Seasonal drivers of tuberculosis: evidence from over 100 years of notifications in Cape Town
METHODS: We reviewed data on TB notifications in Cape Town, South Africa, from 1903 to 2017 (exclusive of 1995–2002, which were unavailable). Data from 2003 onward were stratified by HIV status, age and notification status (new vs. retreatment). We performed seasonal decomposition and time-dependent spectral analysis using wavelets to assess periodicity over time. We estimated monthly peak-to-peak seasonal amplitude of notifications as a percentage of the annual notification rate.
RESULTS: A seasonal trend was intermittently detected between 1904 and 1994, particularly during periods of high notification rates, but was consistently and strongly evident between 2003 and 2017, with peaks in September through November, following winter. Among young children, a second, higher seasonal peak was observed in March. Seasonal variation was greater in children (<5 years, 54%, 95% CI 47–61; 5–14 years, 63%, 95% CI 58–69) than in adults (36%, 95% CI 33–39).
CONCLUSIONS: Stronger seasonal effects were seen in children, in whom progression following recent infection is known to be the predominant driver of disease. These findings may support increased transmission in the winter as an important driver of TB in Cape Town.
Document Type: Research Article
Affiliations: 1: Department of Medicine, Stanford University School of Medicine, Stanford, CA, USA 2: Amsterdam UMC, University of Amsterdam, Amsterdam Institute for Global Health and Development, Department of Global Health, Amsterdam, the Netherlands 3: Department of Epidemiology, Boston University School of Public Health, Boston, MA, US; 4: South African Tuberculosis Vaccine Initiative, Institute of Infectious Disease and Molecular Medicine and Division of Immunology, Department of Pathology, University of Cape Town, Cape Town 5: Desmond Tutu HIV Centre, Institute of Infectious Disease and Molecular Medicine, University of Cape Town, Cape Town, South Africa
Publication date: May 1, 2020
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