West Nile virus past infections in the general population of Southern Spain.

OBJECTIVE: To analyze the prevalence of past and recent infections by West Nile virus (WNV) and the risk factors associated with WNV exposure in a representative population from southern Spain. METHODS: Sample size was established for an estimated prevalence of past WNV infections of 5 +/- 2.5% in 504 subjects. A pre-stratification was performed according to age distribution and place of residence. After random telephone solicitation and acquisition of informed consent, a serum sample was collected and an epidemiologic survey performed on all participating subjects. Samples were tested with ELISA-IgG and MAC-ELISA to detect specific IgG and IgM antibodies; results were confirmed by the plaque reduction neutralization test (PRNT). Multivariate analysis using a forward stepwise logistic regression model was performed to assess potential risk factors associated with WNV exposure. RESULTS: Prevalence of past WNV infections confirmed by PRNT in the 504 participants was 0.6%, affecting mainly older persons (mean age 65 +/- 23 vs. 34 +/- 22 years; P = 0.018), those living in rural areas (5.4% vs. 0% in urban areas; P = 0.01), and individuals with risk professions (prevalence 2.8% vs. 0%; P = 0.048). None of the five recent infections detected by MAC-ELISA was confirmed by PRNT. CONCLUSIONS: These results strongly suggest past circulation and exposure of the human population to WNV in southern Spain.

Seroprevalencia de infecciones por el virus del Nilo Occidental en la población general del sur de España / West Nile virus past infections in the general population of Southern Spain

Objective. To analyze the prevalence of past and recent infections by West Nile virus (WNV) and the risk factors associated with WNV exposure in a representative population from southern Spain. Methods. Sample size was established for an estimated prevalence of past WNV infections of 5 6 2.5% in 504 subjects. A pre-stratification was performed according to age distribution and place of residence. After random telephone solicitation and acquisition of informed consent, a serum sample was collected and an epidemiologic survey performed on all participating subjects. Samples were tested with ELISA-IgG and MAC-ELISA to detect specific IgG and IgM antibodies; results were confirmed by the plaque reduction neutralization test (PRNT). Multivariate analysis using a forward stepwise logistic regression model was performed to assess potential risk factors associated with WNV exposure. Results. Prevalence of past WNV infections confirmed by PRNT in the 504 participants was 0.6%, affecting mainly older persons (mean age 65 6 23 vs. 34 6 22 years; P 5 0.018), those living in rural areas (5.4% vs. 0% in urban areas; P 5 0.01), and individuals with risk professions (prevalence 2.8% vs. 0%; P 5 0.048). None of the five recent infections detected by MAC-ELISA was confirmed by PRNT. Conclusions. These results strongly suggest past circulation and exposure of the human population to WNV in southern Spain (AU)

Objetivo. Analizar la prevalencia de infecciones pasadas y recientes por el virus del Nilo Occidental (VNO), así como los factores de riesgo asociados con la exposición al mismo, en una muestra representativa de la población del sur de España. Métodos. El tamaño de la muestra se estableció para una seroprevalencia de infección pasada del 5 6 2,5% en 504 sujetos, preestratificándose ésta por edad y lugar de residencia. Los voluntarios se incluyeron tras solicitud telefónica y consentimiento, y a todos ellos se les realizó una extracción de suero y una encuesta epidemiológica. Las muestras se analizaron para detectar IgG e IgM específicas, mediante enzimoinmunoensayo (ELISA-IgG) y enzimoinmunoensayo por captura (MAC-ELISA), confirmando ulteriormente los resultados positivos mediantereducción-neutralización en placa (PRNT. Finalmente se realizó un análisis de regresión logística multivariante paso a paso hacia delante para determinar los posibles factores asociados con la exposición al VNO. Resultados. La prevalencia de infecciones por VNO confirmadas por PRNT en los 504 sujetos incluidos fue del 0,6%, y se vieron principalmente afectadas las personas de mayor edad (edad media 65 6 23 frente a 34 6 22 años; p 5 0,018), las que vivían en áreas rurales (prevalencia del 5,4% frente al 0% en áreas urbanas; p 5 0,01), y las personas con profesiones de riesgo (prevalencia del 2,8% frente al 0%; p 5 0,048). Por el contrario, ninguna de las infecciones recientes detectadas por MAC-ELISA fue confirmada ulteriormente por PRNT. Conclusiones. Estos resultados apoyan firmemente la circulación en el pasado del VNO, así como la exposición humana del mismo, en áreas del sur de España (AU)