Household and personal factors are sources of heterogenity in intestinal parasite clearance among Mexican children 6-15 months of age supplemented with vitamin A and zinc.

A randomised, double-blind, placebo-controlled trial was carried out among Mexico children aged 6-15 months to determine how household characteristics modify vitamin A and zinc supplementation efficacy on Ascaris lumbricoides, Giardia intestinalis and Entamoeba histolytica/E. dispar infection durations. Children assigned to receive vitamin A every 2 months, a daily zinc supplement, a combined vitamin A-zinc supplement or a placebo were followed for 1 year. Parametric hazard models were fit to infection durations stratified by personal and household factors. Children supplemented with vitamin A and zinc combined from households lacking piped water and children in all three treatment arms from households with dirt floors had longer G. intestinalis and A. lumbricoides infection durations than their counterparts, respectively. Shorter E. histolytica/E.dispar durations were found among zinc-supplemented children of mothers who had <6 years of education and no indoor bathrooms. Heterogeneity in supplementation efficacy among children may reflect differences in exposure risk and baseline immune responses.

Vitamin A modifies the intestinal chemokine and cytokine responses to norovirus infection in Mexican children.

Vitamin A supplementation is associated with divergent clinical norovirus (NoV) outcomes in Mexican children. Fecal cytokine concentrations following NoV genogroup infections among 127 Mexican children 5-15 mo old enrolled in a randomized, double-blind, placebo-controlled, vitamin A supplementation trial were determined to clarify the role the gut immune response plays in these associations. Stools collected from supplemented children [20,000 IU retinol (3.3 IU = 1 µg retinol) for children < 12 mo of age; 45,000 iu for children ≥ 12 mo] or children in the placebo group were screened for NoV genogroups I (GI) and II (GII). Monocyte chemoattractant protein-1 (MCP-1), TNFα, IL-5, IL-6, IL-8, IL-4, IFNγ, and IL-10 fecal concentrations were also determined. Differences in cytokine levels between the 2 groups following GI and GII infections were determined using ordered logistic regression models. MCP-1 and IL-8 levels were greater among GI- and GII-infected children, respectively, compared with uninfected children, whereas IL-5 levels were greater following both genogroup infections. MCP-1, IL-8, and IL-6 fecal levels were reduced among supplemented children with GII-associated diarrhea compared with the placebo group. Vitamin A-supplemented, GII-infected children had reduced MCP-1 and TNFα levels compared with GII-infected children in the placebo group (P-interaction = 0.02 and 0.03, respectively). Supplemented children with GI-associated diarrhea had higher TNFα and IL-4 levels compared with children in the placebo group with diarrhea (P-interaction = 0.02 and 0.02, respectively). The divergent effects of supplementation on NoV outcomes may result from the different effects vitamin A has on the genogroup-specific immune responses.

Early loss of measles antibodies after MMR vaccine among HIV-infected adults receiving HAART.

OBJECTIVE: The objective of the study was to evaluate the immune response to measles vaccine of HIV-infected adults in comparison to HIV non-infected adults. DESIGN: We conducted a cross-sectional study to identify adults lacking measles antibodies. 26 HIV-infected patients and 22 controls found to be measles seronegative in the cross-sectional study, received the MMR vaccine. We prospectively followed patients and measured measles antibodies, and cellular proliferative responses against measles antigens. We registered all adverse events at baseline, 3 and 12 months after vaccination. METHODS: We determined measles antibodies by ELISA and cellular proliferative response in PBMC's at baseline, and repeated measurements at 3 and 12 months after vaccination. RESULTS: The humoral immune response to the vaccine between HIV-infected adults and the HIV-uninfected group was not statistically different at 3 months (81% vs. 86% respectively). One year after vaccination, a higher proportion of HIV-infected adults had lost measles antibodies in contrast to controls. The cellular response was not statistically different between the groups at baseline, 3 and 12 months after immunization despite the waning of antibodies at 12 months. No severe adverse events were observed. Most patients were receiving HAART and had a mean CD4+ cell count of 496 cells/mL. CONCLUSIONS: The initial humoral immune response to measles vaccine was not different between HIV-infected adults and HIV-uninfected adults. However, HIV-infected adults have a rapid decline of measles antibodies despite their high CD4+ cell count and sustained cellular proliferative response.

Vitamin A supplementation has divergent effects on norovirus infections and clinical symptoms among Mexican children.

