key: cord-0793539-zyckaqtq
authors: Fernández-Niño, Julián Alfredo; Peña-Maldonado. Economist, Carlos; Rojas-Botero, Maylen; Rodríguez-Villamizar, Laura Andrea
title: Effectiveness of contact tracing to reduce fatality from COVID-19: preliminary evidence from Colombia
date: 2021-07-20
journal: Public Health
DOI: 10.1016/j.puhe.2021.07.013
sha: 8df11eecdcd05712b7cf1e1458f8b52bcb5769c0
doc_id: 793539
cord_uid: zyckaqtq

Objectives Conducting contact tracing programs in low and middle-income countries is challenging and there is no evidence of their effectiveness in Latin America. We evaluated the effectiveness of contact tracing on reducing fatality from COVID-19 in Colombia. Study design Retrospective cohort study with nation-wide data of suspected and confirmed cases of SARS-CoV-2 infection and their registered contacts. Methods We analyzed confirmed and suspected COVID-19 cases and their chains of contact using a nation-wide registry from March 28, 2020 to January 13, 2021. To estimate the effect of contact tracing on fatality we adjusted a multilevel negative binomial model using as outcome variable the number of deaths and off-set variable the number of people within a chain of contacts. Sensitivity analysis was conducted using different cut-off values of contacts traced and a logistic model for the effect of contact tracing on death at individual level. Results We analyzed 1,4 million cases, 542 936 chains of contact, and 46 087 deaths. Only 5,8% of total cases and contacts were included in a chain of a case and five or more contacts. We found that tracing of at least five contacts per case reduce fatality by 48% (95% CI: 45-51) and, at the current levels of tracing in Colombia, it prevents 1.8% of deaths. Results obtained from the sensitivity analysis were consistent with the reduction of fatality at individual level and higher protective effect with higher number of contacts traced. Conclusions In Colombia, tracing of at least five contacts per case reduces fatality from COVID-19. The coverage and intensity of tracing needs to be increased as a strategy to mitigate fatality in Colombia.

As of December 31, 2020, the SARS-CoV-2 virus caused 88.8 million infections and the disease that it produces led to a total of 1.8 million deaths 1 . The National

Institute of Health in Colombia registered 1 508 419 confirmed cases and 43 213 deaths as of that same date 2 .

Given that this is a new disease, there is not yet specific pharmacological treatments, and the vaccinations that have recently been introduced are not yet available to the general public in low and middle-income countries. Therefore, since the pandemic began, governments have implemented non-pharmacological interventions (NPIs), including: specific individual interventions such as promoting hand washing 3 and the use of masks 4 ; community interventions such as imposing restrictions on activities in closed spaces and cancelling mass gatherings; and in general, a variety of restrictions on mobility to reduce the rate of close contacts, ranging from partial restrictions to sector isolation and complete lockdowns. Contact tracing of confirmed and suspected cases has also been proposed as a mitigation strategy.

Contact tracing with early isolation of suspected cases is a strategy that is functioning in the midst of the SARS-CoV-2 pandemic. When adequately implemented, it reduces the acceleration of transmission and decreases fatality 5 . Nevertheless, its massive implementation requires great operational efforts, such that its cost-effectiveness has even been questioned 6 (PRASS in Spanish). The aim of this program is to monitor confirmed and suspected cases along with their contacts, as well as provide early and adequate health care throughout the country. Colombia has an insurance-based health system in which insurance companies, called "Beneficiary Plan Administration Companies" (EAPB in Spanish), provide individual health services to the population, such as those performed by the PRASS program. The State's role in the system is to regulate its operations in order to ensure that adequate health services are provided to enrollees. The PRASS program has been implemented in the framework of this insurance model, where responsibilities are shared among different actors and national regulations apply.

Currently in Colombia, with the knowledge that vaccinations will not reduce transmission in the short-term and general restrictions on mobility have negative socioeconomic effects, the transmission of SARS-CoV-2 infection needs to be reduced by using strategies that effectively detect and trace cases and contacts. Nevertheless, the effectiveness of the contract tracing strategy and its impact on meeting that goal for the country has not yet been evaluated. As a first approximation, this study uses nation-wide data to evaluate the effectiveness and impact of contact tracing on fatality from COVID-19. 

This study used anonymized data from the MHSP information system that was designed specifically to address the SARS-CoV-2 pandemic, known as SEGCOVID19. This serves as the source of the PRASS program's integrated national registry on contact tracing. This system collects information from notifications that the National Public Health Surveillance System (SIVIGILA in Spanish) for suspected and confirmed cases and the corresponding contacts identified through direct tracing by the EAPB. The system defines the chains of transmission as the index case and its respective contacts.

In addition, SEGCOVID19 crosses information with the national sampling system, which reports the results from all COVID-19 tests performed in the country, as well as with the database of enrollees in the health system and birth and death records. This cross information supplements the information on cases with the identification of results from diagnostic tests, health system enrollments for assigning who is responsible for follow-up (insurer and geographic entities), and the final vital status of each person.

While the MHSP administers this system of information, the EAPB and local authorities are required to report and contact the COVID-19 cases and their contacts and enter them into the system. The EAPB or local authorities must register in SEGCOVID19, in realtime, the information related to suspected and confirmed cases, their demographic variables, clinical baseline data, and records of contacts for each case. These contacts are then visible to the EAPB responsible for the insurance for the purpose of identification, follow-up, clinical evaluation, and taking samples. Furthermore, since the system also makes it possible to follow-up on cases and contacts, it provides the best input of information on contact tracing in the country.

