Cohort Design

The objective of VDH mpox contact tracing was to identify close contacts, advise them of the virus exposure, and offer vaccination to prevent illness or reduce disease severity to those eligible. Symptom monitoring was implemented to expedite early laboratory testing and case identification to reduce further transmission. To be included in the study, a person needed to have either self-reported an MPXV exposure or have been notified by VDH of a recent exposure. Persons who were not residents of Virginia were not eligible for participation. VDH may have been notified of an mpox case by an in-state healthcare provider, clinic, or laboratory; by another state; or by CDC.

We recorded persons with confirmed and probable mpox identified during the symptom monitoring period as persons in whom mpox developed. We defined a confirmed mpox case as positive detection of MPXV through either molecular testing or genomic sequencing. We defined a probable case as detection of orthopoxvirus by molecular testing and no laboratory evidence of another nonvariola orthopoxvirus, detection of orthopoxvirus by immunohistochemistry or genomic sequencing, or detection of orthopoxvirus IgM in a person with no recent history of vaccination (8).

Mpox Contact Tracing and Symptom Monitoring Data Collection

Local health department staff used REDCap (Research Electronic Data Capture, https://www.project-redcap.org) to collect information on mpox close contacts and symptom monitoring during case and contact interviews. Some hospitals monitored their own employees and provided information to local health departments about their healthcare workers (HCWs) exposed at work. Information was entered into a contact import form that included patient demographics, MPXV exposure (e.g., date of last exposure, exposure risk category, location description and setting), mpox vaccination status, HCW status, immunosuppression status, and public health interviewer details. We also linked close contact to a daily mpox monitoring form, which collected information about mpox symptoms (e.g., temperature, rash, chills, swollen lymph nodes), medications taken, and final disposition. The daily mpox monitoring form was completed and submitted by the contact over text message, email, or by phone with a local health department staff member.

The REDCap project also included a case report form, which was adapted from CDC recommendations (9). The form consisted of 248 fields asking about the interaction(s) that may have been the source(s) of infection, mpox vaccination status, mpox hospitalization, mpox symptoms, date of illness onset, residence, demographics (including sexual orientation and gender identity), recent trips and contacts with whom the person had interacted (and the nature of the interactions), laboratory information about the diagnosis, and interview details.

Contact information obtained from case interviews was recorded in the database, but participation in daily mpox symptom monitoring and exposure or case interviews with the local health department was voluntary. Symptom monitoring lasted for 21 days from a person’s last reported exposure.

Cohort Analyses

Figure 1

Figure 1. Mpox contact tracing and symptom monitoring cohort (n = 991), Virginia, USA, May 1–November 1, 2022. Analyzed subcohorts included persons in whom mpox developed (n = 28) and healthcare workers...

We conducted a retrospective cohort study for persons enrolled in the VDH mpox close contact monitoring cohort during May 1–November 1, 2022 (Figure 1). We excluded data for 16 persons who had not completed symptom monitoring within the study time frame and for 1 person for whom duplicate, conflicting information was recorded. For all analyses, we used R Statistical Software version 4.2.2 (The R Foundation for Statistical Computing, https://www.r-project.org).

Mpox Exposure Analysis

We extracted information regarding demographics, MPXV exposure details, assigned exposure risk category (10), monitoring participation, and outcome (disease did vs. did not develop) of persons included in the monitoring cohort. Exposure settings were mutually exclusive because of limitations in the structure of data collection forms. Exposure risk categories (high, intermediate, lower, and none) characterizing personal risk from the nature of the exposure using criteria defined by CDC (10) were assigned by local health department personnel in the contact import form.

We used descriptive statistics to describe select demographic and exposure data for the full cohort, for persons within the cohort in whom mpox developed, and for HCWs exposed at work (Figure 1). Calculated percentages exclude missing values. We used χ² square analysis to evaluate the association between exposure risk category (excluding the none category) and development of mpox.

