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R S Azevedo

Publications and source records attributed to R S Azevedo.

16 recordsLinked to original sources
PubMed2005

Age-specific seroprevalence to an immunodominant Cryptosporidium sporozoite antigen in a Brazilian population.

The seroepidemiology of Cryptosporidium infection was investigated in a representative sample of a normal population in the State of Sao Paulo, Brazil using a recombinant form of the immunodominant 27-kDa sporozoite antigen. IgG seropositivity was low in infants following loss of maternal antibody but quickly increased to approximately 60% by 5 years, then 80% by the age of 10 years, after which prevalence remained constant. The broad range of antibody concentrations is consistent with previous reports that the IgG response to C. parvum is short-lived. There is also evidence that average antibody concentrations increase with age. Results suggest that the recombinant antigen may be a more sensitive method of measuring seroprevalence than the native antigen in Western blot. Although cross-sectional studies can provide an insight into the epidemiology of C. parvum in normal populations, further studies investigating the dynamics of the humoral immune responses to Cryptosporidium and the use of serology in epidemiological studies are required.

Adolescent↗
PubMed2004

The vulnerability of Brazilian female prisoners to HIV infection.

The purpose of the present study was to determine the vulnerability of women in prison to HIV infection. The study was carried out from August to October 2000 in a São Paulo State Penitentiary, where 299 female prisoners were serving time. We interviewed and obtained a blood sample from 290 females who agreed to enter the study. Sera were tested for the presence of antibodies to HIV, hepatitis C virus (HCV) and syphilis and the odds ratio (OR) was calculated for variables related to HIV positivity on the basis of a questionnaire. The overall prevalence data were: 13.9% for HIV (37 of 267), 22.8% for syphilis (66 of 290), and 16.2% for HCV (47 of 290). Sexual partnership variables were significantly related to HIV infection. These included HIV-positive partners (OR = 7.36, P = 0.0001), casual partners (OR = 8.96, P = 0.009), injectable drug user partners (OR = 4.7, P = 0.0001), and history of sexually transmitted disease (OR = 2.07, P = 0.05). In addition, a relationship was detected between HIV infection and drug use (OR = 2.48, P = 0.04) and injectable drug use (OR = 4.2, P = 0.002). Even women with only one partner presented a significant OR for HIV infection (OR = 2.57, P = 0.009), reflecting their vulnerability due to their trust in their partner, who did not use a condom. Although the use of injectable substances is associated with HIV infection, our results point to sexual behavior as the most important component of HIV transmission in the female prisoner population.

Brazil↗
PubMed2003

Vaccination against rubella: analysis of the temporal evolution of the age-dependent force of infection and the effects of different contact patterns.

In this paper, we analyze the temporal evolution of the age-dependent force of infection and incidence of rubella, after the introduction of a very specific vaccination program in a previously nonvaccinated population where rubella was in endemic steady state. We deduce an integral equation for the age-dependent force of infection, which depends on a number of parameters that can be estimated from the force of infection in a steady state prior to the vaccination program. We present the results of our simulations, which are compared with observed data. We also examine the influence of contact patterns among members of a community on the age-dependent intensity of transmission of rubella and on the results of vaccination strategies. As an example of the theory proposed, we calculate the effects of vaccination strategies for four communities from Caieiras (Brazil), Huixquilucan (Mexico), Finland, and the United Kingdom. The results for each community differ considerably according to the distinct intensity and pattern of transmission in the absence of vaccination. We conclude that this simple vaccination program is not very efficient (very slow) in the goal of eradicating the disease. This gives support to a mixed strategy, proposed by Massad et al., accepted and implemented by the government of the State of São Paulo, Brazil.

Adolescent↗
PubMed2001

Optimal age for vaccination against measles in the State of São Paulo, Brazil, taking into account the mother's serostatus.

