Equine fecal microbiota response to short term antibiotic administration

Though generally safe, research continues to demonstrate negative side effects of antibiotic administration on the gastrointestinal (GIT) microbiota across species. In horses, antibiotic associated diarrhea (AAD) is a life-threatening condition linked to the GIT microbiota. This study tested the hypothesis that short term antibiotic administration to healthy horses would negatively impact the fecal microbiota as measured by their ability to digest nutrients and through fecal shedding of disease-associated-bacteria. Twenty-four horses were assigned to one of four treatment groups: control (CO); potassium penicillin/gentamicin sulfate (KPG); ceftiofur crystalline free acid (EX); trimethoprim/sulfamethoxazole (SMZ); and treated for 4 days. Fecal samples were collected before treatment began (S0), the day after treatment conclusion (S5), and at 10, 14, 21, and 28 days after initiating treatment. Horses had highly individualized responses to antibiotic administration. All horses receiving antibiotics experienced significantly softer stool compared to controls. Lactobacillus spp. were dramatically reduced in all antibiotic treated S5 samples. Horses receiving antibiotics were significantly more likely to test positive for C. difficile or C. perfringens on fecal qPCR. In conclusion, response to antibiotic administration displays high inter-individual variability, but shows changes to the functions of fecal microbiota that may depend on the antibiotic used.

Association of self-directed walking with toxicity moderation during chemotherapy for the treatment of early breast cancer

BACKGROUND

In the field of exercise oncology, there is a need to quantify the potential benefits of moderate, self-directed physical activity during active treatment. In a pooled analysis of three identical single-arm intervention studies, we investigate the association of activity tracker steps with patient-reported toxicities during chemotherapy.

METHODS

Women with early breast cancer who were enrolled in the intervention studies reported their symptom severity every 2-3 weeks throughout chemotherapy, and daily steps were documented through a Fitbit activity tracker. Relative risks (RR) and 95% confidence intervals (CI) were calculated using Poisson regression models with robust variance. For outcomes significant in unadjusted models, adjusted RRs were calculated controlling for race, age, and education level. Tracker step cut point (high step, low step) was determined by the means. Cumulative incidence functions of moderate, severe, and very severe (MSVS) symptoms were estimated using the Kaplan-Meier method and compared using a Cox proportional hazard model.

RESULTS

In a sample of 283 women, mean age was 56 years and 76% were White. Mean tracker-documented steps/week were 29,625, with 55% walking below the mean (low step) and 45% above (high step). In multivariable analysis, high step patients had lower risk for fatigue [RR 0.83 (0.70, 0.99)] (p = 0.04), anxiety [RR 0.59 (0.42, 0.84)] (p = 0.003), nausea [RR 0.66 (0.46, 0.96)] (p = 0.03), depression [RR 0.59 (0.37, 0.03)] (p = 0.02), and ≥ 6 MSVS symptoms [RR 0.73 (0.54, 1.00)] (p = 0.05) and had 36% lower risk for dose reductions [RR 0.64 (95% CI 0.43, 0.97)] (p = 0.03).

CONCLUSION

Self-directed walking at a rate of at least 30,000 steps/week may moderate the severity of treatment side effects during chemotherapy for early breast cancer.

TRIAL NUMBERS

NCT02167932, NCT02328313, NCT03761706.

Clinical guidelines for managing menopausal symptoms in women with (a history of) breast cancer

Background

One in eight women will be diagnosed with breast cancer. At the time of diagnosis, 75% of patients are postmenopausal. Many will receive anti-hormone therapy, which often induces menopausal symptoms. Premenopausal breast cancer patients frequently become postmenopausal as a result of the treatment and often experience menopausal symptoms. The increased incidence of breast cancer, combined with longer survival, has led to an increase in the number of women experiencing menopausal symptoms. Therefore, the management of menopausal symptoms in women with a history or current breast cancer is a relevant and common clinical problem.

Objectives

To provide a clinically useful overview of the steps in the management of menopausal symptoms in women with (a history of) breast cancer.

Materials and Methods

A comprehensive literature review was conducted by authors JS and WT using the PubMed and Medline databases. Abstracts were critically appraised and, where appropriate, the full text was analysed.

Main Outcome Measures

Not applicable.

Results

Depending on the condition, either meta-analyses, randomised controlled trials or retrospective cohorts were identified. No evidence was found for some proposed treatments.

