National Outpatient Sexually Transmitted Infection Testing in Pregnant Patients in the United States

Abstract

Introduction:

Sexually transmitted infections (STIs) continue to increase in the United States and pregnant patients who acquire STIs are at risk for serious complications. This study estimated the utilization of preventative STI testing among pregnant outpatients on a national scale.

Methods:

This was a retrospective, cross-sectional study of outpatient visits in the National Ambulatory Medical Care Survey from 2014 to 2016 and 2018 to 2019. All patients reported as pregnant were included to assess STI testing for chlamydia, gonorrhea, hepatitis, and HIV. STI testing was described per 1,000 total visits overall and by subpopulations. Data weights were applied to generate national estimates.

Results:

Over 177 million visits were included, of which 87.5 per 1,000 included an STI test. Chlamydia testing was the most common, followed by HIV, gonorrhea, and hepatitis (58.0 vs. 42.3 vs. 41.5 vs. 20.3 per 1,000). STI testing rates varied across subpopulations (72.1–236.6 per 1,000 visits). Patients of Hispanic ethnicity, Black race, age ≤25 years old, and those seen by an obstetrics and gynecology (OB/GYN) provider had the highest rates of STI testing. Independent predictors of STI testing included: Black race (adjusted odds ratio [aOR]: 2.24, 95% confidence interval [95% CI]: 2.23–2.24), first trimester (aOR: 5.15, 95% CI: 5.14–5.16), government and private insurance (aOR: 1.90, 95% CI: 1.89–1.91 and aOR: 1.70, 95% CI: 1.69–1.71), and an OB/GYN provider specialty (aOR: 2.93, 95% CI: 2.93–2.94).

Conclusions:

STI testing in United States outpatient physician offices varied by subpopulations and across individual test types. Certain patient attributes, such as race, provider specialty, and payment source, were predictive of testing.

Introduction

Sexually transmitted infections (STIs) during pregnancy can result in significant maternal and fetal adverse health outcomes. Complications that occur across common curable STIs include low birth weight, premature birth, miscarriage, stillbirth, and neonatal death.^1–3 Early STI screening and treatment are essential in reducing the risk of these adverse outcomes.³ STIs may initially present as asymptomatic for both mother and fetus. Depending on the type of infection, symptoms can appear in the later periods of gestation or several weeks after birth.⁴ Specific testing recommendations consider a variety of factors including patient age, pregnancy trimester, and risk level. These risk factors include new or multiple sexual partners, a sexual partner with concurrent partners, or a sexual partner with a recent STI history.⁵ Prior studies suggest that social determinants of health may play a role in STI risk as well, as pregnant women who are Black, younger, have lower income, are unmarried, have limited education, or are uninsured or do not have access to health care are more likely to acquire STIs.^6,7

STI incidence in the United States continues to increase. In a 2021 Centers for Disease Control and Prevention (CDC) Surveillance survey, chlamydia was the most prevalent infection followed by gonorrhea and syphilis.^6,8 In a 2009–2011 survey conducted among 20,268 pregnant women, 3.3% received a diagnosis of chlamydia, gonorrhea, syphilis, or trichomoniasis during their pregnancy.⁶ Beyond these data, few studies have examined STI testing during pregnancy and its adverse effects, likely due to limited resources in obtaining this type of information. Pregnancy status is often not reported during national STI surveillance.⁹ In addition, women who have previously undergone STI testing may not be routinely screened for pregnancy and there may be systemic under-reporting between health departments.^6,9 The lack of reliable data on reporting STI testing during pregnancy poses a problem in accurately estimating STI prevalence rates and creating effective solutions to minimize adverse pregnancy outcomes.

Despite the continued increase of STI cases nationwide, few studies have documented STI screening practices in pregnancy. More specifically, these reports are not indicative of which facility or providers the patients visited. A comprehensive understanding of STI resource utilization in this vulnerable patient population may aid in future efforts to improve maternal and fetal health outcomes in the United States. Therefore, the objectives of this study were to (1) describe overall STI testing in the United States and (2) determine if factors such as age group, race, ethnicity, trimester, and payor type affect testing during pregnancy in the ambulatory care setting.

