Abstract
Background
Despite the sharp increase in mpox (formerly monkeypox) incidence and the wide geographic spread of mpox during the 2022 outbreak, the community prevalence of infection remains poorly characterized. This study is a retrospective epidemiologic survey to estimate mpox prevalence.
Methods
Samples obtained for sexually transmitted infection (STI) testing from April to September 2022 in the public hospital and clinic system of San Mateo County, California were screened for mpox virus (MPXV) using polymerase chain reaction.
Results
16/1,848 samples from 11/1,645 individuals were positive for MPXV by qPCR. 4/11 individuals with positive MPXV testing were cisgender women, 2 of whom were pregnant at the time of sample collection. Both deliveries were complicated by chorioamnionitis. Anorectal and oropharyngeal samples were the most likely to be positive for MPXV (4/60 anorectal samples and 4/66 oropharyngeal samples compared with 5/1,264 urine samples and 3/445 vaginal samples).
Conclusions
Our study is one of the first epidemiologic surveys for MPXV infection outside of sexual health/STI clinic settings. Relatively high rates of MPXV from oropharyngeal and anorectal samples reinforces the importance of MPXV testing at various anatomic sites, particularly if patients are presenting with non-lesional symptoms (pharyngitis, proctitis). However, the United States Food and Drug Administration (FDA) has not yet authorized non-lesional MPXV testing. The identification of MPXV in women in our cohort suggests that the rates of mpox in women may have previously been underestimated and highlights the risk of pregnancy complications associated with mpox.
Keywords: Mpox, Monkeypox, MPXV, MPX, Sexually transmitted infections
1. Introduction
MPXV is an enveloped, double stranded DNA virus in the family Poxvirus, genus Orthopoxvirus. An MPXV outbreak beginning in 2022 has disproportionately impacted gay, bisexual, and other men who have sex with men (MSM). Unlike previous outbreaks, transmission during this outbreak has largely occurred through sexual networks [1]. The first California case of mpox was identified in May 2022. California mpox cases peaked August 2022 with San Francisco county having the highest cumulative state case rate at 94.5 cases per 100,000 [2]. There is limited data around the prevalence of mpox outside of MSM communities. A recent case series of mpox in cis-women and nonbinary individuals highlights the need for data describing mpox across diverse populations, particularly as a significant number of women in that case series were misdiagnosed prior to the identification of mpox [3,4]. In this study, we screened samples collected for STI testing in San Mateo County, California for the presence of MPXV to estimate mpox prevalence.
2. Materials and methods
This study was approved by the Stanford University Institutional Review Board (IRB), protocol #66786. Urine, anorectal, vaginal, cervical, oropharyngeal, and urethral samples collected for Chlamydia trachomatis (CT), Neisseria gonorrhoeae (NG), Trichomonas vaginalis, and Mycoplasma genitalium testing between April and September 2022 were obtained from the San Mateo County Public Health Laboratory. This laboratory processes all STI screening and diagnostic samples from the county hospital and clinics. Samples were collected and processed per manufacturer protocol, and remnant samples are stored at room temperature for 1–5 months after testing. Positive samples are stored for longer than negative samples. The laboratory began saving all samples regardless of testing result on August 19, 2022. All remnant samples available October 5, 2022 were included in our study.
Total nucleic acids were extracted from 300μL of Aptima specimen transport medium on the PerkinElmer Chemagic 360 instrument using the Chemagic viral DNA/RNA 300 Kit H96 according to the manufacturer's recommendations. Screening for MPXV DNA was performed using a laboratory-developed quantitative PCR (qPCR) targeting viral DNA polymerase sequences conserved throughout non-variola orthopoxviruses, including MPXV [5]. All screen positive samples were tested using a second qPCR that targets viral TNF receptor sequence specific for MPXV clade II [6]. Concordant detection of the targets in both tests was interpreted as positive for MPXV. The qPCR reactions were performed as previously described except the BioRad CFX96 thermal cycler was used [7,8].
Demographics were obtained via automated extraction from the electronic medical record. It is unknown what portion of demographics were self-reported or reported by clinicians. Further clinical history for patients who tested positive for MPXV was obtained from manual chart review. The IRB protocol prohibited disclosing results to patients or clinicians.
3. Results
1,848 samples from 1,645 individuals were available for MPXV testing. Most samples (1,664/1,848, 90.0%) were obtained in August and September 2022. The average age was 30 years (range 7–81 years) and 1,008/1,645 (61.3%) of participants were female (Table 1 ).
