .Furthermore, transmission risks of COVID-19 is most likely in prolonged unprotected exposure to a patient with symptomatic COVID-19, but there is no calculation for transmission risk (12) . Therefore, our model was applicable in identification and classification of contacts in a timely and efficient manner. The close contact tracing protocols such as the WHO (4) or ECDC protocol (5) are useful for the next steps of tracing, followup and contact management. In general, after evaluation of close contact transmission risk and contact identification, there are two general measures for contacts management, including: movement restriction (quarantine /isolation in-cluding home isolation, or controlled travel) and symptom monitoring (active or passive monitoring, depending on the exposure risk) (6) . Our model provided the possibility of prioritization of contact tracing cases, especially widespread transmission condition, so the limited resources can be devoted to high-risk contact exposures. Due to the limited resources, high-risk exposure contacts should be traced first. In this protocol, close contact transmission risk depended on the contact environment characteristics, the infectivity of the sentinel case, and contacts characteristics. Based on the close contact transmission risk score, contacts can be classified and specific tracing strategies implemented for each. Ethical issues (Including plagiarism, informed consent, misconduct, data fabrication and/or falsification, double publication and/or submission, redundancy, etc.) have been completely observed by the authors. Coronavirus disease 2019 (COVID-19): A literature review Efficacy of contact tracing for the containment of the 2019 novel coronavirus (COVID-19) Active monitoring of persons exposed to patients with confirmed COVID-19 United States The first few X cases and contacts (FFX) investigation protocol for coronavirus disease 2019 (COVID-19) Contact tracing: Public health management of persons, including healthcare workers, having had contact with COVID-19 cases in the European Union-second update Contact transmission of Covid-19 in South Korea: Novel investigation techniques for tracing contacts Transmission routes of 2019-nCoV and controls in dental practice Transmission risk of SARS-CoV-2 to healthcare workers-observational results of a primary care hospital contact tracing Investigation and analysis on characteristics of a cluster of COVID-19 associated with exposure in a department store in Tianjin 2019 novel coronavirus (COVID-19) pandemic: built environment considerations to reduce transmission Super-spreading events and contribution to transmission of MERS, SARS, and SARS-CoV-2 (COVID-19) First known person-to-person transmission of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) in the USA Airborne transmission of SARS-CoV-2: The world should face the reality Epidemiological characteristics and transmission model of Corona Virus Disease 2019 in China Presumed asymptomatic carrier transmission of COVID-19 Presymptomatic transmission of SARS-CoV-2 Singapore Temporal dynamics in viral shedding and transmissibility of COVID-19 Mathematical modelling of COVID-19 transmission and mitigation strategies in the population of Ontario Coronavirus disease-19: summary of 2,370 contact investigations of the first 30 cases in the Republic of Korea Novel coronavirus disease (COVID-19): a pandemic (epidemiology, pathogenesis and potential therapeutics) The epidemiology and pathogenesis of coronavirus disease (COVID-19) outbreak COVID-19 indirect contact transmission through the oral mucosa must not be ignored COVID-19: From bench to bed side SARS-CoV-2 RNA detection of hospital isolation wards hygiene monitoring during the Coronavirus Disease 2019 outbreak in a Chinese hospital Aerosol and surface distribution of severe acute respiratory syndrome coronavirus 2 in hospital wards Indirect virus transmission in cluster of COVID-19 cases COVID-19 contact tracing and data protection can go together Protecting labor and delivery personnel from COVID-19 during the second stage of labor Risk of nosocomial transmission of coronavirus disease 2019: an experience in a general ward setting in Hong Kong Personal protective equipment for preventing highly infectious diseases due to exposure to contaminated body fluids in healthcare staff Modes of transmission of virus causing COVID-19: implications for IPC precaution recommendations: scientific brief World Health Organization COVID-19 epidemic in Switzerland: on the importance of testing, contact tracing and isolation Resource estimation for contact tracing, quarantine and monitoring activities for COVID-19 cases in the Feasibility of controlling COVID-19 outbreaks by isolation of cases and contacts Contact tracing assessment of COVID-19 transmission dynamics in Taiwan and risk at different exposure periods before and after symptom onset This study was funded and supported by the National Agency for Strategic Research in Medical Education (NASR). The Authors would like to thank all the participants in this study. The authors declare that there is no conflict of interest.