SARS-CoV-2 Infections and Serologic Responses From a Sample of U.S. Navy Service Members

USS Theodore Roosevelt, April 2020

Daniel C. Payne, PhD; Sarah E. Smith-Jeffcoat, MPH; Gosia Nowak, MPH; Uzo Chukwuma, MPH; Jesse R. Geibe, MD; Robert J. Hawkins, PhD, DNP; Jeffrey A. Johnson, PhD; Natalie J. Thornburg, PhD; Jarad Schiffer, MS; Zachary Weiner, PhD; Bettina Bankamp, PhD; Michael D. Bowen, PhD; Adam MacNeil, PhD; Monita R. Patel, PhD; Eric Deussing, MD; CDC COVID-19 Surge Laboratory Group; Bruce L. Gillingham, MD

Disclosures

Morbidity and Mortality Weekly Report. 2020;69(23):714-721. 

In This Article

Abstract and Introduction

Introduction

Compared with the volume of data on coronavirus disease 2019 (COVID-19) outbreaks among older adults, relatively few data are available concerning COVID-19 in younger, healthy persons in the United States.[1,2] In late March 2020, the aircraft carrier USS Theodore Roosevelt arrived at port in Guam after numerous U.S. service members onboard developed COVID-19. In April, the U.S. Navy and CDC investigated this outbreak, and the demographic, epidemiologic, and laboratory findings among a convenience sample of 382 service members serving aboard the aircraft carrier are reported in this study. The outbreak was characterized by widespread transmission with relatively mild symptoms and asymptomatic infection among this sample of mostly young, healthy adults with close, congregate exposures. Service members who reported taking preventive measures had a lower infection rate than did those who did not report taking these measures (e.g., wearing a face covering, 55.8% versus 80.8%; avoiding common areas, 53.8% versus 67.5%; and observing social distancing, 54.7% versus 70.0%, respectively). The presence of neutralizing antibodies, which represent antibodies that inhibit SARS-CoV-2, among the majority (59.2%) of those with antibody responses is a promising indicator of at least short-term immunity. This report improves the understanding of COVID-19 in the U.S. military and among young adults in congregate settings and reinforces the importance of preventive measures to lower risk for infection in similar environments.

In mid-January, the USS Theodore Roosevelt was deployed to the western Pacific. An outbreak of COVID-19 occurred during deployment, which resulted in the aircraft carrier stopping in Guam at the end of March. During this time, approximately 1,000 service members were determined to be infected with SARS-CoV-2, the virus that causes COVID-19. The United States Navy and CDC investigated this ongoing outbreak during April 20–24; 382 service members voluntarily completed questionnaires and provided serum specimens (a convenience sample comprising 27% of 1,417 service members staying at the base on Guam or on the ship). The 1,417 included persons who were previously infected, currently infected, or never infected. Among these 382 service members, 267 (70%) also provided a nasopharyngeal (NP) swab specimen. Serum specimens were tested for antibody reactivity using a CDC-developed, SARS-CoV-2 spike protein enzyme-linked immunosorbent assay (ELISA) (a pan-immunoglobulin assay) as an indicator of previous SARS-CoV-2 exposure and infection; signal threshold ratio ≥1 was defined as a positive ELISA result.[3] ELISA-positive specimens were further tested for neutralizing antibodies using a microneutralization assay to detect presence of SARS-CoV-2 inhibiting antibodies (antibody titers >40 defined as positive). Real-time reverse transcription–polymerase chain reaction (RT-PCR) testing of NP swab specimens was used to detect SARS-CoV-2 RNA.[4] Previous or current SARS-CoV-2 infection was defined as a positive real-time RT-PCR result or positive ELISA result.

At the time of specimen collection, participants completed a questionnaire eliciting information on demographic characteristics, exposure, COVID-19 protective behaviors, health history, and symptoms; participants also reported whether they had had a previous positive COVID-19 test since deployment but before this investigation. Protective behaviors listed on the questionnaire were not mutually exclusive, so participants could select all that applied. Reported symptoms were categorized using the Council of State and Territorial Epidemiologists (CSTE) case definition for COVID-19,[5] including category A (at least cough or shortness of breath/difficulty breathing) and category B (no cough or shortness of breath, but two or more other symptoms*) or neither. Demographic, exposure, and symptom characteristics and engagement in protective behaviors were compared among participants infected with SARS-CoV-2 and those having no evidence of previous or current infection, and unadjusted odds ratios (ORs) with 95% confidence intervals (CIs) were calculated. Analyses were performed using SAS statistical software (version 9.4; SAS Institute).

