key: cord-0757612-ibjnn5sq
authors: Sabourin, Katherine R.; Schultz, Jonathan; Romero, Joshua; Lamb, Molly M.; Larremore, Daniel; Morrison, Thomas E.; Frazer-Abel, Ashley; Zimmer, Shanta; Kedl, Ross M.; Jaenisch, Thomas; Rochford, Rosemary
title: Risk Factors of SARS-CoV-2 Antibodies in Arapahoe County First Responders—The COVID-19 Arapahoe SErosurveillance Study (CASES) Project
date: 2020-12-03
journal: J Occup Environ Med
DOI: 10.1097/jom.0000000000002099
sha: 09afe29697bc61bb6e21b034f35ad2c3830f07aa
doc_id: 757612
cord_uid: ibjnn5sq

OBJECTIVES: Define the seroprevalence and risk factors for SARS-CoV-2 antibodies in Arapahoe County, Colorado first responders (eg, law enforcement, human services, fire departments). METHODS: Two hundred sixty four first responders were enrolled June to July 2020. SARS-CoV-2 seropositivity was defined as detection of immunoglobulin G (IgG) antibodies to both spike receptor binding domain and nucleocapsid in venous blood by validated enzyme-linked immunosorbent assay. We compared risk factors for being seropositive versus seronegative. RESULTS: 4% (11/264) were SARS-CoV-2 seropositive. Seropositive participants were significantly more likely to have lung disease (% seropositive, % seronegative; P-value) (36%, 8%; P = 0.01), prior SARS-CoV-2/COVID-19 testing (36%, 8%; P ≤ 0.01), a prior positive result (18%, less than 1%), and to believe they previously had COVID-19 (64%, 15%; P < 0.01). Only 15% of those believing they had COVID-19 had anti-SARS-CoV-2 antibodies. CONCLUSIONS: Human services employees and individuals with lung disease are at SARS-CoV-2 exposure risk. Few individuals believed they had COVID-19 had prior exposure.

T he United States has become the epicenter of the coronavirus disease 2019 (COVID-19) pandemic, with over 6 million cases and 185,000 deaths as of September 2, 2020. 1 Early in the pandemic, health care workers were identified as a higher risk population for COVID-19. Over 150,000 cases of COVID-19 have been identified among health care professionals in the United States 2 and this population has also been found to have a high seroprevalence of antibodies against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the virus that causes COVID-19. 3 A less well understood, but potentially high-risk group, are first responders including firefighters, police and emergency medical service employees. In the United States, it is assumed that the risk of exposure to SARS-CoV-2 among first responders is similar to health care professionals, but few seroprevalence studies including this population have been conducted.

Information regarding the risk of SARS-CoV-2 exposure among first responders is limited. In New York City by the end of March 2020, it was reported that 11% of emergency medical staff and firefighters were on medical leave for confirmed COVID-19. 4 A study of firefighters and paramedics in a South Florida fire department found that 9% of study participants were seropositive for SARS-CoV-2 antibodies in April 2020 and 4% were assumed to have had a recent infection. 5 In addition, 7% of public safety, healthcare, and first response personnel in Detroit, Michigan, as of June 2020 6 and only 1.5% of first responders in Arizona in May 2020 7 were found to be seropositive. However, the risk factors for infection among first responders remain unclear. To ensure the health and safety of first responders, both at work and in the community, it is critical to understand exposures to SARS-CoV-2 and the risk factors for seroconversion within this population.

Arapahoe County is one of the largest counties in Colorado, consisting of both urban and rural regions with a population of more than 630,000. We invited first responders from Arapahoe County to participate in our study to assess the presence of SARS-CoV-2 antibodies and to identify risk factors for SARS-CoV-2 seropositivity among this potentially high-risk group.

