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

Chapter 11
clinicians to the Public Health Services and laboratories likely to actively approach
clinicians in case of falciparum malaria, a potentially short-term fatal illness requiring
immediate treatment, are identified in the data and incorporated in a relatively
parsimonious log-linear capture-recapture model. In this model the absence of three-way
interaction, i.e. interaction between all three registers, has to be assumed but, when
present, three-way interaction bias is arguably less than in a saturated capture-recapture
model, incorporating all two-way interactions.
For Legionnaires’ disease internal validity analysis and stratified capturerecapture
analysis indicated a significant interaction between the notification and the
laboratory registers. This interaction is expected as the notification criteria specifically
include laboratory diagnosis and at the time of this study many laboratories probably prenotified
positive Legionella test results to public health physicians. Log-linear capturerecapture
analysis for Legionnaires’ disease incidence initially selected the saturated model
as the best-fitting model. However, capture-recapture models with a better fit do not
necessarily produce a more reliable estimate. 10 Three-way interaction cannot be
incorporated in the saturated model and, when present, could render the estimates less
valid. However, violation of the absent three-way interaction assumption does not seem
to explain possible bias in the capture-recapture estimate for Legionnaires’ disease
incidence. This estimate is considered to be high while dependence between the registers
is expected to be positive, resulting in underestimation, and the unbiased estimate would
be even higher. 11-13
The most significant (positive) interactions between the registers are expected
for tuberculosis, not only because tuberculosis is an infectious disease with human to
human transmission but also as a result of the well-organised system of tuberculosis
control and surveillance in the Netherlands. Initially a saturated log-linear capturerecapture
model, with the best goodness-of-fit, was selected but the estimate seemed
implausibly high. For similar reasons as described for Legionnaires’ disease, violation of
the absent three-way interaction assumption cannot explain bias in this estimate. After
corrections for possible violations of the perfect record-linkage and perfect positive
predictive value assumptions, a relatively parsimonious log-linear capture-recapture model
fitted the data best and gave a considerably lower and more plausible estimate. The two
significant two-way interactions in this model are between the notification and laboratory
registers and between the notification and hospital registers. The first interaction can be
partially explained by laboratory pre-notification and partially by tuberculosis control
physicians, who are processing the notifications, diagnosing approximately one-third of all
tuberculosis patients in the Netherlands, almost exclusively patients with pulmonary
tuberculosis and a high bacteriological confirmation rate. The fact that in the Netherlands
two-third of all tuberculosis cases are treated by a limited group of hospital-based
clinicians, often familiar with the notification procedures, and referral of patients by
tuberculosis control physicians for further clinical evaluation or isolation could explain
the interaction between the notification and hospital registers. Perhaps the fact that most
cases of extrapulmonary tuberculosis, less often culture-confirmed, are diagnosed in a
hospital explains why in our capture-recapture model the interaction between the
laboratory and hospital registers is not significant.
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