Archives of Medical Research 31 (2000) S53–S54 0188-4409/00 $–see front matter. Copyright © 2000 IMSS. Published by Elsevier Science Inc. PII S0188-4409(00)00178-8 Seroprevalence of Anti-Entamoeba histolytica Antibodies by IHA and ELISA Assays in Blood Donors from Puebla, Mexico Ma. del Carmen Sánchez-Guillén,* Maurilio Velázquez-Rojas,* Hilda Salgado-Rosas,* Enrique Torres-Rasgado,* Ricardo Pérez-Fuentes,** Jaime Martínez-Munguía*** and Patricia Talamás-Rohana**** *Laboratorio de Parasitología, Centro de Investigación Biomédica de Oriente, Instituto Mexicano de Seguro Social (CIBIOR-IMSS), Puebla, Mexico **Facultad de Medicina, Benemérita Universidad Autónoma de Puebla (BUAP), Puebla, Mexico ***Banco Central de Sangre, Centro Médico Nacional Manuel Avila Camacho, IMSS, Puebla, Mexico ****Departamento de Patología Experimental, Centro de Investigación y de Estudios Avanzados del I.P.N. (Cinvestav), Mexico City, Mexico Key Words: Entamoeba histolytica, Amebiasis, Seroprevalence. Introduction According to the World Health Organization (WHO), ap- proximately 500 million people worldwide suffer from amebiasis. Of these, 40 million develop some of the clinical variants of the invasive disease that cause at least 100,000 deaths a year, mostly secondary to extraintestinal complica- tions such as hepatic abscess (1). Several seropidemiological surveys have been carried out in Mexico since 1972; the seroprevalence reported var- ied between 5 and 9.95% according to age, and biologic, geo- graphic, social, economic, and educational backgrounds (2). The last study was carried out 13 years ago by Mexico’s National Seroepidemiologic Survey (NSS) that showed a seroprevalence of 8.41% in a representative sample of the Mexican Republic, with an estimated seroprevalence for the state of Puebla of 14.9%, the highest of all states in Mexico, using only indirect hemagglutination (IHA), despite the WHO recommendation to employ at least two immunologi- cal methods (3). Our group evaluated the seroprevalences in asymptomatic carriers from a rural area employing IHA, ELISA, and Western blot, and found a seropositivity of 24% by ELISA, 19.2% by IHA, and 28.8% by Western blot (4). The objective of this study was to determine the sero- prevalence of E. histolytica using two techniques—indirect hemagglutination (IHA) and ELISA—in serum samples of blood donors from urban, suburban, and rural areas of the state of Puebla in Mexico. Populations and Methods Study area. The study was developed in Puebla, a Mexican state located in the southeast region of the country in a valley 1800 meters above sea level. Puebla has a warm climate, with an annual average temperature of 22°C. Population is com- posed of 4.5 million inhabitants, with 60% living in urban and suburban areas having appropriate ecologic and socioeconomic conditions for the transmission and development of the disease. Population. Study population included persons who origi- nated in and were residents of Puebla who were registered as blood donors to the clinics and hospitals of the Instituto Mexicano del Seguro Social (IMSS) during 1998. These in- dividuals were selected if they fulfilled the selection ap- proaches of the Technical Norm for Blood Banks (i.e., 18 years of age, weight 50 kg, clinically healthy, and seroneg- ative to the following tests: VIH; VDRL; Brucella abortus; HBs Ag; HBc, and HVC). In the design of the sample, a model was followed, which was stratified into seven regions that included all 217 mu- nicipalities of the State of Puebla based on ecologic and so- cioeconomic characteristics, including urban, suburban, and rural population. Sample size was determined by consider- ing the frequency of antiamebic antibodies based on data obtained from the NSS of 1987, the desired level of preci- sion for Mexican national estimates. With a confidence level (CI) of 95%, the variation coefficient was 0.3, which corresponded to a minimal expected prevalence of 0.01. The level of precision was allowed to decrease for the dif- ferent regions. Sample size was 2140 individuals, deter- mined considering the total population as 4,579, 810 indi- viduals in the entire state. Antigen. Entamoeba histolytica strain HM-1:IMSS culti- vated in TYI-S-33 was employed for the preparation of total Address reprint requests to: Ma. del Carmen Sánchez-Guillén, CIBIOR-IMSS, 19 Sur 4717, Col. Reforma Agua Azul, 72430, Puebla, Puebla, México. Telefax: (+52) (2) 243-9410; E-mail: csanchez_guillen@hot- mail.com Presenting author: Ma. del Carmen Sánchez-Guillén.