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ABSTRACT |
 TOP ABSTRACT INTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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INTRODUCTION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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Trypanosoma cruzi is naturally transmitted by reduviid bugs. Generally, infection is seen in persons who live in the lower economic rural or suburban areas of Latin America, in poor housing conditions, and who have had repeated exposure to the vector. However, a second and increasingly important route of transmission of T. cruzi is by blood transfusion when blood from infected asymptomatic donors is transfused due to poor screening practices. Although not all recipients of T. cruzi-seropositive blood become infected, lack of effective screening poses a substantial risk to populations in endemic areas.2 In addition, congenital transmission has also been documented in Guatemala.3
National vector control programs aimed at the interruption of disease transmission by vector and by transfusion mediated routes, mainly through the application of residual insecticides in house holds and screening practices of blood donors, have proven to be feasible and effective. Based on these principles, the Southern Cone Initiative for the Control of Chagas Disease was launched in 1991 with the participation of several countries (Argentina, Bolivia, Brazil, Chile, Paraguay, and Uruguay).4 Current epidemiologic and entomologic data show that the incidence of T. cruzi transmission has been reduced by 70% in these countries as a result of the control measures.
The interruption of transmission of Chagas disease in Central American countries and Andean countries will likely be achieved by adapting the same vector control strategies successful in the Southern Cone Initiative to the local entomologic conditions of these geographic areas. Towards this goal, the Andean Initiative, including Bolivia, Colombia, Ecuador, Peru, and Venezuela, was launched in February 1997, followed in October 1997 by the Central American Initiative, which includes Belize, Costa Rica, El Salvador, Guatemala, Honduras, Nicaragua, and Panama.
Although there has been no representative sample survey to evaluate the public health impact of Chagas disease in Guatemala, this country is thought to have one of the highest Chagas disease risk levels outside the Southern Cone.5 Indicative information presented at the Tropical Disease Research/World Health Organization (TDR/WHO)–sponsored meeting in Tegucigalpa, Honduras in October 1997 summarized the epidemiologic situation in Guatemala. It is estimated that 3,400,000 persons, 34% of the total population, is at risk of infection. In the endemic regions, house infestation rates range from 10% to 34% with Triatoma dimidiata and from 3% to 18% with Rhodnius prolixus. The prevalence of human infection in the general population approaches 10%, and the prevalence of infected blood in blood banks is 0.97%.
We conducted a cross-sectional study to estimate the seroprevalence rate of Chagas disease in the five Departments of Guatemala thought to comprise the principal endemic area in this country. An additional goal of the study was to determine which areas have active vector-borne transmission. Since infection with T. cruzi and associated seropositivity is life long, the most efficacious way to determine where transmission is ongoing is to evaluate seropositivity in young people. Thus, in collaboration with the Ministry of Education and the Ministry of Health, we conducted the serosurvey in school-age children. These results will be used by the National Program for Chagas Disease Control to stratify the endemic region for a vector control program.
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MATERIALS AND METHODS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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Sample size. Sample size was calculated using the format provided by the TDR/WHO Manager on Applied Research on Chagas Disease. Sample units were the rural schools within each Municipio. The total sample size/Municipio was divided by the number of schools present in the communities located less than 2,000 meters above sea level. A weighted sample of children was then randomly selected from each school. The statistical parameters used to calculate the sample size were 95% confidence level, 90% power, and 5% precision. The a priori estimated rate of seroprevalence for T. cruzi was 5%, based on seroprevalence data from previous studies.3 Using these criteria, 4,450 children were randomly selected from the 58 municipios.
Inclusion/exclusion criteria. Children who met the following criteria were eligible: 1) Apparently healthy male or female children enrolled in elementary schools; 2) residents of the area for at least 12 months before the initiation of the study; and 3) provision of written consent from a parent or legal guardian to participate in the study. Children were excluded from the study for any of the following reasons: presence of severe medical conditions such as severe malnutrition or cardiac, renal, hematologic, or endocrinologic problems.