Conclusions

Menopausal symptoms in women with (a history of) breast cancer require a patient-tailored approach. Shared decision making is paramount and adequate up-to-date knowledge can help the breast cancer specialist to advise and guide patients accordingly.

What is new?

A comprehensive, clinically-based overview of evidence-based treatment options for menopausal symptoms in women with (a history of) breast cancer.

Graft function and incidence of cardiac allograft vasculopathy in donation after circulatory-determined death heart transplant recipients

Experience in donation after circulatory-determined death (DCD) heart transplantation (HTx) is expanding. There is limited information on the functional outcomes of DCD HTx recipients. We sought to evaluate functional outcomes in our cohort of DCD recipients. We performed a single-center, retrospective, observational cohort study comparing outcomes in consecutive DCD and donation after brain death (DBD) HTx recipients between 2015 and 2019. Primary outcome was allograft function by echocardiography at 12 and 24 months. Secondary outcomes included incidence of cardiac allograft vasculopathy, treated rejection, renal function, and survival. Seventy-seven DCD and 153 DBD recipients were included. There was no difference in left ventricular ejection fraction at 12 months (59% vs 59%, P = .57) and 24 months (58% vs 58%, P = .87). There was no significant difference in right ventricular function at 12 and 24 months. Unadjusted survival between DCD and DBD recipients at 5 years (85.7% DCD and 81% DBD recipients; P = .45) was similar. There were no significant differences in incidence of cardiac allograft vasculopathy (odds ratio 1.59, P = .21, 95% confidence interval 0.77-3.3) or treated rejection (odds ratio 0.60, P = .12, 95% confidence interval 0.32-1.15) between DBD and DCD recipients. Post-transplant renal function was similar at 1 and 2 years. In conclusion, cardiac allografts from DCD donors perform similarly to a contemporary population of DBD allografts in the medium term.

Comparing Cardiac Mechanics and Myocardial Fibrosis in DBD and DCD Heart Transplant Recipients

BACKGROUND

Heart transplantation (HTx) after donation after circulatory death (DCD) is an expanding practice but is associated with increased warm ischemic time. The impact of DCD HTx on cardiac mechanics and myocardial fibrosis has not been reported. We aimed to compare cardiac mechanics and myocardial fibrosis using cardiovascular magnetic resonance (CMR) imaging in donation after brain death (DBD) and DCD HTx recipients and healthy controls.

METHODS AND RESULTS

Consecutive HTx recipients between March 2015 and March 2021 who underwent routine surveillance CMR imaging were included. Cardiac mechanics were assessed using CMR feature tracking to compute global longitudinal strain, global circumferential strain, and right ventricular free-wall longitudinal myocardial strain. Fibrosis was assessed using late gadolinium enhancement imaging and estimation of extracellular volume. There were 82 (DBD n = 42, DCD n = 40) HTx recipients (aged 53 years, interquartile range 41-59 years, 24% female) who underwent CMR imaging at median of 9 months (interquartile range 6-14 months) after transplantation. HTx recipients had increased extracellular volume (29.7 ± 3.6%) compared with normal ranges (25.9%, interquartile range 25.4-26.5). Myocardial strain was impaired after transplantation compared with controls (global longitudinal strain -12.6 ± 3.1% vs -17.2 ± 1.8%, P < .0001; global circumferential strain -16.9 ± 3.1% vs -19.2 ± 2.0%, P = .002; right ventricular free-wall longitudinal strain -15.7 ± 4.5% vs -21.6 ± 4.7%, P < .0001). There were no differences in fibrosis burden (extracellular volume 30.6 ± 4.4% vs 29.2 ± 3.2%; P = .39) or cardiac mechanics (global longitudinal strain -13.1 ± 3.0% vs -12.1 ± 3.1%, P = .14; global circumferential strain -17.3 ± 2.9% vs -16.6 ± 3.1%, P = .27; right ventricular free-wall longitudinal strain -15.9 ± 4.9% vs -15.5 ± 4.1%, P = .71) between DCD and DBD HTx.

CONCLUSIONS

HTx recipients have impaired cardiac mechanics compared with controls, with increased myocardial fibrosis. There were no differences in early CMR imaging characteristics between DBD and DCD heart transplants, providing further evidence that DCD and DBD HTx outcomes are comparable.

