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According to the Household Pulse Survey conducted by the US Centers for Disease Control and Prevention in January 2023, up to 15% of all US adults had experienced >1 symptoms [...]

BackgroundIn the United States, human papillomavirus (HPV) vaccination has been recommended for young adult men who have sex with men (MSM) since 2011.MethodsThe Vaccine Impact in Men study surveyed MSM and transgender women aged 18-26 years in 3 US cities during 2016-2018. Self-collected anal swab and oral rinse specimens were assessed for 37 types of HPV. We compared HPV prevalence among vaccinated and unvaccinated participants and determined adjusted prevalence ratios (aPR) and 95% confidence intervals (CI).ResultsAmong 1767 participants, 704 (39.8%) self-reported receiving HPV vaccine. Median age at vaccination (18.7 years) was older than age at first sex (15.7 years). Quadrivalent vaccine-type HPV was detected in anal or oral specimens from 475 (26.9%) participants. Vaccine-type HPV prevalence was lower among vaccinated (22.9%) compared with unvaccinated (31.6%) participants; aPR for those who initiated vaccination at age ≤18 years was 0.41 (CI, 0.24-0.57) and at age >18 years was 0.82 (CI, 0.67-0.98). Vaccine effectiveness of at least 1 HPV vaccine dose at age ≤18 years or >18 years was 59% and 18%, respectively.ConclusionsFindings suggest real-world effectiveness of HPV vaccination among young adult MSM. This effect was stronger with younger age at vaccination.

BackgroundHuman papillomavirus (HPV) is a common sexually transmitted infection. Men who have sex with men (MSM) and transgender women (TGW) are at high risk for anal HPV infection and subsequent anal cancer. This study assessed the association of partner discordances with prevalent high-risk anal HPV (HRAHPV) among MSM and TGW.MethodsParticipants were enrolled in the cross-sectional young men's HPV study of gay, bisexual, and other MSM, and TGW, aged 18 to 26 years, from 2 cities. Participants completed a confidential standardized computer-assisted interview and provided self-collected anal swabs for type-specific HPV DNA testing. Multivariate analyses were conducted for 3 discordances of interest (i.e., partner age, race/ethnicity, and concurrent partner) to calculate adjusted odds ratios (aOR) and 95% confidence intervals (CI).ResultsEight hundred sixty-two participants were included for partner race/ethnicity discordance, 601 for partner age discordance, and 581 for concurrent partner analysis. Most reported being older than 21 years, cisgender male, and gay. Adjusted odds of HRAHPV were not significantly increased among participants reporting partner age discrepancy >10 years (aOR, 0.89; 95% CI, 0.51-1.56), partner race/ethnicity discordance (aOR, 0.88; CI, 0.62-1.24), or partner with concurrent partners (aOR, 0.85; 95% CI, 0.50-1.42), compared with those who did not.ConclusionsThis analysis did not identify any partner discordances associated with HRAHPV. Because HPV infection can persist for years, sexual mixing patterns with early partners might be more relevant than the most recent sex partner. Prevalence of HRAHPV was high and could be preventable by preexposure vaccination, as recommended for everyone through age 26 years including MSM and TGW.

BackgroundHigh-risk anal human papillomavirus (HPV) infection is prevalent among men living with human immunodeficiency virus (HIV); the association between 9-valent (9v) high-risk HPV (HR-HPV) vaccine types and abnormal cytology has not been well characterized.MethodsWe followed a prospective cohort study of persons with HIV at 7 HIV clinics in 4 US cities from March 2004 through June 2012. Annually, providers collected separate anal swabs for HPV detection and cytopathologic examination. Among men, we examined prevalence, incidence, and clearance of 9v HR-HPV vaccine types, compared with other HR types, and associations with abnormal cytology to assess potential vaccine impact.ResultsBaseline prevalence of any anal 9v HR-HPV type among men who have sex with men (MSM) and men who have sex with women (MSW) was 74% and 25% (P < .001), respectively. Among 299 MSM, abnormal cytology was detected in 161 (54%) MSM and was associated with the presence of any 9v HR-HPV (relative risk [RR], 1.8 [95% confidence interval {CI}, 1.3-2.6]; P < .001). Among 61 MSW, abnormal anal cytology was detected in 12 (20%) and was associated with the presence of any 9v HR-HPV (RR, 4.3 [95% CI, 1.6-11.5]; P < .001).ConclusionsAmong men with HIV, the prevalence of the 7 HR-HPV types in the 9v vaccine was high and was associated with abnormal cytology. These findings indicate that men with HIV could benefit from prophylactic administration of the 9v HPV vaccine.

