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Contact Tracing

The power of contact tracing.

Yesterday, the CDC published one of the first comprehensive contact tracing studies. It was conducted in South Korea.

I threw together a figure that depicts the study design. Briefly, South Korea identified 5,706 confirmed cases (i.e. index cases) and asked them to report their contacts (both in the household and out in public). The cases reported a total of 59,073 contacts. The cases and contacts were followed for at least 2 weeks. 

This is what they found:

  • You are more likely to get sick if you’re in the household with an index case than out in public (12% vs. 2%)
  • The age of the index case can INCREASE or DECREASE your chances of infection
    • Interestingly, an older kid (age 10-19) that gets COVID19 has the HIGHEST rate of infecting a contact compared to other ages (20%). This obviously has important implications for the school opening debate. 

Contact tracing (followed by quarantine) is one of the original and BY FAR the most effective ways to curb a pandemic. Other countries have been highly successful in achieving this. The United States has not. It’s a mess. Why?

  • Funding. We have a terrible history of not funding public health. So, when a pandemic hit, health departments were (and still are) scrambling for support (personnel, technology, infrastructure, etc). Even DURING the pandemic, I know of a couple health departments that have asked for funding for contact tracing and were denied. 
  • Spread. COVID19 has reached SO far, that this preventative measure is just not feasible. In Dallas, we are reporting ~7000 NEW cases per week. If each person had at least 2 contacts, this is 21,000 phone calls weeks PLUS follow-up phone calls. Contact tracing is best to use BEFORE uncontrollable spread. This has led to health departments prioritizing who they call; where they can make the most impact in terms of mortality.  
  • Lack of trust. Even if public health departments successfully reach an index case, the majority don’t answer their phone OR they report no contacts (which is most likely false). This chronic distrust in the US government is significantly impeding on public health efforts. 

Nonetheless, health departments are working incredibly hard with what they got. This has resulted in a few important case studies (see figures 2 and 3).

Contact tracing could answer SO MANY questions. This would better inform decision making and planning. For now, we will rely on small case studies in the US and comprehensive data from other countries. 

Love, your local epidemiologist

Data source: https://wwwnc.cdc.gov/eid/article/26/10/20-1315_article

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