The information for this analysis was taken from all observations at the national level that were registered from March 28, 2020 to January 13, 2021 by all the EAPBs and local authorities.

Death from COVID-19 was the outcome of interest for this analysis. Exposure variables included individual level data such as sex, age (in decades), presence of chronic comorbidities (cardiovascular disease, diabetes, cancer, immunodeficiencies), type of health insurance, socioeconomic status, and place of residence. On a second level, the J o u r n a l P r e -p r o o f individuals were grouped into chains defined as a group consisting of a suspected or confirmed index case and its respective contacts who have been registered and contacted.

The variables for the chain included number of incident cases, number of deaths in each chain, and the size of the chain. The main independent variable for the analysis was the size of the chain as an indirect indicator of the intensity of tracing. Based on a sensitivity analysis, this variable was dichotomized as a chain of five or more contacts per case, which was considered to be effective tracing. This conceptually makes sense since it recognizes at least two contacts other than those in the home, given that Colombia has an average of three people per household. An indicator variable was also included when the index case in a chain was a suspected case.

A multilevel negative binomial model was used with the number of deaths of individuals in each chain as the outcome variable, and the number of people identified within the chain as the exposure variable. The model was adjusted by the above-mentioned variables corresponding to the two levels. The model included random intercepts at the chain, insurance, and municipality level, as well as fixed effects. The intraclass correlation coefficient was calculated for each level as was relative risk (RR), with 95% confidence intervals (95% CI). All assumptions of the model were verified, and the goodness-of-fit was evaluated. We used software Stata® version 16 to analyze the data.

To measure the impact on deaths, the preventable fraction (PF) was calculated based on the following formula, recommended by Benichou when the effect of confounding variables is

where: Pd = prevalence of exposure among deceased cases RR = adjusted relative risk

We conducted a multilevel logistic model to calculate the individual risk of death associated with belonging to a chain of at least five contacts, adjusted by sex, age group, type of health insurance, socioeconomic status, and comorbidities (diabetes, cardiovascular disease, chronic respiratory disease, cancer, and immunodeficiencies). We also conducted a sensitivity analysis using different cut-off values of the number of contacts traced to assess their effect on mortality from COVID-19. (Table S1 ). All effect measures were below the null value (RR<1) and statistically significant indicating an overall protective effect of contact tracing on COVID-19 mortality. Although there is not a specific dose-response pattern, the contact tracing with higher number of contacts (more than eight or nine contacts) showed the highest protective effect.

This study aimed to assess the effectiveness of the contact tracing (CT) strategy on epidemic 25 . Modeling studies have estimated that CT coupled with quarantine of people exposed to confirmed or suspected cases prevents 44% to 96% of cases and 31% to 76% of deaths, as compared to no intervention 26 .

The findings herein suggest that identifying and tracing five or more contacts related to a confirmed or suspected case reduces the risk of fatality in that chain of transmission on average by 48%. Nevertheless, the preventable fraction of this effect is still low (1.8%),

probably due to the low prevalence of CT during the study period (5.7%). Different factors may explain this low prevalence, including the program's low coverage in urban areas, limitations in the human and technological resources needed to conduct contact tracing, and a lack of follow-up on program responsibilities that are shared by all involved parties, particularly by EAPB, which provide primary health services to 95% of the population 27 .

One measure that is needed to better control transmission and reduce fatality is to implement strong health system regulations, given that the current health care provider system is market-driven and fragmented. Another possible measure is looking for operational alternatives that improve coverage and increase the intensity of CT.

Automated contact tracing is an alternative to manual procedures and could potentially reduce transmission. Nevertheless, high population uptake is needed for automated contact tracing to be effective, and this may be limited in low-and middle-income countries where internet and mobile phones are not widely available 28 . In addition, privacy and equity concerns exist that need to be considered 29 Therefore, strategies to increase COVID-19 testing coverage will probably also contribute to interrupting chains of transmission and prevent more deaths.

The present study provides strong evidence by using data from a national integrated information system on COVID-19 in Colombia (SEGCOVID19), which allowed for controlling for other potential sociodemographic confounders of COVID-19 fatality. In particular, CT was evaluated with more than one million records, which represent all the suspected and confirmed cases and their contacts that were reported to the country's public washing and use of masks as this data is not available in the dataset used for the analysis.

Regarding the community-based NPI such as mobility restrictions, they were widely used in different cities according to the pandemic situation and are expected to be similar within municipalities. Despite these interventions are associated with lower probability of contagion, they are not related to the contact-tracing process and therefore they are not J o u r n a l P r e -p r o o f acting as potential confounders for our analyses. Therefore, we consider that the absence of this information is not a source of potential bias in our study.

In conclusion, the findings herein show that CT reduces the risk of fatality in the chains of transmission. A reduction in the fatality risk was observed despite the low prevalence of CT. These findings support the need to strengthen government regulations of CT, overcome its operational limitations, increase its intensity, and reach a CT coverage and intensity that contributes to stopping chains of transmission and preventing deaths.

J o u r n a l P r e -p r o o f Tables   Table 1. Characteristics of COVID-19 suspected and confirmed cases and 

Using nation-wide data from March 28, 2020 to January 13, 2021 we analyzed 1.4 million confirmed cases and 542,936 chains of contacts and estimated the effect of contact tracing on fatality in Colombia. We found that tracing of at least five contacts per case reduce fatality by 48% (95% CI: 45-51) and, at the current levels of tracing in Colombia, it prevents 1.8% of deaths.

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