This thesis addresses potential threats to the validity of observational epidemiological studies. Examples of these potential sources of bias are confounding, missing data, selection bias, and... Show moreThis thesis addresses potential threats to the validity of observational epidemiological studies. Examples of these potential sources of bias are confounding, missing data, selection bias, and measurement error. Although various methods have been developed to mitigate these biases, it is often unclear which methods can be used in which empirical settings. It is also common that issues discussed in methodological studies are overlooked in clinical research. Thus, we investigated problems ofmissing data, selection bias, and measurement error occurring in several specific observational settings and discuss how to optimally handle them. Show less
The research provides insight into disease behavior in both rural and semi-urban areas in Serengeti in Tanzania. It focuses on the motives and behaviors that patients exhibit when relying on local... Show moreThe research provides insight into disease behavior in both rural and semi-urban areas in Serengeti in Tanzania. It focuses on the motives and behaviors that patients exhibit when relying on local healthcare systems, classified as traditional, transitional or modern. It describes the availability, accessibility and patterns of use of these healthcare systems, in particular how they are embedded in the local cultural heritage. It shows that behavioral patterns are dominated by psycho-social and cultural factors. In addition, background characteristics, intervening factors and situation-dependent factors that influence usage patterns are described, analyzed and explained. The analytical model based on the school of "Ethnoscience" shows where the use of these medical systems is related to the historical, cultural and economic factors that determine the daily lives of the inhabitants. The analysis of the research data provides recommendations for education and training of local middle management staff in support of integrated transcultural public health policy, as initiated by the local government of Serengeti in collaboration with the local training institutions. The findings are used as input for the intended master course in Transcultural Public Health Management in the area, and elsewhere in similar circumstances. Special attention is paid to the local medical knowledge, beliefs and practices of the target population to improve public health. Show less
Secondary prevention of recurrent venous can be achieved in two ways, either by elimination of modifiable risk factors or by extending the anticoagulant treatment period in patients at high risk... Show moreSecondary prevention of recurrent venous can be achieved in two ways, either by elimination of modifiable risk factors or by extending the anticoagulant treatment period in patients at high risk of recurrence. The aim of this thesis was to identify modifiable risk factors for as well as factors that might be able to predict recurrent venous thrombotic events. This thesis reports on an increased risk of recurrences in women who continue or start using hormonal contraceptives after a first venous thrombotic event, suggesting that refraining from this modifiable risk factor decreases the risk of recurrence. Furthermore, this thesis describes several factors, male sex, unprovoked first event, levels of coagulation factor VIII and antibiotic use to be associated with recurrent venous thrombosis. These factors should eventually be taken together and used to build a prognostic model, which will be able to predict recurrences at a refined and individual level. Show less
The pathogenesis of OA is largely unknown; however, several risk factors are known to contribute to disease development. Treatment modalities are currently limited to alleviation of symptoms. In... Show moreThe pathogenesis of OA is largely unknown; however, several risk factors are known to contribute to disease development. Treatment modalities are currently limited to alleviation of symptoms. In order to develop better treatment modalities, increase of the understanding of the underlying mechanisms leading to OA development may provide targets for disease modification. Furthermore, knowledge regarding appropriate outcome measures that can be applied in OA research has to be increased for adequate assessment of potential treatment effects. Therefore, part I of this thesis describes studies aiming to increase the understanding of mechanisms underlying the association between known risk factors and OA, especially focussing on obesity in relation to OA in weight-bearing and non-weight-bearing joints. Furthermore, it was investigated which specific structural abnormalities on specific locations within the knee joint could best discriminate presence of symptomatic OA, and impact of knee OA and its modifiable or preventable risk on health-related quality of life was evaluated. Part II of this thesis describes two systematic reviews, assessing available instruments for measurement of the domains pain, physical function, patient global assessment and imaging in hand OA in order to enable recommendations for use in clinical trials. Show less