Acquired atrioesophageal fistula: Need it be lethal? Sizing up the problem, diagnostic modalities, and best management

BACKGROUND AND AIM OF THE STUDY

An atrioesophageal fistula is a devastating complication of ablation for atrial fibrillation. For the surgeon facing this dreaded complication, it may be a 'once in a lifetime' case. This review aims to describe the clinical problem and evaluate the outcome of different surgical techniques to start guiding cardiothoracic surgeons toward those which offer the best chance of survival.

METHODS

An electronic search retrieved 125 articles containing 195 cases of atrioesophageal fistula secondary to atrial fibrillation ablation. Reports of pericardio-esophageal or mediastino-esophageal fistula were excluded.

RESULTS

The median age was 61 and 143 (73%) cases occurred in males. Fever (n = 147; 75%) and neurological dysfunction (n = 151; 77%) were the most common symptoms. The median time from ablation to symptom onset was 21 days (interquartile range: 12-28). The most sensitive thoracic imaging modality was computed tomography (n = 135/153; 90%). Immediate deterioration occurred during 11/58 (19%) oesophago-gastro-duodenoscopies. Mortality was lower in patients who had surgery (39%) compared with endoscopic intervention (94%) or conservative management (97%). Patients who had atrial repair combined with esophageal repair or oesophagectomy were more likely to survive than those who had atrial repair alone (OR 6.97; p < .001). Isolation of the esophageal aspect of the fistula conferred an additional survival benefit (OR 5.85; p = .02).

CONCLUSIONS

Fever, neurological symptoms, and chest pain in the context of recent ablation should prompt immediate evaluation. Urgent CT thorax should be arranged and repeated if initially unremarkable. Esophageal instrumentation should be avoided due to the risk of catastrophic air embolism or massive hemorrhage. The best way forward is emergency surgical repair; the combination which offers the best survival benefit is atrial repair combined with esophageal surgery and isolation of the esophageal aspect of the fistula.

Impact of BMI on breast screening participation: a data linkage study

Background

Regular mammographic screening can reduce breast cancer morbidity and mortality. Participation rates are suboptimal in Australia’s fully funded biennial breastscreening program (BreastScreen) for women aged 50-74. Despite obesity being a well-established risk factor for post-menopausal breast cancer, cross sectional data suggests obesity may be a risk factor for non-participation in recommended screening, due to adverse screening experiences. This research aimed to ascertain the link obesity and non-participation by using data linkage of routinely collected data.

Methods

Data for women age eligible for breast screening were linked between the NSW Cancer Registry and the Australian Longitudinal Study of Women’s Health (ALSWH) to create a cohort of women who either participated in screening as recommended or not. Women from the 1946-1951 ALSWH birth cohort were included in the study. These women reported BMI via 8 survey waves. The primary outcome was adherence to breast screening measured by frequency of screening over the follow-up period (1998-2016). Unadjusted risk ratios were calculated using mixed-effects logistic regression for the association between BMI and screening participation.

Results

The study included 2804 linked records of age eligible women (mean age of 52.37[SD 5.47]). 22.8% of the cohort were obese (BMI&gt;30kg/m2). Obesity was significantly associated with non-recommended screening participation (screening within 3 years of last breast screen); odds ratio 1.63 (95% confidence interval 1.32 to 2.00, p &lt; 0.0001).

Conclusions

Obesity has a significantly impact on recommended participation in a nationally provided breast screening program, despite obesity being a risk factor for post- menopausal breast cancer. Optimising participation among higher risk and under-screened women in under utilised breast cancer screening programs is warranted. Development of targeted interventions to increase screening participation among these higher risk women is needed.

Key messages

• Women living with obesity and less likely to participate in recommended breast screening.

• Targeted interventions are needed to optimise participation in breast screening to ensure these higher risk women are not at higher risk of adverse outcomes due to breast cancer.

"Watch Me Grow- Electronic (WMG-E)" surveillance approach to identify and address child development, parental mental health, and psychosocial needs: study protocol

Background

The COVID-19 pandemic and the associated economic recession has increased parental psychosocial stress and mental health challenges. This has adversely impacted child development and wellbeing, particularly for children from priority populations (culturally and linguistically diverse (CALD) and rural/regional communities) who are at an already increased risk of health inequality. The increased mental health and psychosocial needs were compounded by the closure of in-person preventive and health promotion programs resulting in health organisations embracing technology and online services. Watch Me Grow- Electronic (WMG-E) – developmental surveillance platform- exemplifies one such service.

