SARS-CoV-2 seroprevalence among parturient women in Philadelphia

Abstract

Limited data are available for pregnant women affected by SARS-CoV-2. Serological tests are critically important for determining SARS-CoV-2 exposures within both individuals and populations. We validated a SARS-CoV-2 spike receptor binding domain serological test using 834 pre-pandemic samples and 31 samples from COVID-19 recovered donors. We then completed SARS-CoV-2 serological testing of 1,293 parturient women at two centers in Philadelphia from April 4 to June 3, 2020. We found 80/1,293 (6.2%) of parturient women possessed IgG and/or IgM SARS-CoV-2-specific antibodies. We found race/ethnicity differences in seroprevalence rates, with higher rates in Black/non-Hispanic and Hispanic/Latino women. Of the 72 seropositive women who also received nasopharyngeal polymerase chain reaction testing during pregnancy, 46 (64%) were positive. Continued serologic surveillance among pregnant women may inform perinatal clinical practices and can potentially be used to estimate exposure to SARS-CoV-2 within the community.

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CORONAVIRUS
SARS-CoV-2 seroprevalence among parturient women
in Philadelphia
Dustin D. Flannery1,2,3*, Sigrid Gouma4*, Miren B. Dhudasia1,3, Sagori Mukhopadhyay1,2,3,
Madeline R. Pfeifer1, Emily C. Woodford1, Jeffrey S. Gerber2,3,5, Claudia P. Arevalo4,
Marcus J. Bolton4, Madison E. Weirick4, Eileen C. Goodwin4, Elizabeth M. Anderson4,
Allison R. Greenplate6,7, Justin Kim6,7, Nicholas Han6,7, Ajinkya Pattekar6,8, Jeanette Dougherty6,7,
Oliva Kuthuru6,7, Divij Mathew6,7, Amy E. Baxter6,7, Laura A. Vella5,6, JoEllen Weaver9,
Anurag Verma10, Rita Leite11, Jeffrey S. Morris12, Daniel J. Rader9,10, Michal A. Elovitz6,11,
E. John Wherry6,7, Karen M. Puopolo1,2,3†, Scott E. Hensley4,6†
Limited data are available for pregnant women affected by severe acute respiratory syndrome coronavirus 2
(SARS-CoV-2). Serological tests are critically important for determining SARS-CoV-2 exposures within both individuals
and populations. We validated a SARS-CoV-2 spike receptor binding domain serological test using 834 pre-
pandemic samples and 31 samples from COVID-19–recovered donors. We then completed SARS-CoV-2 serolog-
ical testing of 1293 parturient women at two centers in Philadelphia from 4 April to 3 June 2020. We found 80 of
1293 (6.2%) of parturient women had immunoglobulin G (IgG) and/or IgM SARS-CoV-2–specific antibodies. We
found race/ethnicity differences in seroprevalence rates, with higher rates in Black/non-Hispanic and Hispanic/
Latino women. Of the 72 seropositive women who also received nasopharyngeal polymerase chain reaction testing
during pregnancy, 46 (64%) were positive. Continued serologic surveillance among pregnant women may inform
perinatal clinical practices and can potentially be used to estimate exposure to SARS-CoV-2 within the community.
INTRODUCTION
Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2)
can cause serious disease in adult populations, particularly in those
with underlying health conditions (1). Serological tests are important
for determining SARS-CoV-2 viral exposures within individuals and
populations (2). However, many commercial tests have high false-
positive rates and therefore cannot be used to accurately estimate
seroprevalence in populations with relatively low levels of exposures
(3,4). Serological tests are especially important for vulnerable popula-
tions such as pregnant women, because immune status has implica-
tions for management of both the pregnant woman and the newborn.
Admission to the hospital for delivery is one of the few instances in
which otherwise healthy individuals are consistently interacting
with the medical system and therefore provides an opportunity for
surveillance of SARS-CoV-2 serology in the community.
