WASHINGTON, June 29 (Xinhua) -- Testing among quarantined contacts of patients with COVID-19 in a correctional and detention facility in the United States identified a high proportion of asymptomatic and presymptomatic cases, according a report of the Centers for Disease Control and Prevention (CDC) on Monday.

The cases were not identified through symptom screening alone. Approximately one fourth of cases were found through serial testing during quarantine, according to the report.

Correctional and detention facilities face unique challenges in detecting and mitigating transmission of SARS-CoV-2 infection, said the CDC.

On May 7, the CDC and the Louisiana Department of Health initiated an investigation to assess the prevalence of SARS-CoV-2 infection among incarcerated and detained persons residing in quarantined dormitories.

During May 7 to 21, among 98 incarcerated and detained persons who were quarantined because of exposure to the virus, 71 had laboratory-confirmed SARS-CoV-2 infection identified through serial testing.

Among those with positive test results, approximately one fourth had positive test results after one or two negative tests at previous time points in quarantine, and 45 percent did not report any symptoms at the time of testing, according to the CDC.

These findings suggest ongoing transmission among quarantined persons living in congregate settings, said the CDC.

Serial testing, particularly for close contacts of patients, is important for complete identification of cases and prompt public health response in congregate settings, said the CDC.