First responders (refer to Table 1 for full list of job titles) working in Arapahoe County were invited to participate in the study which took place between July and August 2020. Emails were sent to the chiefs of all agencies in the county asking for their agreement to participate at the agency level. They were asked to forward an email containing a web-based (REDCap) link to their employees who were then, individually, given the opportunity to indicate their desire to participate in the study. Individuals were eligible to participate in the study if they were employed by an Arapahoe County agency since January 2020, had direct contact with the public, and were 20 to 69 years old. Individuals were screened for COVID-19-related symptoms prior to study entry and would have been excluded from the study, if symptomatic, to protect study staff and participants. No individuals presenting to the study were symptomatic. Informed consent was obtained from each study participant. All protocol and consent forms were approved by the Colorado Multiple Institutional Review Board (COMIRB).

Interested individuals were asked to come to a central location where they completed a questionnaire. Data on demographics, employment characteristics, high-risk group characteristics, potential SARS-CoV-2 exposures, prior COVID-19 related symptoms, and prior COVID-19/SARS-CoV-2 testing were collected at enrollment (Supplement 1, http://links.lww.com/JOM/A838). Participants provided a venous blood draw of up to 3 mL which was collected in BD vacutainer SST tubes (Franklin Lake, NJ). Whole blood was allowed to clot at room temperature. Samples were centrifuged at $2700 RPM (1300 AE 100 Â g), nine acceleration, nine deceleration, for 10 minutes at 25 8C and the serum removed and stored at -20 8C until testing was completed. Centrifugation never occurred more than 8 hours after sample collection.

Venous blood draws were tested for immunoglobulin G (IgG) antibodies using an enzyme-linked immunosorbent assay (ELISA) developed at the University of Colorado at Exsera BioLabs. The assay was validated to EUA and CAP/CLIA standards in a compliant laboratory. Validation included testing of over 1000 pre-pandemic normal and 100 PCR-confirmed positive sera. ELISA development was based on the work of Stadlbauer et al 8 with some modification. In brief, the SARS-CoV-2 receptor binding domain (RBD) was grown in HEK293T cells and the second antigen utilized was Nucleocapsid purified from Escherichia coli. All specimens were tested for reactivity to both antigens. To be considered seropositive, antibodies to both the spike RBD and nucleocapsid of SARS-CoV-2 had to be detected. The cut-off for positivity was based on the aforementioned validation which yielded a specificity of 98.6% and sensitivity of 85%.

To identify potential risk factors for SARS-CoV-2 seropositivity, we compared the seropositive and seronegative groups to test whether pre-identified risk factors were more or less likely to be associated with the presence of anti-SARS-CoV-2 antibodies. Exposures of interest included age, sex, race/ethnicity, whether an individual self-identified as being in a high-risk group, frequency of interactions with the public, contact with confirmed or suspected COVID-19 cases, use of personal protective equipment (PPE), prior SARS-CoV-2 testing and results, belief of a prior SARS-CoV-2 infection, and existence and timing of COVID-19 related symptoms. Mann-Whitney U test was used to compare median age in seropositive versus seronegative individuals. All other comparisons were performed using a chi-squared or Fisher exact test, where appropriate. Statistical significance was defined as a P < 0.05. All analyses were completed using SAS1 software, Version 9.4 (SAS Institute Inc., Cary, NC).

We enrolled 264 first responders from Arapahoe County. The median age of participants was 38 years old. Slightly more women than men enrolled, and the majority of individuals identified as White, Non-Hispanic/Non-Latinx (Table 1) .

Staff from a sheriff's office or police department represented the largest number of participants followed by those from the Department of Human Services. Less than 10% of participants worked in a rural area and 95% were employed full-time. In addition to individuals traditionally considered first responders (police, firefighters, EMTs, etc), we allowed enrollment of individuals who worked for the county that had direct contact with the public. As such, over 20% of our enrollees worked as caseworkers or in human services, whom provide services to the county including: adult and senior services, child and adult protective services, food, financial, and medical benefits, as well as other child and community services. The next most common roles included those working in police patrol, and those working as firefighters (Table 1) .

