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COVID19 Contact Tracing

contact tracing

Written By Rich Blonna

April 22, 2020

If you’ve been following the ongoing coverage of the COVID19 epidemic on the news recently you’ve probably heard the term contact tracing used more and more. A COVID19 contact is defined as a person who has had close contact with an infected patient. This contact was exposed to a person with symptomatic COVID-19 during period from 48 hours before their symptoms occurred.

I did contact tracing and trained and supervised field workers who were responsible for it during the 12 years that I worked for the NJ State Department of Health STD Control Program.

Contact tracing is one of the primary public health tools used by epidemiologists to control the spread of communicable diseases. It is labor intensive, expensive, and requires a trained staff of field workers who go out into the community and track down and interview people who were exposed to cases of infectious communicable diseases.

There are two primary purposes of contact tracing:

  • To test and preventively-treat contacts who have been exposed to someone with an infectious disease but have not yet developed the infection.
  • To prevent contacts from spreading the disease to others.

The idea behind testing and preventively treating contacts is that they are much more likely to be infected than the general population because they have been exposed to known cases of the disease.

Preventive treatment is also known as prophylactic treatment and involves treating people who have been exposed to an infectious disease but haven’t developed it yet. In essence, you are assuming that their exposure would result in disease development if you did not treat them preventively. While this is a common public health strategy, many medical providers in the private sector are wary of treating exposed contacts who do not have positive test results or clinical symptoms.

The primary way to prevent contacts from spreading the disease to others is to explain to them that they have been exposed to someone with the disease and until their tests come back negative, they should consider themselves capable of spreading their infection to others.

The Role of Incubation Periods

Contact tracing is based on getting to exposed contacts while they are potentially incubating the infection. The incubation period is the time from when someone is exposed to a disease to the maximum time it would take for them to develop it.  The length of a disease’s incubation period can greatly influence the success of contact tracing. The longer the incubation period, the more time field workers have to locate contacts, interview them, and get them tested and preventively treated.

For example, syphilis has a 1-90-day incubation period with the average person developing the disease after 10 days. By contrast, the incubation period for COVID19 is 1-14 days, with most people incubating out after around five days.

The Role of Testing

One of the most effective tools for effective contact tracing is having an inexpensive, sensitive, rapid test, that can let contacts know immediately if they are positive. When I worked in STD control in the 1970s all field workers were equipped with mobile test kits. This was before HIV and the development of universal blood handling precautions. The kits included battery operated centrifuges and Rapid Plasma Regain (RPR) antibody card tests. We were trained to draw blood, spin it down in the centrifuges, and then use the RPR cards to test the plasma for the presence of syphilis antibodies in the serum.

The test was inexpensive, extremely sensitive, and could be done rapidly (hence the name). Unfortunately, sensitive tests are not very specific and are subject to false positive results. At the time I used them, RPR tests could be thrown off by over 50 other diseases and conditions ranging from pregnancy to heroin addiction.

At the present time there is no widely available, inexpensive, sensitive, rapid test for COVID19 that could be used to test contacts.  That said, there is a race to develop such a test. Abbott labs and many other companies are developing inexpensive blood tests that can be read in under 15 minutes. How they will ultimately be integrated into contact tracing is unknown. Abbott is currently field testing their rapid results test in Detroit and hopes to have it available on a broader scale as soon as possible.

The CDC has issued guidelines regarding prioritizing the use of these tests.  The highest priority is to test the following people:

  • Hospitalized patients
  • Healthcare workers
  • Those with highest risk of severe illness if they got COVID-19
  • First responders
  • Individuals with symptoms

As you can see, contacts to known cases are not included in this group (CDC, 2019).

The Role of Preventive Treatment

One of the major differences between contact tracing for a disease like syphilis compared to COVID19 is that syphilis can be treated preventively with antibiotics while COVID19 cannot.

The germ that causes syphilis is a spirochete that is destroyed by antibiotics. The germ that causes COVID19 is a virus for which there is no known cure. Antiviral medications work by stopping the replication of the virus, not killing it completely.

This is a major difference because if contacts are exposed to curable diseases such as syphilis, they can be given prophylactic treatment which will stop the disease from ever developing in the first place. This is not the case for contacts exposed to COVID19.  There is no currently accepted preventive treatment regimen recommended for use with asymptomatic contacts of persons with COVID19

The Role of Education and Counseling

A big part of contact tracing is interviewing contacts once they are found. Public health workers involved in contact tracing are trained to be able to elicit sensitive, personal health information from contacts, and motivate them to get tested and treated. In addition, they are trained to maintain the strictest patient confidentiality.

For example, I trained my public health field workers to follow a script similar to the following one when doing syphilis investigations: “Hello, my name is …. I am a public health worker for the city of …. You’ve been exposed to someone who has syphilis and I need to be sure that you get tested and given preventive treatment. I can arrange for you to get tested and treated today at our clinic or call your doctor if you prefer to go there.”

Contacts invariably asked who they were exposed to and my workers were trained to respond to such questions in the following manner: “ I’m sorry but just like I would protect your confidentiality by refusing to give your name to anyone, I am sworn to do the same thing for the person who named you. All I can say is that the person cared enough about you to want to see that you got tested and treated as soon as possible.”

That usually worked and most contacts were tested and treated in our local clinics. Other patients preferred to go to their private physicians for examinations and treatment.  A typical day in the life of field workers involved doing contact tracing in the morning followed by bringing those contacts into the clinic for further testing and treatment that same afternoon. In many instances contact tracing was done late into the evening if contacts could not be located during the day.

At the present time, interviewing and counseling activities for COVID19 focus on two areas:

  • Assessing whether contacts have symptoms for the disease.
  • Explaining to contacts that because of their exposure they should assume that they are capable of spreading their infections to others.

Contacts need to be told that they should self-quarantine for the maximum incubation period and have  repeat tests at the end of that period.  They should also be told that they need to monitor their temperatures and if they develop symptoms during their self-quarantines they should contact their doctors immediately.

The Future

As inexpensive, sensitive, rapid COVID19 tests and preventive treatments become readily available, the nature of contact tracing will evolve and change. It is important to remember that contact tracing is just one of the many tools available to public health officials to stop the spread of COVID19 and other infectious diseases.



Dr. Rich Blonna is a Professor Emeritus in the Department of Public Health, William Paterson University. He is also a candidate for the Marco Island City Council.


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