Messam, Locksley L. McV.
Messam, Locksley L. McV.
Messam, Locksley L. McV.
Now showing 1 - 10 of 15
- PublicationBlood Drive Day-Related Factors Affecting University Student Blood Donation in Grenada, West Indies: A Case-Control Study(The University of the West Indies, 2018-11-27)
;Objectives: The goal of this study was to determine which factors acting in close temporal proximity to the day of a university campus blood drive were associated with university-student blood donation. Methods: An incidence density case-control study was conducted at St. George’s University, Grenada, West Indies. Cases (69) were students interviewed while donating blood at blood drives (February-April 2010). Controls (437) were non-donating students interviewed on the same days as cases. Exposures of interest were: Sources of knowledge of the blood drive, the presence or lack of academic deadlines within a week of the blood drive, and the number of hours of classes on the day of the blood drive. Data were analysed using logistic regression with adjusted odds ratios approximating risk ratios (RR). Results: Associations with blood donation were higher for electronic and/or personal (RREmail = 5.1; 95% CI: 2.7–9.6, RRFacebook = 4.3; 95% CI: 2.1–9.0, RRPersonalReminder = 2.9; 95% CI: 1.6–5.4) than for impersonal (RRClassAnnouncement = 2.4; 95% CI: 1.3–4.8) sources of blood drive knowledge. Additionally, students with classes only in the morning (RRAMonly = 1.9; 95% CI: 1.2–3.2), or afternoon (RRPMonly = 1.5; 95% CI: 0.7–2.9) and those with no academic deadlines within a week of the blood drive were more likely to donate blood. Conclusion: University-student blood donation shows a stronger association with personal and/or electronic advertising than with impersonal and/or non-electronic advertising. University blood drives should target students with similar timetables at times of reduced academic stress using personal and electronic modes of advertising. 306
- PublicationApplying Haddon’s matrix to bovine injury prevention: An example using white line disease(World Association for Buiatrics, 2016-07-08)
; ; ;Haddon’s matrix is a model used to conceptualize injury occurrence. This model defines injury as energy transfer, by the agent to the host, in quantities or rates exceeding the tolerance of the host’s tissue. While this approach has been used in human injury research for over 30 years to identify risk factors and develop preventive interventions, we have not seen it applied to animal injury. Lameness, an etiologically complex condition, is a source of both economic losses and welfare concerns to the cattle industry. We introduce Haddon’s matrix as an approach to viewing traumatic animal injury using bovine white line disease as an example. 58
- PublicationPooled Testing for Bovine Paratuberculosis: Details Matter(Johne's Disease Integrated Program, 2010-09)
;Pooling of fecal samples with subsequent testing for Mycobacterium avium subspecies paratuberculosis (MAP) by culture or real-time PCR is used for 3 main purposes: herd or group classification, prevalence estimation and as a low-cost initial screening for identification of animals infected with MAP. Though pooling is touted to reduce costs for the latter purpose when prevalence is low, some important considerations have been overlooked. First, there is no consensus as to which pool size is optimal for a given within-herd prevalence. Second, rarely are negative pools retested. Although the choice to not retest might be reasonable if the objective is to find animals shedding moderate to high numbers of MAP (i.e. the most infectious animals), it may be sub-optimal if the goal is to detect all infected animals. Some infected pools will invariably test negative because culture and PCR are only about 50 to 60 % sensitive based on a single sample. Third, more sophisticated pooling protocols (for example those requiring re-creation of pools of half or quarter the original size) might offer cost-saving advantages Reticence about application of the latter two testing modifications is understandable since pooling is not supposed to increase laboratory work-load. 46
- PublicationA protocol to identify and minimise selection and information bias in abattoir surveys estimating prevalence, using Fasciola hepatica as an example(Elsevier, 2017-09-01)
