Long COVID in the Belgian Defence forces: prevalence, risk factors and impact on quality of daily functioning.

INTRODUCTION: Long COVID (LC) is a medical condition first described and documented through anecdotes on social media by patients prior to being recognised by WHO as a disease. Although >50 prolonged symptoms of LC have been described, it remains a diagnostic challenge for military providers and therefore threatens operational readiness. METHODS: On 9 September 2021, an online survey was emailed to 2192 Belgian Defence personnel who had previously tested PCR positive for SARS-CoV-2 between 17 August 2020 and 31 May 2021. A total of 718 validated responses were received.Descriptive analyses determined the prevalence of LC and 10 most common symptoms and their duration following infection. In the explanatory analyses, risk factors related to LC were identified. To establish the health-related impact of LC on quality of life (HRQoL), we used the results from the EuroQol 5 Dimension 5 Level questionnaire. RESULTS: The most frequent symptoms that were reported for >3 months were fatigue, lack of energy and breathing difficulties.47.35% of the respondents reported at least one persistent symptom, while 21.87% reported more than 3 symptoms lasting for at least 3 months after the initial COVID-19 infection. Most patients with LC suffered from symptoms of a neuropsychiatric nature (71.76%).LC was significantly associated with obesity; pre-existing respiratory disease and blood or immune disorders. Physical activity of >3 hours per week halved the risk of LC.The total QoL is reduced in patients with LC. Considering the five dimensions of the questionnaire, only the self-care dimension was not influenced by the presence of LC. CONCLUSIONS: Almost half of Belgian Defence personnel developed LC after a confirmed COVID-19 infection, similar to numbers found in the Belgian population. Patients with LC would likely benefit from a multidisciplinary rehabilitation approach that addresses shortness of breath, fatigue and mood disturbance.

Beware of nonconvulsive seizures in prolonged disorders of consciousness: Long-term EEG monitoring is the key.

OBJECTIVE: Evaluate the prevalence of epileptic seizures (ES) and epileptiform discharges (EDs) in patients with prolonged disorders of consciousness (DOC), and potential influence of amantadine on epilepsy. METHODS: We conducted a retrospective study in 34 patients hospitalized in a DOC care unit for prolonged DOC between 2012 and 2018, who received a long-term EEG monitoring (LTM). We reviewed the prevalence of ES, EDs and nonconvulsive seizures (NCSz), the type of DOC recovery treatment administered, and neurological outcome. RESULTS: LTM was more effective than standard EEGs in detecting EDs (32% vs 21% respectively). Moreover, 12% of the LTM showed NCSz. Among patients with EDs in LTM, 73% showed no EDs in standard EEG recordings, even when performed more than once. The presence of EDs and/or NCSz in LTM was significantly associated with the occurrence of remote clinical epileptic seizures (p = 0.017) but did not influence neurological outcome (p = 1). Amantadine was not associated with higher occurrence of EDs/NCSz or clinical seizures. CONCLUSION: In our prolonged DOC population, LTM showed more pathological results (EDs and NCSz) than standard EEGs, which was significantly associated with remote clinical seizures. SIGNIFICANCE: The use of LTM might be advised to rule out NCSz in patients with prolonged DOC.

The seroprevalence of cytomegalovirus infection in Belgium anno 2002 and 2006: a comparative analysis with hepatitis A virus seroprevalence.

Cytomegalovirus (CMV) infection is endemic worldwide but its seroprevalence varies widely. The goal of this study was to estimate the age-specific seroprevalence of CMV infection in Belgium based on two cross-sectional serological datasets from 2002 and 2006. The seroprevalence was estimated relying on diagnostic test results based on cut-off values pre-specified by the manufacturers of the tests as well as relying on mixture models applied to continuous pathogen-specific immunoglobulin G antibody titre concentrations. The age-specific seroprevalence of hepatitis A virus (HAV), based on three Belgian cross-sectional serological datasets from 1993, 2002 and 2006, was used as a comparator since individuals acquire lifelong immunity upon recovery, implying an increasing seroprevalence with age. The age group weighted overall CMV seroprevalence derived from the mixture model was 32% (95% confidence interval (CI) 31-34%) in 2002 and 31% (95% CI 30-32%) in 2006. We demonstrated that CMV epidemiology differs from the immunizing infection HAV. This was the first large-scale study of CMV and HAV serial datasets in Belgium, estimating seroprevalence specified by age and birth cohort.

