The night before a funeral in February, a Chicago man shared a three-hour takeout meal with two family members of the deceased. The next day, at the service, he took part in a potluck dinner, hugging those in mourning. In the following days, he swung by a birthday party.

Throughout these simple, seemingly innocuous encounters, the man had mild symptoms of what authorities now know to be the novel coronavirus, and health officials believe he may have been a so-called super-spreader who unwittingly transmitted the infection to as many as 16 people, resulting in three deaths.

The account of community spread in an Illinois cluster is the product of an investigation conducted in February and March by the Centers for Disease Control and Prevention and the Chicago Department of Public Health. It shows how easily the virus can be transmitted, even with limited contact—and provides a cautionary tale for Americans thinking of breaking social-distancing guidelines.

The report tracks the possible super-spreader’s contacts with each patient in a five-page study published in the federal agency’s Morbidity and Mortality Weekly Report for April 8.

Super-spreaders—or patients who are extra contagious—have become a notable feature of the virus. Experts have pointed to cases like that of a lawyer in New Rochelle, New York who may have helped trigger an outbreak there, and a man in the United Kingdom who may have transmitted the virus to nearly a dozen people before realizing he was sick earlier this year.

The cluster of patients in the Chicago report were ages 5 to 86 years and had close contact through family gatherings, including the birthday party and funeral, as well as a church service, according to the report. The analysis indicates the group “might have facilitated transmission” of the virus “beyond household contacts into the broader community.”

As of Wednesday afternoon, there were 9,509 confirmed cases of the virus and 249 deaths in Cook County, Illinois.

The February funeral for an unrelated cause of death was attended by the index patient—or first traceable case of the virus in the cluster—who was a close friend of the family and had recently traveled out of state. At the time, he experienced only mild respiratory symptoms and was only later diagnosed with COVID-19 as a part of the epidemiological investigation into the cluster, according to the report.

At both the pre-funeral meal and the event itself, the possible super-spreader expressed condolences and hugged at least four people. Those four people all developed symptoms within six days of the funeral, and one of them was hospitalized, “required endotracheal intubation and mechanical ventilation for acute respiratory failure, and died,” according to the report.

In the following days, another person who had close contact with the index case at the funeral visited the hospital, cared for, and hugged their dying—and COVID-19 infected—relative without wearing personal protective equipment. Three days after that visit, they developed a fever and cough.

Meanwhile, the index case, who was still likely unaware he even had the virus, went to a birthday party with nine other family members, where they talked, hugged, and shared food for three hours.

Seven party attendees subsequently developed the virus within seven days of the event. Several of those patients experienced mild symptoms of cough and a low-grade fever. But two of those patients were hospitalized, required endotracheal intubation and mechanical ventilation, and died.

Two people who provided care for one of the people who died—without using personal protective equipment, including a home care professional and a family member—both exhibited symptoms of the virus soon afterward. A household contact of the other fatality also developed a cough three days after close contact with the patient.

Three of the party attendees who exhibited symptoms attended a church service six days later, leading to another case of the virus after close contact with those individuals, including sitting in a pew for 90 minutes and passing the offering plate, according to the report.

“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 authors wrote. “Despite intensive epidemiologic investigation, not every confirmed or probable case related to this cluster might have been detected. Persons who did not display symptoms were not evaluated for COVID-19, which, given increasing evidence of substantial asymptomatic infection, means the size of this cluster might be underestimated.”

The CDC’s findings highlight the need for social-distancing, even before confirming community transmission in a given area.

“The earlier you react to this, the more proactive you are in your response, the more you will contain it,” said Jeffrey Shaman, a Columbia University epidemiologist whose projections on the virus’ spread in the United States have been cited by the White House and published in The New York Times. “Once the virus gets into a population, it will grow.”

The problem with waiting to confirm community spread before implementing social distancing, Shaman explained to The Daily Beast, is that even the best information about the virus’s presence is still on a 10-16 day lag from transmission to documentation.

As Shaman explained, a person who becomes infected may go through a latent period of three to five days, followed by about one to three days of pre-symptomatic shedding “where they’re contagious but not yet symptomatic.” Then, he continued, over the next three to five days, the person might be sick enough to seek clinical care and be swabbed, with results coming back somewhere between seven hours to seven days, depending on where they live. And many states did not issue shelter-in-place or stay-at-home orders until there were already cases in the community. Some still haven’t, though federal guidelines have encouraged all Americans to avoid gatherings of more than 10 people.

Shaman posited that a super-spreader may have been present during the now-infamous choir practice in Washington state—in which attendees reportedly used hand sanitizer, refrained from touching one another, and stood apart while singing. At least 45 people became infected and two died.

“It was probably aerosol transmission,” said Shaman, referring to the idea that the virus may be more airborne than originally understood.

But many unknowns still remain, including how the virus is transmitted and how effective even the most draconian social-distancing orders in the U.S. have been.

If everyone complies with social-distancing orders, Shaman said, “We may be doing enough right now to pull it back down and alleviate the strain on our healthcare systems, but we don’t know yet.”