Collection of Outbreak Data
The Navy and Marine Corps Public Health Center was tasked with providing public health support for the outbreak investigation and conducting data analysis in alignment with its core public health mission. Data were collected as part of a coordinated public health outbreak investigation conducted by the Navy to bring the outbreak under control, ensure the well-being of the crew, assess the spread and effects of SARS-CoV-2, and implement measures to return the crew to work safely. Under Navy public health support criteria, the intent of the outbreak investigation was to mitigate spread, inform decision making, gather information for use in other outbreaks, and decrease the effect on the health of the crew. This project was deemed to be nonresearch with respect to the use of human subject information and was exempt from review by the institutional review board as an emergency public health outbreak investigation.
A roster of Electronic Data Interchange Personal Identifiers for the shipboard population was matched to Defense Manpower Data Center personnel rosters from February 2020 to identify demographic information for each crew member and to confirm personal identifiers. Civilian personnel and anyone with an Electronic Data Interchange Personal Identifier that did not match with Defense Manpower Data Center were excluded from analysis. The Defense Enrollment Eligibility Reporting System was used to identify race and ethnic group for all crew members. Ages of crew members at time of the outbreak were calculated from the date of birth to March 3, 2020.
Medical surveillance data collected by the ship medical department, Naval Hospital Guam, and the joint medical task force were collated with the roster to create a data set that included dates of symptom onset, daily clinical signs and symptoms, and test results. Data from the Defense Digital Service MySymptoms symptom-tracker application were also collated into the final data set. For the purpose of this analysis, fever is defined as subjective fever reported by the crew member or a measured temperature of 100.0°F or higher. All other symptoms were reported by the crew members. Data on health-related factors were obtained from a number of existing clinical Military Health System data sources, including the Armed Forces Health Longitudinal Technology Application and Military Health System Genesis.
A confirmed case of Covid-19 was defined as one in which a nasopharyngeal swab specimen was positive for SARS-CoV-2 by rRT-PCR. A suspected case of Covid-19 was defined as one that met Council of State and Territorial Epidemiologists clinical criteria for Covid-19 without a positive test result. Confirmed cases were further classified as symptomatic (with symptom onset before the first positive laboratory test), presymptomatic (with the first positive laboratory test before subsequent symptom onset), and asymptomatic (positive laboratory test but clinical criteria never met). Patients with confirmed or suspected infection were classified as having been hospitalized for Covid-19 if the admission diagnosis suggested a Covid-19–related illness.