Table 2.

Characteristics of Seropositive Participants and Indeterminate Participants

Participant	Provider Type	Prior Diagnosis of COVID-19	Likelihood of seropositivity	Antibody Positive at Baseline	Anti-nucleocapsid Antibody Optical Density Ratio			Notes
					Baseline	3 Mo. Follow Up	6 Mo. Follow Up
Seropositive Participants⁎
A	Resident	yes	76–100%	Yes	5.91	3.94	2.66	Travelled to NYC at end of 2/2020. Believes infected at that time.
B	Resident	yes	76–100%	Yes	3.83	1.05	0.45	Experienced fever and cough after travel to Colorado in 6/2020
C	Nurse	no	51–75%	Yes	3.74	2.00	0.73	Experienced fever and cough in 2/2020 prior to availability of PCR testing.
D	Attending	yes	76–100%	Yes	3.34	1.03	0.61	Travelled to NYC at end of 2/2020. Believes infected at that time.
E	Nurse	yes	76–100%	No	1.19	0.39	N/A	Experienced symptoms and positive PCR in 3/2020. Positive antibody test prior to study.
F	Nurse	yes	11–25%	No	0.26	5.00	3.13	Symptomatic with positive PCR in 11/2020.
Indeterminate Participants⁎⁎
W	Attending	no	3–5%	No	1.14	1.19	1.60	Denied COVID-19 symptoms or positive COVID-19 PCR testing. Banked plasma from 2019 (pre-COVID) was near threshold. Negative anti-spike antibody. Probable cross-reacting antibodies to endemic coronavirus.
X	Nurse	no	26–50%	No	0.63	0.74	0.79	Denied COVID-19 symptoms or positive COVID-19 PCR testing.
Y	Resident	no	76–100%	No	0.5	0.27	0.22	No prior diagnosis of COVID-19 on PCR testing.
Z	Nurse	no	6–10%	No	0.44	0.39	0.52	Denied COVID-19 symptoms or positive COVID-19 PCR testing.

^⁎seropositive participants had clinical syndrome, positive PCR, and AU above manufacture's threshold of 1.4 AU.

^⁎⁎Indeterminate patients had antinucleocapsid result below manufacturer's threshold of 1.4 AU but above MHRA suggested threshold of 0.49 AU.