Mpox Vaccination Analysis

Mpox vaccine administration is mandatorily reported to the Virginia Immunization Information System (https://viis.vdh.virginia.gov); we used this system to determine which persons received in-state mpox vaccine(s) and the date(s) of administration. Matching was completed by using exact date of birth, postal (ZIP) code, and the first 3 letters of first and last names.

To assess vaccine uptake, we described how many and what percentage of persons within the cohort received >1 dose of an mpox vaccine. We used those descriptive statistics to measure completion of the 2-dose series. We also specifically assessed vaccine uptake for persons within the cohort in whom mpox developed. Last, to determine if there were differences across exposure risk categories, we measured vaccine uptake by exposure risk category.

We measured vaccination timeliness as time in days from reported MPXV exposure to first dose of an mpox vaccine for the full cohort and for persons in whom mpox developed. We did not analyze preexposure vaccination timeliness. We also assessed timeliness by using CDC postexposure recommendations (7), describing how many doses were administered within 4 and 14 days of the reported exposure.

Cohort Characteristics

During May 1–November 1, 2022, a total of 991 persons were enrolled in Virginia’s mpox close contact monitoring cohort and ended their 21-day monitoring period during the study period. Among the 932 persons for whom data about their method of participation were available, 491 (52.7%) used email, 239 (25.6%) reported directly to their local health department, 143 (15.3%) self-monitored, and 59 (0.06%) used text messaging to access surveys. Of 991 contact records, 943 (95.2%) were complete and 48 (4.8%) were incomplete. During symptom monitoring, 99 (10.0%) contacts were not available for follow-up and 20 (2.2%) declined or no longer needed monitoring (e.g., their reported exposure was beyond the 21-day symptom monitoring period, not determined to be a close contact, or from a person later determined to be MPXV negative). Eleven (1.1%) contact investigations were transferred to another jurisdiction. Of the 28 persons in the close contact monitoring cohort in whom mpox developed, 26 (92.9%) completed their case interview. Among 897 persons in the cohort for whom sex was recorded, 494 (55.1%) were male and 403 (44.9%) female (Table 1). Age information was available for 824 persons; median age was 35 (interquartile range [IQR] 26–49) years.

Persons with Mpox Cohort Characteristics

Within the cohort of 991 persons, mpox developed in 28 (2.8%) while they were being monitored for symptoms (Figure 1); 27 cases were confirmed and 1 was probable. Twenty-seven (96.4%) persons were recorded as male and 1 (3.6%) as female (Table 1). The median age was 36 (IQR 31–40) years. Among 27 persons with mpox who reported their race, 15 (55.6%) self-identified as White, 11 (40.7%) as Black, and 1 (3.7%) as Native Hawaiian or Other Pacific Islander. Among 25 persons with mpox who reported ethnicity, 8 (32.0%) self-identified as Hispanic. Information on sexual orientation and gender identity was available for 20 persons with mpox; 19 (94.7%) self-identified as bisexual or gay cisgender men, and 1 (5%) self-identified as a straight cisgender woman.

Reported Mpox Exposure Settings

Figure 2

Figure 2. Reported monkeypox virus exposure setting categories from mpox contact tracing and symptom monitoring cohort (n = 991), Virginia, USA, May 1–November 1, 2022. For persons in whom mpox developed while...

Exposure information was available for 943 persons in the cohort (Figure 1). Of those, 326 (34.5%) were exposed in households, 310 (32.9%) in healthcare settings, 145 (15.4%) at private gatherings or parties, 58 (6.2%) in workplaces, 52 (5.5%) in an airport or airplane, 33 (3.5%) in a school, 14 (1.5%) in other congregate settings, and 5 (0.5%) in a long-term-care facility (Figure 2).

