Heterogeneity of Herpes Simplex Virus Type 2 Seroprevalence From a National Probability Survey In Mexico, 2012.

BACKGROUND: Herpes simplex virus type 2 (HSV-2) seroprevalence and associated infection risk factors show differences by regions and countries. The aims of the study were to determine the HSV-2 seroprevalence and to evaluate the risk factors for HSV-2 in a national representative survey among adolescents and adults in Mexico. METHODS: A cross-sectional study was carried out in Mexico on the basis of the National Health and Nutrition Survey 2012, a national representative survey. Demographic, sexual behavior, reproductive health, and lifestyles indicators were considered in the current study. Participants provided biological samples-dried blood spots-to test for HSV-2 antibodies using enzyme-linked immunosorbent assay and Western blot. Bivariate and multivariate analyses were performed to identify variables associated with HSV-2 infections analyzed by sex. RESULTS: National HSV-2 seroprevalence was 9.9%, 2.4% among adolescents and 11.7% among adults with HSV-2 seroprevalence heterogeneous across the country. Women had 12.2% of antibodies against HSV-2 and men had 7.5%. The factors associated with HSV-2 infection among women were age (45-49 years; odds ratio [OR], 19.8), region (southwest; OR, 3.0), urbanization (urban; OR, 1.9), age at sexual debut (≤14 years; OR, 3.4), education level (any; OR, 3.0), and previous abortion (≥2 abortion; OR, 2.1). Among men, age (45-49 years; OR, 11.7), region (southwest; OR, 3.0), urbanization (urban, odds ratio [OR], 1.7), and HIV care (OR, 7.1) were associated with the infection. CONCLUSIONS: Approximately 10% of Mexicans aged 15 to 49 years had HSV-2 antibodies, with differences by sex, region, education level, urbanization, HIV care, and childbirth, highlighting the relevance of health inequalities in the country: social inequalities seem to matter in terms of the probability of HSV-2 infections.

Punto Seguro: A Randomized Controlled Pilot Using Conditional Economic Incentives to Reduce Sexually Transmitted Infection Risks in Mexico.

Randomized controlled pilot evaluated effect of conditional economic incentives (CEIs) on number of sex partners, condom use, and incident sexually transmitted infections (STIs) among male sex workers in Mexico City. Incentives were contingent on testing free of new curable STIs and/or clinic attendance. We assessed outcomes for n = 227 participants at 6 and 12 months (during active phase with incentives), and then at 18 months (with incentives removed). We used intention-to-treat and inverse probability weighting for the analysis. During active phase, CEIs increased clinic visits (10-13 percentage points) and increased condom use (10-15 percentage points) for CEI groups relative to controls. The effect on condom use was not sustained once CEIs were removed. CEIs did not have an effect on number of partners or incident STIs. Conditional incentives for male sex workers can increase linkage to care and retention and reduce some HIV/STI risks such as condomless sex, while incentives are in place.

Serological response to Helicobacter pylori infection among Latin American populations with contrasting risks of gastric cancer.

Gastric cancer is a rare outcome of chronic Helicobacter pylori infection. Serologic profiles may reveal bacterial, environmental and/or host factors associated with cancer risk. We therefore compared specific anti-H. pylori antibodies among populations with at least twofold differences in gastric cancer mortality from Mexico, Colombia and Chile. Our study included 1,776 adults (mean age 42 years) from three nationally representative surveys, equally divided between residents of high- and low-risk areas. Antibodies to 15 immunogenic H. pylori antigens were measured by fluorescent bead-based multiplex assays; results were summarized to identify overall H. pylori seropositivity. We used logistic regression to model associations between antibody seroreactivity and regional cancer risk (high vs. low), adjusting for country, age and sex. Both risk areas had similar H. pylori seroprevalence. Residents in high- and low-risk areas were seroreactive to a similar number of antigens (means 8.2 vs. 7.9, respectively; adjusted odds ratio, OR: 1.02, p = 0.05). Seroreactivities to Catalase and the known virulence proteins CagA and VacA were each significantly (p < 0.05) associated with residence in high-risk areas, but ORs were moderate (1.26, 1.42 and 1.41, respectively) and their discriminatory power was low (area under the curve < 0.6). The association of Catalase was independent from effects of either CagA or VacA. Sensitivity analyses for antibody associations restricted to H. pylori-seropositive individuals generally replicated significant associations. Our findings suggest that humoral responses to H. pylori are insufficient to distinguish high and low gastric cancer risk in Latin America. Factors determining population variation of gastric cancer burden remain to be identified.