To identify whether characteristics of patients considered high-risk for COVID-19 were also associated with SARS-CoV-2 seropositivity among first responders, we asked participants to identify if they had any comorbidities based on previously identified categories. More than half did not identify as belonging to any highrisk group. Among individuals that did report a comorbidity, the most frequently reported were being overweight, having a chronic medical condition including diabetes, high blood pressure, and/or kidney disease, followed by those with lung disease (Table 1) . 

To identify potential SARS-CoV-2 exposure and behavioral risk factors among first responders, respondents were asked about their interactions with the public, potential exposures to individuals with COVID-19, use of PPE, prior SARS-CoV-2 testing, and belief about the likelihood they had been previously infected. Most individuals interacted with the public either sometimes, often, or always and at least 1 or more days per week. Around one-third of individuals reported close contact with someone with laboratoryconfirmed COVID-19 or possible COVID-19 in the two months prior to enrollment and the majority of individuals who were exposed reported using PPE either often or always ( Table 2) .

For 89% of participants, the testing done during our study was their first SARS-CoV-2 test of any type, and only three individuals (1%) had previously tested positive. Regardless of test results, around 15% of individuals thought their likelihood of having had COVID-19 was probable, very probable, or definite (Table 2) .

We chose to use a dual-antigen ELISA to assess antibodies to the SARS-CoV-2 spike receptor binding domain (RBD) and nucleocapsid protein. Of the 264 individuals enrolled, 11 (4%) were reactive for antibodies to both the RBD and nucleocapsid of SARS-CoV-2 ( Fig. 1 ). Of those, five (46%) worked in human services/casework, five (46%) worked in a sheriff's office or police department, and one (9%) worked in a fire department. Among human services employees and caseworkers included in our study, the seroprevalence for SARS-CoV-2 was 6%, while the SARS-CoV-2 seroprevalence for sheriff's office or police department employees and fire department employees was 4% and 2%, respectively. These differences in seroprevalence by employment type were not significant. We compared demographics, health characteristics, and potential SARS-CoV-2 exposure and explanatory variables in seropositive and seronegative individuals and found that there was no association between reactivity and age, sex, or race/ethnicity. Seropositive individuals were significantly more likely to report lung disease (P ¼ 0.0114) and marginally more likely to be obese (P ¼ 0.0563) ( Table 3) . Among individuals who reported being in a high-risk group, there was no significant difference in the number of individuals reporting being in one compared with two or more high-risk groups in seropositive compared with seronegative participants (P ¼ 0.1579).

There did not appear to be differences between seropositive and seronegative individuals in how regularly they had contact with the public nor their contact with a known or suspected COVID-19 case. Seropositive individuals were significantly more likely to report prior SARS-CoV-2 testing, and a prior positive SARS-CoV-2 test. They were also significantly more likely to report that they believed they probably, very probably, or definitely had COVID-19 prior to enrollment compared with seronegative individuals (Table 3) . Among individuals seropositive for anti-SARS-CoV-2 antibodies who believed they probably, very probably, or definitely had COVID-19 previously, two had a prior positive COVID-19 test.

Finally, we asked participants about any symptoms they had experienced in the 3 months prior to antibody testing and compared COVID-19 related symptoms between SARS-CoV-2 seropositive and seronegative participants. Of the 11 seropositive individuals, three (27%) reported never having symptoms. Seropositive participants were significantly more likely to report having any symptoms and were also significantly more likely to report ever having shortness of breath or difficulty breathing, coughing, fever more than 100 8F, chills, rigors, sore throat, loss of taste or smell, gastrointestinal symptoms, and other symptoms within the 3 months prior to testing. Myalgias were also more commonly reported by SARS-CoV-2 seropositive individuals though this was not statistically significant at the P < 0.05 level (Table 4 ).