We performed a study of pregnant women presenting for delivery
from 4 April to 3 June 2020 at two academic birth hospitals in
Philadelphia, Pennsylvania. Both hospitals are active clinical and
research centers affiliated with the University of Pennsylvania
and, when combined, represent 50% of live births in Philadelphia
(5). Discarded maternal sera from delivery admission were collected,
de-identified, and tested by enzyme-linked immunosorbent assay
(ELISA) for SARS-CoV-2 immunoglobulin G (IgG) and IgM anti-
bodies to the spike receptor binding domain (RBD) antigen.
RESULTS
Demographics
Demographics and clinical characteristics of the women are shown
in Table1. Most serum specimens were derived from women living
in areas within or immediately bordering the city of Philadelphia
(Fig.1). Pregnant women who were symptomatic or exposed to
SARS-CoV-2 underwent SARS-CoV-2 nasopharyngeal nucleic acid
polymerase chain reaction (PCR) testing from 4 to 12 April 2020;
universal PCR testing was recommended for all pregnant women
presenting for delivery starting 13 April 2020. Of 1514 women who
delivered during the study period, 1293 (85%) had available dis-
carded serum specimens and were included in the analysis.
Assay validation
Our serological assay used a SARS-CoV-2 spike RBD antigen and
modified ELISA protocol first described by Amanat etal. (6). We
validated this serological assay by testing serum samples collected
before the pandemic in 2019 from 834 individuals in the Penn Medicin e
BioBank (PMBB) and 31 individuals who recovered from confirmed
coronavirus disease 19 (COVID-19) infections in 2020 (Fig.2,AandB).
All 31 serum samples from COVID-19–recovered donors con-
tained high, but variable, levels of SARS-CoV-2 IgG (Fig.2A), and
1Division of Neonatology, Children’s Hospital of Philadelphia, Philadelphia, PA, USA.
2Department of Pediatrics, University of Pennsylvania Perelman School of Medicine,
Philadelphia, PA, USA. 3Center for Pediatric Clinical Effectiveness, Children’s Hospital
of Philadelphia, Philadelphia, PA, USA. 4Department of Microbiology, University of
Pennsylvania Perelman School of Medicine, Philadelphia, PA, USA. 5Division of
Infectious Diseases, Children’s Hospital of Philadelphia, Philadelphia, PA, USA. 6In-
stitute for Immunology, University of Pennsylvania Perelman School of Medicine,
Philadelphia, PA, USA. 7Department of Systems Pharmacology and Translational
Therapeutics, University of Pennsylvania, Philadelphia, PA. 8Division of Gastro-
enterology, Department of Medicine, University of Pennsylvania Perelman School
of Medicine, Philadelphia, PA, USA. 9Institute for Translational Medicine and Thera-
peutics, University of Pennsylvania Perelman School of Medicine, Philadelphia, PA,
USA. 10Departments of Genetics and Medicine, Perelman School of Medicine,
University of Pennsylvania, Philadelphia, PA, USA. 11Maternal and Child Health
Research Center, Department of Obstetrics and Gynecology, University of Pennsylvania
Perelman School of Medicine, Philadelphia, PA, USA. 12Department of Biostatistics
Epidemiology and Informatics, University of Pennsylvania, Philadelphia, PA, USA.
*These authors contributed equally to this work.
†Corresponding author. Email: hensley@pennmedicine.upenn.edu (S.E.H.); karen.
puopolo@pennmedicine.upenn.edu (K.M.P.)
Copyright © 2020
The Authors, some
rights reserved;
exclusive licensee
American Association
for the Advancement
of Science. No claim
to original U.S.
Government Works
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22 of 31 samples contained detectable levels of SARS-CoV-2 IgM
(Fig. 2B). Conversely, only 5 of 834 samples collected before the
pandemic contained SARS-CoV-2 IgG, and only 4 of 834 samples
contained SARS-CoV-2 IgM; none contained both IgG and IgM. On
the basis of these data, the estimated sensitivity of the test is 100%
[95% confidence interval (CI), 89.1 to 100.0%], and the specificity is
98.9% (95% CI, 98.0 to 99.5%). Using this test, we have found that
there is heterogeneity in antibody responses among hospitalized
COVID-19 patients and that some actively infected patients are se-
ronegative (7,8). Consistent with our initial validation experiments,
only 1 of 140 samples collected from pregnant women before the
pandemic (from 2009 to 2012) had IgG or IgM SARS-CoV-2 anti-
bodies (Fig.2,CandD).
