Rob van Hest Capture-recapture Methods in Surveillance - RePub ...

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Underreporting of malaria in the Netherlands areas, such as West-Africa. 22 Participation in peace-keeping operations or elections, 23,24 the number and nationalities of immigrants and asylum-seekers24-26 or the extent of certain marginalised groups25,27 can also alter the incidence of imported malaria cases over a certain period of time, as well as influence the proportion of the different malaria parasites. In the Netherlands an increase could be observed in the proportion of malaria caused by P. falciparum. Around 1980 falciparum malaria was responsible for approximately 40% of all notified malaria cases but 10 years later this had increased to almost 70%. 21 In the 1990s the proportion of falciparum malaria stabilised around 60%. Estimates of underreporting are frequently derived from different settings. They can be based upon surveys performed at the national level28 or among small groups. 25,29 The background of the data that are compared with the official notification register may be different, and can vary between hospital admission data, 3 laboratory-based information, 25,28 physicians consulting a Reference Laboratory29 or travellers. 30 The different registers were sometimes matched at the individual level, 25 at times in a stratified manner3 or in another way. 28 In this study we used a well-described and replicable method and estimated the completeness of notification of three different malaria registers through capture-recapture analysis. For the three-sample capture-recapture technique to be valid, four assumptions must hold. 17-20 First, overlap between registers must be established without erroneously misclassifying people as observed in only one, two or all three registers. This can be achieved when cases can be uniquely identified. We used individual identifiers for each of the patients and only two patients could not be identified beyond doubt due to (partially) missing identifiers. It is important that only true cases are counted. Ideally both the positive predictive value and the negative predictive value of the registrations should be 100%. None of our registrations will meet this condition, although in the case of malaria specifically, we assume that the positive predictive value will be high. The large overlap of the hospital records and the notification data with one or two of the other registrations also supports this view. When the positive predictive value of registrations is low capturerecapture analysis will result in overestimating the number of cases. Second, the registers should preferably, but not necessarily, be ‘independent’, meaning that the probability of being recorded in one register is not affected by being (or not being) registered in another. Such dependence can result from co-operation between the agencies that keep the different registrations, exchange of information or a more or less predictable flow of patients along various institutions due to referral. In two-sample capture-recapture methods this assumption is crucial and dependencies can cause underor overestimation. In the three-sample capture-recapture approach pair-wise dependencies between registers can be handled analytically. In the log-linear model they can be identified as interactions in the model. Since we could not rule out pair-wise dependencies, we decided not to rely on the two-sample capture-recapture analysis but instead to use Fienberg’s method. Third, the population should be “homogeneous” meaning that the population under consideration should not be composed of segments that have markedly different capture-recapture probabilities. One way of handling the homogeneity assumption is to 59
Chapter 4 stratify the population into more homogeneous strata and then to carry out capturerecapture analyses for each of the distinct subgroups. We performed a stratified capturerecapture analysis by type of plasmodium. This resulted in a slightly, but not significantly, higher total number of estimated malaria cases of 788 patients. The detection rates of patients with different plasmodia do not show considerable variation. This may indicate the absence of a violation of the homogeneity assumption. However, we cannot exclude the possible presence of other (but unmeasured) sources of heterogeneity. Finally, the population should be ‘closed’ such that the true population size is neither affected by people entering the population (e.g. through in-migration of cases and disease onset) nor by people leaving the population (e.g. through out-migration, recovery or mortality). The closed population assumption should be given critical attention because the aim of this study was to obtain an estimate of the incidence of imported malaria cases and violation might have resulted in overestimation (because incident cases may be late entries who have, therefore, a smaller probability of being captured more than once). When an open population is assumed, this could be handled in two different ways. One method is to perform the analysis of the different registrations within a short period of time and therefore the population could be considered as ‘closed’ during this interval. For imported malaria, a relatively rare disease with a short course, this approach does not seem feasible. An alternative is to use more complicated models, allowing for migration, birth and death to take place, such as the Jolly-Seber model. 31 The design of capturerecapture studies, the data requirements, the validity of the outcome of the different analyses and the selection of the most appropriate model to estimate the incidence of imported malaria and other infectious diseases should be given thought in further studies. In the context of these considerations our results suggest that laboratory-based notification can considerably increase the number of reported malaria cases as compared to notification by physicians. Since we actively approached the laboratories their level of underreporting found in this study cannot necessarily be extrapolated to the level of underreporting for laboratory notification. However, malaria was notified 571 times in 2001. Assuming a similar number of cases of imported malaria, this figure lies well within the range of our laboratory results for 1996. But possibly one-third of the malaria cases may still go unreported. Acknowledgements This study was performed in co-operation with the Office of the Chief Medical Officer in the Netherlands, the Netherlands Society of Parasitology (NVP), the Foundation for Parasitology Laboratory Diagnosis (SPLD), the Foundation for Quality Assessment in Medical Microbiology (SKMM) and the Centre for Communicable Disease Epidemiology of the National Institute of Public Health and the Environmental (RIVM). Permission was obtained from the Inspector-General for Infectious Diseases at the Office of the Chief Medical Officer and the Privacy Commission of the National Morbidity Registration (LMR). We thank the heads of the participating laboratories for their cooperation. 60