In this study we aimed to identify the seroprevalence and risk factors for detection of anti-SARS-CoV-2 antibodies in Arapahoe County first responders. We found a 4% seropositivity for SARS-CoV-2 antibodies among our participants and almost half of those individuals worked in human services/casework, an under-investigated group that is potentially at high-risk of SARS-CoV-2 exposure. Approximately one-third of first responders reported contact with a confirmed or suspected COVID-19 case but most appeared to be taking steps to protect themselves by using PPE. We sought to identify possible risk factors for SARS-CoV-2 exposure among first responders and found that those with anti-SARS-CoV-2 antibodies were more likely to report lung disease and obesity, were more likely to have been previously tested for SARS-CoV-2 infection, have a previous positive test result, believe they had already had COVID-19, and previously have COVID-19 related symptoms. Understanding the seroprevalence and risk factors for SARS-CoV-2 among this high-risk group is paramount to ensuring their health and safety.

The 4% SARS-CoV-2 seroprevalence in our first responder participants was higher than the 1.5% seroprevalence reported among Arizona first responders, 7 similar to that of non-healthcare related first responders in Detroit, Michigan which found 5% seropositivity for SARS-CoV-2 6 but was lower than those found in other studies of US first responders. In New York City as of March 31, 11% of emergency medical staff and firefighters were on medical leave for confirmed COVID-19 4 and in Florida first responders in April 2020, there was a 9% anti-SARS-CoV-2 seropositivity rate when using an assay that measured both IgM and IgG. 5 Both regions have some of the highest reported COVID-19 case counts in the country. 1 In addition, first responders in the Florida study were tested for both IgM and IgG anti-SARS-CoV-2 antibodies whereas the assay used to test our participants detected anti-SARS-CoV-2 IgG only. Most individuals will have detectable anti-SARS-CoV-2 IgG within 14 days after initial symptom onset. 9-11 but by not testing for IgM, we may have missed seropositive individuals with more recent infection. IgM testing in this population should be considered in future studies to adequately determine overall recent and long-term seroconversion. We may also be underestimating the number of individuals who had a previous exposure because some individuals may have lost their antibodies over time. 10, 12 We were unable to explore the concept of antibody decay in this study, but it will be the subject of future follow-up work in this cohort. Among SARS-CoV-2 seropositive individuals, almost half were employed in human services or casework and the rest in protective services (police, firefighters, etc). In the United States, it is estimated that 3.4 million individuals work in protective services (police officers, firefighters, etc) and another 2.1 million in community and social services occupations (probation officers, community health workers, etc), representing a significant number of first line workers at risk of SARS-CoV-2 exposure and COVID-19 development. 13 Identification of seropositive human service or social workers speaks to the close proximity with which they work with the public. Forms of transmission of SARS-CoV-2 include respiratory droplets which can be spread when an individual coughs, sneezes, or speaks, transmission through airborne aerosols and indirect transmission through contact with a contaminated surface or object. 14 As part of their occupation, caseworkers may have closer contact with individuals that last for longer periods of time and may be more likely to be exposed to others in an indoor setting, say in the instance of home inspections, compared with other occupations. There was no difference in the frequency of public interaction for caseworkers compared with other occupations among seropositive participants in our study, which is not unexpected as all individuals received training on safety and use of PPE. In addition to individuals who would classically be considered first Older age, as well as several medical conditions, including cancer, chronic kidney disease, chronic obstructive pulmonary disease (COPD), immunocompromised state, heart disease, diabetes, and obesity, have been suggested as underlying conditions that increase risk for development of severe COVID-19. 15 We aimed to identify whether these conditions were also associated with being SARS-CoV-2 seropositive in first responders. We did not see a difference in seropositivity among individuals with and without cancer, immunocompromised state, heart disease, or diabetes and we did not collect data on chronic kidney disease or COPD, though we did ask about general lung disease. Seropositive individuals in our study were more likely to report having lung disease, which is surprising given that these individuals might perceive themselves to be at higher risk for severe disease and therefore more readily protect themselves. In COVID-19 patients, mixed results have been found with regards to lung disease such as COPD or asthma and risk of more severe disease. [16] [17] [18] [19] [20] [21] Multiple reports of clinical characteristics among COVID-19 patients listed individuals with underlying lung disease, such as COPD and asthma, 22-24 but whether chronic lung diseases are associated with worse outcomes among COVID-19 patients remains unclear. [16] [17] [18] [19] [20] [21] Unfortunately, we did not collect information about the type, history, or severity of lung disease so were not able to describe this relationship further. We also found that individuals who had anti-SARS-CoV-2 antibodies were more likely to report being obese, though this association was not statistically significant. Our findings are in contrast with a study of first responders in Florida that reported no association between seropositivity for SARS-CoV-2 and self-reported body mass index (BMI). Although we found that obesity was more often reported in SARS-CoV-2 seropositive individuals, only 4% of respondents overall reported being obese. This is substantially lower than national estimates that almost 40% of adults are obese in the United States. 25 By relying on individuals to self-identify as obese we may be underestimating the true prevalence of obesity in our study population. It is likely that we had non-differential misclassification, where most individuals reported less obesity, regardless of their blood test result (which they were unaware of when they reported their obesity status), meaning the true association is likely stronger than what we report here. However, it is also possible that the association between obesity and antibody reactivity may be a result of reporting bias where individuals who were seronegative were less likely to report being obese. The limited number of cases (11 out of 264) did not allow for investigating the association between lung disease or obesity and anti-SARS-2 reactivity in a multivariable regression, potentially including other factors, as for example socio-economic status or age. When investigating associations between BMI and COVID-19, future work should rely on physical measurements rather than self-report of height and weight.