Changes in health in Belgium, 1990-2016: a benchmarking analysis based on the global burden of disease 2016 study.

BACKGROUND: Despite increasing of the Belgian health expenditures, several indicators related to population health showed poor results. The objectives of this study were to perform an in-depth analysis of the secular trend of Belgian health status using the Global Burden of Disease (GBD) 2016 study results for Belgium, and to compare these results with other European countries. METHODS: We collected results of the Global Burden of Disease 2016 study through the GBD results and visualization tools. We benchmarked Belgian GBD results with the other initial members of the European Union (EU15). RESULTS: Belgium performed significantly better in 2016 than in 1990 in terms of age-standardized (AS) Year of Life Lost (YLL) rates but not significantly different in terms of AS Year Lived with Disability (YLD) and Disability-Adjusted Life Year (DALY) rates. The contribution of AS YLDs to total of AS DALYs increased from 1990 (42%) to 2016 (54%). Although AS YLD and DALY rates did not seem to differ between Belgium and the EU15 from 1990 to 2016, the ranking of Belgium among the EU15 in terms of AS DALY and YLL rates was worse in 2016 than in 1990. Belgium had significantly higher AS YLL rates for lower respiratory infections (B: 264 AS YLLs [95% uncertainty interval [UI] 231-301] per 100,000; EU15: 188 AS YLLs [95%UI 168-212] per 100,000), chronic obstructive pulmonary disease (B: 368 AS YLLs [95%UI 331-407] per 100,000; EU15: 285 AS YLLs [95%UI 258-316] per 100,000) and tracheal, bronchus, and lung cancer (B: 785 AS YLLs [95%UI 699-879] per 100,000; EU15: 613 AS YLLs [95%UI 556-674] per 100,000). CONCLUSION: Belgium's ranking among the EU15 in terms of AS YLL and DALY rates decreased from 1990 to 2016. Significant health gains appear possible by acting on risk factors directly linked to a significant part of the Belgian burden of diseases, i.e., alcohol and tobacco consumption, and high body mass index. National burden of disease estimates can help defining Belgian health targets and are necessary as external validity of GBD results is not always guaranteed.

Re-visiting the detection of porcine cysticercosis based on full carcass dissections of naturally Taenia solium infected pigs.

BACKGROUND: Taenia solium is a neglected zoonotic parasite. The performances of existing tools for the diagnosis of porcine cysticercosis need further assessment, and their shortcomings call for alternatives. The objective of this study was to evaluate the performance of tongue palpation and circulating antigen detection for the detection of porcine cysticercosis in naturally infected pigs of slaughter age compared to full carcass dissections (considered the gold standard). Additionally, alternative postmortem dissection procedures were investigated. A total of 68 rural pigs of slaughter age randomly selected in the Eastern Province of Zambia were dissected. Dissections were conducted on full carcasses (or half carcass in case cysticerci were already detected in the first half), including all the organs. Total cysticercus counts, location and stages were recorded and collected cysticerci were identified morphologically and molecularly. All sera were analysed with the B158/B60 antigen detecting ELISA (Ag-ELISA). RESULTS: Key findings were the high occurrence of T. solium infected pigs (56%) and the presence of T. solium cysticerci in the livers of 26% of infected animals. More than half of the infected carcasses contained viable cysticerci. Seven carcasses had T. hydatigena cysticerci (10%), out of which five carcasses were co-infected with T. hydatigena and T. solium; two carcasses (3%) had only T. hydatigena cysticerci. Compared to full carcass dissection, the specificity of the Ag-ELISA to detect infected carcasses was estimated at 67%, the sensitivity at 68%, increasing to 90% and 100% for the detection of carcasses with one or more viable cysticerci, and more than 10 viable cysts, respectively. Tongue palpation only detected 10% of the cases, half carcass dissection 84%. Selective dissection of the diaphragm, tongue and heart or masseters can be considered, with an estimated sensitivity of 71%, increasing to 86% in carcasses with more than 10 cysticerci. CONCLUSIONS: Depending on the aim of the diagnosis, a combination of Ag-ELISA and selective dissection, including investigating the presence of T. hydatigena, can be considered. Full carcass dissection should include the dissection of the liver, kidneys, spleen and lungs, and results should be interpreted carefully, as small cysticerci can easily be overlooked.