Serological findings
We found that 80 of 1293 (seropositivity rate of 6.2%; 95% CI, 4.9 to
8.0%) pregnant women presenting for delivery from 4 April
to 3 June 2020 had IgG and/or IgM SARS-CoV-2 antibodies
(P=0.003 comparing samples from pre-pandemic and pandemic
pregnant women; Fig.2, CandD). We identified 55 women with
both SARS-CoV-2 IgG and IgM, 21 women with only SARS-CoV-2
IgG, and 4 women with only SARS-CoV-2 IgM (table S1). SARS-
CoV-2 antibody levels in samples from these women were variable
(Fig.2,CandD), similar to what we found in samples from individuals
recovering from confirmed SARS-CoV-2 infections (Fig.2,AandB).
The seroprevalence rate was not statistically different comparing
women living within the city limits of Philadelphia [62 of 986
(6.3%); 95% CI, 4.9 to 8.0%] with those living in surrounding areas
in Pennsylvania [12 of 191 (6.3%); 95% CI, 3.3 to 10.7%], or surround-
ing areas in New Jersey [5 of 107 (4.7%); 95% CI, 1.5 to 10.6%].
Table 1. Demographics and clinical characteristics of the study cohort. IQR, interquartile range; BMI, body mass index.
Characteristics Total (n = 1293) Seropositive* (n = 80) Seronegative (n = 1213) P value†
Age (in years), median (IQR) 31 (27, 35) 28 (24, 32) 31 (27, 35) <0.001
Race/ethnicity, n (%)‡
Black/non-Hispanic 537 52 (9.7) 485 (90.3) <0.001
White/non-Hispanic 447 9 (2.0) 438 (98.0) <0.001
Hispanic/Latino 125 13 (10.4) 112 (89.6) 0.04
Asian 106 1 (0.9) 105 (99.1) 0.01
Other/unknown§78 5 (6.4) 73 (93.6) 0.93
Pre-pregnancy BMI||, n (%)‡
Overweight (25.0 to <30.0) 345 28 (8.1) 317 (91.9) 0.07
Obese (≥30.0) 337 27 (8.0) 310 (92.0) 0.09
Diabetes¶, n (%)‡113 10 (8.9) 103 (91.1) 0.22
Hypertension¶, n (%)‡404 33 (8.2) 371 (91.8) 0.05
Asthma¶, n (%)‡194 13 (6.7) 181 (93.3) 0.75
Cesarean delivery, n (%)‡400 30 (7.5) 370 (92.5) 0.19
Preterm delivery at
gestational age <37 weeks,
n (%)‡128 11 (8.6) 117 (91.4) 0.23
Live-born infant, n (%)‡1282 79 (6.2) 1203 (93.8) 0.51
*Seropositivity was based on either IgG or IgM level of >0.48 arbitrary units. †Difference in maternal age was tested using Mann-Whitney U test, differences
in proportion of all other characteristics were tested using 2 tests or Fisher’s exact test as appropriate. For race/ethnicity and pre-pregnancy BMI, difference was
tested at each level of the characteristic (e.g., proportion of Black women who were seropositive compared with proportion of non-Black women who were
seropositive). ‡Row percentages are shown, which represent the percent of total in each characteristic (e.g., 9.7% of Black/Non-Hispanic women were
seropositive). §Race/ethnicity was unknown for two seropositive and 26 seronegative women; race was abstracted from documentation at the time of
admission and in clinical practice and is usually self-reported. ||Pre-pregnancy BMI was missing for 2 seropositive and 12 seronegative women; pre-
pregnancy BMI was abstracted from documentation in the medical record or from patient’s self-reported entry in birth registration. ¶Diagnoses were based
on delivery admission ICD-10 diagnosis codes for diabetes (O24, E08-E13, and Z79.4), hypertension (O10, O11, O13-O16, I10-I13, and I15), and asthma (J45).
Fig. 1. Geographical distribution of women tested for SARS-CoV-2 antibodies.
