Characteristics of mpox positive, versus mpox negative, and mpox unsuspected clients from the Centre of Sexual Health, Public Health Service of Amsterdam, 20 May to 15 September 2022.

BACKGROUND: In May 2022, an outbreak of mpox (monkeypox) in men-who-have-sex-with-men (MSM) emerged and quickly affected over 100 countries. In the early stages of the outbreak, overlap in symptoms with sexually transmitted infections (STI) made triage for mpox testing challenging. More information was needed on whom to screen and the main route of transmission. OBJECTIVES: We aimed to identify characteristics of mpox cases to further strengthen case definitions. We also compared Cycle threshold (Ct) values of the DNA positive mpox samples as a proxy for viral load by body location. METHODS: From 20 May 2022 to 15 September 2022, we tested all MSM who presented with malaise, and/or ulcerative lesions, and/or proctitis and/or a papular-vesicular-pustular eruption attending the Centre of Sexual Health in Amsterdam, the Netherlands, for mpox, with a PCR test. In the same period, 6932 MSM mpox unsuspected clients were not tested. We compared those tested positive for mpox with those tested negative and those unsuspected for mpox. RESULTS: Of the 374 MSM tested, 135 (36%) were positive for mpox. The mpox-positive MSM were older (median age, respectively, 36, 34 and 34 years, p = 0.019) and more often lived with HIV (30% vs. 16% and 7%, p < 0.001). Furthermore, mpox-positive patients more often reported receptive anal sex without a condom, sexualized drug use, more sex partners, and were more often diagnosed with bacterial STI (p < 0.001). Systemic symptoms and anogenital lesions were associated with mpox infection. For mpox-positive patients, anal samples (p = 0.009) and lesional samples (p = 0.006) showed significantly lower median mpox Ct values compared to throat samples. CONCLUSIONS: Mpox-positive patients more often reported receptive anal sex without a condom, had more sex partners and more often lived with HIV. Our results suggest that in the current mpox outbreak among MSM, sexual transmission is the main route.

Accurate staging of non-metastatic colon cancer with CT: the importance of training and practice for experienced radiologists and analysis of incorrectly staged cases.

PURPOSE: To investigate whether locoregional staging of colon cancer by experienced radiologists can be improved by training and feedback to minimize the risk of over-staging into the context of patient selection for neoadjuvant therapy and to identify potential pitfalls of CT staging by characterizing pathologic traits of tumors that remain challenging for radiologists. METHODS: Forty-five cases of stage I-III colon cancer were included in this retrospective study. Five experienced radiologists evaluated the CTs; 5 baseline scans followed by 4 sequential batches of 10 scans. All radiologists were trained after baseline scoring and 2 radiologists received feedback. The learning curve, diagnostic performance, reader confidence, and reading time were evaluated with pathologic staging as reference. Pathology reports and H&E slides of challenging cases were reviewed to identify potential pitfalls. RESULTS: Diagnostic performance in distinguishing T1-2 vs. T3-4 improved significantly after training and with increasing number of reviewed cases. Inaccurate staging was more frequently related to under-staging rather than over-staging. Risk of over-staging was minimized to 7% in batch 3-4. N-staging remained unreliable with an overall accuracy of 61%. Pathologic review identified two tumor characteristics causing under-staging for T-stage in 5/7 cases: (1) very limited invasive part beyond the muscularis propria and (2) mucinous composition of the invading part. CONCLUSION: The high accuracy and specificity of T-staging reached in our study indicate that sufficient training and practice of experienced radiologists can ensure high validity for CT staging in colon cancer to safely use neoadjuvant therapy without significant risk of over-treatment, while N-staging remained unreliable.

A randomised controlled trial testing the efficacy of Fit after COVID, a cognitive behavioural therapy targeting severe post-infectious fatigue following COVID-19 (ReCOVer): study protocol.