ObjectiveWe adapted the Quality Assessment of Diagnostic Accuracy Studies 2 (QUADAS-2) tool for studies of cervical cancer screening and management and used the adapted tool to evaluate the quality of studies included in a systematic review supporting the 2019 Risk-Based Management Consensus Guidelines.MethodsWe evaluated the quality of all studies included in our systematic review for postcolposcopy (n = 5) and posttreatment (n = 23) surveillance using QUADAS-2 criteria. Subsequently, we adapted signaling questions to indications of cervical cancer screening and management. An iterative process was carried out to evaluate interrater agreement between 2 study authors (M.A.C. and N.W.). Discrepant ratings were discussed, and criteria were adapted accordingly. We also evaluated the influence of study quality on risk estimates and between study variation using stratified subgroup meta-analyses.ResultsTwelve signaling questions for bias assessment that were adapted to or newly developed for cervical cancer screening and management are described here. Interrater agreement on bias assessment increased from 70% to 83% during the adaptation process. Detailed assessment of bias and applicability showed that all studies on postcolposcopy management and 90% of studies on posttreatment management had high risk of bias in at least 1 domain. Most commonly, high risk of bias was observed for the patient selection domain, indicating the heterogeneity of study designs and clinical practice in reported studies.ConclusionsThe adapted QUADAS-2 will have broad application for researchers, evidence evaluators, and journals who are interested in designing, conducting, evaluating, and publishing studies for cervical cancer screening and management.

ObjectiveFor the 2019 ASCCP Risk-Based Management Consensus Guidelines, we conducted a systematic review of diagnostic assays for postcolposcopy and posttreatment management.Materials and methodsA literature search was conducted to identify articles reporting on tests/assays for cervical cancer screening, triage, postcolposcopy surveillance, and posttreatment surveillance published between 2012 and 2019 in PubMed and Embase. Titles and abstracts were evaluated by co-authors for inclusion. Included articles underwent full-text review, data abstraction, and quality assessment. Pooled absolute pretest and posttest risk estimates were calculated for studies evaluating management of patients after treatment.ResultsA total of 2,862 articles were identified through the search. Of 50 articles on postcolposcopy, 5 were included for data abstraction. Of 66 articles on posttreatment, 23 were included for data abstraction and were summarized in the meta-analysis. The pooled posttreatment risk of cervical intraepithelial neoplasia (CIN) 2+ in all studies was 4.8% (95% CI = 3.4%-6.8%), ranging from 0.4%-19.5% (τ = 0.57) in individual studies. Among individuals testing negative for human papillomavirus (HPV) posttreatment, the risk of CIN 2+ was 0.69% (95% CI = 0.3%-1.5%); among individuals testing positive for HPV posttreatment, the risk of CIN 2+ was 18.3% (95% CI = 12.1%-26.6%) in all studies. All risk estimates were substantially higher for liquid-based cytology. The HPV-cytology co-testing provided slightly better reassurance compared with HPV alone at the cost of much higher positivity.ConclusionsDespite a large number of published studies on postcolposcopy and posttreatment surveillance, only few met criteria for abstraction and were included in the meta-analysis. More high-quality studies are needed to evaluate assays and approaches that can improve management of patients with abnormal screening.

BackgroundHuman papillomavirus (HPV) prevalence is high among men who have sex with men (MSM), yet little is known about HPV among transgender women (TGW). We assessed HPV prevalence and knowledge among TGW compared with MSM.MethodsWe enrolled TGW and MSM aged 18 to 26 years from clinics in Chicago and Los Angeles during 2012 to 2014. Participants self-reported gender identity, HIV status, HPV knowledge, and vaccination status. Self-collected anal and oral specimens were tested for HPV DNA (37 types); serum was tested for HPV antibodies (4 vaccine types). Prevalence among unvaccinated TGW and MSM was compared using prevalence ratios (PRs) and 95% confidence intervals (CIs). Participants without DNA or serologic evidence of HPV were considered naïve.ResultsAmong 1033 participants, 49 were TGW. Among 44 TGW and 855 MSM who were unvaccinated, any HPV DNA was detected in anal specimens from 39 (88.6%) TGW and 606 (70.9%) MSM (PR, 1.3; 95% CI, 1.1-1.4), and oral specimens from 4 (9.1%) TGW and 81 (9.5%) MSM (PR, 1.0; 95% CI, 0.4-2.5). Antibodies were detected among 37 (84.1%) TGW and 467 (54.6%) MSM (PR, 1.5; 95% CI, 1.3-1.8). Most participants were naïve to 1 or more HPV vaccine type/s, including 29 (65.9%) TGW and 775 (90.6%) MSM (PR, 0.7; 95% CI, 0.6-0.9). Most TGW (55.1%) had never heard of HPV vaccine.ConclusionsAmong TGW, HPV prevalence was high and knowledge was low. Most were still naïve to 1 or more HPV vaccine type. Although vaccination ideally occurs prior to exposure, findings support existing national recommendations to vaccinate TGW and MSM, and suggest additional outreach might increase vaccination.