Use of a commercial ELISA for the detection of measles-specific immunoglobulin G (IgG) in dried blood spots collected from children living in low-resource settings.

Seroepidemiological monitoring of population immunity to vaccine-preventable diseases is critical to prevent future outbreaks. Dried blood spots (DBS), drops of capillary blood dried on filter paper, are an affordable, minimally invasive alternative to venipuncture for collecting blood in field settings. However, few proven methods exist to analyze DBS for the presence of protective antibodies. This study validates a novel technique for measuring measles-specific immunoglobulin G (IgG) in capillary DBS using a commercial ELISA. The predictive performance of a new method for analyzing DBS was tested by comparing matched serum and DBS samples from 50 children. The accuracy, precision, and reliability of the procedure were evaluated, and the optimal cut points to classify positive and negative samples were determined. The method was then applied to 1,588 DBS collected during a large survey of children in Mexico and Nicaragua. Measles-specific IgG in serum samples were 62% negative, 10% equivocal, and 28% positive. In comparisons with matched serum, DBS results were 100% sensitive and 96 · 8% specific, and agreed in 46 of 50 (92%) cases. The inter-assay and intra-assay coefficients of variation from kit-provided controls were greater than desired (24.8% and 8.4%, respectively). However, in predictive simulations the average misclassification was only 3.9%. Procedures were found to be acceptable to surveyors and participants. Analyzing DBS collected in low-resources settings is a feasible and accurate means of measuring population immunity to measles and should be used to generate objective measures of health status and health system performance.

Public health services and their relationship with rapid HIV test utilization and access for key populations in Morelos, Mexico.

OBJECTIVE: In 2009, 4 749 rapid HIV tests were run in Morelos, Mexico, despite lacking evidence on their results. This article seeks to analyze how public health organization relates to utility of rapid HIV test among healthcare users. MATERIALS AND METHODS: Joint study: comparison of differences in applied test and positive results for each group with the Bonferroni statistical tool, observational study in 34 health subsystems, and 11 interviews with public healthcare users. RESULTS: Each subsystem processes influenced the use and usefulness of screening; for instance, primary care centers test only pregnant women and exclude men who have sex with men (MSM). That group shows significant differences (p<0.007) in the HIV-positive test with respect to other groups. CONCLUSIONS: Despite the availability of rapid detection tests and epidemiological evidence, the way public health services are organized impedes an efficient diagnosis in the group with higher risk, namely MSM. The distribution of rapid HIV tests was guided by stigmatization.

[Trend analysis of acquired syphilis in Mexico from 2003 to 2013]. / Análisis de la tendencia de sífilis adquirida en México durante el periodo 2003-2013.

OBJECTIVE: To identify the population group in which syphilis increase was concentrated. MATERIALS AND METHODS: The information was collected from the Mexico health statistical yearbooks. The information disaggregated by sex, age group and state during the period 2003 to 2013 was used to form different databases. Linear regression analysis with confidence interval at 95% was used to evaluate changes over time in different population groups. RESULTS: An increase of 0.67 cases per 100,000 population (95%CI 0.30-1.04) in men was detected from 2010. The increase was concentrated in each group of 20-24 and 25-44. The highest incidence of acquired syphilis was reported in the last two years: 2012 and 2013. The last year reported a 1.85 times higher incidence than reported in 2003. Aguascalientes, Distrito Federal, Durango, Mexico, Oaxaca, Puebla, Quintana Roo, Yucatan and Zacatecas reported that syphilis increased during the study period. CONCLUSION: Acquired syphilis may be reemerging in our country among young men; this increase is not uniform across the country, it is necessary to focus intervention measures for this sexually transmitted infection.