WMG-E was developed to monitor child development and guide parents towards more detailed assessments when risk is identified. This Randomised Controlled Trial (RCT) aims to expand WMG-E as a digital navigation tool by also incorporating parents’ mental health and psychosocial needs. Children and families needing additional assessments and supports will be electronically directed to relevant resources in the ‘care-as-usual’ group. In contrast, the intervention group will receive continuity of care, with additional in-person assessment and ‘warm hand over’ by a ‘service navigator’ to ensure their needs are met.

Methods

Using an RCT we will determine: (1) parental engagement with developmental surveillance; (2) access to services for those with mental health and social care needs; and (3) uptake of service recommendations. Three hundred parents/carers of children aged 6 months to 3 years (recruited from a culturally diverse, or rural/regional site) will be randomly allocated to the ‘care-as-usual’ or ‘intervention’ group. A mixed methods implementation evaluation will be completed, with semi-structured interviews to ascertain the acceptability, feasibility and impact of the WMG-E platform and service navigator.

Conclusions

Using WMG-E is expected to: normalise and de-stigmatise mental health and psychosocial screening; increase parental engagement and service use; and result in the early identification and management of child developmental needs, parental mental health, and family psychosocial needs. If effective, digital solutions such as WMG-E to engage and empower parents alongside a service navigator for vulnerable families needing additional support, will have significant practice and policy implications in the pandemic/post pandemic period.

Trial registration

The trial (Protocol No. 1.0, Version 3.1) was registered with ANZCTR (registration number: ACTRN12621000766819) on July 21st, 2021 and reporting of the trial results will be according to recommendations in the CONSORT Statement.

A uniaxial force and stiffness model of the vagina during laparoscopic sacrocolpopexy

BACKGROUND

Laparoscopic sacrocolpopexy is the preferred procedure for restoring vaginal vault prolapse. An assistant uses a vaginal manipulator to position and tension the vault such that the surgeon can dissect the bladder, rectum and vault to eventually suture a synthetic mesh used to suspend the vagina to the longitudinal anterior vertebral ligament. Vaginal vault manipulation requires application of high forces for long periods of time.

METHODS

This work quantifies the task by measuring and analyzing the interaction forces and the workspace during vaginal vault manipulation. From the measurements we developed a uniaxial model, expressing the increase in interaction force and stiffness of the vagina. By adapting the model parameters, the difference in interaction force and stiffness between moderate and severe prolapse is predicted.

FINDINGS

For moderate prolapse the average interaction force and stiffness start at 2.56 N and 0.11 N mm^-1 in the tensionfree state, and go up to 20.14 N and 0.53 N mm^-1 after complete insertion of the instrument. For severe degrees of prolapse, tissue interaction is much lower starting at 1.68 N and 0.06 N mm^-1 while staying limited to 12.20 N and 0.30 N mm^-1 at full extension.

INTERPRETATION

Population data shows that the stage of prolapse and total vaginal length increase with age and parity. The interaction force and stiffness of the vagina are correlated with this degree of prolapse. By adapting the model parameters a good estimation of the tissue interaction is found for patients with mild and severe prolapse.

Donation after circulatory death hearts recipients compared to donation after brain death heart recipients have comparable systolic left ventricular function and better myocardial strain at 1 year

Purpose

Cardiac transplantation from donation after circulatory death (DCD) has been implemented at our hospital since February 2015. Despite encouraging results some concerns may be raised about the impact of the warm ischemia and reperfusion injury on the myocardium status at longer follow-up. Therefore, we aimed to analyse systolic performance of the left ventricle at 1 year follow in DCD and donation after brain death (DBD) cardiac recipients, as assessed by echocardiography with myocardial deformation imaging.

Methods

We identified 46 consecutive DCD cardiac recipients who were transplanted from February 2015 to August 2018 and we matched them with 46 DBD cardiac recipients. Six and 7 patients from DCD and DBD group, respectively, died in the first-year post transplant. In the remaining patients we have compared the classical echocardiographic measurements as well as global longitudinal strain (GLS) and global circumferential strain (GCS) at 1-year follow-up.