Background: Myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) can be triggered by infectious agents including severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). However, the impact of the coronavirus disease 2019 (COVID-19) pandemic on ME/CFS prevalence is not well characterized. Methods: In this population-based cross-sectional study, we enrolled a stratified random sample of 9,825 adult participants in the Kaiser Permanente Northern California (KPNC) integrated health system from July to October 2022 to assess overall ME/CFS-like illness prevalence and the proportion that were identified following COVID-19 illness. We used medical record and survey data to estimate the prevalence of ME/CFS-like illness based on self-reported symptoms congruent with the 2015 Institute of Medicine ME/CFS criteria. History of COVID-19 was based on a positive SARS-CoV-2 nucleic acid amplification test or ICD-10 diagnosis code in the medical record, or self-report of prior COVID-19 on a survey. Results: Of 2,745,374 adults in the eligible population, an estimated 45,892 (95% confidence interval [CI]: 32,869, 58,914) or 1.67% (CI 1.20%, 2.15%) had ME/CFS-like illness. Among those with ME/CFS-like illness, an estimated 14.12% (CI 3.64%, 24.6%) developed the illness after COVID-19. Among persons who had COVID-19, those with ME/CFS-like illness after COVID-19 were more likely to be unvaccinated and to have had COVID-19 before June 1, 2021. All persons with ME/CFS-like illness had significant impairment in physical, mental, emotional, social, and occupational functioning compared to persons without ME/CFS-like illness. Conclusions: In a large, integrated health system, 1.67% of adults had ME/CFS-like illness and 14.12% of all persons with ME/CFS-like illness developed it after COVID-19. Though COVID-19 did not substantially increase ME/CFS-like illness in the KPNC population during the study time period, ME/CFS-like illness nevertheless affects a notable portion of this population and is consistent with estimates of ME/CFS prevalence in other populations. Additional attention is needed to improve awareness, diagnosis, and treatment of ME/CFS. [ABSTRACT FROM AUTHOR]

INTRODUCTION: Myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) is a chronic illness characterized by marked functional limitations and fatigue. Electronic health records can be used to estimate incidence of ME/CFS but may have limitations. METHODS: The authors used International Classification of Diseases (ICD) diagnosis codes to identify all presumptive cases of ME/CFS among 9- to 39-year-olds from 2006 to 2017. The authors randomly selected 200 cases for medical record review to classify cases as confirmed, probable, or possible, based on which and how many current clinical criteria they met, and to further characterize their illness. The authors calculated crude annual rates of ME/CFS coding stratified by age and sex using only those ICD codes that had identified confirmed, probable, or possible ME/CFS cases in the medical record review. RESULTS: The authors identified 522 individuals with presumptive ME/CFS based on having = 1 ICD codes for ME/CFS in their electronic medical record. Of the 200 cases selected, records were available and reviewed for 188. Thirty (15%) were confirmed or probable ME/CFS cases, 39 (19%) were possible cases, 119 (60%) were not cases, and 12 (6%) had no medical record available. Confirmed/probable cases commonly had chronic pain (80%) or anxiety/depression (70%), and only 13 (43%) had completed a sleep study. Overall, 37 per 100,000 had ICD codes that identified confirmed, probable, or possible ME/CFS. Rates increased between 2006 and 2017, with the largest absolute increase among those 30-39 years old. CONCLUSIONS: Using ICD diagnosis codes alone inaccurately estimates ME/CFS incidence. [ABSTRACT FROM AUTHOR]

