Sample Pooling as a Strategy to Detect Community Transmission of SARS-CoV-2

Abstract

We conducted a rapid sentinel surveillance study to determine what proportion of mild, outpatient influenzalike illnesses were caused by SARS-CoV-2.Methods | Between March 12-13 and 15-16, 2020, the Los Angeles County + University of Southern California Medical Center conducted testing among patients presenting with mild influenzalike illness to the emergency department or urgent care.Patients who had nasopharyngeal swabs tested with polymerase chain reaction assays for influenza and respiratory syncytial virus (GeneXpert Flu, Cepheid) were automatically tested for SARS-CoV-2 (Quest Diagnostics).Only the influenza tests conducted during the day shift were automatically tested for SARS-CoV-2 because the process was manual.Patients were excluded if they had specific risk factors for SARS-CoV-2 (eg, travel exposure or known contact with a traveler, severely ill patients admitted for respiratory tract infections).Positive test results were followed up by Department of Public Health experts to assess clinical factors and demographics.The number of influenza tests ordered by physicians at the Los Angeles County + University of Southern California Medical Center between March 2 and March 18, 2020, and the proportion testing positive for influenza were also assessed.In addition, the rate of influenzalike illnesses obtained from weekly surveys of emergency departments over the past 5 years were summarized, as well as the percentage of respiratory specimens testing positive for influenza from ongoing public health sentinel surveillance conducted at 7 clinical laboratories across Los Angeles County, California.This study was approved as expedited with a waiver of informed consent by the University of Southern California health sciences campus institutional review board.