Personal and household factors involved in recent Rickettsia exposure in a rural population from Yucatán, Mexico.

The aim of the study was to describe the epidemiological factors associated with the risks of recent Rickettsia exposure in inhabitants of a rural population from Yucatán, Mexico. The study included 130 inhabitants from Maxcanú, Yucatán. Blood samples were collected to detect IgM and IgG antibodies against Rickettsia typhi and Rickettsia rickettsii by an indirect immunofluorescence antibody test. Additionally, nested polymerase chain reaction was performed to amplify fragments of the 17kDa and sca5 genes. Previously, an epidemiological questionnaire was applied focused on collecting information on personal and housing exposure variables related to the recent infection with Rickettsia to determine epidemiological associations. Results that exhibited a p-value < .25 were included in a generalized multinomial logistic linear model to determine the variables involved with the risk of contact or Rickettsia infection. In all, 76% (99/130) of the participants presented with immunoglobulin titres against the Rickettsia species evaluated, while rickettsial DNA was detected in 35.4% (46/130) of the participants. The association analysis with the personal exposure variables showed that the productive age group (OR = 0.32; 95% CI = 0.10-1.03) and the elders group (OR = 0.12; 95% CI = 0.01-0.83) were protective factors for recent infection with R. typhi, taking as reference the school group. The presence of a family orchard in the home (OR = 7.56; 95% CI = 1.62-35.29) was a risk factor for recent infection with R. rickettsii. Presumably, the presence of ectoparasites (OR = 2.71; 95% CI = 0.90-8.09) at home was a risk factor for recent infection with both Rickettsia species. Recent infection was demonstrated in inhabitants from Maxcanú, Yucatán. A high seropositive frequency was obtained. The results highlight the importance of the family garden and the presence of ectoparasites in the home as risk factors associated with recent infection with Rickettsia in inhabitants from Maxcanú.

Detection of IgG3 antibodies specific to the human immunodeficiency virus type 1 (HIV-1) p24 protein as marker for recently acquired infection.

Reducing the risk of human immunodeficiency virus type 1 (HIV-1) transmission is still a public health priority. The development of effective control strategies relies on the quantification of the effects of prophylactic and therapeutic measures in disease incidence. Although several assays can be used to estimate HIV incidence, these estimates are limited by the poor performance of these assays in distinguishing recent from long-standing infections. To address such limitation, we have developed an assay to titrate p24-specific IgG3 antibodies as a marker of recent infection. The assay is based on a recombinant p24 protein capable to detect total IgG antibodies in sera using a liquid micro array and enzyme-linked immunosorbent assay. Subsequently, the assay was optimised to detect and titrate anti-p24 IgG3 responses in a panel of sequential specimens from seroconverters over 24 months. The kinetics of p24-specific IgG3 titres revealed a transient peak in the 4 to 5-month period after seroconversion. It was followed by a sharp decline, allowing infections with less than 6 months to be distinguished from older ones. The developed assay exhibited a mean duration of recent infection of 144 days and a false-recent rate of ca. 14%. Our findings show that HIV-1 p24-specific IgG3 titres can be used as a tool to evaluate HIV incidence in serosurveys and to monitor the efficacy of vaccines and other transmission control strategies.

Development of antibody biomarkers of long term and recent dengue virus infections.

Dengue virus (DENV) infections elicit antibody responses to the non-structural protein 1 (NS1) that are associated with protection against disease. However, the antibody isotypes and subclasses involved, and their kinetics have not been extensively studied. We characterized the antibody responses to DENV NS1 by enzyme-linked immunosorbent assay (ELISA) in a longitudinal cohort of 266 confirmed dengue cases in Recife, Northeast Brazil. Samples were collected during the febrile phase and up to over 3 years after onset of symptoms. The antibodies investigated [IgA, IgM, total IgG (all subclasses measured together) and each subclass (IgG2, IgG3 and IgG4) measured separately] had distinct kinetic profiles following primary or secondary DENV infections. Of interest, most of these antibodies were consistently detected greater than 6 months after onset of symptoms, except for IgG3. Anti-dengue NS1-specific IgG was consistently detected from the acute phase to beyond 3 years after symptom onset. In contrast, anti-dengue NS1-specific IgG3 was detected within the first week, peaked at week 2-3, and disappeared within 4-6 months after onset of symptoms. The mean duration of the IgG3 positive signal was 149 days (ranging from 126 to 172 days). In conclusion, anti-dengue NS1-specific IgG and IgG3 are potential biomarkers of long-term and recent (less than 6 months) DENV infections, respectively.

MSM in Bogotá are living with HIV for extended periods without diagnosis or treatment.

We examined recency of infection in serum samples obtained from 69 newly identified HIV-positive cases in a sample of 1000 men who have sex with men (MSM) in Bogotá. HIV antibody avidity assays were performed using the Architect HIV Ag/AB combo. Avidity indices ranged from 0.62 to 1.22, with a cut-off score below 0.80 indicative of recent infection. Two samples were classified as recent, six fell within the gray zone (0.75 to 0.85), and the remaining 61 were considered established infections. Results provided evidence of widespread, long-term, undiagnosed HIV infection, as well as an estimate of one-year incidence at .25 in the population of MSM in Bogotá. This incidence rate is approximately 8.5 times the rate estimated for the general adult population in Colombia. The large proportion of newly diagnosed cases found among individuals with established infections indicates that many MSM in Bogotá are living with HIV for extended periods without being diagnosed and treated. Greater efforts to detect and treat undiagnosed infections are crucial to decrease HIV incidence and increase maximum effectiveness of medical intervention. Given the over-representation of MSM and transgender women in the HIV epidemic in Colombia, such efforts should specifically target this population.