Most serum specimens analyzed were from women living in areas within or imme-
diately bordering the city of Philadelphia. Location of birth hospitals where serum
samples were collected are shown as red crosses.
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There were no significant differences in seroprevalence rates in
women with or without comorbidities, preterm delivery, or cesarean
mode of delivery (Table 1). In contrast, we observed significant
race/ethnicity differences in seroprevalence rates, with higher rates
in Black/non-Hispanic (9.7%; 95% CI, 7.3 to 12.5%) and Hispanic/
Latino (10.4%; 95% CI, 5.7 to 17.1%) women and lower rates in
White/non-Hispanic (2.0%; 95% CI, 0.9 to 3.8%) and Asian (0.9%;
95% CI, 0.0 to 5.1%) women (Table1).
Nasopharyngeal swabs from 1109 (85.8%) women were tested
by SARS-CoV-2 PCR during the pregnancy or at the time of delivery.
Most of the sera tested for antibody were obtained before or within
6 days of PCR testing (Table2). SARS-CoV-2 antibodies were de-
tected in all sera obtained from PCR-positive women when serum
samples were obtained more than 7 days after PCR testing (Table2).
Overall, we found that 46 of 72 seropositive women who were tested
by PCR had a SARS-CoV-2–positive PCR result, whereas only 18 of
1037 seronegative women who were tested by PCR had a SARS-
CoV-2–positive PCR result. While all serum samples were collected
during the delivery admission, nasopharyngeal samples were col-
lected at variable times either during the delivery admission or ear-
lier in the pregnancy, and therefore, further study will be required
to evaluate the temporal relationship between SARS-CoV-2 sero-
positivity and PCR positivity in pregnant women.
DISCUSSION
Large-scale serology testing is critical for estimating how many
individuals have been infected during the COVID-19 pandemic.
Because of widely imposed social distancing requirements, and to
decreases in on-site, discretionary medical care, it is currently diffi-
cult to collect serum for population-wide serological testing. The vast
majority of pregnant women, however, continue to have multiple
interactions with the medical system for prenatal care and for delivery
during this pandemic and therefore present an opportunity to con-
sistently assess SARS-CoV-2 exposures within a community. Our
data suggest that 6.2% of parturient women in Philadelphia from
4 April to 3 June 2020 were previously exposed to SARS-CoV-2.
As of 3 June 2020, there were 23,160 confirmed cases of
COVID-19in the city of Philadelphia (9), which has a population
size of nearly 1.6 million people. This suggests an infection rate of
about 1.4%, which is more than four times lower than the estimates
based on our serological data. Serologic studies may provide a more
accurate means of assessing population exposure to SARS-CoV-2
by identifying asymptomatic or minimally symptomatic and symp-
tomatic infections. Further studies are needed to determine how the
immune status of pregnant women compares with that of the gen-
eral population. For example, parturient women may not represent
individuals of different ages within the general population, and
women and men might mount different antibody responses upon
infection with SARS-CoV-2 (10). Furthermore, most pregnant
women cannot fully shelter-in-place during a pandemic, as they
continue to have interactions with the medical system. Our finding
that Black/non-Hispanic and Hispanic/Latino women have higher
SARS-CoV-2 seroprevalence rates relative to women of other races
suggests that there are race/ethnicity differences in SARS-CoV-2
exposures in Philadelphia and surrounding areas. Identification of
factors that contribute to such differences in exposure to SARS-
CoV-2, including factors rooted in systemic racism, may inform public
health measures aimed at preventing further infections (11–13).
Prior perinatal COVID-19 studies have primarily focused on vi-
rus detection (i.e., nucleic acid testing) in pregnant women, and most
of these studies have not evaluated antibody responses (14–22).
Two published studies to date have assessed SARS-COV-2 serology
in pregnant women with active disease. A study of six parturient
women in Wuhan, China with confirmed COVID-19 found that all
six women had elevated levels of SARS-CoV-2 IgG and IgM (23). A
case report from Peru detailed a symptomatic pregnant woman with
positive PCR testing and negative serology at presentation, who devel-
oped severe respiratory failure necessitating delivery; her IgM and
IgG turned positive 4 days after delivery (9 days after symptom onset)
(24). Beyond describing individual response to infection, SARS-
CoV-2 serological testing among pregnant women will be increasingly
important for perinatal disease risk management and for optimizing
vaccine strategies when vaccines become available. Additional studies
will be needed to address the impact of maternal infection on neo-
natal immune responses and to determine those factors that may
contribute to observed disparities in exposure to SARS-CoV-2.