BACKGROUND: Coronavirus disease 2019 (COVID-19) results in debilitating long-term symptoms, often referred to as Post-Acute Sequelae of SARS-CoV-2 Infection (PASC), in a substantial subgroup of patients. One of the most prevalent symptoms following COVID-19 is severe fatigue. Prompt delivery of cognitive behavioural therapy (CBT), an evidence-based treatment that has shown benefit in reducing severe fatigue in other conditions, may reduce post-COVID-19 fatigue. Based on an existing CBT protocol, a blended intervention of 17 weeks, Fit after COVID, was developed to treat severe fatigue after the acute phase of infection with SARS-CoV-2. METHOD: The ReCOVer study is a multicentre 2-arm randomised controlled trial (RCT) to test the efficacy of Fit after COVID on severe post-infectious fatigue. Participants are eligible if they report severe fatigue 3 up to and including 12 months following COVID-19. One hundred and fourteen participants will be randomised to either Fit after COVID or care as usual (ratio 1:1). The primary outcome, the fatigue severity subscale of the Checklist Individual Strength (CIS-fatigue), is assessed in both groups before randomisation (T0), directly post CBT or following care as usual (T1), and at follow-up 6 months after the second assessment (T2). In addition, a long-term follow-up (T3), 12 months after the second assessment, is performed in the CBT group only. The primary objective is to investigate whether CBT will lead to a significantly lower mean fatigue severity score measured with the CIS-fatigue across the first two follow-up assessments (T1 and T2) as compared to care as usual. Secondary objectives are to determine the proportion of participants no longer being severely fatigued (operationalised in different ways) at T1 and T2 and to investigate changes in physical and social functioning, in the number and severity of somatic symptoms and in problems concentrating across T1 and T2. DISCUSSION: This is the first trial testing a cognitive behavioural intervention targeting severe fatigue after COVID-19. If Fit after COVID is effective in reducing fatigue severity following COVID-19, this intervention could contribute to alleviating the long-term health consequences of COVID-19 by relieving one of its most prevalent and distressing long-term symptoms. TRIAL REGISTRATION: Netherlands Trial Register NL8947 . Registered on 14 October 2020.

Differences in prevalence of hepatitis B virus infection and genotypes between ethnic populations in Suriname, South America.

Epidemiological data on hepatitis B virus (HBV) are needed to benchmark HBV elimination goals. We recently assessed prevalence of HBV infection and determinants in participants attending the Emergency Department in Paramaribo, Suriname, South America. Overall, 24.5% (95%CI = 22.7-26.4%) of participants had anti-Hepatitis B core antibodies, which was associated with older age (per year, adjusted Odds Ratio [aOR] = 1.03, 95%CI = 1.02-1.04), Afro-Surinamese (aOR = 1.84, 95%CI = 1.52-2.19) and Javanese ethnicity (aOR = 1.63, 95%CI = 1.28-2.07, compared to the grand mean). 3.2% of participants were Hepatitis B surface Ag-positive, which was also associated with older age (per year, aOR = 1.02, 95%CI = 1.00-1.04), Javanese (aOR = 4.3, 95%CI = 2.66-6.95) and Afro-Surinamese ethnicity (aOR = 2.36, 95%CI = 1.51-3.71). Sex, nosocomial or culturally-related HBV transmission risk-factors were not associated with infection. Phylogenetic analysis revealed strong ethnic clustering: Indonesian subgenotype HBV/B3 among Javanese and African subgenotypes HBV/A1, HBV/QS-A3 and HBV/E among Afro-Surinamese. Testing for HBV during adulthood should be considered for individuals living in Suriname, specifically with Javanese and Afro-Surinamese ancestry.

Prognostic value of patient-reported quality of life for survival in oesophagogastric cancer: analysis from the population-based POCOP study.

BACKGROUND: Accumulating evidence of trials demonstrates that patient-reported health-related quality of life (HRQoL) at diagnosis is prognostic for overall survival (OS) in oesophagogastric cancer. However, real-world data are lacking. Moreover, differences in disease stages and tumour-specific symptoms are usually not taken into consideration. The aim of this population-based study was to assess the prognostic value of HRQoL, including tumour-specific scales, on OS in patients with potentially curable and advanced oesophagogastric cancer. METHODS: Data were derived from the Netherlands Cancer Registry and the patient reported outcome registry (POCOP). Patients included in POCOP between 2016 and 2018 were stratified for potentially curable (cT1-4aNallM0) or advanced (cT4b or cM1) disease. HRQoL was measured with the EORTC QLQ-C30 and the tumour-specific OG25 module. Cox proportional hazards models assessed the impact of HRQoL, sociodemographic and clinical factors (including treatment) on OS. RESULTS: In total, 924 patients were included. Median OS was 38.9 months in potentially curable patients (n = 795) and 10.6 months in patients with advanced disease (n = 129). Global Health Status was independently associated with OS in potentially curable patients (HR 0.89, 99%CI 0.82-0.97), together with several other HRQoL items: appetite loss, dysphagia, eating restrictions, odynophagia, and body image. In advanced disease, the Summary Score was the strongest independent prognostic factor (HR 0.75, 99%CI 0.59-0.94), followed by fatigue, pain, insomnia and role functioning. CONCLUSION: In a real-world setting, HRQoL was prognostic for OS in patients with potentially curable and advanced oesophagogastric cancer. Several HRQoL domains, including the Summary Score and several OG25 items, could be used to develop or update prognostic models.

