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

Chapter 11
11.2 Some findings of this thesis in the context of surveillance of
tuberculosis and other infectious diseases
Hospital episode statistics often are not a reliable source for record-linkage or capturerecapture
analysis for infectious disease surveillance for several reasons. Firstly, it may be
difficult to examine the hospital episode statistics dataset for multiple entries of one
patient, reflecting transfers between wards counted as separate disease episodes during
one uninterrupted stay in the hospital, and cleaning is time-consuming. It is also possible
that day-care visits or out-patient visits erroneously appear as admissions in the hospital
episode statistics. Secondly, the disease codes assigned to hospital episode statistics
records can reflect the differential diagnoses upon admission, e.g. an observation for a
presumed malaria episode or a diagnostic procedure for a specific disease, such as a
bronchoscopy because of radiological abnormalities compatible with tuberculosis among
other lung diseases, without subsequent confirmation of the diagnosis. Finally, the
specificity can be reduced when the absence of specific disease codes causes a proportion
of false-positive records, as reflected in chapter 5. For example, in the Netherlands still
the ICD-9 codes are used for hospital episode statistics instead of the more recent,
comprehensive and internationally used ICD-10 codes. But even in the presence of
detailed and specific disease codes, as exist for tuberculosis, the proportion of falsepositive
records can be high, from 27% among all patients in a local tuberculosis hospital
register in Liverpool, United Kingdom, 8 to possibly 62% among the unlinked patients in a
national tuberculosis hospital register in the Netherlands (chapter 6) and certainly 80%
among the unlinked patients in a regional tuberculosis hospital register in the Piedmont
region, Italy (chapter 7). The logistic regression population mixture model described in
chapter 8 estimated the proportion of false-positive records among the unlinked patients
in a national tuberculosis hospital register in England to be 72%. Possible false-positive
cases in hospital episode registers could explain why most of the published capturerecapture
studies on tuberculosis are local or regional, involving a relatively small number
of patients, as shown in Table 1.1. This allows for the hospital charts to be scrutinised for
false-positive cases manually, although this is time-consuming and comes closer to
counting than estimating patients. Only when the number of patients was too small for a
local study, e.g. tuberculous meningitis patients, capture-recapture analysis was performed
at the national level. 32
The capture-recapture studies for malaria and tuberculosis in chapters 4, 6, 7 and
8 show that in addition to the linked notification and laboratory registers a limited
number of patients were identified through the hospital register, possibly including a
substantial number of false-positive cases. Only the capture-recapture study on the
incidence of Legionnaires’ disease described in chapter 5 found the majority of the cases
through the hospital register. These five chapters of this thesis have shown that capturerecapture
analysis, as a method to estimate infectious disease incidence and completeness
of registration, is not the cheap, quick, simple and reliable method as once advocated.
Instead of capture-recapture analysis including hospital episode registers, record-linkage
and case-ascertainment using the two most relevant sources for infectious disease
surveillance, namely notification and laboratory, both with an expected high specificity
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