In order to investigate if the changing levels of measles antibody in women resulting from extensive vaccination programs influence the susceptibility of children, we measured the seroprevalence of measles virus antibody of children in the first year of life and of their mothers. We compared maternal antibody decay of two groups of children: those whose mothers were 25 years old or more (mothers born in the pre-vaccination era), and less than 25 years old (mothers born in the vaccination era). Therefore, the 25-year-age cut-off was chosen to distinguish between vaccinated and non-vaccinated mothers. We also compared the immunogenicity of measles vaccine in children from 6 to 12 months of age, in these two groups and also according to their mother's serostatus. The optimal age of vaccination for a routine program was estimated by means of mathematical models. This study was carried out in a sample of 1216 mothers and their respective children. Our results indicate that the optimal age for vaccination of the whole sample was 15 months, 17 months for children born from older mothers, 14 months for children born from younger mothers, 17 months for children born from seropositive mothers and 12 months for children born from seronegative mothers. Therefore, a change to an earlier age of routine vaccination is not justified by our results.

Adult↗
PubMed2001

Varicella transmission in two samples of children with different social behaviour in the State of São Paulo, Brazil.

In order to establish the differences in transmission pattern of varicella-zoster virus (VZV), a comparative seroepidemiological study was carried out in two different children samples. Children aged 1-11 years, were randomly selected from state schools of São Paulo city, Brazil. Individuals aged 1-15 years were sampled by cluster from Caieiras city. Children aged 3 years or under from Caieiras were not attending school, while those from São Paulo were attending all-day nurseries or kindergarten. The presence of antibodies to VZV was analysed by ELISA technique. The force of infection and contact rate were determined by mathematical techniques. The average age of first infection was 2.87 +/- 0.14 years and 4.07 +/- 0.47 years for Sao Paulo and Caieiras, respectively. The average force of infection estimated was 0.29 year(-1) for São Paulo and was 0.26 year(-1) for Caieiras. The proportion of seropositivity and the force of infection were higher in São Paulo school children up to 3 years of age compared with Caieiras children, where the social contact starts later. In conclusion, social changes affecting contact among children may influence varicella epidemiology.

Antibodies, Viral↗
PubMed2001

Cytomegalovirus seroepidemiology in an urban community of São Paulo, Brazil.

INTRODUCTION: After the era of rubella vaccine, cytomegalovirus (CMV) infection is one of the most frequently causes of mental retardation and congenital deafness. Seroepidemiological studies are necessary to understand the transmission dynamics of the disease. The purpose of the study was to quantify the transmission rate of CMV disease in a community in the state of São Paulo, Brazil. METHODS: Using ELISA test (IgG), a retrospective serological survey looking for CMV antibodies was performed in an non-immunized community. Frozen sera from 443 individuals, randomly selected by cluster sampling technique in the town of Caieiras, São Paulo, were collected from November 1990 to January 1991. Seroprevalence was stratified by age (0-40 years). Mathematical techniques were applied to determine the age-dependent decay function of maternal antibodies during the first year of life, the age-dependent seroprevalence function and the force of infection for CMV in this community. RESULTS: It was observed a descending phase of seropositivity in the first 9 months, but changes in antibody titration were observed between 8 months old and one year of age. The average age of the first infection was 5.02 months of age and 19.84 years, when the age-dependent seroprevalence and the force of infection were analyzed between 10 months of age and 10 years of age and from 10 to 40 years old, respectively. CONCLUSION: CMV infection is highly prevalent among the population studied and infection occurs in the first year of life. This study shows that most women at reproductive age are vulnerable to the first infection, increasing the risk for congenital infection.

Adolescent↗
PubMed1999

Seroprevalence of HIV, HCV and syphilis in Brazilian prisoners: preponderance of parenteral transmission.

Between November 1993 and April 1994, our physicians' team interviewed and took blood samples of 631 prisoners randomly drawn from the largest prison of South America, which counted about 4700 inmates at that time. The interview consisted of questions related to risk behaviour for HIV infection, and the subjects were asked to provide blood for serological tests for HIV, hepatitis C and syphilis. Our main purpose was to investigate the relationship between HCV and injecting drug use as related to HIV seropositivity. Participation in the study was voluntary and confidentiality was guaranteed. Overall prevalences found were as follows: HIV: 16% (95% confidence interval (CI): 13-19%); HCV: 34% (95% CI: 30-38%), and syphilis: 18% (95% CI: 15-21%). Acknowledged use of ever injecting drug was 22% and no other parenteral risk was reported. Our results, as compared with other studies in the same prison, suggest that HIV prevalence has been stable in recent years, and that the major risk factor for HIV infection in this population is parenteral exposure by injecting drug use.

