The U.S. Centers for Disease Control and Prevention (CDC) released a report Wednesday highlighting the effect the coronavirus pandemic is having within homeless service sites across the country, documenting the difficulty in containing the spread of COVID-19 among homeless communities.

The study investigated 19 shelters in Seattle, San Francisco, Atlanta and Boston testing residents and staff for the coronavirus. Between these shelters, researchers conducted testing in these locations while responding to clusters of confirmed cases (two or more diagnosed in the preceding two weeks). Other shelters tested proactively during the same time period, or before any coronavirus cases were confirmed among staff and residents.

Out of a total of 1,192 shelter residents tested, 293, or 25 percent, were found to have tested positive for the coronavirus. Of 313 shelter staff employees tested, 33, or 11 percent, were found to have confirmed cases.

The testing occurred between March 27 and April 15. Investigators ran reverse transcription-polymerase chain reaction testing at commercial and public health laboratories for SARS-CoV-2, the scientific name for the coronavirus.

"Homelessness poses multiple challenges that can exacerbate and amplify the spread of COVID-19," the study explained. "Homeless shelters are often crowded, making social distancing difficult. Many persons experiencing homelessness are older or have underlying medical conditions, placing them at higher risk for severe COVID-19-associated illness."

Researchers at the CDC note that there were several limitations encountered in the study, including only testing during a single point in time, which may exclude past or future cases. Additionally, some residents or staff members declined testing, and some symptom information for individuals who were rested were "not consistently available," potentially skewing results.

The CDC also told The Hill that the 19 shelters surveyed are not representative of all of the shelters in the U.S.

Still, in a corresponding report focused on COVID-19 outbreaks among homeless service sites in King County, Washington, the study noted that interrupting and mitigating the transmission of coronavirus among the homeless population is "challenging."

The CDC offers guidelines to protect housing-sensitive individuals during the coronavirus pandemic, including implementing hygienic and social distancing practices at shelters and promoting use of cloth face coverings among residents.