BackgroundMen who have sex with men (MSM) are at risk for cancers attributable to human papillomavirus (HPV), including oropharyngeal cancer. Human papillomavirus vaccination is recommended for US MSM through age 26 years. Oral HPV infection is associated with oropharyngeal cancer. We determined oral HPV prevalence and risk factors among young MSM.MethodsThe Young Men's HPV study enrolled MSM aged 18 through 26 years from clinics in Chicago and Los Angeles during 2012 to 2014. Participants self-reported demographics, sexual behaviors, vaccination and human immunodeficiency virus (HIV) status. Self-collected oral rinse specimens were tested for HPV DNA (37 types) by L1-consensus PCR. We calculated adjusted prevalence ratios (aPR) and 95% confidence intervals (CI) for risk factors associated with oral HPV among participants not previously vaccinated.ResultsOral HPV was detected in 87 (9.4%) of 922; 9-valent vaccine types were detected in 37 (4.0%) of 922. Among HIV-positive participants, 17 (19.3%) of 88 had oral HPV detected. Oral HPV was more prevalent among those reporting first sex at 18 years of age or younger (aPR, 2.44; 95% CI, 1.16-5.12); HIV infection (aPR, 1.99; 95% CI, 1.14-3.48); greater than 5 sex partners within the past month (aPR, 1.93; 95% CI, 1.13-3.31); performing oral sex on greater than 5 partners within the last 3 months (aPR, 1.87; 95% CI, 1.12-3.13); and having greater than 5 male sex partners within the last 3 months (aPR, 1.76; 95% CI, 1.08-2.87). Only 454 (49.2%) of 922 were aware that HPV can cause oropharyngeal cancers.ConclusionsMany oral HPV infections were with types targeted by vaccination. Oral HPV infections were significantly associated with HIV and sexual behaviors. Fewer than half of participants were aware that HPV could cause oropharyngeal cancer.

Background:Nonavalent (9v) human papilloma virus vaccine targets high-risk human papillomavirus (HR-HPV) types 16, 18, 31, 33, 45, 52, 58, and low-risk 6, 11. We examined prevalence, incidence, and clearance of anal and cervical HR-HPV in HIV-infected women. Methods:The SUN Study enrolled 167 US women in 2004-2006. Anal and cervical specimens were collected annually for cytology and identification of 37 HPV types: 14 HR included: 9v 16, 18, 31, 33, 45, 52, 58; non-9v 35, 39, 51, 56, 59, 66, 68. Results:Baseline characteristics of 126 women included: median age 38 years; 57% non-Hispanic black; 67% HIV RNA < 400 copies/mL; 90% CD4 counts ≥200 cells/mm3. HPV prevalence at anus and cervix was 90% and 83%; for 9v HR-HPV types, 67% and 51%; non-9v HR-HPV, 54% and 29%, respectively. The 9v and non-9v HR-HPV incidence rates/100 person-years were similar (10.4 vs 9.5; 8.5 vs 8.3, respectively); 9v clearance rates were 42% and 61%; non-9v 46% and 59%, in anus and cervix, respectively. Conclusions:Anal HR-HPV prevalence was higher than cervical, with lower clearance; incidence was similar. Although prevalence of non-9v HR-HPV was substantial, 9v HR-HPV types were generally more prevalent. These findings support use of nonavalent vaccine in HIV-infected women.

Background:The natural history of anal human papilloma virus (HPV) infection among human immunodeficiency virus (HIV)-infected men is unknown. Methods:Annually, from 2004 to 2012, we examined baseline prevalence, incidence, and clearance of anal HPV infection at 48 months, and associated factors among HIV-infected men. Results:We examined 403 men who have sex with men (MSM) and 96 men who have sex with women (MSW) (median age 42 years for both, 78% versus 81% prescribed cART, median CD4+ T-lymphocyte cell count 454 versus 379 cells/mm3, and 74% versus 75% had undetectable viral load, respectively). Type 16 prevalence among MSM and MSW was 38% versus 14% (P < .001), and incidence 24% versus 7% (P = .001). Type 18 prevalence was 24% versus 8% (P < .001), and incidence 13% versus 4% (P = .027). Among MSM and MSW, clearance of prevalent HPV 16 and HPV 18 was 31% and 60% (P = .392), and 47% and 25% (P = .297), respectively. Among MSM, receptive anal sex (with or without a condom) was associated with persistent HPV 16 (OR 2.24, P < .001). Conclusions:MSM had higher prevalence and incidence of HPV than MSW, but similar clearance. Receptive anal sex may predict cancer risk among HIV-infected MSM.