Table 1.
Participant demographics. MPXV: Mpox (monkeypox) virus; IQR: Interquartile range. *Individuals with “Race” listed as “Other” had the following responses listed for “Ethnicity”: Arab (7), Asian Indian (1), Brazilian (18), Central American Indigenous (1), Central American (38), Declined to State (3), European (Other) (1), Filipino (2), Guatemalan (50), Iranian (3), Latin American (Other) (17), Mexican (130), Mexican (Indigenous) (3), Other White (1), Other/Mixed (26), Salvadoran (18), South American (5), and no data (9).
| Total Individuals (%) | MPXV+ (%) | MPXV- (%) | |
|---|---|---|---|
| All participants | 1645 | 11 (0.7) | 1634 (99.3) |
| Age median (IQR), years | 30 (18.0) | 39 (19.0) | 30 (18.0) |
| Sex | |||
| Female | 1008 (61.3) | 4 (36.4) | 1004 (61.5) |
| Male | 630 (38.3) | 7 (63.6) | 623 (38.1) |
| No data | 7 (0.4) | 0 (0) | 7 (0.4) |
| Race and Ethnicity | |||
| Asian | 61 (3.7) | 0 (0) | 61 (3.7) |
| Black/African American | 34 (2.1) | 0 (0) | 34 (2.1) |
| Native American/Eskimo | 13 (0.8) | 0 (0) | 13 (0.8) |
| Pacific Islander | 11 (0.7) | 0 (0) | 11 (0.7) |
| White: Hispanic | 414 (25.2) | 3 (27.3) | 411 (25.1) |
| White: Non-Hispanic | 90 (5.5) | 3 (27.3) | 87 (5.3) |
| White: Unknown | 21 (1.3) | 1 (9.1) | 20 (1.2) |
| Other* | 333 (20.2) | 3 (27.3) | 330 (20.2) |
| No data | 668 (40.6) | 1 (9.1) | 667 (40.8) |
| Sexual Orientation | |||
| Asexual | 2 (0.1) | 0 (0) | 2 (0.1) |
| Bisexual | 24 (1.5) | 2 (18.1) | 22 (1.3) |
| Do not know | 10 (0.6) | 0 (0) | 10 (0.6) |
| Lesbian/Gay/Homosexual | 31 (1.9) | 4 (36.4) | 27 (1.7) |
| Queer | 2 (0.1) | 0 (0) | 2 (0.1) |
| Straight or heterosexual | 551 (33.5) | 5 (45.5) | 546 (33.4) |
| Other | 2 (0.1) | 0 (0) | 2 (0.1) |
| No data | 1023 (62.2) | 0 (0) | 1023 (62.6) |
| Gender Identity | |||
| Female | 437 (26.6) | 4 (36.4) | 433 (26.5) |
| Gender nonconforming/nonbinary | 4 (0.2) | 1 (9.1) | 3 (0.2) |
| Male | 214 (13.0) | 5 (45.5) | 209 (13.0) |
| Transgender Female to Male | 1 (0.1) | 0 (0) | 1 (0.1) |
| Transgender Male to Female | 3 (0.2) | 1 (9.1) | 2 (0.1) |
| No data | 986 (59.9) | 0 (0) | 986 (60.3) |
A total of 16/1,848 samples from 11/1,645 individuals were positive for MPXV (Table 2 ). Of the patients with detectable MPXV DNA, 4/11 were assigned female at birth and 7/11 were assigned male at birth. Of the seven individuals who were assigned male at birth, one identified as transfeminine/nonbinary, and one identified as male to female transgender. The four participants assigned female at birth reported only male sexual partners, 2/7 participants assigned male at birth reported both male and female sexual partners, 4/7 participants assigned male at birth reported only male sexual partners, and 1/7 participants assigned male at birth reported only female sexual partners. Further case details are described in Table 3 .
Table 2.