MATERIALS AND METHODS
Study design
The goal of this study was to estimate SARS-CoV-2 seroprevalence
rates in the community using discarded serum samples from partu-
rient women. The Institutional Review Board at the University of
Pennsylvania approved this study. There was a waiver of consent for
testing of residual serum samples from parturient women, as indi-
cated below. For other cohorts used to validate our assay, subjects
were consented before samples were obtained. De-identified data
were used for analysis.
AB
CD
Pregnant women
Pre-pandemicCOVID-19
+
(n = 834)(n = 31)
Pre-pandemic COVID-19+
(n = 834) (n = 31)
Pre-pandemic Pandemic
(n = 140) (n = 1293)
Pregnant women
Pre-pandemic Pandemic
(n = 140)(n = 1293
)
IgG levels
(arbitrary units)
SARS-CoV-2 IgGSARS-CoV-2 IgM
SARS-CoV-2 IgGSARS-CoV-2 IgM
IgM levels
(arbitrary units)
IgG levels
(arbitrary units)
IgM levels
(arbitrary units)
0.5
1
2
4
8
16
32
64
128
0.5
1
2
4
8
16
32
64
128
0.5
1
2
4
8
16
32
64
0.5
1
2
4
8
16
32
64
Fig. 2. Serum SARS-CoV-2 antibody levels in COVID-19 pandemic and pre-pandem ic
individuals. (A and B) Relative levels of SARS-CoV-2 IgG (A) and IgM (B) in serum
collected before the COVID-19 pandemic (n = 834) and serum collected from
COVID-19 recovered donors (n = 31). (C and D) Relative levels of SARS-CoV-2 IgG
(C) and IgM (D) in serum collected from pregnant women from 2009 to 2012
(n = 140) and from 4 April to 3 June 2020 (n = 1293). Dashed lines indicate
0.48 arbitrary units, which was used to distinguish positive versus negative
samples (see Materials and Methods). Serum samples that were below the cutoff
for seropositivity were assigned an antibody level of 0.40 arbitrary units.
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Serum samples from parturient women
Pregnant women at the two hospitals (Pennsylvania Hospital and
Hospital of the University of Pennsylvania) have blood drawn for
rapid plasma reagin (screening for syphilis per public health guide-
lines) testing as part of routine clinical care on admission to the
hospital for delivery. Residual serum from this testing was obtained
from the clinical laboratory at the time it was otherwise to be dis-
carded. Demographic and clinical data were collected from review
of electronic medical records to assess for differences in sero-
prevalence based on these factors. Race and ethnicity were self-
reported. International Classification of Diseases, 10th revision
(ICD-10) diagnosis codes O24, E08-E13, and Z79.4 were used to
capture type 1 diabetes, type 2 diabetes, and gestational diabetes; codes
O10, O11, O13-O16, I10-I13, and I15 were used to capture hyper-
tensive disorders, gestational hypertension, and pre-eclampsia; and
code J45 was used to capture any history of asthma before or during
pregnancy. To ensure that these codes correctly captured patient
condition, we manually reviewed records for the first 130 (10%)
women with ICD-10 diagnosis of diabetes, hypertension, or asthma
and reviewed a random sampling of 65 records from the first 130
(5% of total) women without any identified ICD-10 codes for these
conditions. Patient numbers in table S1 were assigned at random.
The Institutional Review Board at the University of Pennsylvania
approved this study with waiver of consent.
Serum samples from individuals recovered from COVID-19
Samples from subjects who had recovered from laboratory-confirmed
SARS-CoV-2 infections were obtained at the University of Pennsylva nia .
Subjects were consented, and samples were obtained after laboratory-
confirmed COVID-19 diagnosis and>14 days since resolution of
symptoms. The Institutional Review Board at the University of
Pennsylvania approved this study.
