Population-based prevalence of symptomatic and asymptomatic astrovirus infection in rural Mayan infants.

Symptomatic and asymptomatic astrovirus infection was prospectively determined in a 3-year birth cohort of Mayan infants. Stool samples from 271 infants and 268 older siblings were tested for astrovirus, adenovirus 40/41, rotavirus and Salmonella, Shigella and Campylobacter species. Concurrent diarrhea, vomiting, fever, or anorexia were noted. Astrovirus was detected in 164 infants (61%) and 20 siblings (7%). Rotavirus (4%) and adenovirus 40/41 (13%) were isolated less frequently. Of all diarrheal episodes reported at a visit, 26% (78/305) were associated with astrovirus; 17% (78/452) of astrovirus infections were associated with diarrhea and 9% with other symptoms. Only diarrhea was associated with astrovirus infection (odds ratio, 1.4; 95% confidence interval [CI], 1.07-1.92; P = .01). Of infants with astrovirus, 70% shed at multiple visits over a period of 2-17 weeks (median, 5). The point prevalence of astrovirus infection was significantly higher among infants than siblings (relative risk, 6.18; 95% CI, 3.93-9.72; P < .0001, chi2). Astrovirus was identified throughout the year, peaked in March and May, and decreased in September. In this population, astrovirus was the most common enteric pathogen isolated; symptomatic infection was prevalent among infants.

Host and viral factors affecting the decreased immunogenicity of Sabin type 3 vaccine after administration of trivalent oral polio vaccine to rural Mayan children.

Factors affecting immunogenicity of the first 2 doses of oral poliovirus vaccine (OPV) among unimmunized Mayan infants were prospectively evaluated. The relative impact of multiple variables, including mass or routine vaccination, concurrent enteric bacterial (salmonella, shigella, and campylobacter) and viral (adenovirus 40/41, astrovirus, nonpolio enteroviruses, and rotavirus) infections, interference among Sabin vaccine viruses, and preexisting poliovirus antibodies were studied. Sera were available from 181 infants after 2 OPV doses. Seroresponses were 86% to Sabin type 1, 97% to Sabin type 2, and 61% to Sabin type 3 vaccines. Mass versus routine vaccination and preexisting poliovirus antibodies did not affect immunogenicity. By multiple logistic regression analysis, fecal shedding of homologous Sabin strains was associated with increased seroresponses to all Sabin types, especially to Sabin type 3. Decreased OPV immunogenicity was primarily attributable to interference of Sabin type 3 by Sabin type 2. OPV formulations with higher doses of Sabin type 3 could improve immunogenicity among infants in developing countries.

Application of the polymerase chain reaction to the epidemiology of pathogenic and nonpathogenic Entamoeba histolytica.

We used the polymerase chain reaction (PCR) to study the epidemiology of pathogenic and nonpathogenic Entamoeba histolytica in a rural community in Mexico. Formalin-fixed stool samples were used for extraction of DNA. The PCR amplifications were performed using two sets of primers that discriminate between pathogenic or non-pathogenic E. histolytica. A total of 201 randomly selected individuals were studied. Among them, 25 (12%) were diagnosed to be infected with E. histolytica by microscopy; PCR identified 24 of these as positive (sensitivity = 0.96) and of 176 negative individuals, only three were identified as positive (specificity = 0.98). The PCR analysis defined three populations: 14 cases were positive for both pathogenic and nonpathogenic E. histolytica, nine cases were positive for pathogenic and negative for nonpathogenic E. histolytica, and only one case was negative for pathogenic and positive for nonpathogenic E. histolytica. Infection by E. histolytica was strongly associated to infection with Entamoeba coli (odds ratio [OR] = 9.41, 95% confidence interval [CI] = 3.09, 28.65, P < 0.0004) and Endolimax nana (OR = 6.15, 95% CI = 2.03, 18.17, P < 0.0004). This new technique has high specificity and sensitivity; it is simple, reproducible, fast, avoids the need to culture trophozoites, and can be applied in the field for epidemiologic studies.

Diffuse-adhering Escherichia coli (DAEC) as a putative cause of diarrhea in Mayan children in Mexico.

Diarrhea is a major cause of infantile morbidity and mortality in developing countries. A community-based, case control study was conducted in a southern Mexican Mayan village for 3 weeks during the peak diarrhea period to prospectively identify the infectious agents associated with childhood diarrheal disease. Several enteropathogens were isolated from stools of 34 of 58 cases, although none was significantly associated with diarrhea. For the 24 cases from which no enteropathogens were isolated, diffuse-adhering Escherichia coli (DAEC) strains were significantly associated with diarrheal disease (P less than .02; odds ratio = 6; 95% confidence limit, 1.08-99.0). DAEC were highly heterogeneous with respect to plasmid content and serotype. Three DNA probes designed to differentiate E. coli exhibiting localized, diffuse, or aggregative adherence were compared with results from a standard HeLa cell binding assay to assess the utility of these probes in the field. This study provides evidence for the potential pathogenic capacity of DAEC and underscores the variety of diarrheal agents operating within a community.

[Risk factors for acute infantile diarrhea in a rural community in Chiapas, Mexico. A strategy for intervention]. / Factores de riesgo de diarrea infantil aguda en una communidad rural de Chiapas, México. Una estrategia de intervención.

A community-based, case-control study was conducted during the summer peak season for diarrhea in the highlands of Chiapas, Mexico, to identify risk and protective factors associated with acute diarrhea in children less than 6 years of age. To estimate the diarrheal morbidity rate, the community was divided into 13 sectors, each of about 20 households. A resident (volunteer mother) made daily visits to every household in her sector to identify new cases of diarrhea. During 3 weeks of surveillance, 63 children with diarrhea and 48 control children were identified. The diarrheal attack rate during this period for children less than 6 years of age was 30%. Analysis of 29 neighborhood-matched case-control pairs showed that children with diarrhea were more likely than their controls to have had a mother with diarrhea in the 2 weeks preceding the onset of the child's diarrhea (P less than 0.05; relative risk = 10). The association of childhood diarrhea with maternal diarrhea may serve as a focus for more detailed studies as well as an intervention that may be appropriate and effective for this community.

Risk factors for acute childhood diarrhea in the highlands of Chiapas, Mexico: a strategy for intervention.

A case-control study was conducted in the highlands of Chiapas, Mexico, to identify factors associated with acute diarrhea in children less than six years old. The study found that the diarrhea attack rate among the children surveyed during three weeks in the month of August (the peak diarrhea season) was approximately 30%, and that children whose mothers had diarrhea were especially likely to contract the illness themselves. The methods employed could prove relevant to studies in other areas, and the results obtained could provide the basis for more detailed study of the area involved--and for preventive action.

Direct-smear fluorescent antibody cytology as a field diagnostic tool for trachoma.

A recently developed direct-smear fluorescent antibody (DFA) cytology method of detecting chlamydial infection was evaluated in an area where trachoma is endemic. Four hundred seventy-five children aged 2 to 10 years were examined, and adequate conjunctival cytology specimens were collected from 457 (96%). Trachomatous inflammatory changes were observed in 114 (25%) of the children. The DFA cytologic technique has a high specificity (100%) but a low sensitivity (8%). It offers a number of advantages over existing laboratory methods for diagnosing trachoma in the field. It is a rapid, simple, and easily transferred test that has a high specificity. Although DFA cytology shares the low sensitivity of other laboratory methods of diagnosing trachoma, we believe its logistical advantages make it the laboratory test of choice.