This thesis investigates the validity and usefulness of physician's preference-based instrumental variable analysis in clinical epidemiological studies. Chapter 2 describes a survey amongst general... Show moreThis thesis investigates the validity and usefulness of physician's preference-based instrumental variable analysis in clinical epidemiological studies. Chapter 2 describes a survey amongst general practitioners, showing substantial variation in prescribing preference and showing prescribing patterns which suggest the stochastic monotonicity assumption may be plausible for physician's preference as an instrumental variable. Chapter 3 describes an application of physician's preference-based instrumental variable analysis in a moderate-sized study, showing uninformatively wide confidence intervals which limit the usefulness of instrumental variable analysis in this setting. Chapter 4 focuses on the bias-variance trade-off of instrumental variable analysis in comparison to conventional analyses, using simulations and theoretical derivations. Chapter 5 compares instrumental variable and conventional estimates of the effect of third versus second generation oral contraceptives on occurrence of venous thromboembolism. The similarity of these estimates under different sets of assumptions suggests major confounding is unlikely. Chapter 6 contains a suggestion for an additional step for reporting of instrumental variable analyses. The focus shifts to Mendelian randomisation in the second part of the thesis. Chapter 7 reviews the methodological approaches used in Mendelian randomisation studies and the quality of reporting. Chapter 8 shows that collider-stratification bias may exist in Mendelian randomisation studies in elderly populations. Show less
This thesis aimed to identify possible risks associated with erythropoiesis-simulating agent (ESA) use. First, trends in anemia management are described, showing less ESA use in Swedish patients... Show moreThis thesis aimed to identify possible risks associated with erythropoiesis-simulating agent (ESA) use. First, trends in anemia management are described, showing less ESA use in Swedish patients with chronic kidney disease (CKD) and less ESA-treated patients had a hemoglobin above 12 g/dL. Furthermore it is shown that ESA- treated pre-dialysis patients in the Netherlands received more antihypertensive agents than patients without ESA, confirming the hypertensive effect of ESA. However, no relevant difference in routinely measured blood pressure was observed between patients with and without ESA treatment, thus the hypertensive effect of ESAs could be controlled in clinical practice. In addition, no excess of thrombotic events was shown in ESA-treated dialysis patients compared to patients without ESA treatment. In contrast, a higher risk of cardiovascular events with ESA use was indicated in Danish patients with multiple myeloma and myelodyslastic syndrome. Also, with two analytical approaches, a harmful effect of high ESA doses on mortality was indicated in Dutch dialysis patients. Last, it was shown that ESA resistance was associated with mortality in both hemodialysis and peritoneal dialysis patients. To conclude, treatment with high ESA doses was associated with a higher risk of mortality, but the mechanism is largely unknown. Show less
Currently, 35-45% of newly diagnosed breast cancer patients in developed countries is aged 65 years and older. Older women with breast cancer comprise a heterogeneous group due to large differences... Show moreCurrently, 35-45% of newly diagnosed breast cancer patients in developed countries is aged 65 years and older. Older women with breast cancer comprise a heterogeneous group due to large differences with regard to concomitant diseases, physiological reserve and functional status. Current guidelines for breast cancer are based on studies that were mostly performed in younger patients. Therefore, treatment of older women with breast cancer is not evidence-based, and it cannot be expected that clinical trials will fill this gap of knowledge in the near future. The aim of this thesis was to investigate several aspects of breast cancer treatment in older women. In Part I, several aspects of treatment in older breast cancer patients were assessed. Part II assessed methodological aspects of studying breast cancer in older patients. This thesis has shown that older patients are at increased risk for overdiagnosis of breast cancer due to population screening, with potential harmful effects due to the increased risk of complications of treatment. Despite changing treatment strategies, breast cancer prognosis of older women has not improved. Current treatment strategies and decisions tools are insufficient. Observational studies will become increasingly important in this patient population, the use of accurate methods will be essential. Show less