Results

DCD and DBD patients did not present with differences in terms of classical echocardiographic parameters of left ventricular (LV) structure and systolic function at one-year follow-up. LVEDV was similar in DCD and DBD patients (101±24 vs. 95±32 ml, p=0.4 respectively), as well as LVESV (42±13 vs. 42±16 ml, p=0.9, respectively), LV ejection fraction (58±6 vs. 56±8%, p=0.22) and LV mass (156±39 vs. 163±38 gr, p=0.2, respectively). In contrast, myocardial deformation parameters, such as GLS and GCS, were better in DCD than in DBD (16.1 vs. −14.5%, p&lt;0.01; and −25.2 vs. 22.3%, p&lt;0.05, respectively). The diastolic LV function parameters were similar in DCD and DBD group, as evidenced by E wave velocity, A wave velocity and deceleration time of mitral inflow, however E over E prime was lower in DCD than in DBD recipients (7.7±8.7, p&lt;0.05). Fractional area change of the right ventricle was higher in DCD in comparison with DBD (46±7 vs. 40±7%, p&lt;0.01) while right atrial volume index was lower in DCD than in DBD (25±8 vs. 29±9 ml/m2, p&lt;0.01). Other parameters of RV function (systolic excursion of the tricuspid annulus, TAPSE) were similar in both groups.

Conclusion

DCD and DBD heart recipients present with similar systolic LV function at 1-year follow, as assessed by classical echocardiographic parameters. DCD cardiac recipients have better myocardial deformation parameters as assessed by the speckle tracking, better systolic right ventricular function and lower filling pressures of the left ventricle.

Funding Acknowledgement

Type of funding source: None

A 5-year single-center early experience of heart transplantation from donation after circulatory-determined death donors

BACKGROUND

In an effort to address the increasing demand for heart transplantation within the United Kingdom (UK), we established a clinical program of heart transplantation from donation after circulatory-determined death (DCD) donors in 2015. After 5 years, we report the clinical early outcomes and impact of the program.

METHODS

This is a single-center, retrospective, matched, observational cohort study comparing outcomes of hearts transplanted from DCD donors from March 1, 2015 to February 29, 2020 with those from matched donation after brain death (DBD) donors at Royal Papworth Hospital (RPH) (Cambridge, UK). DCD hearts were either retrieved using thoracoabdominal normothermic regional perfusion or the direct procurement and perfusion technique. All DBD hearts were procured using standard cold static storage. The primary outcomes were recipient 30-day and 1-year survival.

RESULTS

During the 5-year study, DCD heart donation increased overall heart transplant activity by 48% (79 for DCD and 164 for DBD). There was no difference in survival at 30 days (97% for DCD vs 99% for DBD, p = 1.00) or 1 year (91% for DCD vs 89% for DBD, p = 0.72). There was no difference in the length of stay in the intensive care unit (7 for DCD vs 6 for DBD days, p = 0.24) or in the hospital (24 for DCD vs 25 for DBD days, p = 0.84).

CONCLUSIONS

DCD heart donation increased overall heart transplant activity at RPH by 48%, with no difference in 30-day or 1-year survival in comparison with conventional DBD heart transplantations. DCD heart donation is set to make a dramatic difference in the number of patients who can benefit from heart transplantation.

Paediatric donation after circulatory determined death heart transplantation using donor normothermic regional perfusion and ex situ heart perfusion: A case report

This is a report of a unique DCD paediatric heart transplant whereby normothermic regional perfusion was used to assess DCD heart function after death followed by ex situ heart perfusion of the graft during transportation from donor to recipient hospitals. The DCD donor was a 9-year-old boy weighing 84 kg. The recipient was 7-year-old boy with failing Fontan circulation and weighed 23 kg. It was an ABO-compatible heart transplantation. The DCD heart was reperfused and assessed using normothermic regional perfusion followed by portable ex situ heart perfusion during transportation. The orthotopic heart transplantation was successful with good graft function and no evidence of rejection on endomyocardial biopsy at 30 days post-transplant. At 1-year follow-up, excellent graft function is maintained, and he is attending school with a good quality of life. DCD heart transplantation in children is a promising solution to reducing paediatric waiting times. The case demonstrates the feasibility of using normothermic regional perfusion in the donor and ex situ heart perfusion during graft transportation. This combination allowed a functional assessment whilst minimizing warm ischaemia resulting in a successful outcome. More research and long-term follow-up are needed in order to benefit from the huge potential that paediatric DCD heart transplantation has to offer.