Pre-pandemic human serum samples
To validate our serological assay, serum samples from 834 adults
(19 to 89 years old; 52% females) were collected via the PMBB
between October and December 2019, before the COVID-19 pan-
demic. PMBB routinely consents individuals visiting the University
of Pennsylvania health care system and obtains and stores biospecime ns.
Banked serum samples obtained from pregnant women from 2009
to 2012 were also used as pre-pandemic controls. For these banked
samples, maternal serum was collected during the third trimester of
pregnancy as part of an Institutional Review Board–approved study.
From this study, 140 samples were randomly selected from women
who delivered at term (average gestational age at time of sample
collection was 33.8 weeks, 80% were Black women).
Enzyme-linked immunosorbent assay
ELISAs were completed using plates coated with the RBD of the
SARS-CoV-2 spike protein using a previously described protocol with
slight modifications (6,25). Plasmids for expressing this protein were
provided by F. Krammer (Mt. Sinai). SARS-CoV-2 RBD proteins were
produced in 293F cells and purified using nickel–nitrilotriacetic
acid (Ni-NTA) resin (Qiagen). The supernatant was incubated for 2
hours with Ni-NTA resin at room temperature before the Ni-NTA
resin was collected using gravity flow columns, and the protein was
eluted. After buffer exchange into phosphate-buffered saline (PBS),
the purified protein was stored in aliquots at −80°C. ELISA plates
(Immulon 4 HBX, Thermo Fisher Scientific) were coated overnight
at 4°C with PBS (50 l per well) or a recombinant protein (2 g/ml)
diluted in PBS. The next day, ELISA plates were washed three times
with PBS containing 0.1% Tween 20 (PBS-T) and blocked for 1 hour
with PBS-T supplemented with 3% nonfat milk powder. Before
testing in ELISA, serum samples were heat-inactivated at 56°C for
1 hour. Serum samples were serially diluted in twofold in 96-well
round-bottom plates in PBS-T supplemented with 1% nonfat milk
powder (dilution buffer), starting at a 1:50 dilution. Next, ELISA plates
were washed three times with PBS-T, and 50l of serum dilution
was added to each well. Plates were incubated for 2 hours at room
temperature using a plate mixer. Plates were washed again three
times with PBS-T before 50l of horseradish peroxidase (HRP)–
labeled goat anti-human IgG (1:5000; Jackson ImmunoResearch
Laboratories) or goat anti-human IgM-HRP (1:1000; SouthernBiotech)
secondary antibodies were added. After 1-hour incubation at room
temperature using a plate mixer, plates were washed three times with
PBS-T, and 50l of SureBlue 3,3′,5,5′-tetramethylbenzidine substrate
(KPL) was added to each well. Five minutes later, 25 l of 250 mM
hydrochloric acid was added to each well to stop the reaction. Plates
were read at an optical density (OD) of 450nm using the SpectraMax
190 microplate reader (Molecular Devices). Background OD values
from the plates coated with PBS were subtracted from the OD values
from plates coated with recombinant protein. A dilution series of
the IgG monoclonal antibody CR3022, which is reactive to the
SARS-CoV-2 spike protein, was included on each plate as a control
to adjust for interassay variability. The IgG CR3022 monoclonal anti-
body was included on both IgG and IgM plates, and an anti-human
Table 2. Timing of serology testing and seropositivity with respect to nasopharyngeal PCR testing. The table includes 1109 women tested for serology
who were also tested by nasopharyngeal PCR anytime during pregnancy up to discharge from delivery admission. NP, nasopharyngeal.
Serology timing NP-PCR positive NP-PCR negative
Tested Seropositive (%) Tested Seropositive (%)
Before NP-PCR test 17 10 (58.8) 364 9 (2.5)
0–6 days after NP-PCR test 26 15 (57.7) 647 16 (2.5)
7–13 days after NP-PCR test 5 5 (100.0) 8 0
14–20 days after NP-PCR test 2 2 (100.0) 7 0
≥21 days after NP-PCR test 14 14 (100.0) 19 1 (5.3)
Total 64 46 (71.9) 1045 26 (2.5)
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IgG-HRP secondary antibody was added to these standardization
wells on both IgG and IgM plates. In essence, the CR3022 monoclonal
antibody was used to set the OD threshold on each plate and to en-
sure that the same OD threshold was used on all plates, including
both IgG and IgM assays. Serum antibody concentrations were re-
ported as arbitrary units relative to the CR3022 monoclonal antibody.