Risk factors for anal HPV-16/18 infection in Mexican HIV-infected men who have sex with men.

OBJECTIVE: To describe the prevalence of specific HPV types among HIV-positive men who have sex with men (MSM), particularly the presence of HPV-16 and/or -18, and to determine the factors associated with anal HPV-16/18 infections. METHODS: This is a cross-sectional study from a baseline cohort of 525 HIV-positive MSM, who attended an HIV Clinic in Mexico City. Socio-demographic characteristics, sexual behaviors and HIV-related parameters were assessed. Anal samples were tested for HPV DNA using the Linear Array HPV genotyping assay. RESULTS: The overall prevalence of any HPV type in the anal canal among 446 participants was 93.1%. At least one oncogenic HPV type was detected in 72.2% of the subjects and HPV-16 and/or18 were detected in 30.7%. Additionally, 76.9% of patients were infected with multiple HPV types. Having more than 10 receptive sexual partners in the last 6months (OR=2.30; 95% CI 1.12-4.74) and a CD4 cell count ≤350cells/µL (OR=1.97; 95% CI 1.26-3.09) were factors positively associated with HPV-16/18 infection in the anal canal. CONCLUSION: Co-infection with HPV-16/18 and other oncogenic types are predominant in this group of HIV-positive MSM. The recognition of infection with specific oncogenic types will be of aid in designing future preventive strategies that target this high-risk population.

Avidity of antibodies against HSV-2 and risk to neonatal transmission among Mexican pregnant women.

OBJECTIVE: To determine HSV-2 seroprevalence, risk factors, and antibody avidity among a sample of Mexican pregnant women. MATERIAL AND METHODS: The avidity test was standardized with different urea concentrations and incubation times; the cut-off point was calculated to determine the low avidity (early infection). IgG antibodies against HSV-2 were detected from pregnant and postpartum women from Morelos, Mexico, and the avidity test was performed to positive samples. Multivariate regression logistic analysis was employed to evaluate demographic and sexual behavior characteristics associated with HSV-2 infection. RESULTS: HSV-2 seroprevalence among Mexican women analyzed was 14.5% (333/2300), demographic factors (location of General Hospital, age, education level, and civil status), and risky sexual behaviors (STI self-report and number of sexual partners during last year) were associated with HSV-2 infection. Seventeen women were detected with low avidity antibodies (early infection) with a cut-off point of 66.1%. CONCLUSIONS: HSV-2 infection was common among this group of women from Mexico; the avidity test detected women with recent infections, and these women were more likely to transmit HSV-2 to their neonates. Neonatal herpes has no epidemiological surveillance, the disease could be overlooked, and so more studies are needed to estimate the magnitude of neonatal infection.

Human papillomavirus incidence and risk factors among Mexican female college students.

OBJECTIVE: To determine the factors associated with high-risk human papillomavirus (HR-HPV) and its incidence in a cohort of female college students, with particular emphasis on the use of condoms. METHODS: A cohort was created during 2001 to 2005. The students signed informed consent, answered a questionnaire, and provided a vaginal scrape to detect HR-HPV. Incidences were estimated and risk factors were evaluated using Cox proportional risk model. The variable condom use was constructed based on the following 3 measurements: relative frequency throughout one's lifetime, use during the first sexual relationship, and use during the last sexual relationship. RESULTS: A total of 237 women participated, providing 395.6 person-years of follow-up. An incidence of 15.9 HR-HPV infection per 100 person-years was estimated and the factors associated with HR-HPV infection were found to be self-reported sexually transmitted infections (RR = 2.7), use of emergency contraception pill (ECP) (RR = 2.0), and having 2 or more sexual partners (RR = 1.9). University students using the ECP demonstrated more risky sexual behavior than nonusers. Women with 2 or more sexual partners who reported inconsistent condom use had 3.8 times the rate of HR-HPV infection. CONCLUSIONS: The incidence for HR-HPV in this cohort of Mexican female college students is comparable to that found in the United States and Canada. The results suggest that the consistent use of condoms is a protective factor against HR-HPV, especially for women with multiple sexual partners and/or those who use the ECP.

