Tuberculosis seasonality in the Netherlands differs between natives and non-natives: a role for vitamin D deficiency?
OBJECTIVE: To investigate factors associated with seasonal patterns of TB disease in the Netherlands by splitting notifications according to origin (natives vs. non-natives) and disease site (pulmonary TB [PTB] vs. extra-pulmonary TB [EPTB]). We focus on the presence of a seasonal peak, as much debate has centred on factors enhancing transmission vs. disease development.
DESIGN: Monthly notifications were derived from culture sample dates of all cases between 1993 and 2008. We fitted seasonal autoregressive integrated moving average (SARIMA) models to the time series. Seasonal decomposition revealed seasonal trends. To assess the seasonality of the peak, we repeated the analysis omitting December (trough) notifications.
RESULTS: TB notifications show a seasonal pattern, with a peak in spring and a trough in winter, which is present in both PTB and EPTB and in both natives and non-natives. However, when excluding December notifications, seasonality only holds in non-native EPTB and non-native TB notifications.
CONCLUSION: A seasonal peak in TB notifications (March–June) is apparent in non-natives, but is absent in natives. This peak is driven by the seasonality of EPTB notifications, which are highest in June–July. The contribution of winter crowding is discussed. Vitamin D deficiency, enhancing disease development at the end of winter–early spring, seems the most likely factor explaining the yearly peak in EPTB.
Document Type: Research Article
Affiliations: 1: Epidemiology and Surveillance, Tuberculosis and M/XDR-TB Programme, National Institute for Public Health and the Environment, Bilthoven, The Netherlands 2: Centre for Infectious Diseases, World Health Organization, Regional Office for Europe, Copenhagen, Denmark; National Tuberculosis Reference Laboratory, National Institute for Public Health and the Environment, Bilthoven, The Netherlands 3: KNCV Tuberculosis Foundation, The Hague, The Netherlands 4: National Tuberculosis Reference Laboratory, National Institute for Public Health and the Environment, Bilthoven, The Netherlands; Department of Clinical Infectious Diseases, Department of Pulmonary Disease, Radboud University Nijmegen Medical Centre, Nijmegen, The Netherlands
Publication date: 2012-05-01
The International Journal of Tuberculosis and Lung Disease publishes articles on all aspects of lung health, including public health-related issues such as training programmes, cost-benefit analysis, legislation, epidemiology, intervention studies and health systems research. The IJTLD is dedicated to the continuing education of physicians and health personnel and the dissemination of information on tuberculosis and lung health world-wide.
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