The effect of climate variables on the incidence of Crimean Congo Hemorrhagic Fever (CCHF) in Zahedan, Iran
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RESEARCH ARTICLE
Open Access
The effect of climate variables on the incidence of Crimean Congo Hemorrhagic Fever (CCHF) in Zahedan, Iran Sairan Nili1, Narges Khanjani2*, Yunes Jahani3 and Bahram Bakhtiari4
Abstract Background: The Crimean-Congo Hemorrhagic fever (CCHF) is endemic in Iran and has a high fatality rate. The aim of this study was to investigate the association between CCHF incidence and meteorological variables in Zahedan district, which has a high incidence of this disease. Methods: Data about meteorological variables and CCHF incidence was inquired from 2010 to 2017 for Zahedan district. The analysis was performed using univariate and multivariate Seasonal Autoregressive Integrated Moving Average (SARIMA) models and Generalized Additive Models (GAM) using R software. AIC, BIC and residual tests were used to test the goodness of fit of SARIMA models, and R2 was used to select the best model in GAM/GAMM. Results: During the years under study, 190 confirmed cases of CCHF were identified in Zahedan district. The fatality rate of the disease was 8.42%. The disease trend followed a seasonal pattern. The results of multivariate SARIMA showed the (0,1,1) (0,1,1)12 model with maximum monthly temperature lagged 5 months, forecasted the disease better than other models. In the GAM, monthly average temperature lagged 5 months, and the monthly minimum of relative humidity and total monthly rainfall without lag, had a nonlinear relation with the incidence of CCHF. Conclusions: Meteorological variables can affect CCHF occurrence. Keywords: Iran, Forecasting, Time-series analysis, SARIMA, Generalized additive model, Hemorrhagic fever, Crimean-Congo
Background Crimean-Congo hemorrhagic fever (CCHF) is a viral disease with a worldwide distribution [1]. It is transmitted by ticks or through contact with infected animal tissue. The most important route of CCHF transmission in Iran is contact with the blood or tissues of infected domestic animals. The length of incubation period depends on the viral load, the route of transmission, and the source of infection. After tick bites, the incubation period is 1–5 days and a maximum of 9 days, but following contact with infected blood or tissue, the incubation period is 5– * Correspondence: [email protected] 2 Environmental Health Engineering Research Center, Kerman University of Medical Sciences, Kerman, Iran Full list of author information is available at the end of the article
7 days and a maximum of 13 days. The minimum viral load for disease transmission is 1 to 10 organisms [2]. Attention to this disease has increased, because of its severe and numerous outbreaks in recent years, its spread as an epidemic, and its high fatality rate which is 10– 40%. CCHF is now endemic in Africa, Central Asia, Russia, China and the Balkans up to 48 degrees latitude [3]; and its incidence is rising rapidly in the Eastern Mediterranean region [4]. Iran is one of the endemic regions and has a high incidence of CCHF [5]; and needs to be prepared for disease control. Therefore, it is i
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