Materials and Methods

Study design and data source

This was a retrospective, cross-sectional study using data from the CDC’s National Ambulatory Medical Care Survey (NAMCS) from 2014 to 2016 and 2018 to 2019. The NAMCS is a national, three-stage probability sample survey conducted annually by the National Center for Health Statistics (NCHS) that is designed to collect objective and reliable information on ambulatory medical care services in the United States. The first stage uses geographic primary sampling units followed by physician sampling in the second stage and visits to a sampled physician in the third stage. Nonfederally employed providers within the ambulatory setting (e.g., private practice and free-standing clinics) are each randomly assigned to report information on a sample of outpatient visits. It is possible, though highly unlikely, that multiple outpatient visits would be included for a single patient given the complex study design. Extensive data consisting of patient, visit, and practice characteristics are collected directly from providers who are randomly assigned to a one-week reporting period. In addition, each visit is assigned a patient weight under the variable name “PATWT” that can be applied in analyses to generate national estimates. The “PATWT” variable is a right-justified integer developed by NCHS staff.¹⁰ To make the results of this study reliable, data were only reported using applied patient weight if 30 or more observations were reported within each outcome reported as recommended by the CDC NCHS.¹¹ Data for 2017 were not released by the CDC. The 2019 survey data are most recently released due to delays in reporting caused by the COVID-19 pandemic. The NCHS Ethics Review Board determined that the NAMCS protocol (Protocol #2021-03) is a nonresearch, public health surveillance activity under the Common Rule (45 CFR 46.102 (1)(2)).

Patient population and study definitions

All patients reported as pregnant in the NAMCS from 2014 to 2016 and 2018 to 2019 were eligible for inclusion. Pregnancy was defined using the “Pregnant” variable where providers were able to choose between yes, no, unknown, or not applicable. Patients who were reported as not pregnant or with missing pregnancy documentation were excluded from analyses. STI testing ordered for chlamydia, gonorrhea, hepatitis, and HIV are collected as a standard part of the survey distributed to providers and were included for analysis. The hepatitis test variable in the NAMCS survey does not distinguish by strain and includes hepatitis A, B, and C. The study period began in 2014 as this was the first year that the NAMCS included all of the STI tests included in this study. Any STI test was defined as having at least one test ordered for the included infections over the study period.

Patient characteristics included age (in years), age group (less than 25 years, 25 years and older), trimester (first, second, third, unknown), race (Black, White, other), ethnicity (Hispanic, non-Hispanic), and payor type, as defined by the NAMCS. The patient’s trimester was determined using gestation week recorded at the visit and was based on the American College of Obstetricians and Gynecologists definition of each trimester in pregnancy.¹² First trimester was defined as gestational age of 0 to 13 weeks and 6 days. The second trimester was defined as gestational age of 14 weeks to 27 weeks and 6 days. Lastly, the third trimester was defined as gestational age of 28 weeks or more. Imputed race and ethnicity variables provided in the survey were used to account for underreporting of multiple races and missing values. The NAMCS imputed race and ethnicity variables using a model-based, single, sequential regression imputation method. Visit characteristics included whether the patient had been seen before, whether they were referred or not, specialty of provider at the visit (obstetrics and gynecology [OB/GYN], general and primary, other), payor type, and metropolitan status.

Data and statistical analysis

Data analyses were conducted using JMP Pro 17 (SAS Institute, Cary, NC). Data weights were used to generate national estimates from the sampled visits and were applied for all analyses. Baseline characteristics were compared between visits with and without a documented STI test ordered using the χ² or Wilcoxon rank sum test, as appropriate. STI testing rates were calculated as the number of visits that included an STI test per 1,000 total outpatient visits for receiving any STI test and by individual STI test. Subgroup analyses were also conducted by patient age group, race, ethnicity, first trimester, and provider type. Testing rates in each subpopulation were calculated using population-specific denominators.

In addition, multivariable logistic regression was used to identify predictors of receiving at least one STI test during the visit. Variables included in the multivariable logistic regression included age group, trimester, race, ethnicity, payor type, provider specialty, whether the patient was referred, and whether a patient had been seen before by that provider. To avoid reporting inaccurate estimates, the “unknown” category for all variables and the “other” category for both race and provider specialty were excluded from testing rate calculations and prediction modeling as too few STI tests were recorded in these categories. Lastly, the payor type was consolidated into patients with private, government (Medicare and Medicaid), and other (self-pay, worker’s compensation, no charge, other) to avoid the same issue.