Participants who were SARS-CoV-2 seropositive were more likely to have been tested and to have a positive result, which is in contrast with the study of Arizona first responders that reported no difference between seropositive and seronegative individuals and prior testing. 7 However, testing overall in this population prior to our study was low. This may have resulted from expensive or hard to find SARS-CoV-2 tests. This may also represent a recruitment bias in our study participants. Individuals with a previous positive SARS-CoV-2 or COVID-19 test may not have felt as inclined to participate in our study, as one of the main benefits to the participant was a free test result. In addition, individuals may have been more likely to have a previous test if they had any COVID-19-like symptoms. If that is the case, we may be underestimating the seroprevalence of SARS-CoV-2 antibodies in first responders in the region. Interestingly, two of the SARS-CoV-2 seropositive individuals had a prior negative and one of the seronegative individuals had a prior positive SARS-CoV-2 test. Unfortunately, we did not collect data on the type or timing of prior testing and therefore cannot make any direct comparisons to our assay.

As part of our survey, we asked first responders to define how likely they thought they were to have already had COVID-19. We found that SARS-CoV-2 seropositive participants were more likely to believe they had a prior COVID-19 infection when compared with seronegative participants. Overall, 46 (17%) participants thought they probably to definitely had previously had COVID-19, but only seven (15%) were seropositive for anti-SARS-CoV-2 antibodies, denoting a previous infection. An individual's perception of their risk of infection with SARS-CoV-2 has been associated with adoption of protective behaviors (eg, wearing masks, social distancing, improved hand washing). [26] [27] [28] It is possible an individual's perception of past infection may also influence changes in behavior. Individuals who believe they already had COVID-19 may be less likely to follow preventive protocols, assuming protection through immunity. However, we found that a small percentage of individuals who believe they already had COVID-19 had detectable antibodies. It is also unclear at this time how long immunity after infection lasts but there is some evidence that immunity wanes over time 10 and this waning may occur more quickly in individuals with mild illness 29 or asymptomatic individuals. 12 Unfortunately, we did not ask about perceptions of future risk nor did we ask about infection prevention behaviors outside of PPE use. It will be important moving forward to remind and support individuals to practice safety measures both at home and in the workplace, regardless of their past infection status.

