The New York City Department of Health has conducted a large-scale study of New Yorkers that shows household contact and gatherings of 10 or more people as the two main drivers of coronavirus infections.
The analysis, which has yet to be publicly released, comes at a critical period in the pandemic as city and state officials wrestle with how to fight a surge of new infections that could once again overwhelm hospitals. The Department of Health study was based on a controlled study involving interviews with more than 3,600 people conducted over a four month span, one of the largest to date in the city examining the modes of transmission. Of those interviewed, 1,200 were infected with COVID-19.
In an interview with Gothamist, the city's Health Commissioner Dr. Dave Chokshi said that the study showed that people who had close contact with a household member or partner who had contracted the virus were four times as likely to be infected as those who did not have such contact.
In a second major factor, those who attended a social gathering of 10 or more people were found to be twice as likely of becoming infected, he said. In New York state, private gatherings of more than 10 people are currently prohibited.
Although the findings about household contact were not especially surprising, the information reinforces what the city's test and trace officials have found as well as evidence gathered in other parts of the country and world.
During a press conference on Monday, Dr. Amanda Johnson, a director at the city's test and trace program, said that a least one in five cases investigated in recent weeks were due to household transmission.
The data about household infections also underscores the risks and challenges of controlling the virus in a dense city where many residents live in tightly packed quarters either with family members or roommates.
"This is a large part of the spread that we're seeing," Chokshi said. "It also means there's something to be done about it, which is really emphasizing the importance of safe separation."
Chokshi said that once someone is diagnosed with COVID-19, or if they start to develop symptoms, other members in the household should immediately seek to distance themselves. Since the summer, New York City has been offering hotel rooms to infected individuals unable to quarantine in their own homes.
In another important finding substantiated by other research, Chokshi said the study also showed that the likelihood of contracting the virus decreased by about 40% among people who reported always wearing a face covering indoors outside of their household compared to those who said they only occasionally or never wore a face covering while indoors.
But despite the early analysis provided by health officials, unanswered questions still remain. Aside from household transmission, Chokshi did not offer details about other settings that could drive infections, such as indoor dining and gyms, two areas that public health experts have described as high risk and urged government officials to restrict as cases soar.
The city's average positive testing rate has been steadily climbing and is now above 4%. The average number of new cases diagnosed daily has surpassed 1,600, the highest it has been since early May. New hospitalizations due to COVID are also increasing, to more than 100 a day.
Amid this resurgence, epidemiologists have yearned to know more about transmission data the city has collected, specifically through its test and trace program. But city officials have provided bare and unsatisfying details at best.
"Everyone is thirsting for this data," said Dr. Wafaa El-Sadr, an epidemiology professor at Columbia University. "You want to shape policy firmly planted in evidence."
She said it would be useful to look at test and trace interviews to tease out where people are getting infected beyond households.
Karla Griffith, a spokesperson for the city's test and trace program, recently told Gothamist that city investigators attributed 15% of roughly 140 cases to work in an essential work setting, such as a healthcare facility, at least 12% to travel, 10% due to transmission specifically by a close contact, 9% to attending a specific gathering, and 3% to a congregate setting.
The remaining 49% comes from cases where people are unable to recall where they may have been exposed to the virus.
Griffith said many people, especially those who are younger and socialize more, have multiple exposure factors.
"We know that there is an increased risk of transmitting the virus indoors, and this includes facilities like restaurants and gyms," Griffith said. "However, when contact tracers interview people—especially young people—about where they’ve been in the 14 day period they’ll tell you they’ve dined in several times, gone to several parties, and participated in other social activities. There’s no way to prove definitively where these folks got infected."
Dr. Denis Nash, an epidemiology professor at CUNY who previously worked at the city's Department of Health, commended the research effort but urged health officials to release the full results of their s.
"This is a study that will rigorously tell you that," he said.study as soon as possible.
He said that the landscape of risk factors has been changing and that any new findings could potentially identify the "weak spots" in the city's prevention measures.
Given the findings on mask wearing, he argued that the city should issue stronger and clearer guidance about mask wearing in settings outside public spaces. For example, government officials in other places, including Pennsylvania, have issued orders requiring people to wear masks at home when someone is visiting them.
And depending on whether racial data was collected, Nash said the study could also provide reveal the ongoing disparities.
"When you have such a large sample, you can then understand the extent to which certain groups may be higher risk," he said, citing the disproportionate toll of the pandemic on Black and Hispanic residents as well as low-income communitie