Mapping EQ-5D utilities to GBD 2010 and GBD 2013 disability weights: results of two pilot studies in Belgium.

BACKGROUND: Utilities and disability weights (DWs) are metrics used for calculating Quality-Adjusted Life Years and Disability-Adjusted Life Years (DALYs), respectively. Utilities can be obtained with multi-attribute instruments such as the EuroQol 5 dimensions questionnaire (EQ-5D). In 2010 and 2013, Salomon et al. proposed a set of DWs for 220 and 183 health states, respectively. The objective of this study is to develop an approach for mapping EQ-5D utilities to existing GBD 2010 and GBD 2013 DWs, allowing to predict new GBD 2010/2013 DWs based on EQ-5D utilities. METHODS: We conducted two pilot studies including respectively four and twenty-seven health states selected from the 220 DWs of the GBD 2010 study. In the first study, each participant evaluated four health conditions using the standard written EQ-5D-5 L questionnaire. In the second study, each participant evaluated four health conditions randomly selected among the twenty-seven health states using a previously developed web-based EQ-5D-5 L questionnaire. The EQ-5D responses were translated into utilities using the model developed by Cleemput et al. A loess regression allowed to map EQ-5D utilities to logit transformed DWs. RESULTS: Overall, 81 and 393 respondents completed the first and the second survey, respectively. In the first study, a monotonic relationship between derived utilities and predicted GBD 2010/2013 DWs was observed, but not in the second study. There were some important differences in ranking of health states based on utilities versus GBD 2010/2013 DWs. The participants of the current study attributed a relatively higher severity level to musculoskeletal disorders such as 'Amputation of both legs' and a relatively lower severity level to non-functional disorders such as 'Headache migraine' compared to the participants of the GBD 2010/2013 studies. CONCLUSION: This study suggests the possibility to translate any utility derived from EQ-5D scores into a DW, but also highlights important caveats. We observed a satisfactory result of this methodology when utilities were derived from a population of public health students, a written questionnaire and a small number of health states in the presence of a study leader. However the results were unsatisfactory when utilities were derived from a sample of the general population, using a web-based questionnaire. We recommend to repeat the study in a larger and more diverse sample to obtain a more representative distribution of educational level and age.

Predictors of clinicians' underuse of daily sedation interruption and sedation scales.

PURPOSE: The purpose of the study is to identify predictors of underuse of sedation scales and daily sedation interruption (DSI). METHODS: We surveyed all physicians and seven nurses in every Belgian intensive care unit (ICU), addressing practices and perceptions on guideline recommendations. Underuse was defined for sedation scales as use less than 3× per day and for DSI as never using it. Classification trees and logistic regressions identified predictors of underuse. RESULTS: Underuse of sedation scales and DSI was found for 16.6% and 32.5% of clinicians, respectively. Strongest predictors of underuse of sedation scales were agreeing that using them daily takes much time and being a physician (rather than a nurse). Further predictors were confidence in their ability to measure sedation levels without using scales, for physicians, and nurse/ICU bed ratios less than 1.98, for nurses. The strongest predictor of underuse of DSI among physicians was the perception that DSI impairs patients' comfort. Among nurses, lack of familiarity with DSI, region, and agreeing DSI should only be performed upon medical orders best predicted underuse. CONCLUSIONS: Workload considerations hamper utilization of sedation scales. Poor familiarity, for nurses, and negative perception of impact on patients' comfort, for physicians, both reduce DSI utilization. Targeting these obstacles is essential while designing quality improvement strategies to minimize sedative use.

Comorbidities and factors associated with central nervous system infections and death in non-perinatal listeriosis: a clinical case series.