Adherence to event-driven HIV PrEP among men who have sex with men in Amsterdam, the Netherlands: analysis based on online diary data, 3-monthly questionnaires and intracellular TFV-DP.

INTRODUCTION: Event-driven pre-exposure prophylaxis (edPrEP) with oral tenofovir disoproxil fumarate (TDF)/emtricitabine (FTC) is highly effective for preventing HIV acquisition in men who have sex with men (MSM) and is preferred over daily PrEP by some MSM. However, it is largely unknown how well MSM adhere to edPrEP. We then aimed to assess PrEP protection during CAS among MSM using edPrEP and participating in the Amsterdam PrEP demonstration project (AMPrEP). METHODS: We analysed data from participants enrolled in AMPrEP who were taking edPrEP. We measured adherence through (1) a mobile application in which sexual behaviour and PrEP-use were recorded daily, (2) three-monthly self-completed questionnaires and (3) dried blood spot (DBS) samples collected around six, twelve and twenty-four months after PrEP initiation. We assessed the proportion of days with condomless anal sex (CAS) acts that were protected by PrEP, per partner type (i.e. steady partners, known casual partners, unknown casual partners), and the proportion of three-month periods during which PrEP was correctly used. Intracellular TFV-diphosphate (TFV-DP) concentrations were determined from DBS. Good adherence was defined as at least one tablet before and one tablet within 48 hours after a CAS act. RESULTS: Between 11 September 2015 and 6 October 2019, 182 of 376 MSM (48.4%) used edPrEP for at least one three-month period. Of the 8224 CAS days that were reported in the app during edPrEP-use, we observed good protection for most CAS days involving steady partners (n = 1625/2455, 66.9%), known casual partners (n = 3216/3472, 92.6%) and unknown casual partners (n = 2074/2297, 90.3%). Men reported consistently correct PrEP-use in 851 (81.4%) of the 1046 three-month periods of edPrEP-use. The median TFV-DP concentration was 591 fmol/sample (interquartile range = 270 to 896). CONCLUSIONS: Adherence to edPrEP was high as determined from the online app and questionnaire. DBS measurements were consistent with two to three tablets per week on average.

Changes in mental health and drug use among men who have sex with men using daily and event-driven pre-exposure prophylaxis: Results from a prospective demonstration project in Amsterdam, the Netherlands.

BACKGROUND: Gay, bisexual and other men who have sex with men (GBMSM) are at increased risk of mental health disorders and drug use. In GBMSM taking pre-exposure prophylaxis (PrEP) for HIV, the proportion engaging in risk behaviors could increase due to decreased perception in HIV risk. In turn, this could leave them further susceptible to mental health disorders. METHODS: The AMsterdam PrEP study (AMPrEP) is a demonstration project offering a choice of daily PrEP or event-driven PrEP regimen at the STI clinic of the Public Health Service of Amsterdam. Eligible participants were HIV-negative GBMSM and transgender people at risk of HIV, aged ≥18 years. We assessed anxiety and depressive mood disorders (Mental Health Inventory 5), sexual compulsivity (Sexual Compulsivity Scale), alcohol use disorder (Alcohol Use Disorder Identification Test), and drug use disorder (Drug Use Disorder Identification Test) using yearly self-administered assessments (August 2015-September 2018). The proportion of mental health problems were analyzed and changes over time and between regimen were assessed using a logistic regression model. Variables associated with the development or recovery of disorders were assessed using a multistate Markov model. OUTCOMES: Of 376 enrolled, we analyzed 341 participants with data at baseline and at least one follow-up visit. During a median follow-up of 2.5 years (IQR=2.3-2.7), the proportion assessed with sexual compulsivity decreased from 23% at baseline to 10% at the last visit (p<0.001) and drug use disorder decreased from 38% at baseline to 31% at the last visit (p = 0.004). No changes occurred in proportion assessed with anxiety/depressive mood disorders (20% at baseline, 18% at last visit, p = 0.358) or alcohol use disorder (28% at baseline, 22% at the last visit, p = 0.106). During follow-up, participants reported significant less use of alcohol (p<0.001), nitrites (p<0.001) and ecstasy (p<0.001). We found no differences between daily and event-driven PrEP users. The development and recovery of disorders during follow-up were highly interrelated. INTERPRETATION: Mental health disorders are prevalent among those initiating PrEP. We did not find increases in mental health disorders during PrEP use, but rather a decrease in sexual compulsivity and drug use disorders. The initial prevalence of mental health disorders in our study point at the continuous need to address mental health disorders within PrEP programs. FUNDING: ZonMw, H-TEAM, Internal GGD research funds, Aidsfonds, Stichting AmsterdamDiner Foundation, Gilead Sciences, Janssen Pharmaceutica, M A C AIDS Fund, and ViiV Healthcare.