Results of MPXV and CT/NG screening by anatomic site of specimen collection. MPXV: Monkeypox (mpox) virus; CT: Chlamydia trachomatis; NG: Neisseria gonorrhoeae.
| Anatomic Site | Total (%) | MPXV+ (%) | MPXV- (%) | CT+ (%) | NG+ (%) | CT/NG+ (%) |
|---|---|---|---|---|---|---|
| Urine | 1264 (68.4) | 5 (0.4) | 1259 (99.6) | 120 (9.5) | 26 (2.1) | 13 (1.0) |
| Vaginal/Cervical | 445 (24.1) | 3 (0.7) | 442 (99.3) | 25 (5.6) | 2 (0.5) | 0 (0) |
| Oropharyngeal | 66 (3.6) | 4 (6.1) | 62 (93.9) | 1 (1.5) | 8 (12.1) | 1 (1.5) |
| Anorectal | 60 (3.3) | 4 (6.7) | 56 (93.3) | 8 (13.3) | 5 (8.3) | 4 (6.7) |
| Urethral | 2 (0.1) | 0 (0) | 2 (100) | 0 (0) | 1 (50.0) | 0 (0) |
| Unknown | 11 (0.6) | 0 (0) | 11 (100) | 1 (12.5) | 0 (0) | 0 (0) |
| Total | 1848 (100) | 16 (0.9) | 1832 (99.1) | 155 (8.4) | 42 (2.3) | 18 (1.0) |
Table 3.
Clinical history from positive cases with polymerase chain reaction cycle threshold values for all samples, including negative samples from other body sites. Samples were considered positive only if viral DNA was detected by both the screening vDNA pol and confirmatory vTNFR qPCR assays. CT: Chlamydia trachomatis; HIV: human immunodeficiency virus; HIV neg: HIV negative; MSM: Men who have sex with men; NDET: not detected; NG: Neisseria gonorrhoeae; NP: not performed; PEP: Post-exposure prophylaxis; PrEP: Pre-exposure prophylaxis; STI: Sexually transmitted infections; vDNA Pol: viral DNA polymerase; vTNFR: viral tumor necrosis factor receptor.
| Age (years)/ Sex and Gender | Specimen Type and Cycle Threshold | Known Mpox | Clinical History | STI History prior 2 years | HIV/PrEP |
|---|---|---|---|---|---|
| (vDNA Pol/vTNFR) | |||||
| 19/Female | Vaginal: 35.8/30.7 | No | Presented to 24-week prenatal visit with vaginitis. Limited prenatal care prior to 19 weeks. 1 male partner in past year. Induced at 37 weeks 3 days for severe pruritis and cholestasis of pregnancy. Delivery complicated by chorioamnionitis with fever and fetal tachycardia. No neonatal complications. | None | HIV neg |
| 23/Female | Vaginal: 35.0/29.2 | No | Asymptomatic STI screening at 36-week prenatal visit. Reported male partners. Induced at 39 weeks 4 days after 48 h of amniotic fluid leakage with oligohydramnios. Delivery complicated by chorioamnionitis with fever and fetal tachycardia. No neonatal complications. | None | HIV neg |
| 32/Male | Urine: 38.9/26.2 | No | Asymptomatic STI screening when establishing primary care. Reported 1 female partner in past year. | None | HIV neg |
| 39/Male | Oral: 39.2/39.1 | No | Presented to STI clinic to initiate HIV PEP/PrEP and underwent asymptomatic STI screening. Unprotected sex with unknown number of male and female partners 4–6 weeks prior to testing. | Syphilis, NG | PrEP |
| Rectal: 37.0/31.6 | |||||
| Urine: NDET/NP | |||||
| 42/Female | Urine: 35.3/30.4 | No | Asymptomatic STI screening when establishing primary care. Reported 1 male partner in past year. | None | HIV neg |
| 62/Female | Vaginal: 38.8/31.9 | No | Thin yellow vaginal discharge with itching. Denies sexual contact for many years but reports previous male partners. | None | Unknown |
| 67/Male | Oral: 34.0/28.3 | No | 5 days of penile irritation and anal irritation with dark stools and rectal discharge. MSM. | Syphilis | HIV |
| Rectal: 32.0/26.6 | |||||
| Urine: NDET/NP | |||||
| 20/Assigned male at birth; Transfeminine and nonbinary | Rectal: 24.9/19.7 | Yes | Pustules on buttocks, extremities, trunk, genital, and pharyngitis. Receptive oral and anal sex with 1 male partner two weeks prior to testing, but possible sexual assault 3 days prior. Concurrent rectal NG. | Rectal and oral CT, NG | PrEP |
| 28/Male to Female Transgender | Oral: 28.3/23.8 | Yes | Diffuse small lesions on trunk, inguinal region, penile shaft. No oral or rectal symptoms. MSM. | Syphilis, rectal CT | HIV |
| Rectal: 41.0/NDET | |||||
| Urine: NDET/NP | |||||
| 39/Male | Urine #1:25.5/21.3 | Yes | Penile lesions, phimosis, and truncal lesions for 3 weeks. Male and female partners, 1 male partner in past 6 months. Concurrent urine CT/NG. | Syphilis, CT, NG | PrEP |
| Urine #2: 23.6/18.4 | |||||
| 42/Male | Oral: 28.9/24.1 | Yes | Diffuse rash involving genitals with fevers for 4 days. 8 male partners in past 2 months, 20–30 in past year. | Syphilis, NG | HIV |
| Rectal: 35.5/29.1 | |||||
| Urine: 36.0/30.7 |
No individual who tested positive was vaccinated against orthopoxviruses. 4/11 individuals with positive MPXV testing had previously confirmed mpox and presented with cutaneous lesions. The seven individuals without known mpox did not present with cutaneous lesions: 4/7 were asymptomatic and undergoing routine STI screening, 2/7 had vaginitis, and 1/7 had anogenital irritation.
