Investigation and Serologic Follow-Up of Contacts of an Early Confirmed Case-Patient with COVID-19, Washington, USA

Abstract

We describe the contact investigation for an early confirmed case of coronavirus disease (COVID-19), caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), in the United States. Contacts of the case-patient were identified, actively monitored for symptoms, interviewed for a detailed exposure history, and tested for SARS-CoV-2 infection by real-time reverse transcription PCR (rRT-PCR) and ELISA. Fifty contacts were identified and 38 (76%) were interviewed, of whom 11 (29%) reported unprotected face-to-face interaction with the case-patient. Thirty-seven (74%) had respiratory specimens tested by rRT-PCR, and all tested negative. Twenty-three (46%) had ELISA performed on serum samples collected ≈6 weeks after exposure, and none had detectable antibodies to SARS-CoV-2. Among contacts who were tested, no secondary transmission was identified in this investigation, despite unprotected close interactions with the infectious case-patient.

Keywords: 2019 novel coronavirus disease; COVID-19; SARS-CoV-2; contact tracing; coronavirus; coronavirus disease; respiratory infections; serology; severe acute respiratory syndrome coronavirus 2; viruses; zoonoses.

Figure 1

Case-patient investigation and contact identification during the investigation of an early confirmed US COVID-19 case, Washington, USA, 2020. The case-patient was asymptomatic when he arrived home from Wuhan, China. The next day, he developed a cough (day 1), followed by chills (day 2) and a subjective fever (day 3). When he arrived at the urgent care clinic (day 4), he was given a facemask and sat in the waiting room for ≈20 minutes. He was evaluated in a standard examination room, and received a chest radiograph in a radiology room down the hallway from the exam room. The case-patient was identified as meeting the Centers for Disease Control and Prevention (CDC) criteria at the time for a person under investigation for COVID-19, and specimens (nasopharyngeal and oropharyngeal swabs and serum samples) were collected for testing (6). He was clinically stable and discharged home pending SARS-CoV-2 test results. When COVID-19 was confirmed (day 5), the case-patient was admitted to a hospital for observation and isolation. After 11 days, he was discharged to home isolation until 2 negative sets of nasopharyngeal and oropharyngeal specimens were obtained >24 hours apart, in accordance with CDC guidance at the time (7). Persons exposed during transient interactions, such as restaurant waitstaff and persons encountered at the grocery store, were not considered community contacts. COVID-19, coronavirus disease.

Figure 2

Contact investigation flowchart of identified contacts, active monitoring, and participation in the enhanced contact investigation of an early confirmed US coronavirus disease case, Washington, USA, 2020. NP, nasopharyngeal; OP, oropharyngeal; PUI, person under investigation. *Includes contacts from whom specimens obtained for PUI testing. †Specimens were unable to be tested if blood could not be obtained (n = 5) or if the standard specimen requirements for testing were not met (n = 2).