Comparison among the BED capture enzyme immunoassay test and AxSYM avidity index assay for determining recent HIV infection and incidence in two Voluntary Counselling and Testing Centres in Northeast Brazil.

The aims of this study were to compare the automated AxSYM avidity assay index with the BED capture enzyme immunoassay test and to calculate the HIV-1 incidence using the BED capture enzyme immunoassay and AxSYM avidity assay index algorithms within a population seeking the Voluntary Counselling and Testing Centres in two municipalities in the Metropolitan Region of Recife, Northeast of Brazil. An analysis was conducted in 365 samples that tested positive for HIV infection from frozen serum collected during the period 2006-2009. There was a similar proportion of males and females; most patients were heterosexual (86%) with a median age of 29 years. Of the 365 samples, 102 (28%) and 66 (18.1%) were identified as recent infections by BED capture enzyme immunoassay and AxSYM avidity assay index, respectively. The HIV-1 total incidence in the BED capture enzyme immunoassay and AxSYM avidity assay index algorithms were: 0.79 (95% CI: 0.60-0.98) and 0.34 (95% CI: -0.04 to 0.72), respectively. Incidence was higher among men. There was good agreement between the tests, with a kappa of 0.654 and a specificity of 95.8%. AxSYM avidity assay index may be helpful in improving the quality of the estimates of recent HIV infection and incidence, particularly when used in a combined algorithm with BED capture enzyme immunoassay.

Probabilidad de infección reciente por VIH en pacientes con presencia de antigeno p24 y prueba confirmatoria negativa / Probability of recent HIV Infection in Patients with Presence of p24 Antigen and Negative Confirmation Test

La inclusión en las pruebas de detección del VIH de la capacidad de determinar el antígeno P24 ha potenciado su capacidad diagnóstica para infecciones recientes, el articulo busca evaluar el antígeno P24 como predictor de infecciones recientes por VIH en pacientes con prueba comprobatoria negativa, estudio descriptivo de seroconversión en 245 muestras de personas desde los 14 años de edad con resultado confirmatorio negativo para el VIH en muestras de las serotecas de los laboratorios de salud pública Distrital y el centralizado de VIH en la ciudad de Bogotá.

Probabilidad de infección reciente por VIH en pacientes con presencia de antígeno p24 y prueba confirmatoria negativa / Probability of recent HIV infection in patients with presence of p24 antigen and negative confirmation test

Introducción: La inclusión en las pruebas de detección del VIH de la capacidad de determinar el antígeno p24 ha potenciado su capacidad diagnóstica para infecciones recientes. Objetivos: Evaluar el antígeno p24 como predictor de infección reciente por VIH en pacientes con prueba confirmatoria negativa. Método: Estudio descriptivo de seroconversión en 245 muestras de personas desde los 14 años de edad con resultado confirmatorio negativo para el VIH, en muestras de las serotecas de los laboratorios de Salud Pública Distrital y el Centralizado de VIH en la ciudad de Bogotá, Colombia. Se encontraron en 12 de ellas y se estudió la seroconversión en 6. Resultados: Se confirmó seroconversión en el 60% de pacientes positivos para prueba presuntiva de p24 y en el 75% de los positivos para confirmatoria del mismo antígeno. Conclusiones: Estos resultados sugieren la necesidad de realizar pruebas diagnósticas adicionales a todos los casos con resultado reactivo en prueba presuntiva y negativo para confirmatoria, en los que la reactividad de la primera pueda estar determinada por la presencia del antígeno p24 en a muestra, a fin de establecer una posible infección reciente por este virus.

Background: The inclusion of the capacity to generate p24 antigen in presumptive tests to detect the Human Immunodeficiency Virus (HIV) have enhanced its diagnosing potential in recent infection cases. The absence of this condition in confirmatory tests creates a risk of false negatives. Aims: To assess p24 antigen as a predictor of recent HIV infection in patients with negative confirmation test. Methods and design: Descriptive study of seroconversion of patients with confirmed negative test for HIV. Scenario: A study based on samples taken from the erum banks of the District Public Health Lab and Centralized HIV Lab in Bogotá, D.C., Colombia. Participants: p24 antigen was sought in 245 samples of people aged 14 or older, either reactive for presumptive tests or negative for confirmatory tests. The antigen was found in 12 of them and seroconversion took place in 6 of them. Interventions: 253 blood samples, either reactive for presumptive tests or negative for confirmatory tests were obtained out of 393,247 samples taken between January 2006 and November 2007. Finally, seroconversion was studied in patients with reactive test for p24 antigen. Outcome measurement: Seroconversion took place in patients with reactive tests for p24 antigen test for presumptive test and negative confirmatory test. Results: Seroconversion was confirmed in 60% of the patients tested positive for presumptive p24 antigen and in 75% of the patients tested positive for confirmatory test of the same antigen. Conclusions: These results suggest the need to carry out additional diagnostic tests to all cases with reactive results in presumptive testing and negative confirmatory testing in which the reactivity of the presumptive testing can be determined by the presence of p24 antigen in the sample, in order to establish a possible recent infection by this virus.