Contact tracing
The terms contact tracing and contact tracers have become the hot topic of 2020. Almost every country in the world is racing towards finding effective methods of contact tracing to contain Covid-19 spread within their communities. The question really is why do scientists, governments, and epidemiologists think this will be a useful tool for containing Covid-19? The answer to this lies in knowing what happened during other epidemics.
Contact tracing in the public health context is a process of identifying the people (called ‘contacts’) who may have come in contact with an infected person for a particular infectious disease. This is a crucial step to understand not only how the disease spreads from an infected person, who is showing symptoms, but also how the disease behaves by observing asymptomatic contacts of the infected individual. Contact tracing gives an idea of how long the incubation period is before a person shows symptoms, how quickly the disease spreads and the rate of recovery from infection. This process has been used during several epidemics before the world faced the Covid-19 pandemic. In certain epidemics, contact tracing helped to successfully stop the spread of disease, while in other epidemics, this method was ineffective. Details of contact tracing in some past epidemics are described below.
Smallpox is a contagious disease that has been completely eradicated since 1977. Before vaccination was widely used, 3 out of 10 infected people died from this viral infection, which spreads from person to person via air droplets (coughing/sneezing) and skin-to skin-contact, as well as through saliva and blood. In the twentieth century, it is estimated that 200-500 million deaths occurred from smallpox as recently as the 1950s, nearly 50 million cases were reported each year. Some of the earliest symptoms are the appearance of red dots all over the infected person’s body. Using this hard-to-miss visual symptom, a robust contact tracing process was followed all over the world, leading to successful eradication of the disease. Eradication of smallpox throughout the world is considered as one of the most successful events in public health, which was due to a combination of both contact tracing and vaccination. In 1959, the World Health Organization (WHO) started a global eradication program that, unfortunately, was not successful. A second, more intense eradication program was started in 1967, which included extensive contact tracing as well as improvements in vaccination programs. In fact, when one of the last cases of smallpox was identified in Bangladesh in 1975, the patient was isolated with guards guarding the house 24 hours a day till the patient was no longer infectious. In addition, a health care provider visited every house, school and other communal areas close to the patient’s house to ensure that the disease had not spread within the community.
Human Immunodeficiency Virus / Acquired Immunodeficiency Syndrome (HIV / AIDS) is a disease that evoked fear in people for many decades. It is estimated that close to 38 million people worldwide lived with HIV at the end of 2018. In 2015, approximately 2.6 million people were newly infected from HIV. Even though no effective vaccine has been discovered yet, contact tracing is one of the most effective methods that is in use for effective control of disease transmission. A simulation study conducted for the HIV/AIDS epidemic in Africa concluded that contact tracing is more effective than random screening to prevent disease spread.
Severe Acute Respiratory Syndrome (SARS) a close relative of Covid-19, first appeared in November 2002; the global SARS epidemic ended in July 2003. Similar to Covid-19, the virus that causes SARS mainly resides in bats. SARS spread to 26 countries and caused 8000 infections. Although no country reports SARS cases today, the disease has reappeared around four times since 2003, mainly because of laboratory accidents. In the SARS epidemic, the evolution of contact tracing strategies emerged with better understanding of the outbreak. In one instance of contact tracing in the UK, a two-tiered strategy was used. First, the methodology of contact tracing was applied; and second, medical monitoring of traced contacts was implemented. This strategy was a targeted approach to contact tracing, especially in places having vulnerable populations such as nursing homes. Even though there were several challenges for contact tracing of SARS, once effective systems were established between health departments and the general public, contact tracing became more standardized. As a result, contact tracing helped in significant reduction of SARS transmission in locations such as Hong Kong.
The few example epidemics that we have seen above show that contact tracing indeed played a crucial role in helping either manage or eradicate the diseases, reassuring us that experts are rightful in implementing this strategy for the Covid-19 pandemic. However, a quick Google search did not yield any contact tracing methodology that has proved to be effective for Covid-19. This may very well be due to a lack of deep understanding of the disease itself. Seeing how the world has handled some previous epidemics, whether completely eliminating disease as in smallpox or figuring out strategies to manage disease such as in HIV, I am hopeful that we will figure out an effective strategy for the Covid-19 pandemic. Therefore,I believe that yes, we should believe the experts with regards to contact tracing.
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