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Home / The International Journal of Tuberculosis and Lung Disease, Volume 17, Number 11

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.

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: 01 November 2013

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  • The International Journal of Tuberculosis and Lung Disease (IJTLD) is for clinical research and epidemiological studies on lung health, including articles on TB, TB-HIV and respiratory diseases such as COVID-19, asthma, COPD, child lung health and the hazards of tobacco and air pollution. Individuals and institutes can subscribe to the IJTLD online or in print – simply email us at [email protected] for details.

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