BACKGROUND: The effect of vitamin A supplementation on viral gastrointestinal infections among young children living in developing countries remains unclear. METHODS: The effect of vitamin A supplementation on norovirus (NoV) infection among 127 Mexican children 5-15 months of age was studied in a randomized, placebo-controlled trial during June-August 1998. Stool samples collected every 2 weeks and after diarrheal episodes were screened for NoV and characterized at the genogroup level (GI and GII). RESULTS: Of the stool samples collected, 29.9% were positive for NoV, and NoV GI and NoV GII were found in 55.4% and 46.4% of the positive samples, respectively. Vitamin A supplementation reduced the prevalence of NoV GII infections (rate ratio [RR], 0.60 [95% confidence interval {CI}, 0.20-0.82]), increased the length of both NoV GI and GII shedding, and decreased the prevalence of NoV-associated diarrhea (RR, 0.51 [95% CI, 0.26-0.97]). CONCLUSIONS: These findings suggest that NoV is an important cause of pediatric diarrhea in this study population and that vitamin A supplementation has divergent effects on specific outcomes of NoV infection.

Anticapsular polysaccharide IgG concentrations in Mexican children formerly immunized with Haemophilus influenzae b PRP-T vaccine.

BACKGROUND: In 1999 H. influenzae b (Hib) PRP-T vaccine was introduced into primary immunization schedule in Mexico. There have been no studies evaluating antibody response after widespread immunization in our country. It is now recognized that Hib conjugates induce significant initial antibody levels that in some cases wane over time. This study relies on the measurement of IgG serum antibody concentrations to Hib capsular polysaccharide (PS) and is interpreted in the light of the accepted levels > or =0.15 microg/mL for short-term protection against Hib invasive disease and > or =5.0 microg/mL for protection against Hib oropharyngeal carriage. METHODS: Using a validated ELISA assay, we measured the IgG serum antibody concentrations in 115 children between 7 and 93 months of age who had received three doses of PRP-T. We used the standard reference serum US FDA 1983 for quantification of PS antibody levels. Concentrations were estimated using 3(rd) degree polynomial regression lines. As there was no unvaccinated group available (>95% of Mexican children have received the Hib vaccine), the study was designed as a cross-sectional. RESULTS: All children had serum IgG concentrations > or =0.15 microg/mL [range 0.24-54.64 microg/mL]; 69.6 % (80/115) had > or =1.0 microg/mL and 14 % (16/115) showed concentrations > or =5.0 microg/mL. The vaccine elicited geometric mean concentrations (GMC) of 4.0, 1.6, 1.4 and 2.4 microg/mL in groups of 7-12, 13-24, 25-48 and 49-93 month-old respectively. CONCLUSIONS: PRP-T vaccination in this group of Mexican children has resulted in serum IgG concentrations > or =0.15 microg/mL, suggesting that Hib immunization has conferred protection against invasive disease.

Shedding and reversion of oral polio vaccine type 3 in Mexican vaccinees: comparison of mutant analysis by PCR and enzyme cleavage to a real-time PCR assay.

A uracil-to-cytosine mutation at nucleotide position 472 of oral poliovirus vaccine type 3 (OPV3) contributes to the development of vaccine-associated paralytic poliomyelitis (VAPP). To analyze OPV3 shedding patterns, we previously used the multistep method of mutant analysis by PCR and enzyme cleavage (MAPREC). This involves conventional reverse transcription-PCR to detect OPV3, followed by a restriction digest to quantify position 472 reversion. Real-time PCR detects and quantifies nucleic acid as PCR occurs and avoids postreaction processing. The goal of this study was to compare a real-time PCR method to MAPREC. Seventy-three stool samples from Mexican OPV recipients underwent the reverse transcription-PCR step of MAPREC and real-time PCR. Real-time PCR identified 23% more OPV3-positive samples than conventional reverse transcription-PCR. When reversion was compared, the revertant proportion (RP), defined as the percentage of revertants in a sample, differed by < or =10% in 21/25 (84%) samples. The four samples differing by >10% were obtained within 5 days of OPV administration. The real-time PCR assay identified samples with an RP of > or =85% with 94% sensitivity and 86% specificity compared to MAPREC. The mean difference in RP between the two methods was 3.6% (95% confidence interval, -0.3 to 7.5%). Real-time PCR methods reliably detect OPV3, and reversion estimates correlate more consistently with MAPREC when OPV3 reversion rates are high. Detecting VAPP-related mutations by real-time PCR is rapid and efficient and can be useful in monitoring ongoing global polio eradication efforts.

Asymptomatic norovirus infection in Mexican children.

Sixty-three children in periurban Mexico City were examined for the occurrence of asymptomatic norovirus (NoV) infection from June to August 1998. NoV was detected in 48 of 161 stool specimens (29.8%), with 31 children (49.2%) having at least one positive stool. Asymptomatic NoV infection occurred commonly during summertime in a Mexican pediatric population.

A double-blind, randomized, clinical trial of the effect of vitamin A and zinc supplementation on diarrheal disease and respiratory tract infections in children in Mexico City, Mexico.