Incidence and time-varying predictors of HIV and sexually transmitted infections among male sex workers in Mexico City.

BACKGROUND: Male sex workers are at high-risk for acquisition of sexually transmitted infections (STIs), including human immunodeficiency virus (HIV). We quantified incidence rates of STIs and identified their time-varying predictors among male sex workers in Mexico City. METHODS: From January 2012 to May 2014, male sex workers recruited from the largest HIV clinic and community sites in Mexico City were tested for chlamydia, gonorrhea, syphilis, hepatitis, and HIV at baseline, 6-months, and 12-months. Incidence rates with 95% bootstrapped confidence limits were calculated. We examined potential time-varying predictors using generalized estimating equations for a population averaged model. RESULTS: Among 227 male sex workers, median age was 24 and baseline HIV prevalence was 32%. Incidence rates (per 100 person-years) were as follows: HIV [5.23; 95% confidence interval (CI): 2.15-10.31], chlamydia (5.15; 95% CI: 2.58-9.34), gonorrhea (3.93; 95% CI: 1.88-7.83), syphilis (13.04; 95% CI: 8.24-19.94), hepatitis B (2.11; 95% CI: 0.53-4.89), hepatitis C (0.95; 95% CI: 0.00-3.16), any STI except HIV (30.99; 95% CI: 21.73-40.26), and any STI including HIV (50.08; 95% CI: 37.60-62.55). In the multivariable-adjusted model, incident STI (excluding HIV) were lower among those who reported consistently using condoms during anal and vaginal intercourse (odds ratio = 0.03, 95% CI: 0.00-0.68) compared to those who reported inconsistently using condoms during anal and vaginal intercourse. CONCLUSIONS: Incidence of STIs is high among male sex workers in Mexico City. Consistent condom use is an important protective factor for STIs, and should be an important component of interventions to prevent incident infections.

HSV-2 seroincidence among Mexican college students: the delay of sexual debut is not enough to avoid risky sexual behaviours and virus transmission.

OBJECTIVES: Early sexual debut is a behaviour that has been associated with acquiring sexually transmitted infections. Higher schooling may delay sexual debut, thus the university population is categorised with low-risk sexual behaviours. The rate ratio of herpes simplex virus type 2 (HSV-2) seroincidence according to demographic characteristics and sexual behaviour was estimated for a cohort of university students. METHODS: A dynamic cohort of university students was followed at the Autonomous University of Morelos, in central Mexico, during the years 2001-5. After obtaining informed consent, information was gathered annually regarding demographic characteristics and sexual behaviour and blood samples were obtained to determine HSV-2 antibodies. Seroincidence was estimated and the incidence rate ratio was evaluated using the Poisson regression model. RESULTS: A total of 404 students participated, with 669.2 person-years of follow-up. An incidence of 4.2 cases per 100 person-years was estimated. The variables delayed sexual debut (≥18 years) and multiple sexual partners (two or more sexual partners during the past year) had a rate ratio of 4.1 (95% CI 1.2 to 14.3) and 2.5 (95% CI 1.1 to 5.6), respectively. Incidence for students with delayed sexual debut and multiple partners is estimated to be 10.3 cases per 100 person-years. CONCLUSIONS: Delayed sexual debut was a risk factor for acquiring HSV-2, due to a subgroup with sexual debut at 18 years of age or older that had multiple sexual partners; therefore, in the university population that tends to delay sexual debut, it is necessary to implement prevention programmes to promote the decrease of other risky sexual behaviours, as well as the promotion of the consistent use of condoms.

Performance of ELISA and Western blot to detect antibodies against HSV-2 using dried blood spots.