BACKGROUND: Listeriosis is a rare disease caused by the bacterium Listeria monocytogenes and mainly affects at risk people. Listeriosis can lead to sepsis, central nervous system (CNS) infections and death. The objectives of this study were to describe and quantify comorbidities and neurological sequelae underlying non-perinatal listeriosis cases and to describe the factors associated with death and CNS infections in non-perinatal listeriosis. METHODS: We retrospectively collected clinical data through computerized, paper or microfilmed medical records in two Belgian university hospitals. Logistic regression models and likelihood ratio tests allowed identifying factors associated with death and CNS infections. RESULTS: Sixty-four cases of non-perinatal listeriosis were included in the clinical case series and 84 % were affected by at least one comorbid condition. The main comorbidities were cancer, renal and severe cardio-vascular diseases. Twenty-nine patients (45 %) suffered from a CNS infection and 14 patients (22 %) died during hospitalization, among whom six (43 %) had a CNS involvement. Among surviving patients, eleven suffered from neurological sequelae (22 %) at hospital discharge; all had CNS infection. Five of these patients (45 %) still suffered of their neurological sequelae after a median follow-up of one year (range: 0.08-19). The factor associated with death during the hospitalization was the presence of a severe cardiovascular disease (OR = 4.72, p = 0.015). Two factors inversely related with CNS infections were antibiotic monotherapy (OR = 0.28, p = 0.04) and the presence of renal disease (OR = 0.18, p = 0.02). CONCLUSIONS: In a public health context these results could be a starting point for future burden of listeriosis studies taking into account comorbidity.

Classification and regression tree analysis vs. multivariable linear and logistic regression methods as statistical tools for studying haemophilia.

INTRODUCTION: Haemophilia is a rare genetic haemorrhagic disease characterized by partial or complete deficiency of coagulation factor VIII, for haemophilia A, or IX, for haemophilia B. As in any other medical research domain, the field of haemophilia research is increasingly concerned with finding factors associated with binary or continuous outcomes through multivariable models. Traditional models include multiple logistic regressions, for binary outcomes, and multiple linear regressions for continuous outcomes. Yet these regression models are at times difficult to implement, especially for non-statisticians, and can be difficult to interpret. AIMS: The present paper sought to didactically explain how, why, and when to use classification and regression tree (CART) analysis for haemophilia research. MATERIALS & METHODS: The CART method is non-parametric and non-linear, based on the repeated partitioning of a sample into subgroups based on a certain criterion. Breiman developed this method in 1984. Classification trees (CTs) are used to analyse categorical outcomes and regression trees (RTs) to analyse continuous ones. RESULTS: The CART methodology has become increasingly popular in the medical field, yet only a few examples of studies using this methodology specifically in haemophilia have to date been published. Two examples using CART analysis and previously published in this field are didactically explained in details. CONCLUSION: There is increasing interest in using CART analysis in the health domain, primarily due to its ease of implementation, use, and interpretation, thus facilitating medical decision-making. This method should be promoted for analysing continuous or categorical outcomes in haemophilia, when applicable.

Long term outcome after lichtenstein hernia repair using general, locoregional or local anaesthesia.

BACKGROUND: Chronic pain or discomfort after hernia surgery is nowadays a more challenging concern than recurrence. This study aimed to evaluate the long-term impact of local anaesthetic repair (LA) on pain, discomfort, paraesthesia and functional outcome after Lichtenstein hernia repair as compared to locoregional (LRA) and general anaesthesia (GA). METHODS: patients with primary or recurrent inguinal hernia underwent Lichtenstein repair with a polypropylene mesh. All patients with a follow-up of at least three years were sent a detailed questionnaire and offered an outpatient visit. Kaplan-Meier estimates and Cox proportional hazard regressions were used to analyse the relationship between time to event variables and explanatory variables including anaesthesia type. RESULTS: Between 1994 and 2006, in two cohorts, 330 patients answered the questionnaire: 100 under GA, 35 under LRA, and 195 under LA. This represented a response rate of 95, 94, and 98% respectively. Compared to GA and LRA, LA resulted in less long term pain, discomfort and paraesthesia. Moreover, resumption of social and professional activities was faster after LA. Recurrence rates were 1, 0, and 0.5% respectively. CONCLUSIONS: After Lichtenstein inguinal hernia repair, LA results in beneficial effects beyond the immediate postoperative period.