; ; ;Abattoir surveys and findings from post-mortem meat inspection are commonly used to estimate infection or disease prevalence in farm animal populations. However, the function of an abattoir is to slaughter animals for human consumption, and the collection of information on animal health for research purposes is a secondary objective. This can result in methodological shortcomings leading to biased prevalence estimates. Selection bias can occur when the study population as obtained from the abattoir is not an accurate representation of the target population. Virtually all of the tests used in abattoir surveys to detect infections or diseases that impact animal health are imperfect, leading to errors in identifying the outcome of interest and consequently, information bias. Examination of abattoir surveys estimating prevalence in the literature reveals shortcomings in the methods used in these studies. While the STROBE-Vet statement provides clear guidance on the reporting of observational research, we have not found any guidelines in the literature advising researchers on how to conduct abattoir surveys. This paper presents a protocol in two flowcharts to help researchers (regardless of their background in epidemiology) to first identify, and, where possible, minimise biases in abattoir surveys estimating prevalence. Flowchart 1 examines the identification of the target population and the appropriate study population while Flowchart 2 guides the researcher in identifying, and, where possible, correcting potential sources of outcome misclassification. Examples of simple sensitivity analyses are also presented which approximate the likely uncertainty in prevalence estimates due to systematic errors. Finally, the researcher is directed to outline any limitations of the study in the discussion section of the paper. This protocol makes it easier to conduct an abattoir survey using sound methods, identifying and, where possible, minimizing biases. 374Scopus© Citations 7
- PublicationRisk factors for dog bites occurring during and outside of play: Are they different?(Elsevier, 2012-11-01)
; ; ;The aim of this study was to determine whether the effects of selected human-canine interaction/ environmental factors on bites occurring when the victim was and was not playing with the dog differed from each other. A veterinary clinic-based retrospective cohort study was conducted in Kingston, Jamaica (709), and San Francisco, USA (513) to compare the effects of selected exposures on non-play bites (161) relative to bites preceded by play with the dog (110) as reported by veterinary clients. Additionally, 951 non-biting dogs were used for a risk factor analysis of bites occurring during play. Using directed acyclic graphs and the change-in-estimate procedure to select and adjust for confounders, modified Poisson regression was used to estimate (a) the ratios of proportions of non-play bites out of all bites comparing exposed to unexposed dogs (proportionate bite ratios) and (b) risk ratios for bites occurring during play for each factor of interest. Proportionate bite ratios ranged from 0.84 to 1.29, with most 95% confidence intervals including one, thus implying a lack of specificity of effects of the examined factors on non-play bites relative to bites occurring during play with the dog. Consistent with this lack of specificity, risk ratios for bites occurring during play were similar in magnitude and direction to risk ratios previously published for non-play bites using the same non-biting dogs as a reference group. No country-specific differences in proportionate bite ratios were detected. Each human-canine environmental factor showed similar levels of association with both types of bites. One possible explanation is that both types of bites have a common causal pathway leading from each factor up to the point of human-canine contact. If the human-canine contact then leads to either play or non-play interactions with dogs and subsequently to both types of bites, the presence of such a common pathway would make the factor non-specific to either type of bite. As some of the examined factors are associated with increased frequencies of both types of bites, this could explain high percentages of bites occurring during play with the dog as reported in various case series of dog bites. If so, dog bite prevention strategies targeting these factors will simultaneously reduce the incidence of both types of bites. 339Scopus© Citations 14
- PublicationFirst confirmation by PCR of Jaagsiekte sheep retrovirus in Ireland and prevalence of ovine pulmonary adenocarcinoma in adult sheep at slaughter(BioMed Central, 2017-12-19)
