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The objective of this study was to examine the independent effect of infection with each of four helminths (Ascaris lumbricoides, Schistosoma japonicum, Necator americanus, and Trichuris trichiura) on cognitive function after adjusting for the potential confounders nutritional status, socioeconomic status (SES), hemoglobin, sex, and the presence of other helminthes. This cross-sectional study was carried out in a rural village in Leyte, The Philippines in 319 children 7–18 years old. Three stools were collected and read in duplicate by the Kato Katz method. Infection intensity was defined by World Health Organization criteria. Cognitive tests were culturally adapted and translated. Learning and memory cognitive domains were each defined by three subscales of the Wide Range Assessment of Memory and Learning, which had an inter-rater reliability 
0.92 and test-retest reliabilities ranging from 0.61 to 0.89. A household SES questionnaire was administered. A logistic regression model was used to quantify the association between performance in different cognitive domains (learning, memory, verbal fluency, and the Philippine Non-Verbal Intelligence Test) and helminth infections. After adjusting for age, sex, nutritional status, hemoglobin, and SES, S. japonicum infection was associated with poor performance on tests of learning (odds ratio [OR] = 3.04, 95% confidence interval [CI] = 1.1–6.9), A. lumbricoides infection was associated with poor performance on tests of memory (OR = 2.2, 95% CI = 1.04–4.7), and T. trichiura infection was associated with poor performance on tests of verbal fluency (OR = 4.5, 95% CI = 1.04–30). Helminth infection was associated with lower performance in three of the four cognitive domains examined in this study. These relationships remained after rigorous control for other helminths and important confounding covariates.
Received June 21, 2004. Accepted for publication July 26, 2004.
Acknowledgments: We thank our field staff for their diligence and energy: Blanca Jarilla, Mario Jiz, Archie Pablo, Raquel Pacheco, Patrick Sebial, Mary Paz Urbina, and Jemaima Yu. We also thank the study participants from Macanip, Buri, and Pitogo in Leyte, The Philippines.
Financial support: This work supported by National Institutes of Health grants RO1 AI48123 and K23 AI52125.
* These authors contributed equally to this work.
Authors’ addresses: Amara Ezeamama, Jennifer F. Friedman, Gretchen C. Langdon, and Jonathan D. Kurtis, and Stephen T. McGarvey, International Health Institute, Brown University, Providence, RI 02912, E-mails: Amara_Ezeamama{at}brown.edu,, Jennifer_Friedman{at}brown.edu,, Gretchen_Langdon{at}brown.edu,, Jonathan_Kurtis{at}brown.edu, and Stephen_McGarvey{at}brown.edu. Luz P. Acosta, Daria L. Manalo, and Remigio M. Olveda, Research Institute of Tropical Medicine, Alabang, Muntinlupa, Metro Manila 1770, The Philippines, E-mails: lacosta{at}ritm.ph.gov and Dmanalo{at}ritm.ph.gov. David C. Bellinger, Department of Environmental Health, Children’s Hospital, Farley Basement, Box 127, 300 Longwood Avenue, Boston, MA 02115, E-mail: David.Bellinger{at}tch.harvard.edu.
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