ObjectiveIt is unknown if human papillomavirus (HPV) serum antibody responses vary by anatomic site of infection. We aimed to assess the seroprevalence for HPV 6, 11, 16 and 18 in association with HPV DNA detection in different anatomic sites among women.MethodsThis cross sectional population-based study analyzed data from 524 women aged 16-64 years living in the San Juan metropolitan area of Puerto Rico (PR). Questionnaires were used to assess demographic and lifestyle variables, while anogenital and blood samples were collected for HPV analysis. Logistic regression models were used to estimate the adjusted prevalence odds ratio (POR) in order to determine the association between HPV DNA infection status in the cervix and anus and serum antibody status, controlling for different potential confounders.ResultsOverall, 46.9% of women had detectable antibodies to one or more types whereas 8.7% had HPV DNA for one or more of these types detected in cervix (4.0%) or anus (6.5%). Women with cervical HPV detection tended to be more HPV seropositive than women without cervical detection (adjusted POR (95%CI): 2.41 (0.90, 6.47), p=0.078); however the type-specific association between cervical DNA and serum antibodies was only significant for HPV 18 (adjusted POR (95% CI): 5.9 (1.03, 33.98)). No significant association was detected between anal HPV and seropositivity (p>0.10).ConclusionDifferences in the anatomic site of infection could influence seroconversion, however, longitudinal studies will be required for further evaluation. This information will be instrumental in advancing knowledge of immune mechanisms involved in anatomic site response.

BackgroundGay, bisexual, and other men who have sex with men (MSM) are at high risk for human papillomavirus (HPV) infection; vaccination is recommended for US males, including MSM through age 26 years. We assessed evidence of HPV among vaccine-eligible MSM and transgender women to monitor vaccine impact.MethodsDuring 2012-2014, MSM aged 18-26 years at select clinics completed a computer-assisted self-interview regarding sexual behavior, human immunodeficiency virus (HIV) status, and vaccinations. Self-collected anal swab and oral rinse specimens were tested for HPV DNA (37 types) by L1 consensus polymerase chain reaction; serum was tested for HPV antibodies (4 types) by a multiplexed virus-like particle-based immunoglobulin G direct enzyme-linked immunosorbent assay.ResultsAmong 922 vaccine-eligible participants, the mean age was 23 years, and the mean number of lifetime sex partners was 37. Among 834 without HIV infection, any anal HPV was detected in 69.4% and any oral HPV in 8.4%, yet only 8.5% had evidence of exposure to all quadrivalent vaccine types. In multivariate analysis, HPV prevalence varied significantly (P < .05) by HIV status, sexual orientation, and lifetime number of sex partners, but not by race/ethnicity.DiscussionsMost young MSM lacked evidence of current or past infection with all vaccine-type HPV types, suggesting that they could benefit from vaccination. The impact of vaccination among MSM may be assessed by monitoring HPV prevalence, including in self-collected specimens.

BackgroundAnal cancer rates are higher for human immunodeficiency virus (HIV)-infected adults than for uninfected adults. Limited published data exist characterizing the incidence of precursor lesions detected by anal cytology.MethodsThe Study to Understand the Natural History of HIV/AIDS in the Era of Effective Therapy was a prospective cohort of 700 HIV-infected participants in 4 US cities. At baseline and annually thereafter, each participant completed a behavioral questionnaire, and healthcare professionals collected anorectal swabs for cytologic examination and human papillomavirus (HPV) detection and genotyping.ResultsAmong 243 participants with negative baseline results of anal cytology, 37% developed abnormal cytology findings (incidence rate, 13.9 cases/100 person-years of follow-up; 95% confidence interval [CI], 11.3-16.9) over a median follow-up duration of 2.1 years. Rates among men having sex with men, among women, and among men having sex with women were 17.9 cases/person-years of follow-up (95% CI, 13.9-22.7), 9.4 cases/person-years of follow-up (95% CI, 5.6-14.9), and 8.9 cases/person-years of follow-up (95% CI, 4.8-15.6), respectively. In multivariable analysis, the number of persistent high-risk HPV types (adjusted hazard ratio [aHR], 1.17; 95% CI, 1.01-1.36), persistent high-risk HPV types except 16 or 18 (aHR, 2.46; 95% CI, 1.31-4.60), and persistent types 16 or 18 (aHR, 3.90; 95% CI, 1.78-8.54) remained associated with incident abnormalities.ConclusionsThe incidence of abnormal anal cytology findings was high and more likely to develop among persons with persistent high-risk HPV.