When asked about the presence of COVID-19 associated symptoms, SARS-CoV-2 seropositive first responders were more likely to report ever having symptoms 3 months prior to testing. Interestingly, there were no associations seen with symptoms present within 1 or 2 months of testing and being SARS-CoV-2 seropositive. This suggests that individuals in our study may have been infected early in the pandemic potentially because of increased risk of infection due to a lack of recognition of the severity of the pandemic, an inadequate supply of PPE, and/or delays in the implementation of prevention protocols for the general population (eg., stay at home order, wearing masks, etc). When broken down by symptom we found that SARS-CoV-2 seropositive participants were more likely to report ever having any of the COVID-19 related symptoms asked about, except for headaches. Headache was the most reported symptom among participants, regardless of their SARS-CoV-2 serostatus, which is consistent with studies of COVID-19 symptoms among health care workers. 30 Headaches have been found to be associated with wearing PPE. 31 Since first responders in our study were all trained on and were, presumptively, wearing proper PPE, we would expect to see similar frequencies of headaches regardless of an individual's previous SARS-CoV-2 exposure status. We also found that 27% of SARS-CoV-2 seropositive participants reported no symptoms in the 3 months prior to testing. This is slightly lower than the current centers for disease control and prevention estimates that 40% of SARS-CoV-2 infections are asymptomatic 32 but similar to reports that 29% of frontline health care personnel with SARS-CoV-2 antibodies were asymptomatic. 33 In comparison, over 70% of first responders in Arizona with detection of anti-SARS-CoV-2 IgG antibodies reported having no COVID-19 symptoms. 7 There is strong evidence that supports presymptomatic transmission of SARS-CoV-2 34-37 but whether truly asymptomatic individuals can infect others is still up for debate. 38, 39 Regardless, proper training on and continued use of PPE is important for protecting first responders as well as the general population.

One strength of our study was enrollment of individuals from a variety of first responder roles and agencies within Arapahoe County, including those working in both rural and urban areas. We used a validated ELISA assay with a high sensitivity and specificity to test for anti-SARS-CoV-2 IgG antibodies to measure prior infection and were able to report on SARS-CoV-2 serology among human services workers, a previously unidentified potentially highrisk group for exposure to SARS-CoV-2. There were also limitations. We did not collect data on smoking status, a potentially important risk factor for COVID-19. Enrolled individuals identified predominately as White, Non-Hispanic/Non-Latinx which may have reduced the generalizability of our results, though it is in line with the demographics of individuals employed in protective service and community and social service occupations in the United States. 40 In addition, our study may have had some selection bias as we had low acceptance of the study in rural areas and so may have an underrepresentation of SARS-CoV-2 seroprevalence in that subregion.

We were able to estimate the seroprevalence of SARS-CoV-2 in Arapahoe County first responders and to identify factors that may be driving seropositivity and SARS-CoV-2 exposure in this population. The identification of caseworkers as having similar risk of SARS-CoV-2 exposure compared with other first responders points to a need to analyze types of exposure (eg, limited outdoors vs extensive indoor) among first responder populations, and to ensure their inclusion in future risk assessments. Our findings will help with public health strategies regarding the COVID-19 response and provide guidance towards risk assessments of first responders during this pandemic. To ensure the health and safety of first responders, both at work and in the community, future studies need to continue to identify risk factors for transmission both among first responders and the general population, identify the transmission dynamics of SARS-CoV-2, and elucidate the immune systems response to this virus.

