RT Journal Article SR Electronic T1 Non-annual seasonality of influenza-like illness in a tropical urban setting JF bioRxiv FD Cold Spring Harbor Laboratory SP 100222 DO 10.1101/100222 A1 Ha Minh Lam A1 Amy Wesolowski A1 Ngyuyen Thanh Hung A1 Tran Dang Nguyen A1 Nguyen Thi Duy Nhat A1 Stacy Todd A1 Dao Nguyen Vinh A1 Nguyen Ha Thao Vy A1 Tran Thi Nhu Thao A1 Nguyen Thi Le Thanh A1 Phan Tri Tin A1 Ngo Ngoc Quang Minh A1 Juliet E Bryant A1 Caroline O Buckee A1 Tran Van Ngoc A1 Nguyen Van Vinh Chau A1 Guy E Thwaites A1 Jeremy Farrar A1 Dong Thi Hoai Tam A1 Ha Vinh A1 Maciej F Boni YR 2017 UL http://biorxiv.org/content/early/2017/01/13/100222.abstract AB In temperate countries, influenza and other viral respiratory diseases often have distinct seasonal peaks occurring during colder, wintertime months. However, little is known about the dynamics of influenza and viral respiratory disease dynamics in the tropics, despite high morbidity and a clear epidemiological link between tropical and temperate countries. In temperate countries, the dynamics of influenza and other respiratory diseases are often analyzed using syndromic surveillance data describing influenza-like illness (ILI) as ILI is highly correlated with virological surveillance for influenza. To obtain a detailed picture of respiratory disease incidence patterns in a large tropical city, we established an mHealth study in community outpatient clinics in Ho Chi Minh City, Vietnam (11N latitude). From August 2009 through December 2015, clinics reported daily case numbers of ILI using standard mobile-phone SMS messaging. A subset of these clinics performed molecular diagnostics for influenza A and B viruses. Unlike the annual patterns seen in temperate countries, ILI activity in Ho Chi Minh City exhibited strong non-annual periodicity and was not correlated with PCR-confirmed influenza. The dominant periodicity in the data was approximately 200 days. This was confirmed by a time series decomposition, a step-wise regression analysis on annual and non-annual covariates, and a forecasting exercise showing that forecasting was 30% to 40% more accurate when a 200-day non-annual cycle was included in the forecast. This suggests, for the first-time, that a non-annual cycle may be an essential driver of ILI dynamics in the tropics. This raises new questions about the seasonality and drivers of respiratory disease transmission in tropical countries.