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

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General discussion studies). Obtaining additional data sources through surveys contravenes one of the alleged advantages of capture-recapture analysis for (infectious) disease surveillance, namely of being cheap, quick and simple by using existing data sources. 1 Absence of a specific code for Legionnaires’ disease in ICD-9 had another negative influence on the feasibility of this study. The hospital episode statistics used a proxy-code for Legionnaires’ disease, ICD-9 code 482.8, inviting the presence of an unknown number of false-positive patients without Legionnaires’ disease. These experiences underpin the need for thorough examination of availability, quality and specificity of infectious disease registrations as part of the preparation of possible capture-recapture studies. Validity Closed population assumption Violation of the closed population assumption is intuitively highest for malaria as malaria infection occurs almost by definition abroad while Legionnaires’ disease and tuberculosis are both partly endemic diseases. However, for all three infectious diseases, translated into the capture-recapture probabilities for an individual patient, violation of the closed population assumption is presumably limited as the opportunities for notification, laboratory-confirmation or hospitalisation are determined within a relatively short period of time. All three diseases were category B disease at the time of the study, i.e. to be notified by the diagnosing physician within 24 hours. For malaria both thick and thin smear microscopy and serological antigen tests are processed fast. For Legionnaires’ disease, with the increased use of the urinary antigen test, laboratory results are also rapidly available. 2 For tuberculosis sputum collection or bronchoscopy can be done quickly and smear-microscopy results are readily available. The culture can take weeks to become positive but this does not influence the capture-probability in the laboratory register. Laboratory pre-notification of positive test results to public health physicians contributes to rapid notification. Laboratory pre-notification of positive tuberculosis and Legionnaires’ disease results to the Public Health Services is arguably more likely than for malaria because tuberculosis is transmitted from human to human and Legionnaires’ disease can be caused by local contaminated water sources and urgent preventive interventions may be necessary. When Legionnaires’ disease, a disease with a relatively high case-fatality rate, is suspected on clinical and/or epidemiological grounds, patients are likely to be immediately hospitalised, as suggested by the highest ascertained registerspecific coverage for the hospital register (85%) of the three infectious diseases studied. For malaria the ascertained hospitalisation rate is lower (49.3%), indicating that mild presentations of benign forms of malaria are treated on an out-patient basis, but Plasmodium falciparum malaria patients are likely to be immediately hospitalised. The probability for hospitalisation for tuberculosis (40.7%) is less compared to Legionnaires’ disease and malaria because in the Netherlands non-infectious tuberculosis patients are predominantly treated as out-patients and even infectious cases are preferably isolated at home. But for most tuberculosis patients the decision on hospitalisation will be taken rapidly. Limited violation of the closed population assumption could result in some 159
Chapter 11 overestimation of the number of malaria, Legionnaires’ disease and tuberculosis patients in the Netherlands. Perfect record-linkage assumption For all three infectious diseases studied, unique identification numbers, such as a social security number, used in all registers, allowing optimal record-linkage, did not exist. In all studies record-linkage was manual, through almost similar procedures described in chapters 4 to 6, using patients’ identifiers such as date of birth and postcode. The malaria and tuberculosis studies were performed before 1999 when in the Netherlands a new Infectious Diseases Act came into force, 3 recording only year of birth instead of date of birth, effectively ruling out reliable record-linkage between the notification and other registers. Therefore still sufficient demographical, geographical and microbiological identifiers could be collected at source for adequate record-linkage. In addition, for tuberculosis record-linkage was relaxed and near-links were double-checked. Despite these efforts still indications for imperfect record-linkage exist. First, the notification register and the Netherlands Tuberculosis Register (NTR) should overlap completely but we found only 91.1% overlap after record-linkage. Second, some culture-positive tuberculosis patients could not be found in the notification register but were linked to the NTR. Although before cross-validation misclassification of tuberculosis patients was considered to be minimal, this study demonstrated that imperfect record-linkage can exceed expectations, with considerable impact on the capture-recapture estimates. Initially unidentified indications for misclassification could not be investigated for malaria and Legionnaires’ disease. The capture-recapture study on the incidence of Legionnaires’ disease was performed after the new Infectious Diseases Act came into force. Therefore information on the date of birth of the patients could no longer be collected from the national notification register at source but had to be obtained from the local Public Health Services processing the notifications, creating more opportunities for clerical errors and remaining incomplete information on personal identifiers in some records, jeopardising reliable record-linkage. This may have caused more misclassification of patients over the registers compared to the malaria and tuberculosis capture-recapture studies. The impact of changes in the infectious disease legislation in the Netherlands on the validity of capture-recapture estimates was demonstrated in a follow-up capturerecapture study on malaria incidence in the Netherlands between 1995 and 2003. 4 After 1999 the malaria incidence estimates more than doubled, almost certainly reflecting overestimation as a result of imperfect record-linkage. Inaccurate record-linkage, i.e. incorrectly establishing the recapture, can substantially alter the observed and unobserved fractions. 5 Depending on the number of missed links and mislinks, violation of the perfect record-linkage assumption can result in overestimation or underestimation of the number of malaria, Legionnaires’ disease and tuberculosis patients in the Netherlands. 160