; ; ; ;Background: Ovine pulmonary adenocarcinoma (OPA), caused by Jaagsiekte sheep retrovirus (JSRV), is characterised by the development of invariably fatal lung tumours primarily in adult sheep. High infection rates and disease prevalence can develop during initial infection of flocks, leading to on-farm economic losses and animal welfare issues in sheep with advanced disease. The disease has been reported in Ireland and is notifiable, but the presence of JSRV has never been confirmed using molecular methods in this country. Additionally, due to the difficulties in ante-mortem diagnosis (especially of latently-infected animals, or those in the very early stages of disease), accurate information regarding national prevalence and distribution is unavailable. This study aimed to confirm the presence of JSRV in Ireland and to obtain estimates regarding prevalence and distribution by means of an abattoir survey utilising gross examination, histopathology, JSRV-specific reverse transcriptase polymerase chain reaction (RT-PCR) and SU protein specific immunohistochemistry (IHC) to examine the lungs of adult sheep. Results: Lungs from 1911 adult sheep were examined macroscopically in the abattoir and 369 were removed for further testing due to the presence of gross lesions of any kind. All 369 were subject to histopathology and RT-PCR, and 46 to IHC. Thirty-one lungs (31/1911, 1.6%) were positive for JSRV by RT-PCR and/or IHC but only ten cases of OPA were confirmed (10/1911, 0.5%) Four lung tumours not associated with JSRV were also identified. JSRV-positive sheep tended to cluster within the same flocks, and JSRV-positive sheep were identified in the counties of Donegal, Kerry, Kilkenny, Offaly, Tipperary, Waterford and Wicklow. Conclusions: The presence of JSRV has been confirmed in the Republic of Ireland for the first time using molecular methods (PCR) and IHC. In addition, an estimate of OPA prevalence in sheep at slaughter and information regarding distribution of JSRV infection has been obtained. The prevalence estimate appears similar to that of the United Kingdom (UK). Results also indicate that the virus has a diverse geographical distribution throughout Ireland. These data highlights the need for further research to establish national control and monitoring strategies. 301Scopus© Citations 13
- PublicationFrequentist and Bayesian approaches to prevalence estimation using examples from Johne's disease(Cambridge University Press, 2008-01-01)
; ; ;Although frequentist approaches to prevalence estimation are simple to apply, there are circumstances where it is difficult to satisfy assumptions of asymptotic normality and nonsensical point estimates (greater than 1 or less than 0) may result. This is particularly true when sample sizes are small, test prevalences are low and imperfect sensitivity and specificity of diagnostic tests need to be incorporated into calculations of true prevalence. Bayesian approaches offer several advantages including direct computation of range-respecting interval estimates (e.g. intervals between 0 and 1 for prevalence) without the requirement of transformations or large-sample approximations, direct probabilistic interpretation, and the flexibility to model in a straightforward manner the probability of zero prevalence. In this review, we present frequentist and Bayesian methods for animal- and herd-level true prevalence estimation based on individual and pooled samples. We provide statistical methods for detecting differences between population prevalence and frequentist methods for sample size and power calculations. All examples are motivated using Mycobacterium avium subspecies paratuberculosis infection and we provide WinBUGS code for all examples of Bayesian estimation. 533Scopus© Citations 58
- PublicationThe human–canine environment: A risk factor for non-play bites?(Elsevier, 2008-08)
; ; ;Few dog bite risk factor studies have been conducted. This veterinary clinic-based retrospective cohort study was aimed at identifying human-canine environmental risk factors for non-play bites in Kingston, Jamaica (660) and San Francisco (SF), USA (452). Data were analysed using modified Poisson regression with confounders selected using directed acyclic graphs (DAGs) and the change-in-estimate procedure. Dogs acquired for companionship were more likely (RR = 1.66; 95% CI 1.02-2.70) to bite than those acquired for protection. Routinely allowing a dog into the presence of visitors was also positively associated with it biting. A dog sleeping in a family member's bedroom was a risk factor for biting in Kingston (RR = 2.54; 95% CI 1.43-4.54) but not in SF, while being able to leave the yard unaccompanied was a risk factor for biting in SF (RR = 3.40; 95% CI 1.98-5.85) but not in Kingston. Overall, dogs which were less restricted in their interactions with humans were at elevated risk for biting. An observed association with dog bites in one cultural setting might not exist in another. 625Scopus© Citations 33