Results

Population characteristics

Over 177 million outpatient visits among pregnant patients were included for analysis. In total, 15,512,605 (8.7%) patient visits included documentation of at least one STI test ordered. Patient baseline characteristics are shown in Table 1. Patients with at least one STI test (e.g., chlamydia, gonorrhea, HIV, hepatitis) were slightly younger (median age: 28 vs. 30 years) and more often Black (22.7% vs. 13.6%), Hispanic (35.6% vs. 30.2%), and had Medicare or Medicaid (48.4% vs. 40.5%). Furthermore, patients who had received at least one STI test were more often in the first trimester (45.1% vs. 15.7%) and were more often seen by an OB/GYN specialist (65.9% vs. 52.5%).

Table 1.

Baseline Characteristics Of Patient Visits With and Without Any STI Test

Characteristic	No STI test (n = 161,821,971)	Any STI test (n = 15,512,605)	p-value
Age, median (IQR)	30 (25–34)	28 (23–33)	<0.0001
Age group, n (%)			<0.0001
25 years and older	122,584,688 (75.8)	10,452,389 (67.4)
Less than 25 years	39,237,283 (24.2)	5,060,215 (32.6)
Trimester, n (%)			<0.0001
First	20,152,693 (15.7)	6,245,742 (45.1)
Second	42,143,097 (32.8)	3,209,985 (23.2)
Third	61,342,115 (47.8)	3,672,807 (26.5)
Unknown	4,757,286 (3.7)	728,112 (5.2)
Race, n (%)			<0.0001
Black	22,035,186 (13.6)	3,524,644 (22.7)
White	125,208,658 (77.4)	10,858,584 (70.0)
Other	14,578,127 (9.0)	1,129,377 (7.3)
Hispanic ethnicity, n (%)	48,916,765 (30.2)	5,520,546 (35.6)	<0.0001
Payor, n (%)			<0.0001
Private insurance	86,162,029 (54.0)	7058188 (45.6)
Medicare/Medicaid	64,564,100 (40.5)	7,489,104 (48.4)
Self-pay	3,586,481 (2.2)	151,078 (1.0)
Other	1,924,345 (1.2)	2,341 (0.0)
Unknown	3,260,850 (2.0)	778,965 (5.0)
Seen before, n (%)	146,089,753 (90.3)	12,429,989 (80.1)	<0.0001
Referred, n (%)	26,779,045 (22.3)	2,149,621 (21.1)	<0.0001
Specialty of provider, n (%)			<0.0001
Obstetrics and gynecology	84,961,845 (52.5)	10,219,010 (65.9)
General and primary	64,079,818 (39.6)	4,981,408 (32.1)
Other	12,780,308 (7.9)	312,186 (2.0)
Metropolitan status, n (%)	149,629,957 (92.5)	14,564,516 (93.9)	<0.0001

IQR, interquartile range; STI, sexually transmitted infection.

STI testing rates overall and by subpopulations

Overall, 87.5 per 1,000 patient visits included at least one STI test ordered. Of the individual STI tests in the overall population, chlamydia was the most tested STI (58.0 per 1,000 visits), followed by HIV (42.3 per 1,000 visits), gonorrhea (41.5 per 1,000 visits), and hepatitis (20.3 per 1,000 visits).

STI testing rate differences were observed for all subgroups evaluated (Fig. 1). Among race groups, Black patients had the highest testing rate for any STI (137.9 per 1,000 total visits) compared to White patients (79.8 tests per 1,000 visits). Regarding ethnicity, Hispanic patients had a higher testing rate (101.4 per 1,000 visits) for any STI in comparison to non-Hispanic patients (81.3 per 1,000 visits). Differences were also observed between age groups. Patients less than 25 years had a higher testing rate for any STI at 114.2 per 1,000 total visits compared to patients 25 years and older (78.6 tests per 1,000 visits). Of the population in the first trimester of pregnancy, 236.6 per 1,000 patient visits included at least one STI test ordered. Like the overall population, the rate of ordering individual STI tests for first-trimester patients was highest for chlamydia (182.8 per 1,000 visits), followed by HIV (128.4 per 1,000 visits), gonorrhea (105.4 per 1,000 visits), and hepatitis (77.0 per 1,000 visits). When compared with patients in the third trimester of pregnancy, those in the first trimester were over five times more likely to have any STI ordered at their visits (aOR: 5.15, 95% confidence interval [95%CI]: 5.14–5.16). Overall, providers with an OB/GYN specialty had a much higher order rate of any STI test (211.3 per 1,000 visits) compared to providers in a general or primary care specialty (72.1 per 1,000 visits).