The Subacromial Impingement Syndrome (SIS) is the most prevalent disorder of the shoulder in primary health care. Acromionplasty, as the main surgical treatment of SIS, is one of the most performed... Show moreThe Subacromial Impingement Syndrome (SIS) is the most prevalent disorder of the shoulder in primary health care. Acromionplasty, as the main surgical treatment of SIS, is one of the most performed orthopedic surgeries. However, its results are highly variable. Possibly, there are different etiologic subgroups of patients, that might need specific treatment approaches. Several etiologic mechanisms have been described for subacromial narrowing or __impingement__: i.e. 1) structural causes, including acromion shape, subacromial bony spurs, osteophytes; 2) narrowing of the subacromial space due to humerus cranialisation in patients with (micro)instability, or scapular dyskinesia; 3) intrinsic mechanisms such as primary degenerative tendinopathy of the rotator cuff. The aim of this thesis is to unravel the clinical entity __Subacromial Impingement Syndrome__ and to develop methods for identifying distinct etiological patient subgroups that need specific diagnostics and treatment strategies. To this end, we explore the terminological problems and opinions on the main characteristics of SIS amongst international health practitioners, study the prevalence of previously reported etiologic mechanisms in patients with SIS symptoms, develop clinical and biomechanical methods to evaluate and categorize patients with SIS symptoms in diagnostic subgroups, and compare treatment outcomes in trials and follow-up studies. Show less
The main objective of this thesis was to study the role of autonomic nervous system (ANS) function in the development of diabetes and cardiovascular disease using an epidemiological approach. Based... Show moreThe main objective of this thesis was to study the role of autonomic nervous system (ANS) function in the development of diabetes and cardiovascular disease using an epidemiological approach. Based on earlier studies it has remained unclear whether impaired ANS function is a risk factor for the development of diabetes and cardiovascular disease, or merely a consequence of pre-existing disease. The main conclusions of this thesis are that excess body fat, in particular visceral fat, is associated with activation of the sympathetic nervous system in individuals without diabetes and cardiovascular disease. Furthermore, this thesis showed that impaired ANS function is not a risk factor for the development of diabetes mellitus. The presented studies suggest that insulin resistance precedes the impairment of the ANS. The results from this thesis also show that impaired ANS function is a risk factor for the development of cardiovascular disease in populations without pre-existing cardiovascular disease. Furthermore, individuals with a higher heart rate have higher concentrations of cholesterol and triglycerides in the circulation and a higher intrahepatic triglyceride content, suggesting that an altered lipid metabolism may be a mechanism underlying the association between ANS function and cardiovascular disease. Show less
Clostridium difficile is a spore-forming bacterium, the toxin-producing strains of which cause colitis. Risk factors are antibiotics, advanced age and severe comorbidity. C. difficile infection ... Show moreClostridium difficile is a spore-forming bacterium, the toxin-producing strains of which cause colitis. Risk factors are antibiotics, advanced age and severe comorbidity. C. difficile infection (CDI) has been regarded as mostly a hospital-acquired infection. Preventing relapses is considered the biggest challenge in CDI management. In this thesis, we show that CDI occurs in Dutch general practices, often in patients without contact with hospitals. Also, we show that the emerging virulent strain PCR ribotype 027 has not become dominant in European hospitals, but community-associated type 078 has become highly prevalent. Furthermore, we found that cystic fibrosis outpatients are frequently colonized with C. difficile, though mostly with nonpathogenic strains. Thus, acquisition of C. difficile in the community appears more important than previously thought. Next, we show that renal failure at the time of diagnosis predicts relapses. In addition, patients who fail to develop antibodies against C. difficile toxins have a higher chance of relapse. We describe an experimental product derived from the milk of cows vaccinated against C. difficile and its toxins, which might prevent relapses. The last part of the thesis consists of the European guideline for CDI treatment and its recent update Show less