Multivalent weak interactions enhance selectivity of interparticle binding.

Targeted drug delivery critically depends on the binding selectivity of cargo-transporting colloidal particles. Extensive theoretical work has shown that two factors are necessary to achieve high selectivity for a threshold receptor density: multivalency and weak interactions. Here, we study a model system of DNA-coated particles with multivalent and weak interactions that mimics ligand-receptor interactions between particles and cells. Using an optomagnetic cluster experiment, particle aggregation rates are measured as a function of ligand and receptor densities. The measured aggregation rates show that the binding becomes more selective for shorter DNA ligand-receptor pairs, proving that multivalent weak interactions lead to enhanced selectivity in interparticle binding. Simulations confirm the experimental findings and show the role of ligand-receptor dissociation in the selectivity of the weak multivalent binding.

Nasal carriage of methicillin-resistant Staphylococcus aureus (MRSA) among undocumented migrants and uninsured legal residents in Amsterdam, the Netherlands: a cross-sectional study.

BACKGROUND: Nasal carriage of methicillin-resistant Staphylococcus aureus (MRSA) is associated with an increased risk of infection. Colonization with MRSA is observed in < 1% of the general Dutch population. Increased risk for MRSA carriage is known to occur in several key groups, one of which is asylum seekers. However, little is known about MRSA carriage among undocumented migrants and uninsured legal residents. This study aimed to determine the prevalence of nasal MRSA carriage among these groups in Amsterdam, the Netherlands. METHODS: In this cross-sectional study, between October 2018 and October 2019, undocumented migrants and uninsured legal residents aged 18 years or older who were able to understand one of the study languages were recruited at an NGO health care facility in Amsterdam, the Netherlands, for general practitioner (GP) consultations. Participants were asked questions on demographics, migration history, antibiotic use and other possible risk factors for MRSA carriage and were screened for nasal MRSA carriage by selective culturing e-swabs. Characteristics of MRSA-negative and MRSA-positive participants were compared using univariable logistic regression analysis with Firth's correction. RESULTS: Of the 3822 eligible patients, 760 were screened for nasal MRSA carriage (19.9%). Of the 760 participants, over half were male (58%; 442/760) and originated mainly from Africa (35%; 267/760), Asia (30%; 229/760) and North or South America (30%; 227/760). In total, 705/760 participants (93%) were undocumented migrants and 55/760 (7%) were uninsured legal residents of Amsterdam. The overall prevalence of nasal MRSA carriage was 2.0% (15/760) (95%CI 1.1 to 3.2%), with no difference between undocumented migrants (14/705) (2.0, 95%CI 1.1 to 3.3%) and uninsured legal residents (1/55) (1.8, 95%CI 0.1 to 9.7%). Genotyping showed no clustering of the 15 isolates. MRSA carriage was not associated with sociodemographic, migration history or other possible risk factors. Nevertheless, this study had limited power to detect significant determinants. Three participants (3/15; 20%) harbored Panton-Valentine leukocidin (PVL)-positive isolates. CONCLUSION: Even though our study population of undocumented migrants and uninsured legal residents had a higher prevalence of nasal MRSA carriage compared to the general Dutch population, the prevalence was relatively low compared to acknowledged other high-risk groups.

Inter-particle biomolecular reactivity tuned by surface crowders.

