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COVID Check-In: Index Case and the Two Routes of Transmission

Each week, Forum Director of Research Noreen Sugrue provides insight into the political implications of the latest COVID-19 health data. This week, she explains index case and looks into two main types of transmission: behavioral choice and occupational necessity.

By Noreen Sugrue, Director of ResearchNoreen Sugrue (@NoreenSugrue) | Twitter

As we monitor the patterns of how and where people are infected, we must also look at what is referred to as the index case. This refers to how the person who infects others with the virus is initially exposed. There are two broad routes of transmission.

One is infection via behavioral choices. Behavioral choices include going to bars, restaurants, parties, not wearing a mask, and attending or hosting large social gatherings. The other route of infection is occupational necessity: in other words, people working in essential jobs where they are at high risk for exposure. In both scenarios, people who become infected often go home, meet friends, talk to coworkers, and take care of family.

When the index case is due to occupational necessity, the interaction with family or others is often due to close living conditions, shared spaces, or shared rides to work or the grocery store. It also may involve shared child-care arrangements. These cases are the result of working in high-risk occupations and sharing necessary day-to-day living arrangements. These people, by and large, are Latino or Black. They are disproportionately represented in high-risk jobs. Transmission due to close proximity is not the result of a behavior choice, but rather of economic necessity. 

The behavioral-choice transmission is often the result of people choosing to live their lives as if there were no pandemic. It is people going to restaurants, bars, and engaging in social activities as if it were 2019, not 2020. They too will then spread the virus to others in their social, familial, and professional spheres. But unlike those who are exposed due to occupational necessity, these behavioral-choice spreaders are making social and economic decisions based on what they want to do, rather than what they must do to survive.

It is important to note that close proximity with no masks, family and social gatherings, and gatherings of children are all high-risk activities and must be avoided whenever possible. However, it is also important to understand the difference between those who have no choice but to risk exposure, and those who are choosing to risk exposure.