Heart transplantation from donation after circulatory determined death

Fifty years since the first successful human heart transplant from a non-heart beating donor, this concept of heart transplantation from donation after circulatory determined death (DCD) promises to be one of the most exciting developments in heart transplantation. Heart transplantation has established itself as the best therapeutic option for patients with end-stage heart failure, with the opportunity to provide these patients with a near-normal quality of life. However, this treatment is severely limited by the availability of suitable donor hearts. In recent times, heart transplantation has been limited to using donor hearts from donors following brain stem death. The use of donor hearts from DCD had been thought to be associated with high risk and poor outcomes until recent developments in organ perfusion and retrieval techniques have shown that this valuable resource may provide an answer to the global shortage of suitable donor hearts. With established DCD heart transplant programmes reporting encouraging results, this technique has been shown to be comparable to the current gold standard of donation after brain death (DBD) heart transplantation.

Pain in femoral arteriography: A double-blind, randomized, clinical study comparing safety and efficacy of the iso-osmolar iodixanol 270mgI/ml and the low-osmolar iomeprol 300 mgI/ml in 9 European centers

Purpose: To compare the injection-associated pain and heat sensation after administration of the iso-osmolar contrast medium (IOCM) iodixanol (Visipaque™ 270 mg I/ml) and the low osmolar contrast medium (LOCM) iomeprol (Iomeron™ 300 mg I/ml) in femoral arteriography.

Material and Methods: 352 patients received iodixanol or iomeprol in a prospective, double-blind, randomized, parallel-group clinical trial. The first injection during femoral arteriography (DSA with automated stepping) was standardized. Injection-associated pain and heat sensation, efficacy and safety up to 72 h were evaluated.

Results: The iodixanol group reported significant less injection-associated pain than the iomeprol group after the first injection (7.4% vs. 17.6%; p = 0.007), and after all injections (11% vs. 19.4%; p = 0.045). Iodixanol caused less heat sensation after the first injection ( p = 0.007) and after all injections ( p = 0.029). Heat sensations in the iodixanol group were less intense after all injections ( p < 0.0001). No difference was found between the groups regarding the frequency of patients having adverse reactions (5.1% vs. 4%).

Conclusion: The IOCM iodixanol caused significantly less frequent injection-associated pain and heat sensation than the LOCM iomeprol during femoral arteriography.

Spatiotemporal variation and social determinants of suicide in China, 2006-2012: findings from a nationally representative mortality surveillance system

BACKGROUND

Suicide in China has declined since the 1990s. However, there has been limited investigation of the potential spatiotemporal variation and social determinants of suicide during subsequent periods.

METHOD

Annual suicide counts from 2006 to 2012 stratified by county, 5-year age group (⩾15 years) and gender were obtained from the Chinese Disease Surveillance Points system. Trends and geographic differentials were examined using multilevel negative binomial regression models to explore spatiotemporal variation in suicide, and the role of key sociodemographic factors associated with suicide.

RESULTS

The suicide rate (per 100 000) in China decreased from 14.7 to 9.1, 2006-2012. Rates of suicide were higher in males than females and increased substantially with age. Suicide rates were higher in rural areas compared with urban areas; however, urban-rural disparities reduced over time with a faster decline for rural areas. Within both urban and rural areas, higher rates of suicide were evident in areas with lower socio-economic circumstances (SEC) [rate ratio (RR) 1.85, 95% confidence interval (CI) 1.31-2.62]. Suicide rates varied more than twofold (median RR 2.06) across counties, and were highest in central and southwest regions of China. A high proportion of the divorced population, especially for younger females, was associated with lower suicide rates (RR 0.60, 95% CI 0.46-0.79).

CONCLUSIONS

Geographic variations for suicide should be taken into account in policy making, particularly for older males living in rural areas and urban areas with low SEC. Measures to reduce disparities in socio-economic level and alleviate family relation stress are current priorities.

Human behavior. Sex equality can explain the unique social structure of hunter-gatherer bands

The social organization of mobile hunter-gatherers has several derived features, including low within-camp relatedness and fluid meta-groups. Although these features have been proposed to have provided the selective context for the evolution of human hypercooperation and cumulative culture, how such a distinctive social system may have emerged remains unclear. We present an agent-based model suggesting that, even if all individuals in a community seek to live with as many kin as possible, within-camp relatedness is reduced if men and women have equal influence in selecting camp members. Our model closely approximates observed patterns of co-residence among Agta and Mbendjele BaYaka hunter-gatherers. Our results suggest that pair-bonding and increased sex egalitarianism in human evolutionary history may have had a transformative effect on human social organization.