In Africa, polyparasitism is the rule rather than the exception. The aim of this thesis was to get a detailed insight into the micro-geographical distribution and patterns of S. mansoni and S.... Show moreIn Africa, polyparasitism is the rule rather than the exception. The aim of this thesis was to get a detailed insight into the micro-geographical distribution and patterns of S. mansoni and S. haematobium co-infections, and how this affects host morbidity. A community-wide study was carried out in a co-endemic focus in the north of Senegal, combining epidemiological, ecological, immunological, and geographical analyses. This multidisciplinary approach led to several new insights. Spatial analyses showed significant clustering of Schistosoma infection and morbidity even on a micro scale; S. mansoni and S. haematobium hotspots were found in different sections of one community. Another major finding was that the presence of S. mansoni in co-infections might protect against S. haematobium-specific urinary tract morbidity. Furthermore, it was observed that S. haematobium antigens induced stronger cytokine responses than those of S. mansoni, indicating that the first species may be more immunogenic. The results of this thesis provide new leads for further research on disease etiology and underlying mechanisms in Schistosoma co-infections. Such knowledge is key to rationalizing and optimizing current schistosomiasis control strategies in co-endemic areas and to developing successful elimination strategies in the future. Show less
In this thesis, we studied both implants and patient and surgeon factors as predictors of clinical outcome after total hip and knee replacement. Additionally, we studied a number of methodological... Show moreIn this thesis, we studied both implants and patient and surgeon factors as predictors of clinical outcome after total hip and knee replacement. Additionally, we studied a number of methodological aspects of orthopaedic research, such as competing risks in estimating the probability of revision surgery, minimal clinically important differences and clinically important differences in health-related quality of life after total hip and knee replacement, patient acceptable symptom states in oxford hip and knee score after total hip and knee replacement and patient preference for questionnaire mode Show less
Since a decade, Clostridium difficile infection (CDI) has increased progressively in incidence and severity of disease. Currently, CDI is considered the leading cause of nosocomial diarrhoea,... Show moreSince a decade, Clostridium difficile infection (CDI) has increased progressively in incidence and severity of disease. Currently, CDI is considered the leading cause of nosocomial diarrhoea, associated with an increased duration of hospitalization, healthcare expenses, morbidity and mortality. This thesis describes our findings with outbreak control, diagnosis, identification of specific risk factors and treatment of CDI after the discovery of the emergence of C. difficile PCR-ribotype 027 in the Netherlands. The studies illustrate the role of antibiotics in relation to persistence, severeness and spreading of CDI. Antibiotics are shown to be a primary risk factor for the development of (ribotype-specific) CDI and an essential part of the outbreak control measures (__bundle-approach__), namely antibiotic stewardship. The use of antibacterials is a risk for selection of novel endemic C. difficile strains in e.g. animals, which introduce an increasing risk of alternative zoonotic transmission routes. Except for very mild CDI, which is clearly induced by usage of specific antibiotics, antibacterial treatment is advised. This thesis reviews the comparative effectiveness of the currently available treatment modalities, thereby providing evidence-based recommendations for CDI remedies. Treatment options include: oral and non-oral antibiotics, toxin-binding resins and polymers, immunotherapy, probiotics, faecal or bacterial intestinal transplantation. Show less
