Nonannual seasonality of influenza‐like illness in a tropical urban setting

Abstract

BackgroundIn temperate and subtropical climates, respiratory diseases exhibit seasonal peaks in winter. In the tropics, with no winter, peak timings are irregular.MethodsTo 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 6000 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.ResultsFrom August 2009 to December 2015, 63 clinics were enrolled and 36 920 SMS reports were received, covering approximately 1.7M outpatient visits. Approximately 10.6% of outpatients met the ILI case definition. ILI activity in HCMC exhibited strong nonannual dynamics with a dominant periodicity of 206 days. This was confirmed by time series decomposition, stepwise 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 nasopharyngeal 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).ConclusionThis suggests, for the first time, that a nonannual cycle may be an essential driver of respiratory disease dynamics in the tropics. An immunological interference hypothesis is discussed as a potential underlying mechanism.

Age-seroprevalence curves for the multi-strain structure of influenza A virus

“…In fact, the bottom six panels of Figure 3 show that individuals' antibody profiles do not change much after an individual is likely to have been exposed to both H3N2 and H1N1 viruses; certain age groups will have high titers to viruses they were exposed to in childhood, but these exposure profiles are not qualitatively distinguishable from each other using PC1 alone. The utility of performing a PCA analysis on this generalpopulation serological data set from central and southern Vietnam lies in its location (tropical) and vaccination history (nearly none); reconstructing the natural age-seroprevalence relationship allows us to measure influenza A attack rates in a part of the world where influenza persists year-round and does not cause regular or predictable epidemics [28][29][30]60 .…”

“…Finally, in this study, we focus on influenza age-seroprevalence relationship in the tropics, as seasonal influenza attack rates are generally not known for tropical countries. One reason for the lack of measurement is an inability to identify a tropical influenza season [28][29][30][31][32][33][34][35] if one exists.…”

Seasonal Disease in the United States Has the Hallmarks of an Entrained Circannual Clock

“…However, attempts to demonstrate the effect of such conditions on the susceptibility of human subjects to rhinovirus have been inconclusive (29)(30)(31). Furthermore, it is difficult to reconcile these explanations of seasonality with the significant burden of respiratory illness in the tropics, where some seasonal variation is observed despite the warm and humid climate conditions year-round (32)(33)(34)(35)(36)(37).…”

Vietnam Climate Change and Health Vulnerability and Adaptation Assessment, 2018

“…1,2 The health effects of climate change can be direct and immediate, such as drownings, injuries, and heatrelated illnesses, or indirect and delayed, such as waterborne infections, vector-borne diseases, air-borne diseases, mental health consequences, and food shortages. [3][4][5][6][7] Increases in the number of cases of climate-sensitive diseases can increase pressures on health care system, especially in low-and middleincome countries. WHO 8 projected the potential risks of climate change for priority climate-sensitive health risks in 2030 Under a base case socioeconomic scenario, climate change was estimated to cause approximately 250 000 additional deaths per year worldwide from heat stress, diarrhea, malaria, and undernutrition in 2030 and to put 4.26 billion people at risk of dengue in 2030, 4.64 billion people at risk in 2050, and an additional 48 000 deaths in 2030 and 33 000 deaths in 2050 among children below 15 years due to diarrheal diseases.…”

“…1,2 The health effects of climate change can be direct and immediate, such as drownings, injuries, and heatrelated illnesses, or indirect and delayed, such as waterborne infections, vector-borne diseases, air-borne diseases, mental health consequences, and food shortages. [3][4][5][6][7] Increases in the number of cases of climate-sensitive diseases can increase pressures on health care system, especially in low-and middleincome countries. WHO 8 projected the potential risks of climate change for priority climate-sensitive health risks in 2030 2 Environmental Health Insights and 2050 under different climate and development scenarios.…”