Seasonal patterns of dengue fever in rural Ecuador: 2009-2016

Abstract

Season is a major determinant of infectious disease rates, including arboviruses spread by mosquitoes, such as dengue, chikungunya, and Zika. Seasonal patterns of disease are driven by a combination of climatic or environmental factors, such as temperature or rainfall, and human behavioral time trends, such as school year schedules, holidays, and weekday-weekend patterns. These factors affect both disease rates and healthcare-seeking behavior. Seasonality of dengue fever has been studied in the context of climatic factors, but short- and long-term time trends are less well-understood. With 2009–2016 medical record data from patients diagnosed with dengue fever at two hospitals in rural Ecuador, we used Poisson generalized linear modeling to determine short- and long-term seasonal patterns of dengue fever, as well as the effect of day of the week and public holidays. In a subset analysis, we determined the impact of school schedules on school-aged children. With a separate model, we examined the effect of climate on diagnosis patterns. In the first model, the most important predictors of dengue fever were annual sinusoidal fluctuations in disease, long-term trends (as represented by a spline for the full study duration), day of the week, and hospital. Seasonal trends showed single peaks in case diagnoses, during mid-March. Compared to the average of all days, cases were more likely to be diagnosed on Tuesdays (risk ratio (RR): 1.26, 95% confidence interval (CI) 1.05–1.51) and Thursdays (RR: 1.25, 95% CI 1.02–1.53), and less likely to be diagnosed on Saturdays (RR: 0.81, 95% CI 0.65–1.01) and Sundays (RR: 0.74, 95% CI 0.58–0.95). Public holidays were not significant predictors of dengue fever diagnoses, except for an increase in diagnoses on the day after Christmas (RR: 2.77, 95% CI 1.46–5.24). School schedules did not impact dengue diagnoses in school-aged children. In the climate model, important climate variables included the monthly total precipitation, an interaction between total precipitation and monthly absolute minimum temperature, an interaction between total precipitation and monthly precipitation days, and a three-way interaction between minimum temperature, total precipitation, and precipitation days. This is the first report of long-term dengue fever seasonality in Ecuador, one of few reports from rural patients, and one of very few studies utilizing daily disease reports. These results can inform local disease prevention efforts, public health planning, as well as global and regional models of dengue fever trends.

Key Findings and Comparisons From Analogous Case-Cluster Studies for Dengue Virus Infection Conducted in Machala, Ecuador, and Kamphaeng Phet, Thailand

“…Three hundred twenty-three Initiates were enrolled in Thailand between November 2009 and November 2012 ( Table 3), with enrollment thus capturing three peak periods for DENV transmission (i.e., the rainy season), which variably reaches its maximum in July-August and wanes in October-November each year. Forty-four Initiates were enrolled in Ecuador between January 2014 and June 2015, with enrollment thus spanning two peak periods for DENV transmission, which typically reaches its maximum in March-May and wanes in June-July each year (22) of JEV (in Thailand) or YFV vaccination (in Ecuador); however, 96.1% of Thai children (aged <18 years) reported a history of JEV vaccination and 19.6% of Ecuadorian children reported a history of YFV vaccination. Three hundred three Associates in Thailand (24.3%) and 96 in Ecuador (25.0%) were confirmed to have acute or recent DENV infection.…”

Epidemiology of dengue fever in Guatemala

“…Interestingly the later peaks in dengue case detection between 2003 and 2005 occurred around two El Niño events [ 27 ], which have been shown to increase dengue transmission in Central America [ 28 ]. The understanding of the seasonality of dengue is an important epidemiological feature that enables timely control efforts for maximize prevention effectiveness, and public health planning [ 29 ].…”

“…been shown to increase dengue transmission in Central America [28]. The understanding of the seasonality of dengue is an important epidemiological feature that enables timely control efforts for maximize prevention effectiveness, and public health planning [29]. Globally, DENV1 has been the most common serotype detected since 2010, particularly in Africa, Europe and the Western Pacific region [30].…”

Assessing critical gaps in COVID-19 testing capacity: the case of delayed results in Ecuador

“…Moreover, persistent social, geographic and economic inequalities in Ecuador negatively influence access to health care [ 13 ], with health services not being similarly available across different municipalities and provinces, and urban areas having higher concentrations of health providers. Further, Ecuador’s ongoing economic crisis has prompted underfunding of the MoH while patterns in laboratory diagnostics indicate possible shortcomings in capabilities [ 14 ]. As a reference, more remote provinces such as Bolívar, Zamora Chinchipe and Galápagos do not have healthcare resources such as intensive care units (ICU), and Cotopaxi, Cañar and Morona Santiago have ICU bed rates as low as 0.11, 014 and 0.15 per 10,000 people, respectively [ 15 ].…”