Three individuals with positive MPXV testing were using pre-exposure prophylaxis for human immunodeficiency virus (HIV), and three patients with positive MPXV testing had HIV, all of whom were on antiretroviral therapy and had CD4+ T-cell counts greater than 500 cells/mm3. 6/11 individuals with positive MPXV testing were positive for at least one STI in the previous 24 months, including CT (2), NG (3), and syphilis (5). 2/4 cisgender women with positive MPXV testing were pregnant at the time of testing. Both pregnant individuals had term deliveries complicated by chorioamnionitis.
4. Conclusions
The 2022 outbreak of mpox is the largest on record and the first to cause a pandemic. The clinical presentation of mpox has differed from past outbreaks, with an increase in patients presenting with atypical symptoms like pharyngitis or proctitis [9,10]. However, the FDA has not yet authorized non-lesional MPXV assays. Two similarly designed studies to screen STI samples for MPXV also identified cases without classic lesions, though these studies primarily enrolled MSM presenting to sexual health clinics [11,12]. Our study included participants undergoing routine STI screening who are likely more representative of the general population than patients seeking STI testing at sexual health clinics.
Our findings confirm that MPXV infection occurs asymptomatically and subclinically and raises questions about the epidemiology of mpox in women and men who have sex with women. While the current outbreak of mpox has disproportionately impacted MSM, four of twelve MPXV-infected individuals in our study were cisgender women who reported having sex only with men, and one individual was a cisgender man who reported having sex only with women.
Two of the four cisgender women with MPXV infection were pregnant at the time of testing, and both deliveries were complicated by chorioamnionitis though no neonatal complications were noted. A prior study of four pregnant individuals with mpox notes significant complications associated with infection, including fetal demise [13]. A more recent case series reports 21 cases of mpox in pregnant individuals, but only three of those cases have known outcomes: two uncomplicated term deliveries and one spontaneous abortion at 11 weeks [14]. Further investigation is needed to determine the risk of mpox during pregnancy.
A limitation of our study is that samples were stored for prolonged periods at room temperature prior to testing, which could decrease the sensitivity for MPXV due to degradation of nucleic acids. To address this possibility, qPCR for the human β-globin gene was used as an internal control to ensure specimen adequacy; only 0.87% (16/1,848) of samples lacked detectable human β-globin. However, given the relatively large amount of human nucleic acid compared with mpox nucleic acid, even samples with detectable human β-globin could be falsely negative for mpox.
Of note, there was a higher proportion of samples obtained that were positive for CT or NG because positive samples are stored for longer by the public health lab, and nearly all samples obtained prior to August were positive for CT or NG. However, this is unlikely to impact our estimate of mpox prevalence because 15/16 samples positive for MPXV were obtained in August and September 2022, the period during which samples were saved regardless of CT or NG status.
The strengths of our study include the large sample size, inclusion of patients undergoing routine STI screening, surveillance at the peak of the 2022 mpox outbreak, and use of sample types from various anatomic sites. Our data suggests that during outbreaks clinicians should test patients who present with mpox symptoms at the anatomic sites where symptoms are occurring, regardless of gender identity or sexual orientation.
Funding
This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.
Declaration of Competing Interest
The authors have no competing interests to declare.
Data availability
Available upon request. Submit inquiries to cacontag@stanford.edu
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Associated Data
This section collects any data citations, data availability statements, or supplementary materials included in this article.
Data Availability Statement
Available upon request. Submit inquiries to cacontag@stanford.edu