Venous thrombosis is a disease that occurs in 1-2 per 1000 people per year. At the time of their first venous thrombosis, approximately 50% of women are exposed to reproductive risk factors (oral... Show moreVenous thrombosis is a disease that occurs in 1-2 per 1000 people per year. At the time of their first venous thrombosis, approximately 50% of women are exposed to reproductive risk factors (oral contraception, postmenopausal hormone therapy, pregnancy and the puerperium). In this thesis, we showed that these women are at particularly high risk of venous thrombosis if they have previously experienced an episode of superficial vein thrombosis, or are over the age of 50 years (Chapters 2 and 3). There is no known male counterpart to female reproductive risk factors. Nevertheless, the incidence of venous thrombosis is approximately similar in men and women. In this thesis we established that, once female reproductive risk factors are taken into account, men have an approximately twofold higher risk of both first and recurrent venous thrombosis than women (Chapters 4 and 5). Further to these findings, in Chapter 6, we reviewed the literature on sex-specific risk factors for venous thrombosis. We hypothesized that sex-specific genetic risk factors, an excess in overweight and smoking, or hypercoagulable changes such as microalbuminuria may explain the higher risk of venous thrombosis in men than in women. Show less
This thesis investigated the effect of several risk factors on objectively assessed disease progression (renal function decline and time until the start of renal replacement therapy) and... Show moreThis thesis investigated the effect of several risk factors on objectively assessed disease progression (renal function decline and time until the start of renal replacement therapy) and subjectively assessed disease progression (disease-related symptoms and health-related quality of life) in patients with chronic kidney disease on specialized pre-dialysis care. Furthermore, we explored (un)known mechanisms that may determine renal function decline in pre-dialysis patients. The conclusions are: low blood pressure, low proteinuria levels, and low cholesterol levels are associated with a slower objectively assessed disease progression. However, in elderly patients low blood pressure is a marker for an earlier start of renal replacement therapy. Concerning subjectively assessed disease progression, only in young patients treated with anemia-medication, high hemoglobin levels are associated with a better health-relate d quality of life. Furthermore, symptoms increase and health-related quality of life decreases during pre-dialysis care. Therefore, these markers are good candidates for defining the optimal moment to start with dialysis. This thesis also showed that black patients experience a faster renal function decline than white patients. A possible explanation could be the stronger negative consequences of diabetes mellitus in black patients. Finally, at middle-age, renal function is higher in longevity families, revealing possible new genetic mechanisms. Show less
H2: Hensgens MP, Goorhuis A, Notermans DW, van Benthem BH, Kuijper EJ. Decrease of hypervirulent Clostridium difficile PCR ribotype 027 in the Netherlands. Euro Surveill. 2009 H3: Hensgens MP,... Show moreH2: Hensgens MP, Goorhuis A, Notermans DW, van Benthem BH, Kuijper EJ. Decrease of hypervirulent Clostridium difficile PCR ribotype 027 in the Netherlands. Euro Surveill. 2009 H3: Hensgens MP, Keessen EC, Squire M, Riley TV, Koene MG, de Boer E, Lipman LJ, Kuijper EJ. Clostridium difficile infection in the community: a zoonotic disease? Clin Microbiol Infect. 2012 H4: Hensgens MP / Goorhuis A, van Kinschot CM, Crobach MJ, Harmanus C, Kuijper EJ. Clostridium difficile infection in an endemic setting in the Netherlands. Eur J Clin Microbiol Infect Dis. 2011 H5: Hensgens MP, Goorhuis A, Dekkers OM, Kuijper EJ. Time-interval of increased risk for Clostridium difficile infection after exposure to antibiotics. J Antimicrob Chemother. 2012 H7: Hensgens MP, Goorhuis A, Dekkers OM, van Benthem BH, Kuijper EJ. Outcome of nosocomial Clostridium difficile infections; results of a multicenter cohort study. Clin Infect Dis. 2013 H8: Hensgens MP / Bauer MP, Miller M, Gerding DN, Wilcox MH, Dale AP, Fawley WN, Kuijper EJ, Gorbach SL. Renal failure and leukocytosis are predictors of a complicated course of Clostridium difficile infection (CDI) if measured on day of diagnosis. Clin Infect Dis. 2012 H9: Hensgens MP, Kuijper EJ. Clostridium difficile infection due to binary toxin positive strains. Emerg Infect Dis. 2013 H10: Hensgens MP, Dekkers OM, Goorhuis A, Le Cessie S, Kuijper EJ. Predicting a severe course of Clostridium difficile infection at the bedside. Clin Microbiol Infect. 2012 Show less
