EMBED >More News Videos It started with a funeral. This is how one person who did not know they had COVID-19 infected 15 others, including 3 who died, in February.

EMBED >More News Videos With the number of coronavirus deaths increasing, some Chicago-area communities are concerned that funeral homes are holding ceremonies where social distancing isn't taking place.

CHICAGO (WLS) -- A Centers for Disease Control and Prevention investigation showed how one person in Chicago spread COVID-19 back in February to as many as 15 people, three of whom have died.The CDC report calls that person the "index patient." They did not know they had COVID-19 and the interactions started before the state issued a stay-at-home order.The cluster began with a funeral. The night before the funeral, the index patient, who was experiencing mild symptoms of the coronavirus, shared a take-out meal that lasted several hours with several other people. The next day, at the funeral, the index patient hugged family members of the deceased.Four of the people at the funeral became infected. One of those people was hospitalized more than a week later and then died.Three days after the funeral, the index patient went to a birthday party, where the individual hugged family members and shared food. At least three of those family members became infected, and two of them were hospitalized and later died.A family member and health professional providing care to one of the sick patients also began showing signs of infection, and spread it to another household contact. Three symptomatic people from the birthday party attended a church gathering where someone else became infected after sitting near them and passing the offering plate.City and health officials pointed to this case study as demonstrating exactly why it's so crucial to follow social distancing guidelines."Please, please, please keep up the social distancing," said Northwestern Medicine pulmonologist Dr. Khalilah Gates. "It's working It shows that it's working, the study shows that it's working."Dr. Gates reiterated that it's essential to maintain social distancing in general, and especially at life events like funerals and birthdays. Dr Gates said after the stay-at-home order was issued, infections like those in the CDC case study dropped off, proof you can make a difference by staying home."If we don't maintain the social distancing we need, we will lose ground," said Mayor Lori Lightfoot.The patients in the report ranged in age from five to 86. The three people who died were each over 60 and had at least one underlying medical condition.