The rate at which colloidal particles can form biomolecular bonds controls the kinetics of applications such as particle-based biosensing, targeted drug delivery and directed colloidal assembly. Here we study how the reactivity of the particle surface depends on its molecular composition, quantified by the inter-particle rate of aggregation in an optomagnetic cluster experiment. Particles were functionalized with DNA or with proteins for specific binding, and with polyethylene glycol as a passive surface crowder. The data show that the inter-particle binding kinetics are dominated by specific interactions, which surprisingly can be tuned by the passive crowder molecules for both the DNA and the protein system. The experimental results are interpreted using model simulations, which show that the crowder-induced decrease of the particle surface reactivity can be described as a reduced reactivity of the specific binder molecules on the particle surface.

The Pelvic Girdle Pain deadlock: 2. Topics that, so far, have remained out of focus.

INTRODUCTION: In our preceding paper, we concluded that Pelvic Girdle Pain (PGP) should be taken seriously. Still, we do not know its causes. Literature reviews on treatment fail to reveal a consistent pattern, and there are patients who do not respond well to treatment. We designated the lack of progress in research and in the clinic as 'deadlock', and proposed a 'deconstruction' of PGP, that is to say, taking PGP apart into its relevant dimensions. PURPOSE: We examine the proposition that PGP may emerge as local inflammation. Inflammation would be a new dimension to be taken into account, between biomechanics and psychology. To explore the consequences of this idea, we present four different topics that, so far, have remained out of focus. One: The importance of microtrauma. Two: Ways to counteract chronification. Three: The importance of sickness behaviour when systemic inflammation turns into neuroinflammation of the brain. And Four: The mainly emotional and cognitive nature of chronic pain, and how aberrant neuroinflammation may render chronic pain intractable. For intractable pain, sleep and stress management are promising treatment options. IMPLICATIONS: The authors hope that the present paper helps to stimulate the flexible creativity that is required to deal with the biological and psychological impact of PGP. Measuring inflammatory mediators in PGP should be a research priority. It should be understood that the boundaries between biology and psychology are becoming blurred. Clinicians must frequently monitor pain, disability, and mood, and be ready to switch treatment whenever the patient does not improve.

The pelvic girdle pain deadlock: 1. Would 'deconstruction' help?

INTRODUCTION: Pelvic Girdle Pain (PGP) is an important clinical problem that deserves more attention. Several treatment regimens have been presented that appear to be somewhat promising, but it was reported that about 10% of patients still suffer from the problems 11 years after their inception. This situation should be improved. PURPOSE: We present a personalized history, with first the acceptance of the concept of 'PGP', around 2005, and then continued problems in really understanding PGP's nature and causes. We propose to engage in 'deconstruction' of PGP, that is, disentangling the large variety of processes involved. IMPLICATIONS: Deconstructing PGP is a venture into the unknown. Still, science should proceed on the basis of what we know already. To understand PGP, experts emphasize the importance of biomechanics or of psychology, and we propose to insert 'inflammation' between these two levels of understanding, that is to say, the full development from low grade local inflammation to systemic inflammation and neuroinflammation. Inflammation is bidirectionally related to biomechanical as well as psychological processes. For clinicians, challenging our "beliefs and understanding of PGP, rather than being 'stuck' with a preferred modus operandi" has major practical implications. It requires continuous monitoring of the patient, and a willingness to change direction. More scientific disciplines are relevant to understanding, and treating, PGP than a single human being can master. Creative flexibility of clinicians would be a promising starting point to improve overall treatment effects in PGP.

[18F]FDG PET/CT in the staging of inflammatory breast cancer: A systematic review.

Up to 78 % of patients with inflammatory breast cancer (IBC) present with axillary lymph node involvement and up to 40 % with distant metastases. Previous studies indicate that 2-deoxy-2-(18F)fluoro-d-glucose ([18F]FDG) positron emission tomography/computed tomography (PET/CT) might be used for initial staging in patients with inflammatory breast cancer (IBC). In other cancer types, [18F]FDG PET/CT has been demonstrated to be a sensitive technique, providing complementary information on locoregional and distant disease to conventional imaging modalities. This systematic review showed that 18F]FDG PET/CT detects additional locoregional lymph node metastases and distant metastases in 10.3 % of patients, that were not detected with standard staging imaging. Compared with conventional imaging procedures, [18F]FDG PET/CT had better diagnostic performance for detection of locoregional and distant metastases and should standardly be used in the diagnostic work-up of IBC patients.

Knowledge of the audiological effects, symptoms and practices related to personal listening devices of health sciences students at a South African university.