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Capture-recapture Methods in Survei
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Colofon Capture-recapture methods i
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Promotiecommissie Promotor: Prof.dr
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Contents Page 1 Introduction 9 2 Me
Page 11 and 12: Chapter 1 1.1 Assessing completenes
Page 13 and 14: Chapter 1 94% among AIDS patients w
Page 15 and 16: Table 1.1 Objectives, methods, data
Page 17 and 18: Researchers Objective Method Data-s
Page 19 and 20: Chapter 1 source capture-recapture
Page 21 and 22: Chapter 1 32. Bradley BL, Kerr KM,
Page 24 and 25: 2 Methodology of capture-recapture
Page 26 and 27: Methodology of capture-recapture an
Page 36: Methodology of capture-recapture an
Page 39 and 40: Chapter 3 3.1 Application of captur
Page 41 and 42: Table 3.1 Published capture-recaptu
Page 43 and 44: Disease Authors Objective Method Da
Page 49 and 50: Chapter 3 3.3 References 1. Hook EB
Page 51 and 52: Chapter 3 52. Reintjes R, Termorshu
Page 53 and 54: Chapter 4 Abstract The aim of this
Page 55 and 56: Chapter 4 Methods Nearly all Dutch
Page 57 and 58: Chapter 4 Table 4.2 The number of m
Page 59: Chapter 4 diagnosis. Other patients
Page 63 and 64: Chapter 4 25. Lambeth, Southwark an
Page 65 and 66: Chapter 5 Abstract To estimate inci
Page 67 and 68: Chapter 5 patients. Capture-recaptu
Page 69 and 70: Chapter 5 Figure 5.1 Four regions o
Page 71 and 72: Chapter 5 Hospital records From 385
Page 73 and 74: Chapter 5 Table 5.1 Epidemiological
Page 75 and 76: Table 5.2 Number and proportion of
Page 77 and 78: Chapter 5 cautious about the associ
Page 79 and 80: Chapter 5 Incidence of community-ac
Page 81 and 82: Chapter 6 Abstract The aim of this
Page 83 and 84: Chapter 6 3. Hospitalised patients
Page 85 and 86: Chapter 6 Record-linkage of all 537
Page 87 and 88: Chapter 6 Figure 6.1 Schematic view
Page 89 and 90: Chapter 6 Table 6.2 Total and strat
Page 91 and 92: Chapter 6 administrative discrepanc
Page 93 and 94: Chapter 6 the patients, and complet
Page 96 and 97: 7 Undetected burden of tuberculosis
Page 98 and 99: Introduction Underreporting of tube
Page 100 and 101: Underreporting of tuberculosis in t
Page 102 and 103: Table 7.1 Total and subset numbers
Page 104 and 105: Table 7.2 Capture-recapture estimat
Page 106 and 107: Underreporting of tuberculosis in t
Page 108: Underreporting of tuberculosis in t
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Chapter 8 Abstract In 1999 the Enha
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Chapter 8 bacteriological confirmat
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Chapter 8 Results Table 8.1 shows t
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Table 8.3 Annual and overall observ
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Table 8.4 Annual and overall estima
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Chapter 8 interaction however, i.e.
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Chapter 8 shows that observed under
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9 Estimating the coverage of tuberc
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Introduction Estimating targeted mo
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Estimating targeted mobile tubercul
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References Estimating targeted mobi
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10 Estimating infectious diseases i
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Introduction Estimating infectious
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Estimating infectious disease incid
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Study Disease and number of patient
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4. Gallay A, Vaillant V, Bouvet P,
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Table 10.3 Comparison of the variou
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Discussion Estimating infectious di
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Chapter 11 The aim of this thesis i
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Chapter 11 overestimation of the nu
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Chapter 11 clinicians to the Public
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Chapter 11 operation with the chest
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Chapter 11 of the proportion of fal
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Chapter 11 Question 3: What is the
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Chapter 11 11.2 Some findings of th
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Chapter 11 • To improve timelines
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Summary Summary Surveillance is an
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Summary linkage of notification and
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Samenvatting Samenvatting Surveilla
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Samenvatting subgroepen binnen de b
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Acknowledgements Acknowledgements W
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Curriculum vitae Rob van Hest was b
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Publications This thesis Van Hest N
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