BACKGROUND AND AIMS: Herpes simplex virus type 2 (HSV-2) is a sexually transmitted agent and is detected worldwide. HSV-2 is the main cause of genital ulcers and is diagnosed mainly with serological tests. The objective of current study was to evaluate the use of DBS samples to detect HSV-2 antibodies using commercial ELISA and Western blot tests. MATERIALS AND METHODS: IgG-G2 ELISA (Human® Diagnostics, Germany) and Western blot IgG/IgM (EUROLINE-WB, Euroimmun® Germany) tests were modified to use DBS samples. Samples were processed by both methods to determine ELISA cutoff points using ROC curves. ELISA was performed with 100µl and the Western blot with 200µl of eluted DBS. A 1:5 dilution was used and the incubation times were increased for the Western blot. RESULTS: 908 DBS samples were processed and the following cutoff points were determined: negative (0-3.79), undetermined (3.8-4.6) and positive (≥4.61), with sensitivity and specificity close to 95%. CONCLUSION: Modifications of the cutoff points of the ELISA test were obtained with technical adjustments done to detect HSV-2 antibodies by ELISA and Western blot using DBS samples.

Core group approach to identify college students at risk for sexually transmitted infections.

OBJECTIVE: To analyze the core group for sexually transmitted infections (STI) among college students. METHODS: Cross-sectional study carried out in a convenience sample comprising 711 college students of the public university of Morelos, Mexico, between 2001 and 2003. Sociodemographic and sexual behavior information were collected using self-applied questionnaires. Herpes simplex 2 (HSV-2) infection was tested in the blood. The number of sexual partners in the last year and cocaine consumption were used as indicators to construct the dependent variable "level of STI risk" in three categories: low, medium and high risk (core group). A multinomial analysis was conducted to evaluate whether different sex behaviors were associated with the variable "level of STI risk". RESULTS: There was significant association between HSV-2 seroprevalence and the variable "level of STI risk": 13%, 5.6% and 3.8% were found in high (core group), medium and low categories, respectively. There were gender differences regarding the core group. Men started having sexual intercourse earlier, had more sex partners, higher alcohol and drug consumption, higher frequency of sex intercourse with sex workers, exchanging sex for money, occasional and concurrent partners compared to women. CONCLUSIONS: The study findings suggest existing contextual characteristics in the study population that affect their sex behavior. In Mexico, the cultural conception of sexuality is determined mainly by gender differences where men engage in higher risky sexual behavior than women.

College women, HPV genotyping and sexual behavior before HPV vaccination: Results from samples stored for a long time.

HPV is the sexually transmitted agent most common among young people, like college students. The aim of study was to associate sexual behavior characteristics of women with HPV, detected in genital samples taken before the introduction of the HPV vaccine. Female students during 2001-2005 donated genital samples and the samples were re-analyzed in 2013 for HPV genotyping by RT-PCR. The frozen storage of the students' genital samples allowed the detection of HPV DNA and its genotyping after years of sample collection. HPV prevalence was 22%, HPV16 3.9%, and HPV18 1.1%. Age, multiple sexual partners and the partner's age at first sexual intercourse were significantly associated to HPV. Students with ≥ 3 sexual partners and who did not use condom had 12.8 higher odds of being HPV positive. These results made possible the analysis of HPV prevalence changes, before HPV vaccine introduction.

Evaluation of a rapid strip and a particle agglutination tests for syphilis diagnosis.

The availability of new diagnostic approaches, which are easier and faster to perform than conventional tests, offers the opportunity to improve the attention given to public health problems as syphilis. This study aimed to evaluate a rapid immunochromatographic strip test (Determine TP; Abbott Laboratories, Chicago, IL) and a nonequipment demanding particle microagglutination test (Serodia TP-PA; Fujirebio, Japan) for qualitative detection of treponemic antibodies. Sera from 548 women belonging to 3 population groups were tested; one of them showing low syphilis seroprevalence (1.5%) and the other 2 showing higher seroprevalences (>15%). By comparison with the gold standard (Venereal Disease Research Laboratories plus fluorescent treponemal antibody absorption), sensitivity and specificity values for both diagnostic tests were calculated. Sensitivity values of both tests evaluated were higher than 95% for 2 groups of 3 addressed; in one of the high syphilis prevalence groups, Serodia TP-PA showed 88.6% sensitivity. Specificity values were above 95% for all 3 groups. The use of simple/rapid treponemic tests as those included here may prove to be a suitable replacement for the traditional syphilis serology diagnosis approach, particularly at primary care settings.