Plasmids to express the CR3022 monoclonal antibody were provided
by I. Wilson (Scripps). All samples were first tested in duplicate at a
1:50 serum dilution. Samples with an IgG and/or IgM concentration
above the lower limit of detection (0.20 arbitrary units) were repeated
in at least a seven-point dilution series to obtain quantitative results.
Establishment of an ELISA cutoff to distinguish seropositive
versus seronegative
We used results from the 2019 cohort (Fig.2A) to set ELISA cutoffs
for seropositivity and seronegativity. Over the course of establish-
ing our serological assay, we identified rare individuals who had
pre-pandemic SARS-CoV-2 cross-reactive serum antibodies. Most
of these individuals had very low levels of cross-reactive SARS-
CoV-2 antibodies. We found that ~1% of samples from the pre-
pandemic 2019 cohort had IgG and/or IgM levels of >0.48 arbitrary
units, which was subsequently used as the cutoff for defining sero-
positivity in the 2020 cohort.
Statistical methods
Standard descriptive analyses using 2 test, Fisher’s exact test, and
Mann-Whitney U test as appropriate, compared the demographic
and clinical characteristics between the seropositive and seronegative
women. CIs for proportions were computed using the Clopper-
Pearson (exact) method. Statistical significance was set at P < 0.05.
Statistical analyses were performed using Stata version 16 (StataCorp,
College Station, TX) and Prism version 8 (GraphPad Software).
Figure1 was created using QGIS version 3.12.3.
SUPPLEMENTARY MATERIALS
immunology.sciencemag.org/cgi/content/full/5/49/eabd5709/DC1
Table S1. Relative levels of SARS-COV-2 IgG and IgM in serum collected from seropositive
pregnant women (n = 80).
View/request a protocol for this paper from Bio-protocol.
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Acknowledgments: We thank all members of the Wherry Lab and the Penn COVID-19 Sample
Processing Unit for sample procurement, processing, and logistics. We thank the staff of the
PMBB. We thank F. Krammer (Mt. Sinai) for sending us the SARS-CoV-2 spike RBD expression
plasmids. We thank S. Melly (Drexel University) for the assistance in geographic analyses.
Funding: This work was supported by institutional funds from the University of Pennsylvania
and NIH grants AI082630 (to E.J.W.) and UL1TR001878 (to D.J.R.). We thank J. Lurie, J. Embiid,
J. Harris, and D. Blitzer for philanthropic support. E.J.W. is supported by the Parker Institute for
Cancer Immunotherapy, which supports the cancer immunology program at University of
Pennsylvania. Author contributions: D.D.F. conceptualized and designed the study, collected
the data, drafted the initial manuscript, and revised the manuscript. S.G. led the serological
experiments, collected the data, and revised the manuscript. M.B.D. designed the data
collection instruments, collected the data, carried out the analyses, and revised the
manuscript. S.M. conceptualized and designed the study, designed the data collection
instruments, carried out the analyses, and revised the manuscript. M.R.P. and E.C.W. collected
data and revised the manuscript. J.S.G. conceptualized and designed the study and revised the
manuscript. C.P.A., M.J.B., M.E.W., E.C.G., and E.M.A. completed serological assays, analyzed the
data, and revised the manuscript. A.R.G., J.K., N.H., A.P., and J.D. obtained and proceeded
samples from recovered donors. O.K. and L.A.V. designed and established recovered donor
cohort. D.M. processed and characterized samples from recovered donors. A.E.B. oversaw
acquisition, processing, and characterization of samples from recovered donors. J.W.