FIG. 1.

STI testing rates overall and by subgroup. STI, sexually transmitted infection.

Lastly, all patient characteristics were evaluated simultaneously in the multivariable logistic regression model (Table 2). The strongest independent predictors of receiving any STI test included: the first trimester compared with the third trimester (aOR: 5.15, 95%CI: 5.14–5.16), OB/GYN specialist compared with other provider (aOR: 2.93, 95%CI: 2.93–2.94), Black compared with White race (aOR: 2.24, 95%CI: 2.24–2.24), Hispanic compared with non-Hispanic ethnicity (aOR: 1.32, 95%CI: 1.32–1.32), and those with Medicare/Medicare (aOR: 1.90, 95% CI: 1.89–1.91) and private insurance (aOR: 1.70, 95%CI: 1.69–1.71) when compared with “other” insurance. Other predictors included: age 25 years or older compared to younger patients (aOR: 1.28, 95%CI: 1.28–1.28), patients not seen before (aOR: 1.19, 95%CI: 1.19–1.19), and patients who were referred (aOR: 1.17, 95%CI: 1.17–1.17).

TABLE 2.

Predictors of Receiving Any STI Test During a Visit

Variable	Unadjusted odds ratio (95%CI)	Adjusted odds ratio (95%CI)
Age group
25 years and older	0.66 (0.66–0.66)	1.28 (1.28–1.28)
Less than 25 years	1.00 (reference)	1.00 (reference)
Trimester
First	5.18 (5.17–5.18)	5.15 (5.14–5.16)
Second	1.27 (1.27–1.27)	1.39 (1.39–1.39)
Third	1.00 (reference)	1.00 (reference)
Race
Black only	1.84 (1.84–1.85)	2.24 (2.24–2.24)
White only	1.00 (reference)	1.00 (reference)
Ethnicity
Hispanic	1.28 (1.27–1.28)	1.32 (1.32–1.32)
Non-Hispanic	1.00 (reference)	1.00 (reference)
Referred
Yes	0.93 (0.93–0.93)	1.17 (1.17–1.17)
No	1.00 (reference)	1.00 (reference)
Seen before
No	2.30 (2.30–2.31)	1.19 (1.19–1.19)
Yes	1.00 (reference)	1.00 (reference)
Payor type
Medicare/Medicaid	4.17 (4.15–4.19)	1.90 (1.89–1.91)
Private insurance	2.94 (2.93–2.96)	1.70 (1.69–1.71)
Other	1.00 (reference)	1.00 (reference)
Specialty
Obstetrics and gynecology	1.55 (1.55–1.55)	2.93 (2.93–2.94)
General and primary care	1.00 (reference)	1.00 (reference)

CI, confidence interval.

Discussion

In this nationally representative, retrospective, cross-sectional study of ambulatory care clinic visits across the United States, STI testing rates during pregnancy varied by patient age group, trimester, race, ethnicity, payor type, and specialty of the provider. Specifically, patients younger than 25 years, of Black race, of Hispanic ethnicity, in their first trimester, and those seen by an OB/GYN specialist had higher rates of STI testing compared to other population groups. Testing was also more likely in pregnant women with Medicare or Medicaid insurance.

Chlamydia was the most tested STI in the overall population and among first-trimester patients, potentially due to chlamydia being the most prevalent STI in the general population. Chlamydia prevalence has increased since 1993 and was the most reported STI (1.6 million cases in 2021) in the most recent CDC 2021 surveillance report.^8,13 Despite the growing need to lower infection rates, testing has been shown to be underutilized in the pregnant population. A study by Blatt et al.¹⁴ examined laboratory data from Quest Diagnostics on pregnant patients from 2005 to 2008 and found that 59% and 57% were tested at least once during pregnancy for chlamydia or gonorrhea, respectively. Although gonorrhea is the second most reported STI in the United States (710,151 cases in 2021), HIV testing was slightly higher than gonorrhea testing in this study. This difference increased further when limited to first-trimester patients. Though the difference is small (42.3 vs. 41.5 per 1,000 visits), this finding may be explained by changes in guideline recommendations over time. The CDC’s 2010 and 2015 Sexually Transmitted Diseases Treatment Guidelines both consistently recommend that women be tested for HIV early in pregnancy and if at risk; however, the 2010 guidelines recommend that all women be screened as early as possible whereas the 2015 guidelines specify that testing be done at the first prenatal visit.^15,16 Conversely, while similar in initial testing, the 2010 recommendations suggest retesting positive patients for gonorrhea within 3 to 6 months, but preferably in the third trimester, whereas the 2015 guidelines changed to retesting within 3 months and again in the third trimester if still at risk.

