PhD thesis - University of Hertfordshire Research Archive

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On average, four risk factors were identified in each study, with the number of factors ranging from one to twenty. Single variable Poisson regression analysis revealed that the number of risk factors identified in studies was unaffected by the decade in which it was undertaken, the area covered, or the duration of the study (Appendix 3; table A3.5). Limiting studies to indigenous cases, altering the exposure period, or applying multivariate statistical techniques in analysis also had no effect. However, the number of reported risk factors identified in studies was positively influenced by the number of cases or controls included in the study (and hence the overall study size), and the number of variables considered. Multivariable analysis controlling for study year demonstrated that only the number of controls included (Relative Risk (RR) 1.42; 95% Confidence Interval (CI) 1.03-1.94; P=0.031) and the number of variables investigated (RR 1.33; 95%CI 1.00- 1.77; P=0.048) were independently associated with the number of risk factors identified. There are two possible explanations for each of these associations. It is possible that an increase in the number of controls in the studies has increased the statistical power, making it possible to detect true risk differences which exist between cases and controls which had hitherto remained unidentified. However, if this was the case one would expect a synergistic effect with the number of cases in studies, but this was not observed, although it was noted that the case and control variables were highly correlated (coefficient 0.86; p
The content of peer-reviewed publications are influenced by editorial restrictions and researchers‟ perceptions of the most important aspects of their studies, and these factors might influence the analysis of data derived from published case-control studies. Nevertheless, the body of evidence available in the literature suggests that case-control studies of Campylobacter infection are increasing in size and complexity without the corresponding improvement in our understanding of disease transmission. If anything, the move towards larger studies is perhaps magnifying the biases inherent in the methodology. Furthermore, they appear to be influenced heavily by investigator and reporter bias, as evidenced by the disproportionate pursuit of the poultry hypothesis, which continues to explain only a fraction of cases. 4.3 Case-case comparisons Case-case comparisons have been suggested as an alternative to case- control studies for studying the epidemiology of infectious diseases (McCarthy & Giesecke, 1999). These rely on comparing the exposures of one set of cases with those from another similar, but suitably different, set of cases. These studies have a number of advantages. Firstly, as the name suggests, there is no need to enrol healthy controls for comparison as the study consists wholly of cases. This means that studies are not only easier to conduct (control selection and recruitment is often problematic and labour- intensive) but there is also no need (in most instances) to obtain ethical approval if these studies are conducted within a primary surveillance framework. Indeed, this is a prerequisite in most instances, otherwise selection bias might occur. Second, case-case studies have the potential to use all (or most) of the cases within a study population, meaning that any findings relate to the entire study population. This does not usually occur in case-control studies, where only a small proportion of cases within a study population are used and the findings are (rightly or wrongly) extrapolated to the entire population. Thirdly, assuming suitable groups of cases are 30
Page 1 and 2: Population-Based Sentinel Surveilla
Page 3 and 4: The research carried out by the can
Page 5 and 6: Dedication. This thesis is dedicate
Page 7 and 8: 7. Results (the published work). ..
Page 9 and 10: Statement identifying the degree fo
Page 11 and 12: Paper Reference Page 6 Gillespie IA
Page 13 and 14: Statement of the candidate’s cont
Page 15 and 16: Declaration form. I, Iain Andrew Gi
Page 17 and 18: 2. History. In contrast to other co
Page 19 and 20: The application of veterinary techn
Page 21 and 22: The incidence of laboratory-confirm
Page 23 and 24: were elderly or had a pre-existing
Page 25 and 26: they would for other bacterial gast
Page 27 and 28: papers (Pearson et al., 1977; Bruce
Page 29: Studies were most frequently conduc
Page 33 and 34: infection. An approximation of the
Page 35 and 36: hypotheses a „blank canvas‟ app
Page 37 and 38: 6. Materials and methods. Regional
Page 39 and 40: presentation and severity, foreign
Page 41 and 42: together, etc). The results of the
Page 43 and 44: and improve response during the stu
Page 45 and 46: The published work. 7.1 Epidemiolog
Page 47 and 48: community illness was more common a
Page 49 and 50: north west England and in Yorkshire
Page 51 and 52: community was no different from oth
Page 53 and 54: provide useful insights into the ep
Page 55 and 56: Cases in case-control studies of la
Page 57 and 58: 8. Discussion. The research carried
Page 59 and 60: The sentinel health authorities wer
Page 61 and 62: fundamentally flawed. Since the app
Page 63 and 64: control studies. The potential role
Page 65 and 66: Campylobacter spp. from cattle farm
Page 67 and 68: Cameron, S., Ried, K., Worsley, A.,
Page 69 and 70: Doyle, L. P. 1948, "The etiology of
Page 71 and 72: other industrialised countries," in
Page 73 and 74: Hanel, C. M. & Atanassova, V. 2007,
Page 75 and 76: Hudson, S. J., Lightfoot, N. F., Co
Page 77 and 78: Kessel, A. S., Gillespie, I., O'Bri
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Department of Health and Human Serv
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Potter, R. C., Kaneene, J. B., & Ha
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Siemer, B. L., Harrington, C. S., N
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Sopwith, W., Birtles, A., Matthews,
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Campylobacter infection: a general
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The published work 90
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Table A1.1: Notable events in the h
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Year Human medicine Veterinary medi
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Levy, A. J. 1928, "A gastro-enterit
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Appendix 2. An assessment of the ro
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compare the period after 2000 with
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condition was significantly associa
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Deaths/100,000 cases 600 500 400 30
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Table A2.1: Factors affecting the u
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Appendix 3. An analytical review of
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to indigenously acquired infection
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susceptibility to Campylobacter inf
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year demonstrated that only the num
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Table A3.1 Reported epidemiological
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Table A3.3 Selected reported risk f
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Table A3.5. The effect of various r
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Deming, M. S., Tauxe, R. V., Blake,
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Harris, N. V., Weiss, N. S., & Nola
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Kist, M. & Rossner, R. 1985a, in Ca
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Oosterom, J., den Uyl, C. H., Banff
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Severin, W. P. J. 1982, "Epidemiolo
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Appendix 4. The Campylobacter Senti
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