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Non-annual seasonality of influenza-like illness in a tropical urban setting.

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Lam, Ha Minh, Wesolowski, Amy, Hung, Nguyen Thanh, Nguyen, Tran Dang, Nhat, Nguyen Thi Duy, Todd, Stacy, Vinh, Dao Nguyen, Vy, Nguyen Ha Thao, Thao, Tran Thi Nhu, Thanh, Nguyen Thi Le, Tin, Phan Tri, Minh, Ngo Ngoc Quang, Bryant, Juliet E, Buckee, Caroline O, Ngoc, Tran Van, Chau, Nguyen Van Vinh, Thwaites, Guy E, Farrar, Jeremy, Tam, Dong Thi Hoai, Vinh, Ha and Boni, Maciej F (2018) 'Non-annual seasonality of influenza-like illness in a tropical urban setting.'. Influenza and Other Respiratory Viruses, Vol 12, Issue 6, pp. 742-754.

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Abstract

BACKGROUND
In temperate and sub-tropical climates, respiratory diseases exhibit seasonal peaks in winter. In the tropics, with no winter, peak timings are irregular.

METHODS
To obtain a detailed picture of influenza-like illness (ILI) patterns in the tropics, we established an mHealth study in community clinics in Ho Chi Minh City (HCMC). During 2009-2015, clinics reported daily case numbers via SMS, with a subset performing molecular diagnostics for influenza virus. This real-time epidemiology network absorbs 6,000 ILI reports annually, one or two orders of magnitude more than typical surveillance systems. A real-time online ILI indicator was developed to inform clinicians of the daily ILI activity in HCMC.

RESULTS
From August 2009 to December 2015, 63 clinics were enrolled and 37,676 SMS reports were received, covering approximately 1.8M outpatient visits. Approximately 10.6% of outpatients met the ILI case definition. ILI activity in HCMC exhibited strong non-annual dynamics with a dominant periodicity of 206 days. This was confirmed by time-series decomposition, step-wise regression, and a forecasting exercise showing that median forecasting errors are 30%-40% lower when using a 206-day cycle. In ILI patients from whom naso-pharyngeal swabs were taken, 31.2% were positive for influenza. There was no correlation between the ILI time series and the time series of influenza, influenza A, or influenza B (all p > 0.15).

CONCLUSION
This suggests, for the first-time, that a non-annual cycle may be an essential driver of respiratory disease dynamics in the tropics. An immunological interference hypothesis is discussed as a potential underlying mechanism. This article is protected by copyright. All rights reserved.

Item Type: Article
Subjects: WA Public Health > WA 4 Works on general hygiene
WC Communicable Diseases > Virus Diseases > Viral Respiratory Tract Infections. Respirovirus Infections > WC 515 Human influenza
Faculty: Department: Clinical Sciences & International Health > Clinical Sciences Department
Digital Object Identifer (DOI): https://doi.org/10.1111/irv.12595
Depositing User: Stacy Murtagh
Date Deposited: 31 Jul 2018 15:53
Last Modified: 31 Oct 2018 16:24
URI: http://archive.lstmed.ac.uk/id/eprint/9005

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