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Free Content Similar seasonal peak in clustered and unique extra-pulmonary tuberculosis notifications: winter crowding hypothesis ruled out?

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BACKGROUND: The incidence of extra-pulmonary tuberculosis (EPTB) in the Netherlands shows a seasonal trend, with a peak in spring and a trough in autumn. Possible causes of this peak are winter crowding and a seasonal decrease in immune competence in spring. A third explanation may be a reporting bias.

OBJECTIVE: To investigate the role of winter crowding by a time-series analysis of notification data. DNA fingerprinting clustering status can differentiate between recent and remote infections. Seasonality in clustered cases would reflect enhanced transmission in winter and/or seasonally lowered immunity, while seasonality in unique cases would only reflect seasonally lowered immunity.

METHODS: We fitted (seasonal) auto-regressive moving average models to culture-positive TB notifications in the Netherlands (1993–2008) to assess seasonality. We then used seasonal trend Loess decompositions to derive the seasonal pattern, and compared the heights of the seasonal peaks.

RESULTS: Clustered and unique EPTB notifications showed a seasonal trend that was absent in clustered and unique PTB notifications. The seasonal peak in clustered EPTB cases was not significantly higher than in unique EPTB cases.

CONCLUSIONS: The similar timing and height of the seasonal peak of clustered and unique EPTB cases suggests that winter crowding is unlikely to cause the seasonal trend in notifications.
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Keywords: ARMA; disease localisation; seasonal peak; statistical model; vitamin D

Document Type: Research Article

Affiliations: 1: National Institute for Public Health and the Environment, Epidemiology and Surveillance, Bilthoven, The Netherlands; ResultsinHealth, Leiderdorp, The Netherlands 2: National Institute for Public Health and the Environment, Department of Statistics and Mathematical Modelling, Bilthoven, The Netherlands 3: National Institute for Public Health and the Environment, Epidemiology and Surveillance, Bilthoven, The Netherlands

Publication date: November 1, 2013

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  • 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.

    Certain IJTLD articles are selected for translation into French, Spanish, Chinese or Russian. They are available on the Union website

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