The aim of this thesis was to identify new risk factors for first and recurrent venous thrombosis of both the upper and lower extremity, and assess the incidence of recurrence and mortality after a... Show moreThe aim of this thesis was to identify new risk factors for first and recurrent venous thrombosis of both the upper and lower extremity, and assess the incidence of recurrence and mortality after a first venous thrombosis. An overview was provided of the current literature on risk factors and treatment for a first venous thrombosis of the upper extremity (chapter 2). We investigated the association between levels of coagulation factors, blood group and a first venous thrombosis of the upper extremity (chapter 3), and studied risk factors for a recurrent event in patients with a first venous thrombosis of the upper extremity (chapter 4). Furthermore, we studied the association between venous thrombosis and long-term mortality (chapter 5). In this study we found that patients with thrombosis died more of chronic obstructive pulmonary disease (COPD) than expected from population figures. COPD was found to be a risk factor for a first venous thrombosis in chapter 6. We studied the incidence of recurrent venous thrombosis, as well as sex, age and an idiopathic first venous thrombosis as risk factors for recurrence (chapter 7). Body height was studied as a risk factor for both first and recurrent venous thrombosis in combination with mobility (chapter 8). Show less
Myasthenia gravis (MG) is hallmarked by acquired and fluctuating weakness of voluntary muscles. In the majority of patients, weakness is caused by autoantibodies to the postsynaptic acetylcholine... Show moreMyasthenia gravis (MG) is hallmarked by acquired and fluctuating weakness of voluntary muscles. In the majority of patients, weakness is caused by autoantibodies to the postsynaptic acetylcholine receptor (AChR) in the neuromuscular junction. Approximately 10% of MG patients are seronegative (SNMG). In 2001, antibodies to muscle-specific kinase (MuSK) were discovered within this group. This dissertation describes the epidemiology, clinical characteristics and immunological aspects of this new disease. In the Netherlands, MuSK MG is rare. Incidence was 0.17 per million person-years. Prevalence was 2.8 per million on January 1st 2004. Weakness was more often bulbar, and lead to frequent respiratory crises. MuSK MG was linked to the HLA-DR14-DQ5 haplotype and the disease severity was associated to antigen-specific IgG4 antibodies instead of IgG1. This is in contrast to AChR MG in which autoantibodies are mainly of the IgG1 and IgG3 subclass, and the disease is linked to HLA-B8-DR3. In SNMG patients, no antibodies to postsynaptic ErbB receptors were found. A case-report describes the transmission of MuSK autoantibodies from mother to her newborn child, causing transient weakness in the infant. A second case-report illustrates the effect of MuSK antibodies on both pre- and postsynaptic signal transmission in the neuromuscular junction. Show less
We investigated the clinical and radiographic disease course of hand osteoarthritis as well as determinants of poor clinical outcome and radiographic progression over a period of six years in 289... Show moreWe investigated the clinical and radiographic disease course of hand osteoarthritis as well as determinants of poor clinical outcome and radiographic progression over a period of six years in 289 patients with hand osteoarthritis. Because these patients had osteoarthritis at multiple joints this enabled us to not only assess the association between progression of osteoarhtiritis in different hand joints groups but also between progression of hand osteoarthritis and osteoarthritis change at the knee. In addition, genetic factors in hand osteoarthritis progression were investigated as well as the influence of illness perceptions. The hand osteoarthritis subsets erosive osteoarthritis and thumb base osteoarthritis are further characterised. In the last part of the thesis the clinimetric properties of a pain score for osteoarthritis and radiographic outcome measures for hand osteoarthritis are evaluated. Show less
Falls in Parkinson__s (PD) and Huntington__s disease (HD) are common. 50 % of moderately affected PD patients sustained two or more falls during a prospective follow-up of 6 months. During a 3... Show moreFalls in Parkinson__s (PD) and Huntington__s disease (HD) are common. 50 % of moderately affected PD patients sustained two or more falls during a prospective follow-up of 6 months. During a 3 month period 40 % of HD patients reported one or more fall. Many falls resulted in minor injuries and 42 % of PD patients reported a fear of future falls. A different study on quality of life in PD showed that quality of life scores were significantly related to fear of falling in PD. In order to predict future falls several clinical tests and risk factors were studied. However, it proved difficult to identify future fallers and asking for prior falls was the best predictor of falls in the near future in PD. Analysis with quantative measurements in HD patients showed that an increased medio lateral trunk sway and a decreased stride length were associated with an increased fall risk. Based on the findings in these studies and on a literature study, the thesis concludes with a proposal for a multidisciplinary intervention program to prevent falls in Parkinson__s disease. Show less