Data collection. A structured questionnaire was used to obtain basic data on individual and demographic characteristics, living conditions, and children’s knowledge about Chagas disease. Questionnaires were coded with a unique identification (ID) number for each participant.
In addition, three drops of blood were collected onto Whatman No. 1 filter paper (Fisher Scientific, Pittsburgh, PA) from each child by the finger prick method. Samples were coded using the same unique ID number assigned during the questionnaire, and stored at 4°C until processed.
Laboratory methods. Antibodies were eluted from the filter paper samples and analyzed by an enzyme-linked immunosorbent assay (ELISA) essentially as described.6 Briefly, 6-mm diameter pieces of filter paper containing dried blood were incubated in phosphate-buffered saline (PBS) containing 0.5% Tween 20 (Sigma, St. Louis, MO). Samples were then diluted in PBS containing 5% non-fat dry milk approximating a 1:500 dilution of plasma, and placed in 96-well plates that had been previously coated with T. cruzi antigens prepared from culture forms of the Brazil strain (primarily epimastigotes) as previously described.7 Antibodies to T. cruzi were detected using goat anti-human IgG conjugated to horseradish peroxidase (Biosource, Sunnyvale, CA), developed with 3,3',5,5'-tetramethylbenzidine (Kirkegaard and Perry Laboratories, Gaithersburg, MD), and read using an automated ELISA reader (Molecular Devices, Sunnyvale, CA) This assay had been previously tested in our laboratory, and showed a close correlation (r2 = 0.96) with results obtained using a radioimmunoprecitation assay (RIPA)8 and a commercial ELISA (Abbott Laboratories, Abbott Park, IL). Compared with the RIPA and the commercial ELISA, using a standardized panel of sera, we showed that our assay has a specificity of 85% and 95%, respectively, a sensitivity of 100%, and a positive predictive value of 97%. Infection with Leishmania or Trypanosoma rangeli has not been reported in the study area.
Data analysis. The questionnaire data were entered into a database and response frequencies were calculated for each question. Data from the serologic analysis were integrated into the database and the associations between the questionnaire data and the serology results were established. The chi-square test was used to assess differences between proportions (seronegative versus seropositive persons). Results were considered significant at P < 0.05. When appropriate, relative risk, with 95% confidence limits, was calculated using Epi-Info Version 6.04b software (Centers for Disease Control and Prevention, Atlanta, GA).
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RESULTS |
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Demographic and household characteristics of the study subjects.
Fifty-one percent (2,272) of the participants were male and 49% (2,175) were female. The mean ± SD age for both males and females was 10.1 ± 2.2 years. Most (84.7%, 3,765) had lived in their current house since birth, while only a small proportion (15.3%, 682) had lived less than five years in their current house. Household construction characteristics are shown in Table 1
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Serologic survey.
The seropositivity rates by department are shown in Table 2. The overall seropositivity rate for Chagas disease obtained in the survey was 5.28% (235 of 4,450). Of 173 communities evaluated, 35 (20.23%) had a seropositivity rate of 10–45%. The geographic seroprevalence rate by Municipio is shown in Figure 1. The association of seropositivity with the different parameters assessed during the survey is shown in Table 3.
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DISCUSSION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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The age-specific prevalence rates, expressed in five-year intervals, are similar to those reported in epidemiologic surveys in Mexico and Venezuela, and in a selected area of Guatemala, where a consistent increase in seroprevalence with chronologic age was observed.6 However, because the sample size in the present study was small in the youngest and oldest age brackets, this relationship was not statistically significant.
As in many previous studies, we identified several factors, especially those related to house construction (Table 3
), to be associated with human infection, including type of roof, walls, and floor.9–11 Other investigators have also reported that T. cruzi infection is associated with the presence or evidence of triatomines inside dwellings. We also found a correlation between the risk of testing seropositive with the antecedent of "seeing a chinche inside the house." Similarly, in our previous study conducted with blood donors, this variable was found to be significantly associated with seropositivity (relative risk = 16.2; Huang S and others, unpublished data).