Clinical indicators of exposure to Coxiella burnetii in dairy herds.

Q fever is a zoonosis occurring worldwide in livestock. Often neglected in differential diagnoses, Q fever can persist in herds causing financial losses in the long run. In ruminants, well-known manifestations of Q fever are abortion, stillbirth, delivery of weak offspring and premature delivery. In cattle, Q fever is frequently asymptomatic and/or under-reported. The use of new methodologies in veterinary clinical epidemiology is of prime importance to find accurate clinical indicators of exposure to C. burnetii at herd level. A retrospective randomly cross-sectional survey was conducted to estimate the seroprevalence of Q fever in southern Belgium by means of an ELISA test performed on the bulk tank milk (n = 206 cattle herds). At the same time, a questionnaire was accomplished allowing the investigation of presumptive clinical signs observed at herd level during the previous twelve months for dairy cows. A multivariate logistic regression analysis was used to identify abortion and irregular repeat breeding as two indicators associated with Q fever exposure in dairy herds. In addition, a bootstrapped quantile regression revealed that the average score of putative clinical signs related to Q fever was significantly more important in exposed versus non-exposed herds. A classification and regression tree (CART) analysis confirmed the importance of the average clinical score and the irregular repeat breeding as main splitters, considering or not each clinical sign separately. Considering herd clinical patterns, instead of taking each clinical sign separately, seems to be more useful to differentiate herds at risk of Q fever exposure.

Health-related quality of life in patients with melanoma expressed as utilities and disability weights.

BACKGROUND: Few studies about health-related quality of life (HRQoL) in patients with melanoma have expressed their results in terms of utilities or disability weights (DWs). Utilities are required for calculating quality-adjusted life years and therefore for cost-effectiveness analyses. DWs are useful to assess the burden of diseases through disability-adjusted life years. OBJECTIVES: To provide utilities and DWs regarding patients with melanoma. METHODS: The patients were classified into eight groups using four stages based on the 2009 American Joint Committee on Cancer stages, with each stage subdivided into treatment and remission phases. The EuroQoL Five Dimensions Five Levels (EQ-5D-5L) questionnaire was completed by the patients with melanoma to provide a mean utility for each group. In addition to this, the EuroQoL visual analogue scale (VAS) and a validated quality-of-life questionnaire dedicated to patients with melanoma [Functional Assessment of Cancer Therapy Melanoma (FACT-M)] were completed by the same patients in order to compare their results with the obtained utilities. DWs were obtained by calculating, for each patient, the difference between his/her utility and the corresponding sex- and age-specific population norm. RESULTS: A total of 395 questionnaire sets were completed. Utilities and DWs showed significant differences between follow-up groups. Treatment groups had similar utilities and DWs but these results were obtained during different treatment durations and therefore have different weights. The VAS and the FACT-M were found to be less sensitive. Nevertheless, the FACT-M identified some problems not found by the EQ-5D-5L questionnaire. CONCLUSIONS: The EQ-5D-5L questionnaire seems adequate to provide utilities and DWs in patients with melanoma. Lower HRQoL in female patients with melanoma is probably linked to lower HRQoL in the general population.

Reduction of potentially inappropriate medications using the STOPP criteria in frail older inpatients: a randomised controlled study.