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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
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Chapter 1 1.1 Assessing completenes
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Chapter 1 94% among AIDS patients w
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Table 1.1 Objectives, methods, data
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Researchers Objective Method Data-s
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Chapter 1 source capture-recapture
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Chapter 1 32. Bradley BL, Kerr KM,
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2 Methodology of capture-recapture
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Methodology of capture-recapture an
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Chapter 3 3.1 Application of captur
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Table 3.1 Published capture-recaptu
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Disease Authors Objective Method Da
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Chapter 3 3.3 References 1. Hook EB
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Chapter 3 52. Reintjes R, Termorshu
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Chapter 4 Abstract The aim of this
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Chapter 4 Methods Nearly all Dutch
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Chapter 4 Table 4.2 The number of m
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Chapter 4 diagnosis. Other patients
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Chapter 4 stratify the population i
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Chapter 4 25. Lambeth, Southwark an
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Chapter 5 Abstract To estimate inci
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Chapter 5 patients. Capture-recaptu
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Chapter 5 Figure 5.1 Four regions o
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Chapter 5 Hospital records From 385
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Chapter 5 Table 5.1 Epidemiological
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Table 5.2 Number and proportion of
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Chapter 5 cautious about the associ
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Chapter 5 Incidence of community-ac
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Chapter 6 Abstract The aim of this
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Chapter 6 3. Hospitalised patients
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Chapter 6 Record-linkage of all 537
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Chapter 6 Figure 6.1 Schematic view
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Chapter 6 Table 6.2 Total and strat
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Chapter 6 administrative discrepanc
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Chapter 6 the patients, and complet
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7 Undetected burden of tuberculosis
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Introduction Underreporting of tube
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Underreporting of tuberculosis in t
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Table 7.1 Total and subset numbers
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Table 7.2 Capture-recapture estimat
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Page 126 and 127: 9 Estimating the coverage of tuberc
Page 128 and 129: Introduction Estimating targeted mo
Page 130 and 131: Estimating targeted mobile tubercul
Page 136 and 137: References Estimating targeted mobi
Page 138 and 139: 10 Estimating infectious diseases i
Page 140 and 141: Introduction Estimating infectious
Page 142 and 143: Estimating infectious disease incid
Page 144 and 145: Study Disease and number of patient
Page 146 and 147: 4. Gallay A, Vaillant V, Bouvet P,
Page 148 and 149: Table 10.3 Comparison of the variou
Page 150 and 151: Discussion Estimating infectious di
Page 156: Estimating infectious disease incid
Page 159: Chapter 11 The aim of this thesis i
Page 163 and 164: Chapter 11 clinicians to the Public
Page 165 and 166: Chapter 11 operation with the chest
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Page 169 and 170: Chapter 11 Question 3: What is the
Page 171 and 172: Chapter 11 11.2 Some findings of th
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Page 176 and 177: Summary Summary Surveillance is an
Page 178 and 179: Summary linkage of notification and
Page 180 and 181: Samenvatting Samenvatting Surveilla
Page 182 and 183: Samenvatting subgroepen binnen de b
Page 184 and 185: Acknowledgements Acknowledgements W
Page 186 and 187: Curriculum vitae Rob van Hest was b
Page 188 and 189: Publications This thesis Van Hest N
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