Adolescent↗
PubMed1999

Serodiagnosis of hepatitis C virus. Effect of new evaluation of cutoff values for enzyme-linked immunosorbent assay in Brazilian patients.

With the goal of reducing false-positive results in enzyme-linked immunosorbent assay (ELISA) serodiagnosis of hepatitis C virus in clinical practice, a study was undertaken to establish better cutoff values. We examined 277 serum samples from patients with hepatitis (non-A, non-B; B; autoimmune); subjects with antinuclear antibodies or rheumatoid factor, anticytomegalovirus or Epstein-Barr virus IgG or IgM antibodies, or parasitic disease (Chagas disease, leishmaniasis); and healthy volunteers. Concordant positive results in 2 different immunoblot assays in 250 samples were taken as indicative of true-positive, and when negative, of absence of infection. Reactivity in 3 ELISA tests were evaluated for the manufacturer recommended cutoff (CO) and for 2CO, 3CO, and 4CO; and corresponding sensitivity and specificity were calculated for single or combined pairs of ELISA tests. Although CO is adequate for blood bank screening, because it provides maximal sensitivity, the frequently observed false-positive results could be significantly reduced by increasing the cutoff value to 2CO, with no significant loss in sensitivity either in relation to pairs of immunoenzymatic tests or to a single ELISA.

Brazil↗
PubMed1999

HIV infection and related risk behaviours in a disadvantaged youth institution of São Paulo, Brazil.

In order to study the prevalence of HIV and related risky behaviours among disadvantaged youth, we interviewed and bled, between December 1994 and April 1995, 1122 young males and 93 young females who were serving time in FEBEM, a state institution that cares for homeless and offender youth of São Paulo, Brazil. Our questionnaire covered the following areas: sexual practices and use of illicit drugs; knowledge of HIV and STDs and their prevention; and myths and beliefs about AIDS. Seroprevalence of HIV was assessed and related with risk-taking behaviours by means of uni-, bi- and multivariate analysis. We found 2.6% of the males and 10.3% of the females to be positive to HIV. The prevalence of hepatitis C virus (HCV) antibodies resulted in 5.9% for males and 4.6% for females, respectively. The risk for parenterally transmitted HIV among the males was higher than that for sexually related transmission. The inverse relationship was found among the females.

Acquired Immunodeficiency Syndrome↗
PubMed1998

Seroepidemiological study of respiratory syncytial virus in São Paulo state, Brazil.

Transmission of respiratory syncytial virus is thought to be highly seasonal based on reported clinical cases, although transmission resulting in mild disease in all age groups has been little studied. This has been investigated in a seroepidemiological survey using sera from São Paulo, Brazil. Seroprevalence was found to increase rapidly with age, reaching over 90% by three years of age. This is typical of viral infections, which produce life-long immunity following primary infection. One-hundred percent seropositivity was attained by five years of age and maintained throughout adulthood, whereas mean antibody titers continued to increase with age. The mean duration of maternal antibodies was estimated to be 3.3 months with antibody decay demonstrated in paired samples from infants. The results are discussed in relation to possible mechanisms generating such a profile.

Adolescent↗
PubMed1998

Seroepidemiology of group A rotavirus in suburban São Paulo, Brazil.

Age-specific patterns of rotavirus infection were investigated using a randomly selected and representative sample of sera from a suburban community of São Paulo, Brazil screened for class-specific antibodies to group A rotavirus. Age-serology of anti-rotavirus IgG showed primary infection predominant in young infants with a median age of around 18 months consistent with IgM serology suggesting highest rates of recent infection between ages 4 and 48 months. Anti-rotavirus serum IgA prevalence increased gradually with age. Paired samples from infants, collected 1 month apart, indicated high exposure rates with seroconversion occurring in several infants during the reported low transmission season. Between 5 and 10% of adults had elevated IgM levels indicative of recent infection and, potentially, of an important contribution adults may play to rotavirus transmission. Further understanding of the dynamics of rotavirus transmission within populations, at group and serotype level, would benefit the design and monitoring of future immunization programmes.

Adolescent↗
PubMed1998

Infection with group C rotavirus in a suburban community in Brazil.

