How Effective is Contact Tracing?

Contact tracing has become one of the most effective ways to break the chain of infection continuously spreading a deadly virus such as Covid-19. However, several reports of asymptomatic carriers becoming 'superspreaders' proves that we know so little about the infection rate of coronavirus.

For instance, a woman rode an elevator heading home as she self-quarantined after travel. Following guidelines, she would stay home and ordered food.

(Photo : Downloaded From Getty Images official website )

Through contact tracing of 71 people that tested positive for coronavirus, the source all pointed back to the asymptomatic woman. Her case is reported in a new study by the US Centers for Disease Control and Prevention (CDC) to be released in September.

In late May, Dr. Nate Favini from Forward, a medical health membership program, said, 'Given the rapidity of the spread of COVID-19, it seems plausible that people who are asymptomatic or mildly symptomatic could be playing a role in spreading the virus.' At the time, medical experts were uncertain if asymptomatic people were highly infectious or not.

CDC Study

The CDC study analyzed the contact tracing that occurred in Heilongjiang Province, China, where there had been no new reported cases since March 11. In April a man suffered a stroke, yet was not yet diagnosed with a disease.

When he was hospitalized, his three sons were with him the entire time. After some time, 28 people became infected because at least one member of the family had been unknowingly asymptomatic.

Before being diagnosed with his condition, he was moved to another hospital to recover. Alarmingly, 20 more people got infected with the coronavirus.

Conducting intensive contact tracing led them to a different patient, Patient B, who had close contact with the man who had a stroke. All the people in contact with the coronavirus positive patient were infected as well.

The people who were traced to be in close contact or proximity with the man who tested positive were put into lockdown. However, about 50 people already became infected and had spread the virus to other people.

Contact tracers continued to search for the source of the virus and how Patient B had infected the man who had a stroke. They discovered that Patient B and the stroke victim met at a party of one of his sons on March 29, yet no one else who attended tested positive.

At the time, the city was not on lockdown and many businesses were open. When they tested Patient B's girlfriend and daughter, they both tested positive for coronavirus.

Finding Patient 0

Patient B last visited them on March 26, yet no one had traveled so the contact tracers were at a dead end. Eventually, they conducted a standard genome sequencing of SARS-CoV-2 to check of a new strain had been in circulation.

The genetic sequence revealed that the virus came from another country. By April 9 and still, at a dead end, the contact tracers believed it was impossible for the virus to suddenly appear although no one had traveled recently.

They began doing a background check on everyone living in the same apartment building and found a woman who recently returned from the United States; she was Patient 0, where all the other infections had started from. She was asymptomatic and had followed self-isolation guidelines.

Yet, she had not been in direct contact with Patient B's girlfriend and daughter. The only thing left for them to have in common is the elevator. The researchers wrote, 'Therefore, we believe A0 (the traveler from the US) was an asymptomatic carrier and that B1.1 (the daughter) was infected by contact with surfaces in the elevator in the building where they both lived.' They concluded that 'Our results illustrate how a single asymptomatic SARS-CoV-2 infection could result in widespread community transmission.'