Though there are limited studies examining racial and ethnic differences in STI testing during pregnancy on a national level in the United States, this study found that Black and Hispanic women had higher overall testing rates and were more likely to receive testing when compared to White women, which aligns with previous literature. In a study by Leichliter et al.,¹⁷ the National Survey of Family Growth from 2011 to 2015 was used to assess self-reporting of STD testing in women who were pregnant over the past 12 months. Non-Hispanic Black women were more likely to receive a chlamydia test (aOR: 2.82, 95% CI: 1.86–4.26) and any other STI test (aOR: 2.43, 95% CI: 1.58–3.74) when compared with non-Hispanic White patients. Though Hispanic women were shown to have higher odds of receiving both a chlamydia test (aOR: 1.47, 95% CI: 0.90–2.42) and any other STD test (aOR: 1.52, 95% CI: 0.99–2.33) when compared to Non-Hispanic White women, these findings were not statistically significant. These findings, in addition to the present study, may be associated with the provider perspective on the known increased risk for infection in these patient populations. Multiple studies have established that Black and Hispanic women experience higher STI rates than White patients both in the pregnant and overall U.S. population.^6,9,18,19 It is also possible that structural, cultural, or individual-level racism plays a role in STI prevalence and testing rates,²⁰ though we were unable to determine this association in the study design.

Similar to race and ethnicity, younger age has been previously associated with an increased prevalence and risk of STI.^9,18,21 A study using the National Health and Nutrition Examination Survey from 2007 to 2012 demonstrated that the prevalence of chlamydia decreased with age among sexually active females.¹⁸ Similarly, patients between 15 and 24 years of age demonstrate a disproportionate burden of disease with 50% of all new STI cases in the United States despite only making up 25% of the sexually active population.²¹ Furthermore, past and more recent guidelines identify patients less than 25 years of age and any others at increased risk as priority groups to be tested for chlamydia and gonorrhea at the first prenatal visit.^5,16 With a well-established history of disparity among young patients, providers may be more likely to order testing.

Other social and behavioral determinants of health have been found to be associated with increased STI infection rates and potentially a perceived need for testing. Leichliter et al.¹⁷ reported that recently pregnant women who live in a metropolitan statistical area (MSA) that is not a principal city were less likely to receive testing for chlamydia (aOR: 0.62, 95% CI: 0.44–0.86) or any other STI (aOR: 0.57, 95%CI: 0.40–0.81) when compared with women living in a principal city of an MSA. In addition, women with Medicaid/Medicare insurance were more likely to receive chlamydia testing when compared to those without insurance (aOR: 2.55, 95% CI: 1.52–4.28), and those who received prenatal services within the past year were more likely to receive chlamydia (aOR: 2.10, 95% CI: 1.35–3.28) and all other testing (aOR: 2.32, 95% CI: 1.54–3.49). These findings suggest that increased access to care aided by insurance coverage and favorable proximity to healthcare services improve preventative care for pregnant women. Additional factors reported in prior literature to be associated with increased STI prevalence include a lower level of education, lack of health insurance, poverty, unmarried status, smoking during pregnancy, late timing of prenatal care, and risky sexual behaviors (e.g., multiple-sex partners).^6,9,18

In line with this study, prior literature has documented a difference in STI testing between different provider specialties. A 2021 study by Zeidan et al. used the NAMCS survey to evaluate testing rates and preventative education of the entire U.S. population and found that providers with an OB/GYN specialty had higher rates of ordering STI testing and providing STI preventative education than providers with a general/family specialty (103.75 per 1,000 visits vs. 20.83 per 1,000).¹⁹ Primary care providers may have lower STI testing rates for a variety of reasons. First, OB/GYNs may be more likely to proactively screen for STIs based on guideline recommendations, whereas primary care providers may be more likely to test only for symptomatic infection. A 2019 study utilizing the CDC’s NAMCS survey from 2006 to 2015 found that of women aged 15 to 25 years who had chlamydia tests ordered, 59.2% were asymptomatic while 31.6% presented with symptoms.²² Next, pregnant patients who visit a primary care provider may be concurrently seen by an OB/GYN provider; thus, duplicate STI testing may not be warranted. The cross-sectional design of this study does not allow confirmation of this hypothesis, nor can we confirm that STI testing rates are lower than recommended or necessary in either specialty.