In addition, it is important to note the significant impact that housing improvement has made in reducing the risk of becoming seropositive for T. cruzi. For example, we found a highly significant correlation between seropositivity and living in a house with either a straw or palm tree roof, even though persons living in houses with this type of roof comprised only 6.4% of the study population. Similarly, persons living in houses with dirt floors were significantly more likely to be seropositive than those with cement or other types of floors. Clearly, continued efforts to improve living conditions will lessen the risk of infection by T. cruzi in these areas.
The findings of this study have permitted an epidemiologic stratification of the communities endemic for Chagas disease, enabling local health authorities to focus vector control operations in those communities with high seroprevalence in schoolchildren. The results from this investigation, together with the findings from an entomologic survey currently under way, will provide essential information for the ongoing monitoring and evaluation of the National Chagas Disease Control Program.
Received March 5, 2002. Accepted for publication February 6, 2003.
Acknowledgments: We thank Dr. Julio C. Argueta (Ministry of Health and Social Assistance, Guatemala) for assistance, Ava Navin for her critically reviewing and editing the manuscript, Dr. Edwin C. Rowland (Ohio University, Athens, OH) for providing the T. cruzi antigen used in the ELISA, and Xiomara Munoz and Liliana Alverez for their expert technical assistance both in the field and in the laboratory.
Financial support: This investigation received financial support from the UNDP/World Bank/World Health Organization Special Program for Research and Training in Tropical Diseases (TDR).
Authors’ addresses: Nidia R. Rizzo and Byron A. Arana, Aniate Diaz, and Celia Cordon-Rosales, Center for Health Studies, Universidad del Valle de Guatemala/Medical Entomology Research and Training Unit/Guatemala, Division of Parasitic Diseases, Centers for Disease Control and Prevention, Apartado Postal No. 082, Guatemala City, Guatemala, Telephone: 502-369-0791, Fax: 502-364-0354; E-mails: nnrz{at}cdc.gov, baaz{at}cdc.gov, ad1z{at}cdc.gov and ccrz{at}cdc.gov. Robert E. Klein, Medical Entomology Research and Training Unit/Guatemala, Division of Parasitic Diseases, National Center for Infectious Diseases, Centers for Disease Control and Prevention, American Embassy, APO, AA, Miami, FL, 34024-3321, Telephone: 502-369-0791, Fax: 502-364-0354, E-mail: reks{at}cdc.gov. Malcolm R. Powell, Division of Parasitic Diseases, National Center for Infectious Diseases, Centers for Disease Control and Prevention, 4770 Buford Highway, NE, Mailstop F-13, Atlanta, GA 30341, Telephone: 770-488-4529, Fax: 770-488-4108, E-mail: mrp5{at}cdc.gov.
Reprint requests: Malcolm R. Powell, Division of Parasitic Diseases, Centers for Disease Control and Prevention, 4770 Buford Highway, NE, Mailstop F-13 Atlanta, GA 30341.
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This article has been cited by other articles:
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  S. Williams-Blangero, T. Magalhaes, E. Rainwater, J. Blangero, R. Correa-Oliveira, and J. L. VandeBerg Electrocardiographic Characteristics in a Population with High Rates of Seropositivity for Trypanosoma cruzi Infection Am J Trop Med Hyg, September 1, 2007; 77(3): 495 - 499. [Abstract] [Full Text] [PDF]
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K. HASHIMOTO, C. CORDON-ROSALES, R. TRAMPE, and M. KAWABATA IMPACT OF SINGLE AND MULTIPLE RESIDUAL SPRAYINGS OF PYRETHROID INSECTICIDES AGAINST TRIATOMA DIMIDIATA (REDUVIIADE; TRIATOMINAE), THE PRINCIPAL VECTOR OF CHAGAS DISEASE IN JUTIAPA, GUATEMALA. Am J Trop Med Hyg, August 1, 2006; 75(2): 226 - 230. [Abstract] [Full Text] [PDF]
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