At least 11 contractors working on a top-to-bottom renovation of the Cannon House Office Building have tested positive for COVID-19, forcing them and other construction workers on the project to go into quarantine.

On Thursday, Clark Construction and Christman, the two companies selected for the decade-long project, notified workers that five people at the site had tested positive for COVID-19.  And in response to questions from DCist, the Architect of the Capitol, which is overseeing the project, said the total number of positives so far is more than double that.

“Our safety office identified a possible emerging trend among contractors working in Cannon. In 10 days, contractors have gone from no confirmed positive cases to 11. All of those contractors, and those who worked with them, are quarantining,” spokeswoman Erin Courtney said in an email.

The positive cases have cropped up despite what Courtney says are additional measures implemented in March to limit transmission, including social distancing during security screening and construction, enhanced cleaning, the use of face coverings, and hand-washing stations.

By both federal and D.C. standards, construction is considered “essential” and can continue during the pandemic. Still, some residents and critics worry that social distancing is tough to practice on large construction projects or in confined spaces. The D.C. Department of Health has laid out guidelines for construction during the pandemic, and the Department of Consumer and Regulatory Affairs says it has visited more than 120 construction sites to monitor for compliance with social distancing rules.

But projects on Capitol Hill and within federal facilities largely escape D.C. regulations; the Cannon project, for one, is overseen by the Architect of the Capitol and the General Services Administration.

The Cannon House Office Building was originally constructed in 1908, and currently serves as office space for hundreds of U.S. representatives and their staff, and also has numerous committee rooms. But some of the existing occupants of the building have been moved elsewhere during the work, and Courtney says the construction workers do not come into contact with members of Congress or their staff.

“The project personnel are isolated from contact with the occupants of the building,” she wrote. “They enter through a dedicated entry and the project is sealed off from the remainder of the building.”