Several factors should be considered to improve monitoring and sexual health in pregnant patients. First, there have been multiple, often inconsistent recommendations on STI screening in pregnancy. For example, the U.S. Preventive Services Task Force (USPSTF) has consistently recommended since 1996 that all pregnant women younger than 25 years or those at risk for infection receive chlamydia testing.²³ Alternatively, the CDC’s STI treatment guidelines have changed over time. Previously published treatment guidelines have all agreed with the USPSTF recommendation aside for a period of time between 2002 and 2015 to include all pregnant women at their first prenatal visit.^16,24 Ensuring that all providers are aware and educated on the best, most recent guidelines and recommendations to follow is essential for improving adherence. Second, OB/GYN specialists are becoming less accessible to the U.S. population. In 2019, 47.9% of U.S. counties did not have an OB/GYN and 55.1% lacked a certified nurse midwife.²⁵ As access to OB/GYN specialists continues to decrease in the United States,²⁶ primary care providers may be necessary to meet patient needs. Lastly, nationally representative data on STI testing and infection rates in pregnancy are scarce. Many of the available sources lack socioeconomic variables, are reliant on self-reporting or convenience sampling, and have too few data points which potentially may be due to underreporting and may contribute to unreliable estimates. An emphasis on improving how we collect data to meet future goals is crucial to tracking progress and identifying additional areas of improvement.

This study has some potential limitations. First, the NAMCS only provides cross-sectional information on patient visits; therefore, further information about past or future visits for longitudinal follow-up is unavailable. Second, there were only a limited number of variables collected pertinent to this patient population, thus making it difficult to define pregnancy and appropriate STI testing. For example, syphilis was not included in this dataset despite being an important STI to test for early in pregnancy. In addition, patients were only defined as pregnant using the variables answered by the physician in the survey; data could not be confirmed through laboratory testing, and missing data were common. Due to small event rates of STI testing in each year of data, extrapolating national estimates to trend testing rates over time was not possible as it would likely be unreliable. Third, there were a limited number of pregnant patients recorded, making it difficult to perform subgroup analyses that would provide reliable national estimates. Fourth, this study was not able to account for important socioeconomic and physician characteristics that may influence STI testing, including access to care and other social determinants of health. The patient’s race was reported by the provider on the survey, and it is unknown whether the answer was based on provider perception as opposed to self-report by the patient, which may result in misclassification bias. Lastly, the NAMCS only accounts for testing that is ordered by providers in the outpatient setting; therefore, it is not possible to confirm whether testing is completed or the results of the test.

Conclusions

In this nationally representative study, STI testing varied by race, ethnicity, age, trimester, and provider specialty. Although this is one of the first studies to describe outpatient STI testing rates in pregnancy nationally, future studies are needed to determine guideline-concordant testing (i.e., the prevalence of indicated testing), as well as health, social, structural, and behavioral reasons for differences among subpopulations, to better understand their impact on testing, infection rates, and maternal and fetal health outcomes. Outpatient primary care providers, especially in settings with few OB/GYN providers, may be needed to bridge the gap in care for pregnant patients. Lastly, timely and accurate reporting of STI testing rates will help gauge the impact of care implementation efforts over time.

Authors’ Contributions

K.A.S: Data curation (lead); Formal analysis (lead); Conceptualization (equal); Methodology (equal); Writing—original draft (equal); Writing—review and editing (equal). H.C.A: Writing—original draft (equal); writing—review and editing (equal). V.M.M: Conceptualization (equal); Writing—review and editing (equal). K.R.R: Supervision (lead); Conceptualization (equal); Writing—original draft (equal); Writing—review and editing (equal); Methodology (equal).

Author Disclosure Statement

The authors declare no conflict of interest.

Funding Information

There is no funding to report in support of this research.