Risk behaviors of 15-21 year olds in Mexico lead to a high prevalence of sexually transmitted infections: results of a survey in disadvantaged urban areas.

BACKGROUND: Due to the fact that adolescents are more likely to participate in high-risk behaviors, this sector of the population is particularly vulnerable to contracting sexually transmitted infections (STIs) and resultant health problems. METHODS: A survey was carried out among adolescents from poor homes in 204 small-urban areas of Mexico. Information was collected in relation to risk behaviors and socio-economic environment. A sub-group of the participants also provided blood and urine samples which were analyzed to detect sexually transmitted infections. RESULTS: The presence of Chlamydia was detected in nearly 8% of participants who had stated that they were sexually active (18%) and approximately 12% were positive for herpes type 2-specific antibodies. For both, a greater proportion of girls resulted positive compared to boys. The presence of these biological outcomes of sexual risk behavior was associated with other risk behaviors (smoking), but not with self-reported indicators of protected sex (reported use of condom during most recent sexual activity). CONCLUSION: The results presented in this study show a startlingly high prevalence of HSV-2 among sexually active Mexican adolescents in poor urban areas, suggesting that this group has participated to a great extent in risky sexual practices. The relationships between socioeconomic environment and adolescent risk behavior need to be better understood if we are to design preventive interventions that modify the determinants of risk behaviors.

Sexual behavior and herpes simplex virus 2 infection in college students.

BACKGROUND: Given the relevance of HSV-2 infection in youth, the aim of this study was to determine the seroprevalence of HSV-2 in college students in Cuernavaca, Mexico, as well as the sociodemographic and sexual behavioral characteristics associated with this infection. METHODS: A cross-sectional study was carried out using convenience sampling with consenting students of both genders. Students answered a questionnaire and provided a blood sample to detect antibodies to HSV-2 by Western blot. To establish the magnitude of the association between the prevalence of HSV-2 infection and the selected risk factors, we estimated prevalence odds ratios by performing logistic analyses of these results RESULTS: Overall seroprevalence of HSV-2 was 5.9% (20/340; CI(95%) 3.7-8.9), 7.0% (14/200; CI(95%) 3.9-11.5) for women and 4.3% (6/140; CI(95%) 1.6-9.1) for men. HSV-2 infection was independently associated with female sex (POR=5.3, CI(95%) 1.4-19.7), age (26 years and over, POR=4.7, CI(95%) 1.0-22.2), number of sexual partners over the last year (two or more partners POR=4.1, CI(95%) 1.2-14.2), a history of genital ulcers (POR=6.1, CI(95%) 1.9-19.8), and having been paid for sex (POR=21.4, CI(95%) 1.0-447.5). CONCLUSIONS: The frequency of HSV-2 infection among these students was lower than in other Mexican populations who have high-risk sexual behavior. However, there was a subgroup of participants identified as having high-risk sexual behavior. These individuals could, therefore, be prone to acquiring and transmitting HSV-2 infection and represent the target group for whom preventive interventions against HSV-2 and other STIs might be developed.

A Cross-Sectional Study of Prisoners in Mexico City Comparing Prevalence of Transmissible Infections and Chronic Diseases with That in the General Population.

OBJECTIVES: To describe patterns of transmissible infections, chronic illnesses, socio-demographic characteristics and risk behaviors in Mexico City prisons, including in comparison to the general population, to identify those currently needing healthcare and inform policy. MATERIALS AND METHODS: A cross-sectional study among 17,000 prisoners at 4 Mexico City prisons (June to December 2010). Participation was voluntary, confidential and based on informed consent. Participants were tested for HIV, Hepatitis B & C, syphilis, hypertension, obesity, and, if at risk, glucose and cholesterol. A subset completed a questionnaire on socio-demographic characteristics and risk behaviors. Positive results were delivered with counseling and treatment or referral. RESULTS: 76.8% (15,517/20,196) of men and 92.9% (1,779/1,914) of women participated. Complete data sets were available for 98.8%. The following prevalence data were established for transmissible infections: HIV 0.7%; syphilis: Anti-TP+/VDRL+ 2.0%; Hepatitis B: HBcAb 2.8%, HBsAg 0.15%; Anti-HCV 3.2%. Obesity: 9.5% men, 33.8% women. Compared with national age- and sex-matched data, the relative prevalence was greater for HIV and syphilis among women, HIV and Hepatitis C in men, and all infections in younger participants. Obesity prevalence was similar for women and lower among male participants. The prevalence of previously diagnosed diabetes and hypertension was lower. Questionnaire data (1,934 men, 520 women) demonstrated lower educational levels, increased smoking and substance use compared to national data. High levels of non-sterile tattooing, physical abuse and histories of sexual violence were found. CONCLUSION: The study identified that health screening is acceptable to Mexico City prisoners and feasible on a large-scale. It demonstrated higher prevalence of HIV and other infections compared to national data, though low rates compared to international data. Individual participants benefited from earlier diagnosis, treatment and support. The data collected will also enable the formulation of improved policy for this vulnerable group.