OBJECTIVE: This study aimed to determine the knowledge of first year health sciences students at a South African university regarding hearing loss and symptoms attributable to personal listening devices and their practices concerning the use of personal listening devices. METHOD: This was a cross-sectional study carried out using an anonymous self-administered questionnaire. RESULTS: Of 336 students, 269 (80.1 per cent) completed the questionnaire. While most participants could identify symptoms that could be caused by extensive use of personal listening devices, almost 30 per cent did not know that it could cause permanent hearing loss. Personal listening devices were used by 90.7 per cent of participants, with 77.8 per cent having used them for more than five years. Use was at a high volume in 14.9 per cent of participants and for more than 2 hours per day in 52.7 per cent. CONCLUSION: The findings indicate the need for an educational programme to inform students as to safe listening practices when using personal listening devices.

Probing Flow-Induced Biomolecular Interactions With Micro-Extensional Rheology: Tau Protein Aggregation.

Biomolecules in solutions subjected to extensional strain can form aggregates, which may be important for our understanding of pathologies involving insoluble protein structures where mechanical forces are thought to be causative (e.g., tau fibers in chronic traumatic encephalopathy (CTE)). To examine the behavior of biomolecules in solution under mechanical strains requires applying rheological methods, often to very small sample volumes. There were two primary objectives in this investigation: (1) To probe flow-induced aggregation of proteins in microliter-sized samples and (2) To test the hypothesis that tau protein aggregates under extensional flow. Tau protein (isoform:3R 0 N; 36.7 kDa) was divided into 10 µl droplets and subjected to extensional strain in a modified tensiometer. Sixteen independent tests were performed where one test on a single droplet comprised three extensional events. To assess the rheological performance of the fluid/tau mixture, the diameter of the filament that formed during extension was tracked as function of time and analyzed for signs of aggregation (i.e., increased relaxation time). The results were compared to two molecules of similar and greater size (Polyethylene Oxide: PEO35, 35 kDa and PEO100, 100 kDa). Analysis showed that the tau protein solution and PEO35 are likely to have formed aggregates, albeit at relatively high extensional strain rates (∼10 kHz). The investigation demonstrates an extensional rheological method capable of determining the properties of protein solutions in µl volumes and that tau protein can aggregate when exposed to a single extensional strain with potentially significant biological implications.

Diffuse pulmonary meningotheliomatosis - a case report.

Diffuse pulmonary meningotheliomatosis is a rare condition of the lung that presents with nonspecific respiratory symptoms, and usually follows a benign course. It should, however, be considered in the differential diagnosis of a miliary pattern on chest-imaging studies, as illustrated in the case reported.

Single-Dimer Formation Rate Reveals Heterogeneous Particle Surface Reactivity.

Biofunctionalized micro- and nanoparticles are important for a wide range of applications, but methodologies to measure, modulate, and model interactions between individual particles are scarce. Here, we describe a technique to measure the aggregation rate of two particles to a single dimer, by recording the trajectory that a particle follows on the surface of another particle as a function of time. The trajectory and the interparticle potential are controlled by a magnetic field. Particles were studied with and without conjugated antibodies in a wide range of pH conditions. The data shows that the aggregation process strongly depends on the particle surface charge density and hardly on the antibody surface coverage. Furthermore, microscopy videos of single particle dimers reveal the presence of reactive patches and thus heterogeneity in the particle surface reactivity. The aggregation rates measured with the single-dimer experiment are compared to data from an ensemble aggregation experiment. Quantitative agreement is obtained using a model that includes the influence of surface heterogeneity on particle aggregation. This single-dimer experiment clarifies how heterogeneities in particle reactivity play a role in colloidal stability.

Rate of Dimer Formation in Stable Colloidal Solutions Quantified Using an Attractive Interparticle Force.

We describe an optomagnetic cluster experiment to understand and control the interactions between particles over a wide range of time scales. Aggregation is studied by magnetically attracting particles into dimers and by quantifying the number of dimers that become chemically bound within a certain time interval. An optomagnetic readout based on light scattering of rotating clusters is used to measure dimer formation rates. Magnetic field settings, that is, field rotation frequency, field amplitude, and on- and off-times, have been optimized to independently measure both the magnetically induced dimers and chemically bound dimers. The chemical aggregation rate is quantified in solutions with different pH and ionic strengths. The measured rates are extrapolated to effective dimer formation rates in the absence of force, showing that aggregation rates can be quantified over several orders of magnitude, including conditions of very low chemical reactivity.