Disease detectives with the Centers for Disease Control and Prevention are on the case of a new COVID-19 outbreak—the one at their very own conference, which has sickened around 35 attendees as of Tuesday.

Last week, the CDC hosted the 2023 Epidemic Intelligence Service (EIS) Conference in Atlanta, the first time the conference has been held in person since 2019. The annual event, which dates back seven decades, was fully virtual last year and was canceled entirely in 2020 and 2021 while EIS officers were immersed in the pandemic response.

"The COVID-19 pandemic has been hard on everyone and especially for our public health workforce. … We are thankful you are back with us at the EIS conference," EIS leaders wrote in the preface of this year's conference agenda, celebrating the return of the in-person gathering.

But signs of trouble turned up quickly. Several attendees reportedly tested positive during the conference, which spanned Monday, April 24 to Thursday, April 27, and drew about 2,000 participants. Some told The Washington Post that moderators at the conference warned several times about positive cases. CDC spokesperson Kristen Nordlund told Ars in an email that EIS leaders noted the cases during the closing session of the conference. The conference leaders also canceled an in-person training, emailed all officers with current CDC guidance, and offered to extend the hotel stays of sick attendees who needed to isolate, according to the Post.

On Friday, April 28, a CDC branch chief emailed staff about the potential outbreak. The email, obtained by the Post, read: “We’re letting you know that several people who attended the EIS Conference have tested positive for COVID-19," The email said that at least one person at a recruiting event on Wednesday had tested positive.

As of Tuesday, May 2, the CDC has identified approximately 35 attendees who have tested positive, Nordlund told Ars. She added that everyone the CDC knows of who has tested positive is now isolating at home and monitoring symptoms.

Rapid response

"CDC is working with the Georgia Department of Health to conduct a rapid epidemiological assessment of confirmed COVID-19 cases that appear to be connected to the 2023 EIS Conference to determine transmission patterns in this phase of the COVID-19 pandemic," Nordlund wrote in an email to Ars. She told the Post that such an investigation could help refine "future public health guidance as we move out of the public health emergency and to the next phase of COVID-19 surveillance and response."

The conference followed current CDC guidance, Nordlund told Ars, and "many conference attendees chose to mask."

"Whenever there are large gatherings, especially indoors, such as at a conference, there is the possibility of COVID-19 spread, even in periods of low community spread," she added.

The Post reports that other attendees, however, did not wear masks, socially distance, or take other precautions to prevent COVID-19 transmission during the event, though they were all likely to be up to date on their vaccinations.

The CDC outbreak comes when official case counts are among the lowest recorded since the pandemic began, but monitoring and reporting of cases have fallen dramatically. While the virus is still killing over 250 people a day in the US, largely the elderly, and millions have developed long COVID, many Americans have moved on from the pandemic and no longer regard COVID-19 as an urgent threat. Federal pandemic responses are also wrapping up, with the public health emergency set to lift next week. Still, the possibility of such outbreaks remains, and the virus continues to evolve, with the latest omicron subvariants XBB.1.5, now predominant nationally, and XBB.1.16 gaining ground.

"CDC continues to recommend that everyone ages six months and older stay up to date with all COVID-19 vaccines, including an updated vaccine," Nordlund concluded in her email to Ars. "COVID-19 vaccines are effective at protecting people from getting seriously ill, being hospitalized, and dying."