Comparative Estimates of Crude and Effective Coverage of Measles Immunization in Low-Resource Settings: Findings from Salud Mesoamérica 2015.

Timely and accurate measurement of population protection against measles is critical for decision-making and prevention of outbreaks. However, little is known about how survey-based estimates of immunization (crude coverage) compare to the seroprevalence of antibodies (effective coverage), particularly in low-resource settings. In poor areas of Mexico and Nicaragua, we used household surveys to gather information on measles immunization from child health cards and caregiver recall. We also collected dried blood spots (DBS) from children aged 12 to 23 months to compare crude and effective coverage of measles immunization. We used survey-weighted logistic regression to identify individual, maternal, household, community, and health facility characteristics that predict gaps between crude coverage and effective coverage. We found that crude coverage was significantly higher than effective coverage (83% versus 68% in Mexico; 85% versus 50% in Nicaragua). A large proportion of children (19% in Mexico; 43% in Nicaragua) had health card documentation of measles immunization but lacked antibodies. These discrepancies varied from 0% to 100% across municipalities in each country. In multivariate analyses, card-positive children in Mexico were more likely to lack antibodies if they resided in urban areas or the jurisdiction of De Los Llanos. In contrast, card-positive children in Nicaragua were more likely to lack antibodies if they resided in rural areas or the North Atlantic region, had low weight-for-age, or attended health facilities with a greater number of refrigerators. Findings highlight that reliance on child health cards to measure population protection against measles is unwise. We call for the evaluation of immunization programs using serological methods, especially in poor areas where the cold chain is likely to be compromised. Identification of within-country variation in effective coverage of measles immunization will allow researchers and public health professionals to address challenges in current immunization programs.

Diagnostic-test evaluation of immunoassays for anti-Toxoplasma gondii IgG antibodies in a random sample of Mexican population.

INTRODUCTION: There are few articles on evaluation of Toxoplasma gondii serological tests. Besides, commercially available tests are not always useful and are expensive for studies in open population. The aim of this study was to evaluate in-house ELISA and western blot for IgG antibodies in a representative sample of people living in Mexico. METHODOLOGY: Three hundred and five serum samples were randomly selected from two national seroepidemiological survey banks; they were taken from men and women of all ages and from all areas of the country. ELISA cut-off was established using the mean plus three standard deviations of negative samples. Western blots were analysed by two experienced technicians and positivity was established according to the presence of at least three diagnostic bands. A commercial ELISA kit was used as a third test. Two reference standards were built up: one using concordant results of two assays leaving the evaluated test out and the other in which the evaluated test was included (IN) with at least two concordant results to define diagnosis. RESULTS: the lowest values of diagnostic parameters were obtained with the OUT reference standards: in-house ELISA had 96.9% sensitivity, 62.1% specificity, 49.6% PPV, 98.1% NPV and 71.8% accuracy, while western blot presented 81.8%, 89.7%, 84.0%, 88.2% and 86.6% values and the best kappa coefficient (0.72-0.82). CONCLUSIONS: The in-house ELISA is useful for screening people of Mexico, due to its high sensitivity, while western blot may be used to confirm diagnosis. These techniques might prove useful in other Latin American countries.