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. 2012 Jun;54(11):1553-60.
doi: 10.1093/cid/cis235. Epub 2012 Apr 3.

Seasonality of tuberculosis in the United States, 1993-2008

Matthew D Willis  1 , Carla A Winston, Charles M Heilig, Kevin P Cain, Nicholas D Walter, William R Mac Kenzie
Affiliations

Seasonality of tuberculosis in the United States, 1993-2008

Matthew D Willis et al. Clin Infect Dis. 2012 Jun.

Abstract

Background: Although seasonal variation in tuberculosis incidence has been described in several recent studies, the mechanism underlying this seasonality remains unknown. Seasonality of tuberculosis disease may indicate the presence of season-specific risk factors that could potentially be controlled if they were better understood. We conducted this study to determine whether tuberculosis is seasonal in the United States and to describe patterns of seasonality in specific populations.

Methods: We performed a time series decomposition analysis of tuberculosis cases reported to the Centers for Disease Control and Prevention from 1993 through 2008. Seasonal amplitude of tuberculosis disease (the difference between the months with the highest and lowest mean case counts), was calculated for the population as a whole and for populations with select demographic, clinical, and epidemiologic characteristics.

Results: A total of 243 432 laboratory-confirmed tuberculosis cases were reported over a period of 16 years. A mean of 21.4% more cases were diagnosed in March, the peak month, compared with November, the trough month. The magnitude of seasonality did not vary with latitude. The greatest seasonal amplitude was found among children aged <5 years and in cases associated with disease clusters.

Conclusions: Tuberculosis is a seasonal disease in the United States, with a peak in spring and trough in late fall. The latitude independence of seasonality suggests that reduced winter sunlight exposure may not be a strong contributor to tuberculosis risk. Increased seasonality among young children and clustered cases suggests that disease that is the result of recent transmission is more influenced by season than disease resulting from activation of latent infection.

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Conflict of interest statement

Potential conflicts of interest. All authors: No reported conflicts.

All authors have submitted the ICMJE Form for Disclosure of Potential Conflicts of Interest. Conflicts that the editors consider relevant to the content of the manuscript have been disclosed.

Figures

Figure 1
Figure 1
Seasonal decomposition of laboratory-confirmed tuberculosis cases per month, United States, 1993–2008; raw data (A) with trend (B), seasonal factor (C), and irregular (random) factor (D).
See this image and copyright information in PMC

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