Reported Mpox Exposures in Persons in Whom Mpox Developed

Reported exposure setting information was available for 18 of the 28 persons in whom mpox developed; 10 reported MPXV exposures from a household (55.6%) and 7 from a private gathering or party (38.9%). One (5.6%) person was being monitored for exposure on an airplane or in an airport, but investigators later determined that that was not the most likely source of infection (Figure 2).

Among the 25 persons in whom mpox developed and who provided additional information about their MPXV exposure, 22 (88.0%) reported recent sexual activity. Seven men reported sexual activity with multiple male partners, and 3 of them reported that their partners were anonymous. Mpox developed in 1 straight cisgender woman within the cohort after a reported sexual exposure from a male household contact. Of the 3 persons in whom mpox developed without their having reported recent sexual contact, 2 persons reported that their exposure was from a congregate setting (specifically, a prison and a convention event) and 1 person reported close nonsexual contact. Geographic exposure location was available for 24 persons: 18 (75.0%) reported in-state exposures and 6 (25.0%) reported exposures during out-of-state domestic travel (to Georgia, North Carolina, New York, and Massachusetts) or international travel (Mexico).

Mpox Exposure Risk Categories

Among 971 persons for whom exposure risk categories were assigned by using CDC criteria (10) (Figure 1), 374 (38.5%) were assigned intermediate risk, 360 (37.1%) lower risk, 225 (23.2%) higher risk, and 12 (1.2%) no risk (Table 2). Among the 28 persons in whom mpox developed for whom an exposure risk category was assigned, 20 (71.4%) exposures were categorized as high risk, 4 (14.3%) as intermediate risk, and 3 (10.7%) as lower risk; 1 person (3.6%) was not assigned an exposure risk category (Table 2). The degree of association between assigned exposure risk category and likelihood of mpox development was high (p<0.001) (Table 2).

HCW Occupational Exposures

A total of 275 persons self-identified as HCWs who were exposed at work (Figure 1). Among the HCWs who reported their role, 2 (2.1%) were administrators, 14 (15.4%) worked in emergency medical services, 1 (1.1%) was an imaging technician, 27 (29.7%) were nurses, 7 (7.7%) were nurse assistants, 14 (15.4%) worked as other direct care HCWs, 1 (1.1%) worked as an other nondirect care HCW, 21 (23.1%) were healthcare providers, and 3 (3.3%) worked in registration. Among 273 HCWs exposed at work for whom an exposure risk category was assigned, 34 (12.5%) exposures were categorized as high risk, 48 (17.6%) as intermediate risk, 180 (65.9%) as low risk, and 11 (4.0%) as no risk (e.g., personal protective equipment was appropriately worn during exposure encounter[s]).

Vaccine Uptake

Of the 991 persons in the cohort, 333 (33.6%) received >1 vaccine dose that was recorded in Virginia’s Immunization Information System (Table 3; Figure 1). In addition, 212 received a second dose, representing 63.7% of those available for follow-up and indicating that 21.4% of the cohort completed the mpox series during May–November 2022.

Of the 225 persons identified as having had a high-risk exposure, 121 (53.8%) received >1 dose. A total of 166 (44.3%) of 374 persons who had intermediate risk exposures received >1 dose, and 35 (9.7%) of 360 persons self-identified as having lower exposure risk received >1 dose.

Information about exposure and vaccination dates were available for 322 of the 333 vaccinated persons. A total of 295 (91.6%) persons received postexposure vaccination, and 27 (8.4%) received preexposure prophylaxis (Table 3).

Timeliness of Postexposure Vaccination

Among the 295 persons who received postexposure vaccination, the median time of first vaccine administration after MPXV exposure was 8 (IQR 4–12) days (Table 3). In terms of timeliness of recommended postexposure administration, 82 (27.8%) persons were vaccinated <4 days after MPXV exposure and 252 (85.4%) were vaccinated <14 days after exposure (Table 3). Information on exposure and vaccination dates were available for 3 of the vaccinated persons in whom mpox developed; all had received postexposure prophylaxis within 14 days (4, 11, and 12 days).