Among the 382 survey participants (Figure 1), 289 (75.7%) were male; their median age was 30 years (interquartile range [IQR] = 24–35 years), 223 (58.4%) were non-Hispanic white, and 28 (7.3%) reported a history of asthma, hypertension, diabetes, or immunosuppression (Table). Among 238 (62.0%) participants with previous or current SARS-CoV-2 infection, 194 (81.5%) reported one or more symptoms, 44 (18.5%) were asymptomatic, and two (0.8%) were hospitalized for COVID-19. Among all participants, the prevalence of previous or current infection among males was higher than that among females (OR = 1.8) but did not differ significantly by age, race, ethnicity, or history of a preexisting medical condition.

Figure 1.

Laboratory results among a convenience sample of U.S. service members who provided serum specimens* (N = 382) and nasopharyngeal swabs (N = 267) for SARS-CoV-2 testing — USS Theodore Roosevelt, April 2020
Abbreviations: Ab = antibody; ELISA = enzyme-linked immunosorbent assay; Inc = inconclusive; Neg = negative; Pos = positive; RT-PCR = real-time reverse transcription– polymerase chain reaction.
*Of those with positive serum ELISA tests, 59% demonstrated positive microneutralization tests.

Among 284 symptomatic participants (194 [68.3%] with previous or current SARS-CoV-2 infections and 90 [31.7%] without), loss of taste (ageusia) or smell (anosmia) were the symptoms most strongly associated with previous or current infection (OR = 10.3), followed by fever (OR = 2.8), chills (OR = 2.7), and myalgia (OR = 2.6) (Figure 2). CSTE-defined category B symptoms were more strongly associated with infection (OR = 5.8) than were category A symptoms (OR = 3.5). Reporting four or more symptoms and seeking medical care for symptoms (OR = 2.3) were significantly associated with infection.

Figure 2.

Odds ratios and 95% confidence intervals of previous or current SARS-CoV-2 infection, by individual symptoms among service members reporting at least one symptom (n = 284) — USS Theodore Roosevelt, April 2020

Overall, 228 (59.7%) participants had a positive ELISA result, and among those, 135 (59.2%) also had a positive microneutralization test result. Among those with positive ELISA results, Hispanic/Latino participants were more likely to have positive microneutralization test results (33 of 44; 75.0%) than were participants of non-Hispanic/Latino or unspecified ethnicity (102 of 184; 55.4%) (OR = 2.4; 95% CI = 1.1–5.1). Among the 267 participants who provided an NP swab, 98 (36.7%) had a positive real-time RT-PCR result; 171 (64.0%) persons who provided an NP swab had a positive ELISA result. Among 235 participants who reported a positive SARS-CoV-2 test result before this investigation (defined as during this deployment, mid-January to April 20–24, 2020), 212 (90.2%) had positive ELISA results compared with 16 (10.9%) among 147 not reporting previous positive test results for SARS-CoV-2 (OR = 75.5; 95% CI = 38.5–148.1).

Among 191 symptomatic participants who reported a symptom onset date and had positive real-time RT-PCR results, positive ELISA results, or both, eight had positive real-time RT-PCR and negative ELISA results; for these participants, ≤15 days had elapsed since symptom onset at the time of specimen collection (Figure 3). Among symptomatic participants with positive ELISA results and positive microneutralization test results (n = 107), a median of 22 days (IQR = 15–26) had elapsed since symptom onset at the time of specimen collection (Figure 3). Among 12 participants with positive ELISA results >40 days after symptom onset, eight maintained positive microneutralization test results, including two participants who were tested >3 months after symptom onset.

Figure 3.

Days from symptom onset* to specimen collection (A) among a convenience sample of participants who had positive real-time reverse transcription–polymerase chain reaction (RT-PCR) or positive enzyme-linked immunosorbent assay (ELISA) test results for SARS-CoV-2 (n = 191) and (B) microneutralization results among those with positive ELISA test results (n = 183) — USS Theodore Roosevelt, April 2020
Abbreviations: Ab = pan-immunoglobulin antibody response; Mn = microneutralization test.
*Three persons who reported symptoms and had previous or current infection did not report a date of symptom onset and were not included in this figure.

Prevalence of previous or current infection was higher among participants who reported contact with someone known to have COVID-19 (64.2%), compared with those who did not (41.7%) (OR = 2.5; 95% CI = 1.1–5.8); prevalence was also higher among persons who reported sharing the same sleeping berth with a crewmember who had positive test results (65.6%), compared with those who did not (36.4%) (OR = 3.3; 95% CI = 1.8–6.1). Lower odds of infection were independently associated with self-report of wearing a face covering (55.8% versus 80.8%; OR = 0.3; 95% CI = 0.2–0.5), avoiding common areas (53.8% versus 67.5%; OR = 0.6; 95% CI = 0.4–0.9), and observing social distancing (54.7% versus 70.0%; OR = 0.5; 95% CI = 0.3–0.8), compared with service members who did not report these behaviors.

*Fever, chills, muscle pain, headache, sore throat, new taste or smell disorder.

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