In February, a Chicago man hugged members of a grieving family at a funeral and shared meals with them. A few days later, he attended a birthday party, where he hugged and shared food with members of another family.

With these friendly gestures at family gatherings, the man - who later tested positive for COVID-19 - unwittingly infected as many as 15 other people with the virus before social distancing measures were implemented in Illinois and other states in the US.

Three of those people died of the virus.

The chain of transmission triggered by the man - who had had mild respiratory symptoms at the time he attended the funeral and party - was detailed in a report released by the CDC on Wednesday.

The report highlighted the dangerous potential of a "super-spreading event" and showed how extended family gatherings might have facilitated the transmission of COVID-19 "beyond household contacts and into the broader community."

The patients in this multifamily cluster in Chicago were between the ages of 5 and 86 years old. They came into contact with each other at the funeral, the birthday, and a church service.

The three patients who died were over the age of 60, and all three had at least one underlying cardiovascular or respiratory medical condition, the report said.

The CDC said the findings in this tragic case illustrate how important social distancing is to preventing the spread of COVID-19, even within families.

The evening before the funeral in February, the Chicago man shared a three-hour takeout meal, eaten from common serving dishes, with two family members of the deceased at their home.

The man (referred to as "an index patient" in the report) was the grieving family's close friend. He had recently traveled out of state and was experiencing mild respiratory symptoms at the time. He was only tested later as part of the broader epidemiological investigation and was then diagnosed with COVID-19.

The next day, at the two-hour funeral, the man shared a potluck meal with other attendees and hugged at least four members of the grieving family to express his condolences. These four people developed symptoms of COVID-19 within six days of the funeral.

One of them was hospitalized, required "endotracheal intubation and mechanical ventilation for acute respiratory failure," and died.

Before the person died, they were visited in the hospital by a family member who had also been in close physical contact with the index patient at the funeral.

That family member embraced their COVID-19–infected relative in the hospital ward and took care of the patient without wearing personal protective equipment. Three days after that visit, the person developed COVID-19 symptoms, including a fever and a cough.

The index patient, who was still experiencing mild respiratory symptoms, then attended a birthday party with nine members of another family, three days after he attended the funeral.

At the three-hour party, the man hugged and shared food with the other guests. Seven of the guests developed COVID-19 within a week.

Five of them experienced mild symptoms, including a cough and a low-grade fever. Two others were hospitalized, required endotracheal intubation and mechanical ventilation, and died.

A family member and a home care professional who took care of one of the party guests who died also probably developed COVID-19, the report said. The other party guest who died likely transmitted the virus to a household contact who had not attended the birthday party.

Three symptomatic birthday party attendees with probable cases of COVID-19 then attended a church service, six days after they developed their first symptoms.

They conversed with and passed the offering plate to another church attendee who was sitting in the same row for 90 minutes. That church attendee, a health care professional, was diagnosed with COVID-19.

The index patient "was apparently able to transmit infection to 10 other persons, despite having no household contacts and experiencing only mild symptoms for which medical care was not sought," the report said.

It's not yet clear how common this type of transmission has been during the current pandemic, the report noted.

"Super-spreading events have played a significant role in transmission of other recently emerged coronaviruses," the report said, but added that their relevance to COVID-19 spread is "debated."

The most notable "super-spreading event" likely occurred at a choir practice in Washington state when at least 45 of 60 singers were either diagnosed with COVID-19 or showed symptoms. In another potential super-spreading case, a New York lawyer was connected to one of the earliest clusters of COVID-19 cases that developed in New Rochelle.

Dr. Mark Dworkin, an epidemiology professor at the School of Public Health at the University of Illinois at Chicago, noted that it was important not to refer to people as "super-spreaders" but to instead acknowledge how funerals and birthday parties are the kinds of events that allow for super-spreading.

These events include a close congregation of people who are socially and physically more familiar with each other, Dworkin told BuzzFeed News.

At a family event, "it's kiss, kiss, kiss, hug, hug, hug," with people sitting inches away from each other, he said.

The authors of the CDC report said their findings highlighted the importance of adhering to current social distancing recommendations.

Eight states have not yet issued stay-at-home orders, and those that have are forced to remind residents to take social distancing measures seriously. As of Wednesday, Illinois has reported 15,078 positive cases and 462 people have died. Gov. J.B. Pritzker issued a stay-at-home order in the state on March 20.

While the Chicago cluster occurred before social distancing measures were implemented, Dworkin said he could not fault authorities for introducing them at a time when community spread of the disease was already evident across the US.

He said that the current stay-at-home orders and social distancing measures were at that time considered "really super-extreme thing to do."

"It's really hard to pull off a recommendation to the public like that if you don't have evidence of why it's absolutely necessary," he said. And how much evidence the general public needs "right in front of them to buy into these extreme recommendations varies from population to population and from culture to culture," Dworkin said.

He called the Chicago cluster a tragedy that shows how "the virus is taking advantage of our positive behaviors" when it comes to celebrating milestones, supporting loved ones, or turning to faith.

"It's really sad that such events need to be curtailed at a time in order to promote our health," Dworkin said. "But we need to remember this is temporary. We need to be patient. The more we accept and are patient with this evolving science, the more successful we will be."