BACKGROUND: Hospital admissions may provide an opportunity to discontinue potentially inappropriate medications (PIMs) in older patients. Little is known about the effect of using the Screening Tool of Older People's potentially inappropriate Prescriptions (STOPP) in this context. This study aimed to test the hypothesis that specific STOPP recommendations from an inpatient geriatric consultation team (IGCT) to the hospital physician leads to reductions in PIMs for patients at discharge. METHODS: This was a randomised controlled study in 146 frail inpatients (in 2011). The intervention consisted of STOPP recommendations made by the IGCT to ward physicians to discontinue PIMs, in addition to the standard geriatric advice. RESULTS: Intervention (n = 74) and control (n = 72) groups were similar in terms of patient characteristics (median age 85 years; median number of daily drugs, seven) and PIM distribution (68 and 57 PIMs in 53 and 51 % of patients, respectively). At discharge, the reduction in PIMs was twice as high for the intervention group as for the control group (39.7 and 19.3 %, respectively; p = 0.013). The proportion of patients who still had one or more PIM at discharge did not differ between groups. In the 50 patients followed-up a year later, the majority of PIMs that had been stopped during hospitalisation had not been restarted after discharge (17/28; 61 %). The clinical relevance of PIMs identified at baseline in those patients was considered major (29 %), moderate (37 %), minor (5 %), deleterious (8 %), or not assessed (11 %). Discontinuation rate was not associated with clinical importance. CONCLUSION: Specific STOPP recommendations provided to hospital physicians doubled the reduction of PIMs at discharge in frail older inpatients. To further improve the appropriateness of prescribing in older patients, clinicians should focus on the STOPP criteria that are of major clinical importance, and general practitioners should be actively involved.

Understanding the burden of disease in Nepal: a call for local evidence.

The burden of disease, most commonly expressed in terms of Disability-Adjusted Life Years, has become a crucial component in decision making processes within the health sector. In Nepal, however, burden of disease estimates are scarce and lack representativeness. To improve our understanding of the burden of disease in Nepal and thereby increase the efficiency of health policies, there is an urgent need to strengthen the local evidence base. All relevant stakeholders should therefore collaborate to generate new data, improve existing data generation mechanisms, make generated data available, and optimize the use of available data.

An agent-based model of exposure to human toxocariasis: a multi-country validation.

Seroprevalence data illustrate that human exposure to Toxocara is frequent. Environmental contamination with Toxocara spp. eggs is assumed to be the best indicator of human exposure, but increased risk of exposure has also been associated with many other factors. Reported associations are inconsistent, however, and there is still ambiguity regarding the factors driving the onset of Toxocara antibody positivity. The objective of this work was to assess the validity of our current conceptual understanding of the key processes driving human exposure to Toxocara. We constructed an agent-based model predicting Toxocara antibody positivity (as a measure of exposure) in children. Exposure was assumed to depend on the joint probability of 3 parameters: (1) environmental contamination with Toxocara spp. eggs, (2) larvation of these eggs and (3) the age-related contact with these eggs. This joint probability was linked to processes of acquired humoral immunity, influencing the rate of antibody seroreversion. The results of the simulation were validated against published data from 5 different geographical settings. Using simple rules and a stochastic approach with parameter estimates derived from the respective contexts, plausible serological patterns emerged from the model in nearly all settings. Our approach leads to novel insights in the transmission dynamics of Toxocara.

Availability of digital dermoscopy in daily practice dramatically reduces the number of excised melanocytic lesions: results from an observational study.

BACKGROUND: Digital dermoscopy has been shown to permit an earlier detection of melanoma. However, few studies have investigated its added value in reducing unnecessary excisions in everyday clinical practice. OBJECTIVES: To compare, in daily practice, the efficiency of three dermoscopy methods: dermoscopy alone with little training, dermoscopy alone with adequate training and dermoscopy with adequate training and access to digital dermoscopy, and to confirm the safety of this latter approach. METHODS: Thirty-six dermatologists working without digital dermoscopy were divided into two groups according to their training in dermoscopy. The third group constituted of two dermatologists working in a pigmented lesion clinic with access to the digital dermoscopy technique and eight additional dermatologists working in the same dermatology department. These 46 dermatologists included all presumed melanocytic lesions excised over a period of 1 year. The primary endpoint was the melanoma/nonmelanoma ratio (M/NM-R); secondary endpoints were the ratio of 'problem' naevi to common naevi (PN/CN-R), specificity and sensitivity for the diagnosis of melanoma, in situ/invasive melanoma ratio, and the mean Breslow thickness. RESULTS: In total, 1865 excised lesions, including 231 melanomas, were included. In the digital dermoscopy availability group (DD-G) the M/NM-R was significantly better (1/2.43), as was the PN/CN-R (1/1.48) (P < 0.001 in both cases). The specificity was significantly higher in the DD-G and significantly higher for trained examiners as compared with examiners with little training. More that one-third of all melanomas discovered by digital dermoscopy were in situ, and the mean Breslow thickness was 0.32 mm for the invasive ones. CONCLUSIONS: The reduction of unnecessary excisions when using digital dermoscopy compared with dermoscopy alone in our study suggests that access to digital dermoscopy offers a better management of pigmented lesions in daily practice. The high number of early lesions diagnosed by this technique confirms that its use is safe.

