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

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
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