United States COVID-19 Cases and Deaths by State

CDC COVID Data Tracker -Cases & Deaths among Healthcare Personnel

Prevalence of IgG antibodies to SARS-CoV-2 among emergency department employees

Medical leave associated with COVID-19 among emergency medical system responders and firefighters in New York City

Epidemiology of SARS-CoV-2 antibodies among firefighters/paramedics of a US fire department: a cross-sectional study

SARS-CoV-2 seroprevalence among healthcare, first response, and public safety personnel, detroit metropolitan area

COVID-19 exposure among first responders in Arizona

SARS-CoV-2 seroconversion in humans: a detailed protocol for a serological assay, antigen production, and test setup

Profiling early humoral response to diagnose novel coronavirus disease (COVID-19)

Dynamics and significance of the antibody response to SARS-CoV-2 infection

Humoral immune response to SARS-CoV-2 in Iceland

Clinical and immunological assessment of asymptomatic SARS-CoV-2 infections

Estimating the burden of United States workers exposed to infection or disease: a key factor in containing risk of COVID-19 infection

WHO World Health Organization. Transmission of SARS-CoV-2 -implications for infection prevention precautions: Scientific brief

peoplewith-medical-conditions.html?CDC_AA_refVal=https%3A%2F%2Fwww. cdc.gov%2Fcoronavirus%2F2019-ncov%2Fneed-extra-precautions%2F groups-at-higher-risk

Prevalence and characterization of asthma in hospitalized and nonhospitalized patients with COVID-19

The impact of COPD and smoking history on the severity of COVID-19: a systemic review and meta-analysis

Clinical Characteristics of 138 Hospitalized Patients With 2019 Novel Coronavirus-Infected Pneumonia in Wuhan, China

Analysis of factors associated with disease outcomes in hospitalized patients with 2019 novel coronavirus disease

Clinical course and risk factors for mortality of adult inpatients with COVID-19 in Wuhan, China: a retrospective cohort study

A retrospective study on the epidemiological characteristics and establishment of an early warning system of severe COVID-19 patients

Clinical characteristics of Covid-19 in New York City

Hospitalization rates and characteristics of patients hospitalized with laboratory-confirmed coronavirus disease 2019 -COVID-NET, 14 States

Clinical characteristics of 140 patients infected with SARS-CoV-2 in Wuhan

Table 21, Selected health conditions and risk factors, by age: United States, selected years

Relationships between initial COVID-19 risk perceptions and protective health behaviors: a national survey

COVID-19: risk perception and Coping strategies

Functional fear predicts public health compliance in the COVID-19 pandemic

Rapid Decay of Anti-SARS-CoV-2 antibodies in persons with mild Covid-19

A multinational, multicentre study on the psychological outcomes and associated physical symptoms amongst healthcare workers during COVID-19 outbreak

Headaches associated with personal protective equipment -a cross-sectional study among frontline healthcare workers during COVID-19

CDC Centers for Disease Control and Prevention. Coronavirus Disease/ Healthcare Workers/Pandemic Planning Scenarios

CDC COVID-19 response team; IVY network. Seroprevalence of SARS-CoV-2 among frontline health care personnel in a multistate hospital network -13 Academic Medical Centers

Serial interval of COVID-19 among publicly reported confirmed cases

COVID-19 transmission within a family cluster by presymptomatic carriers in China

Asymptomatic and presymptomatic SARS-CoV-2 infections in residents of a long-term care skilled nursing facility

Presymptomatic transmission of SARS-CoV-2 -Singapore

Asymptomatic transmission of SARS-CoV-2 on evacuation flight

A study on infectivity of asymptomatic SARS-CoV-2 carriers

Labor Force Statistics from the Current Populatoin Survey -Employed persons by detailed occupation, sex, race, and Hispanic or Latino ethnicity

The authors would like to acknowledge the support provided by the Arapahoe County Office of Emergency Management, the University of Colorado Graduate Experience for Multicultural Students For Health Professional Students (GEMS-HP) Program, the staff and facilities of Center Pointe Plaza, our field staff, and all study participants, without whom this work would not have been possible.