Group C rotaviruses are associated with sporadic outbreaks of gastroenteritis worldwide. Age-specific seroprevalence of group C rotavirus antibodies was investigated in sera, randomly collected and representative of a suburban community in Brazil which had previously been screened for group A rotavirus antibodies. Antibody prevalence to group C rotavirus was low in children under 5 years and increased slowly with age to 36% seropositivity in adults, reflecting continuous exposure to primary infection in all age groups. This suggests a higher incidence of infection than disease might predict. Adult antibody prevalence was similar to that in other geographical settings. No obvious patterns of infection with group A and group C rotavirus were found within individuals, which suggests independent transmission. However, further epidemiological studies are required to understand group C rotavirus dynamics and possible interactions with group A rotavirus transmission and immunity.

Adolescent↗
PubMedDate not supplied

Measles antibody levels in a vaccinated population in Brazil.

An epidemiological study of measles-specific immunoglobulin G antibody levels was conducted using a representative sample of a vaccinated suburban population in São Paulo State, Brazil. The study aimed to determine immunity status in relation to age and infection or vaccination experience. 549 age-structured samples of sera, collected in 1990, were screened and calibrated to the international reference serum, using measles nucleoprotein in an enzyme immunoassay. In the age group with direct experience of vaccination (9 months to 15 years), whether routine or campaign, over 90% had detectable antibody > or = 50 miu/mL. However, 14% of these had antibody concentrations between 50 and 100 miu/mL and 30% between 50 and 255 miu/mL. In those over 15 years of age, 94% had antibody levels > 255 miu/mL, assumed to be the result of past infection. The study suggested that, within highly vaccinated populations, a proportion of individuals had measles antibody levels which may be insufficient to protect against reinfection or clinical disease. The implications of these results, and similar findings elsewhere, in relation to the persistence of measles requires investigation; this has particular relevance in São Paulo following the recent measles outbreak.

Adolescent↗
PubMedDate not supplied

Detection of antibodies against hepatitis A virus in eluates of blood spotted on filter-paper: a pilot study in Rio de Janeiro, Brazil.

The validity of blood spotted on to filter-paper (BSOFP) eluates for the detection of antibodies against hepatitis A virus (HAV) was investigated in 718 individuals (children and adults) during a field study in a small area in Rio de Janeiro State, Brazil. Serum samples were considered the 'gold standard'. BSOFP eluates were analyzed by 2 different techniques: microplate competitive enzyme-linked immunosorbent assay (ELISA) of the whole study group and microparticle enzyme immune assay (MEIA) of a subsample of 59 individuals. For BSOFP eluates by ELISA, sensitivity and specificity were 89.6% (95% CI: 84.7-93.1) and 97.5% (95% CI: 95.6-98.7), respectively. For a seroprevalence of anti-HAV antibodies of 32%, the positive predictive value was 94.5% (95% CI: 90.3-97.0) and the negative predictive value was 95.2% (95% CI: 92.8-96.8). The test efficiency was 95.0% (95% CI: 93.1-96.4). Similar results were found for BSOFP eluates by MEIA. Agreement between the 2 techniques used for BSOFP (ELISA and MEIA) was also high (kappa = 0.93). These results encourage the more widespread application of BSOFP as a means of surveillance for large-scale epidemiological studies for hepatitis A.

Adolescent↗
PubMedDate not supplied

Three year seroepidemiological study of varicella-zoster virus in São Paulo, Brazil.

A serosurvey of varicella has been carried out in children attending the public school network of São Paulo city, Brazil, from 1992 to 1994. This study was performed in order to establish the age related prevalence of antibodies against varicella-zoster virus (VZV) and its age specific transmission dynamics pattern in these children. Among 2500 schools in the city of São Paulo public network, 304 were randomly selected; 7 children of a given age (ranging from 1 to 15 years) were randomly selected in each school, and blood samples were obtained by fingerprick into filter paper. Blood eluates were analyzed for the presence of antibodies to VZV by ELISA. Proportion of seropositivity were calculated for each age group. Samples consisted of 1768 individuals in 1992, 1758 in 1993, and 1817 in 1994, resulting in 5343 eluates. A high proportion of seropositive children from 1 to 3 years of age was observed, ascending until 10 years of age and reaching a plateau around 90% afterwards. VZV transmission in this community was similar along the three years of the study. In children attending public schools in the city of São Paulo, contact with VZV occurs in early childhood. If immunization against VZV is considered it should be introduced as soon as possible.

Adolescent↗