BACKGROUND: The efficacy of micronutrient supplementation in improving childhood health and survival in developing countries may be specific to the micronutrient used and health outcome measured. OBJECTIVE: We evaluated the effect of vitamin A and zinc supplementation on overall rates of childhood diarrheal disease and respiratory tract infections and rates stratified by household and personal characteristics. DESIGN: A double-blind, randomized, placebo-controlled trial was carried out in which 736 children aged 6-15 mo living in a periurban area of Mexico City were assigned to receive vitamin A every 2 mo, zinc daily, vitamin A and zinc together, or placebo. Children were followed for 12 mo to determine overall counts of diarrheal episodes and respiratory tract infections. RESULTS: Vitamin A supplementation was associated with a 27% increase in diarrheal disease [risk ratio (RR): 1.27; 95% CI: 1.10, 1.45; P < 0.001] and a 23% increase in cough with fever (RR: 1.23; 95% CI: 1.02, 1.47; P = 0.02), whereas zinc had no effect on these outcomes. Vitamin A supplementation decreased diarrhea in children from households with dirt floors but increased diarrhea in children from households with nondirt floors, piped water, and indoor bathrooms. Zinc supplementation decreased diarrhea in children from households with dirt floors and whose mothers were more educated. Vitamin A supplementation increased cough with fever in children from less-crowded households that lacked indoor bathrooms and in children of less-educated mothers. CONCLUSIONS: Vitamin A increases diarrheal disease and respiratory tract infections in young children in periurban areas of Mexico City. Vitamin A and zinc have more heterogeneous effects in different subgroups of children.

Nosocomial bacteremia and urinary tract infections caused by extended-spectrum beta -lactamase-producing Klebsiella pneumoniae with plasmids carrying both SHV-5 and TLA-1 genes.

We describe the prevalence and molecular characteristics of extended-spectrum beta -lactamase (ESBL)-producing Klebsiella pneumoniae causing nosocomial bacteremia and urinary tract infections in a Mexican general hospital. We analyzed 82 episodes of bacteremia (approximately 60% of episodes) and urinary tract infection (approximately 40% of episodes) due to K. pneumoniae during a 23-month surveillance period. The neonatal intensive care unit accounted for 49% of all episodes. All strains were imipenem susceptible; 62.2% of the strains were resistant to ceftazidime, cefotaxime, and aztreonam; 69.5% were resistant to amikacin; 58.5% were resistant to gentamicin; and 7.3% were resistant to ciprofloxacin. All strains were associated with 28 pulsed-field gel electrophoresis patterns, and dissemination of 2 ceftazidime-resistant clones produced 44% of the cases. The ESBL phenotype in these clones was transferred by identical or highly related megaplasmids. The ESBL activity corresponded to SHV-5 and TLA-1. Cross-transmission of 2 ceftazidime-resistant clones and the horizontal spread of identical or highly related megaplasmids explain the high prevalence of ESBL phenotype in these infections.

Hepatitis B seroprevalence in Latin America / La seroprevalencia de hepatitis B en América Latina

The seroprevalence of hepatitis B was investigated in over 12.000 subjects in six countries of Latin America: Argentina, Brazil, Chile, the Dominican Republic, Mexico and Venezuela. Each study population was stratified according to age, gender and socioeconomic status. Antibodies against hepatitis B core antigen (anti-HBc) were measured in order to determine hepatitis B infection. The highest overall seroprevalence was found in the Dominican Republic (21.4 por ciento), followed by Brazil (7,9 por ciento), Venezuela (3,2 por ciento), Argentina (2,1 por ciento), Mexico (1,4 por ciento) and Chile (0,6 por ciento). In all the countries an increase in seroprevalence was found among persons 16 years old and older, suggesting sexual transmission as the major route of infection. In addition, comparatively high seroprevalence levels were seen at an early age in the Dominican Republic and Brazil, implicating a vertical route of transmission

Se investigó la seroprevalencia de hepatitis B en más de 12 000 sujetos en seis países de América Latina: Argentina, Brasil, Chile, México, República Dominicana y Venezuela. Cada una de las poblaciones estudiadas fue estratificada por edad, sexo y nivel socioeconómico. Se hicieron determinaciones de anticuerpos contra el antígeno nuclear del virus de la hepatitis B (anti-HBc) con el fin de detectar la infección. La seroprevalencia general más alta se encontró en la República Dominicana (21,4%), seguida del Brasil (7,9%), Venezuela (3,2%), Argentina (2,1%), México (1,4%) y Chile (0,6%). En todos los países se encontró un aumento de la seroprevalencia en personas de 16 años de edad o mayores, lo cual indica que la transmisión sexual es la principal fuente de infección. También se hallaron tasas de seroprevalencia elevadas en personas jóvenes en la República Dominicana y el Brasil, fenómeno que apunta hacia la vía de transmisión vertical