supervised the recruitment of participants in PMBB and identification of samples for serology
testing. A.V. analyzed demographic data of PMBB participants. R.L. provided samples for the
pre-pandemic pregnant controls. J.S.M. provided statistical advice, performed statistical
analyses, and revised the paper. D.J.R. provided input on the use of PMBB controls and revised
the manuscript. M.A.E. provided input and samples for the pre-pandemic pregnant controls
and revised the manuscript. E.J.W. designed, established, and oversaw healthy donor cohort
studies and made revisions to the manuscript. K.M.P. conceptualized and designed the study,
coordinated and supervised data collection, and revised the manuscript. S.E.H. conceptualized
and designed the study, coordinated and supervised serological studies, and revised the
manuscript. Competing interests: S.E.H. has received consultancy fee from Sanofi Pasteur,
Lumen, Novavax, and Merck for work unrelated to this report. E.J.W. is a member of the Parker
Institute for Cancer Immunotherapy. E.J.W. has consulting agreements with and/or is on the
scientific advisory board for Merck, Roche, Pieris, Elstar, and Surface Oncology. E.J.W. is a
founder of Surface Oncology and Arsenal Biosciences. E.J.W. has a patent licensing agreement
on the PD-1 pathway with Roche/Genentech. All other authors declare that they have no
competing interests. Data and materials availability: All data needed to evaluate the
conclusions in the paper are present in the paper or the Supplementary Materials.
Submitted 29 June 2020
Accepted 24 July 2020
Published 29 July 2020
Final published 24 August 2020
10.1126/sciimmunol.abd5709
Citation: D. D. Flannery, S. Gouma, M. B. Dhudasia, S. Mukhopadhyay, M. R. Pfeifer, E. C. Woodford,
J. S. Gerber, C. P. Arevalo, M. J. Bolton, M. E. Weirick, E. C. Goodwin, E. M. Anderson, A. R. Greenplate,
J. Kim, N. Han, A. Pattekar, J. Dougherty, O. Kuthuru, D. Mathew, A. E. Baxter, L. A. Vella,
J. Weaver, A. Verma, R. Leite, J. S. Morris, D. J. Rader, M. A. Elovitz, E. J. Wherry, K. M. Puopolo,
S. E. Hensley, SARS-CoV-2 seroprevalence among parturient women in Philadelphia. Sci. Immunol.
5, eabd5709 (2020).
by guest on August 24, 2020http://immunology.sciencemag.org/Downloaded from

SARS-CoV-2 seroprevalence among parturient women in Philadelphia
Wherry, Karen M. Puopolo and Scott E. Hensley
Laura A. Vella, JoEllen Weaver, Anurag Verma, Rita Leite, Jeffrey S. Morris, Daniel J. Rader, Michal A. Elovitz, E. John
Greenplate, Justin Kim, Nicholas Han, Ajinkya Pattekar, Jeanette Dougherty, Oliva Kuthuru, Divij Mathew, Amy E. Baxter,
S. Gerber, Claudia P. Arevalo, Marcus J. Bolton, Madison E. Weirick, Eileen C. Goodwin, Elizabeth M. Anderson, Allison R.
Dustin D. Flannery, Sigrid Gouma, Miren B. Dhudasia, Sagori Mukhopadhyay, Madeline R. Pfeifer, Emily C. Woodford, Jeffrey
DOI: 10.1126/sciimmunol.abd5709
First published 29 July 2020
, eabd5709.5Sci. Immunol.
as compared with Asian and White/non-Hispanic women.
racial differences in exposure rates, with higher rates of seropositivity in Black/non-Hispanic and Hispanic/Latino women
to SARS-CoV-2 and found that 6.2% of these women had evidence of exposure to the virus. They found considerable
between 4 April and 3 June 2020. Using IgG and IgM antibody tests, they evaluated exposure of 1293 parturient women
measured the exposure rate of SARS-CoV-2 in parturient women in Philadelphia who came to the hospital to deliver
et al.near their delivery dates, continued to have regular interactions with their medical care providers. Flannery
appointments, making it difficult to perform community-level seroprevalence studies. Pregnant women, particularly those
When the SARS-CoV-2 pandemic started, stay-at-home orders led to postponement of routine medical
Monitoring SARS-CoV-2 exposure
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REFERENCES http://immunology.sciencemag.org/content/5/49/eabd5709#BIBL
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