- PublicationEffect of changes in testing parameters on the cost-effectiveness of two pooled test methods to classify infection status of animals in a herd(Elsevier, 2010-05-01)
; ; ;Monte Carlo simulation was used to determine optimal fecal pool sizes for identification of all Mycobacterium avium subsp. paratuberculosis (MAP)-infected cows in a dairy herd. Two pooling protocols were compared: a halving protocol involving a single retest of negative pools followed by halving of positive pools and a simple protocol involving single retest of negative pools but no halving of positive pools. For both protocols, all component samples in positive pools were then tested individually. In the simulations, the distributions of number of tests required to classify all individuals in an infected herd were generated for various combinations of prevalence (0.01, 0.05 and 0.1), herd size (300, 1000 and 3000), pool size (5, 10, 20 and 50) and test sensitivity (0.5-0.9). Test specificity was fixed at 1.0 because fecal culture for MAP yields no or rare false-positive results. Optimal performance was determined primarily on the basis of a comparison of the distributions of numbers of tests needed to detect MAP-infected cows using the Mann-Whitney U test statistic. Optimal pool size was independent of both herd size and test characteristics, regardless of protocol. When sensitivity was the same for each pool size, pool sizes of 20 and 10 performed best for both protocols for prevalences of 0.01 and 0.1, respectively, while for prevalences of 0.05, pool sizes of 10 and 20 were optimal for the simple and halving protocols, respectively. When sensitivity decreased with increasing pool size, the results changed for prevalences of 0.05 and 0.1 with pool sizes of 50 being optimal especially at a prevalence of 0.1. Overall, the halving protocol was more cost effective than the simple protocol especially at higher prevalences. For detection of MAP using fecal culture, we recommend use of the halving protocol and pool sizes of 10 or 20 when the prevalence is suspected to range from 0.01 to 0.1 and there is no expected loss of sensitivity with increasing pool size. If loss in sensitivity is expected and the prevalence is thought to be between 0.05 and 0.1, the halving protocol and a pool size of 50 is recommended. Our findings are broadly applicable to other infectious diseases under comparable testing conditions. 287Scopus© Citations 5
- PublicationEstimation of the serial interval and proportion of pre-symptomatic transmission events of COVID-19 in Ireland using contact tracing data(BioMed Central, 2021-04-27)
; ; ; ; ; ; ; ; ; ; ;The serial interval is the period of time between the onset of symptoms in an infector and an infectee and is an important parameter which can impact on the estimation of the reproduction number. Whilst several parameters influencing infection transmission are expected to be consistent across populations, the serial interval can vary across and within populations over time. Therefore, local estimates are preferable for use in epidemiological models developed at a regional level. We used data collected as part of the national contact tracing process in Ireland to estimate the serial interval of SARS-CoV-2 infection in the Irish population, and to estimate the proportion of transmission events that occurred prior to the onset of symptoms. Results After data cleaning, the final dataset consisted of 471 infected close contacts from 471 primary cases. The median serial interval was 4 days, mean serial interval was 4.0 (95% confidence intervals 3.7, 4.3) days, whilst the 25th and 75th percentiles were 2 and 6 days respectively. We found that intervals were lower when the primary or secondary case were in the older age cohort (greater than 64 years). Simulating from an incubation period distribution from international literature, we estimated that 67% of transmission events had greater than 50% probability of occurring prior to the onset of symptoms in the infector. Conclusions Whilst our analysis was based on a large sample size, data were collected for the primary purpose of interrupting transmission chains. Similar to other studies estimating the serial interval, our analysis is restricted to transmission pairs where the infector is known with some degree of certainty. Such pairs may represent more intense contacts with infected individuals than might occur in the overall population. It is therefore possible that our analysis is biased towards shorter serial intervals than the overall population. 136Scopus© Citations 3