Novel insights in the faecal egg count reduction test for monitoring drug efficacy against gastrointestinal nematodes of veterinary importance.

The faecal egg count reduction test (FECRT) is the method of choice to monitor anthelmintic efficacy against gastro-intestinal nematodes in livestock. Guidelines on how to conduct a FECRT are made available by the World Association for the Advancement of Veterinary Parasitology (WAAVP). Since the publication of these guidelines in the early 1990 s, some limitations have been noted, including (i) the ignorance of host-parasite interactions that depend on animal and parasite species, (ii) their feasibility under field conditions, (iii) appropriateness of study design, and (iv) the high detection limit of the recommended faecal egg count (FEC) method. Therefore, the objective of the present study was to empirically assess the impact of the level of excretion and aggregation of FEC, sample size and detection limit of the FEC method on the sensitivity and specificity of the FECRT to detect reduced efficacy (<90% or <95%) and to develop recommendations for surveys on anthelmintic resistance. A simulation study was performed in which the FECRT (based on the arithmetic mean of grouped FEC of the same animals before and after drug administration) was conducted under varying conditions of mean FEC, aggregation of FEC (inversely correlated with k), sample size, detection limit and 'true' drug efficacies. Classification trees were built to explore the impact of the above factors on the sensitivity and specificity of detecting a truly reduced efficacy. For a reduced-efficacy threshold of 90%, most combinations resulted in a reliable detection of reduced and normal efficacy. For the reduced-efficacy threshold of 95% however, unreliable FECRT results were found when sample sizes <15 were combined with highly aggregated FEC (k=0.25) and detection limits ≥ 5 EPG or when combined with detection limits ≥ 15 EPG. Overall, an increase in sample size and mean preDA FEC, and a decrease in detection limit improved the diagnostic accuracy. FECRT remained inconclusive under any evaluated condition for drug efficacies ranging from 87.5% to 92.5% for a reduced-efficacy-threshold of 90% and from 92.5% to 97.5% for a threshold of 95%. The results highlight that (i) the interpretation of this FECRT is affected by a complex interplay of factors, including the level of excretion and aggregation of FEC and (ii) the diagnostic value of FECRT to detect small reductions in efficacy is limited. This study, therefore, provides a framework allowing researchers to adapt their study design according to a wide range of field conditions, while ensuring a good diagnostic performance of the FECRT.

Estimating the prevalence of infections in vector populations using pools of samples.

Several statistical methods have been proposed for estimating the infection prevalence based on pooled samples, but these methods generally presume the application of perfect diagnostic tests, which in practice do not exist. To optimize prevalence estimation based on pooled samples, currently available and new statistical models were described and compared. Three groups were tested: (a) Frequentist models, (b) Monte Carlo Markov-Chain (MCMC) Bayesian models, and (c) Exact Bayesian Computation (EBC) models. Simulated data allowed the comparison of the models, including testing the performance under complex situations such as imperfect tests with a sensitivity varying according to the pool weight. In addition, all models were applied to data derived from the literature, to demonstrate the influence of the model on real-prevalence estimates. All models were implemented in the freely available R and OpenBUGS software and are presented in Appendix S1. Bayesian models can flexibly take into account the imperfect sensitivity and specificity of the diagnostic test (as well as the influence of pool-related or external variables) and are therefore the method of choice for calculating population prevalence based on pooled samples. However, when using such complex models, very precise information on test characteristics is needed, which may in general not be available.