ObjectiveThe primary cervical cancer screening strategy for women over age 30 is high-risk human papillomavirus (HPV) testing combined with Papanicolaou (Pap) testing (cotesting) every 5 years. This combination strategy is a preventive service that is required by the Affordable Care Act to be covered with no cost-sharing by most health insurance plans. The cotesting recommendation was made based entirely on prospective data from an insured population that may have a lower proportion of women with HPV positive and Pap negative results (ie, discordant results). The discordant group represents a very difficult group to manage. If the frequency of discordant results among underserved women is higher, health care providers may perceive the cotesting strategy to be a less favorable screening strategy than traditional Pap testing every 3 years.Study designThe Centers for Disease Control and Prevention's Cervical Cancer Study was conducted at 15 clinics in 6 federally qualified health centers across Illinois. Providers at these clinics were given the option of cotesting for routine cervical cancer screening. Type-specific HPV detection was performed on residual extracts using linear array.ResultsPap test results were abnormal in 6.0% and HPV was positive in 7.2% of the underserved women screened in this study (mean age, 45.1 years). HPV prevalence decreased with age, from 10.3% among 30- to 39-year-olds to 4.5% among 50- to 60-year-olds. About 5% of the women had a combination of a positive HPV test and normal Pap test results; HPV 16/18 was identified in 14% of discordant women.ConclusionThe rate of discordant results among underserved women was similar to those reported throughout the US in a variety of populations. Typing for HPV 16/18 appears to assist in the management in a small proportion of women with discordant results.

Objectives: Although invasive cervical cancer (ICC) rates have declined since the advent of screening, the annual age-adjusted ICC rate in the United States remains 7.5 per 100,000 women. Failure of recommended screening and management often precedes ICC diagnoses. The study aimed to evaluate characteristics of women with incident ICC, including potential barriers to accessing preventive care. Materials and Methods: We abstracted medical records for patients with ICC identified during 2008–2020 in five U.S. population-based surveillance sites covering 1.5 million women. We identified evidence of adverse social and medical conditions, including uninsured/underinsured, language barrier, substance use disorder, incarceration, serious mental illness, severe obesity, or pregnancy at diagnosis. We calculated descriptive frequencies and compared potential barriers by race/ethnicity, and among women with and without symptoms at diagnosis using chi-square tests. Results: Among 1,606 women with ICC (median age: 49 years; non-White: 47.4%; stage I: 54.7%), the majority (68.8%) presented with symptoms. Forty-six percent of women had at least one identified potential barrier; 15% had multiple barriers. The most common potential barriers among all women were being underinsured/uninsured (17.3%), and language (17.1%). Presence of any potential barrier was more frequent among non-White women and women with than without symptoms (p < 0.05). Conclusions: In this population-based descriptive study of women with ICC, we identified adverse circumstances that might have prevented women from seeking screening and treatment to prevent cancer. Interventions to increase appropriate cervical cancer screening and management are critical for reducing cervical cancer rates. [ABSTRACT FROM AUTHOR]

Background: One of the goals of the Multi-site Clinical Assessment of Myalgic Encephalomyelitis/Chronic Fatigue Syndrome (MCAM) study was to evaluate whether clinicians experienced in diagnosing and caring for patients with myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) recognized the same clinical entity. Methods: We enrolled participants from seven specialty clinics in the United States. We used baseline data (n = 465) on standardized questions measuring general clinical characteristics, functional impairment, post-exertional malaise, fatigue, sleep, neurocognitive/autonomic symptoms, pain, and other symptoms to evaluate whether patient characteristics differed by clinic. Results: We found few statistically significant and no clinically significant differences between clinics in their patients' standardized measures of ME/CFS symptoms and function. Strikingly, patients in each clinic sample and overall showed a wide distribution in all scores and measures. Conclusions: Illness heterogeneity may be an inherent feature of ME/CFS. Presenting research data in scatter plots or histograms will help clarify the challenge. Relying on case–control study designs without subgrouping or stratification of ME/CFS illness characteristics may limit the reproducibility of research findings and could obscure underlying mechanisms. [ABSTRACT FROM AUTHOR]