Rubella seroepidemiology in a non-immunized population of São Paulo State, Brazil

Systematic Review of Measles and Rubella Serology Studies

Serological tests provide information about individual immunity from historical infection or immunization. Cross-sectional serological studies provide data about the age- and sex-specific immunity levels for individuals in the studied population, and these data can provide a point of comparison for the results of transmission models. In the context of developing an integrated model for measles and rubella transmission, we reviewed the existing measles and rubella literature to identify the results of national serological studies that provided cross-sectional estimates of population immunity at the time of data collection. We systematically searched PubMed, the Science Citation Index, and references we identified from relevant articles published in English. We extracted serological data for comparison to transmission model outputs. For rubella, serological studies of women of child-bearing age provide information about the potential risks of infants born with congenital rubella syndrome. Serological studies also document the loss of maternal antibodies, which occurs at different rates for the different viruses and according to the nature of the induced immunity (i.e., infection or vaccine). The serological evidence remains limited for some areas, with studies from developed countries representing a disproportionate part of the evidence. The collection and review of serological evidence can help program managers identify immunity gaps in the population, which may help them better understand the characteristics of individuals within their populations who may participate in transmission and manage risks.

Serological makers of rubella infection in Africa in the pre vaccination era: a systematic review

BACKGROUND

Rubella infections in susceptible women during early pregnancy often results in congenital rubella syndrome (CRS). World Health Organisation (WHO) recommends that countries without vaccination programmes to assess the burden of rubella infection and CRS. However; in many African countries there is limited data on epidemiology of rubella infection and CRS. This review was undertaken to assess the serological markers and genotypes of rubella virus on the African continent in order to ascertain the gap for future research.

FINDINGS

A systematic search of original literatures from different electronic databases using search terms such as 'rubella' plus individual African countries such as 'Tanzania', 'Kenya', 'Nigeria' etc. and different populations such as 'children', 'pregnant women' etc. in different combinations was performed. Articles from countries with rubella vaccination programmes, outbreak data and case reports were excluded. Data were entered in a Microsoft Excel sheet and analyzed. A total of 44 articles from 17 African countries published between 2002 and 2014 were retrieved; of which 36 were eligible and included in this review. Of all population tested, the natural immunity of rubella was found to range from 52.9 to 97.9 %. In these countries, the prevalence of susceptible pregnant women ranged from 2.1 to 47.1 %. Rubella natural immunity was significantly higher among pregnant women than in general population (P < 0.001). Acute rubella infection was observed to be as low as 0.3 % among pregnant women to 45.1 % among children. All studies did not ascertain the age-specific prevalence, thus it was difficult to calculate the rate of infection with increase in age. Only two articles were found to report on rubella genotypes. Of 15 strains genotyped; three rubella virus genotypes were found to circulate in four African countries.

CONCLUSION

Despite variations in serological assays, the seroprevalence of IgG rubella antibodies in Africa is high with a substantial number of women of childbearing age being susceptible to rubella infection. Standardized sero-epidemiological data in various age groups as well as CRS data are important to implement cost-effective vaccination campaigns and control strategies.

Will people change their vector-control practices in the presence of an imperfect dengue vaccine?

Human behaviours, which are influenced by social, cultural, economic and political factors, can increase or decrease the risk of dengue infection, depending on the relationship with the insect vector. Because no vaccine is currently available, the spread of dengue can only be curtailed by controlling vector populations (Aedes aegypti and others) and by protecting individuals. This study tested the hypothesis that dengue-affected populations are likely to relax their vector-control habits if a potentially protective vaccine becomes available. The hypothesis was tested using two approaches: a mathematical model designed to describe dengue transmission and an empirical field test in which the local population of an endemic area was interviewed about their vector-control habits given the presence of a theoretical vaccine. The model demonstrated that depending on the level of vector-control reduction, there is a threshold in vaccine efficacy below which it is better not to introduce the vaccine. The interview showed that people who were informed that a very effective vaccine is available would reduce their vector-control habits significantly compared to a group that was informed that the vaccine is not very effective.

Kinetics of maternal antibodies against rubella and varicella in infants

Kinetics of maternal rubella and varicella antibodies in 213 mother-infant pairs are described in a longitudinal study in Belgium. Blood samples are taken at 7 time points (week 36 of pregnancy, birth (cord), 1, 3, 6, 9, and 12 months), and analyzed for anti-rubella IgG and anti-varicella IgG by enzyme linked immunosorbent assay (ELISA). A generalized exponential model is used to analyse maternal antibody decay in infants. Model based, the mean duration of passive immunity is 2.1 months for rubella and 2.4 months for varicella. Infants are susceptible at young age for rubella, a disease with high vaccination coverage, as well as for varicella, an endemic disease in Western Europe.

Seroepidemiology of Toxoplasma infection in a metropolitan region of Brazil

Seroprevalence data from a representative population were used to estimate the annual incidence of congenital toxoplasmosis in São Paulo Metropolitan Region (SPMR). Retrospective anti-toxoplasma IgG serological analysis was conducted to determine age-dependent seroprevalence, force of infection, average age of acquisition of infection and curve of decay of maternally derived antibodies. Seroprevalence was used to calculate the number of new infections. Toxoplasmosis in pregnant women was estimated by total number of deliveries in a given year as a proxy for the number of pregnancies per year. Toxoplasma seroprevalence was 64.9% in women of childbearing age. Average age of acquisition of toxoplasmosis was 10.74 years. The estimated annual incidence of congenital toxoplasmosis varied from 9.5 to 10.6/1000 births in the studied period. The toxoplasmosis seroprevalence model allowed a good incidence estimation of congenital disease in SPMR compared to other published data, indicating that this mathematical approach is useful in calculating the potential demand of congenital disease due to Toxoplasma gondii in a given community.

Spatio-temporal tracking and phylodynamics of an urban dengue 3 outbreak in São Paulo, Brazil

The dengue virus has a single-stranded positive-sense RNA genome of ∼10.700 nucleotides with a single open reading frame that encodes three structural (C, prM, and E) and seven nonstructural (NS1, NS2A, NS2B, NS3, NS4A, NS4B, and NS5) proteins. It possesses four antigenically distinct serotypes (DENV 1–4). Many phylogenetic studies address particularities of the different serotypes using convenience samples that are not conducive to a spatio-temporal analysis in a single urban setting. We describe the pattern of spread of distinct lineages of DENV-3 circulating in São José do Rio Preto, Brazil, during 2006. Blood samples from patients presenting dengue-like symptoms were collected for DENV testing. We performed M-N-PCR using primers based on NS5 for virus detection and identification. The fragments were purified from PCR mixtures and sequenced. The positive dengue cases were geo-coded. To type the sequenced samples, 52 reference sequences were aligned. The dataset generated was used for iterative phylogenetic reconstruction with the maximum likelihood criterion. The best demographic model, the rate of growth, rate of evolutionary change, and Time to Most Recent Common Ancestor (TMRCA) were estimated. The basic reproductive rate during the epidemics was estimated. We obtained sequences from 82 patients among 174 blood samples. We were able to geo-code 46 sequences. The alignment generated a 399-nucleotide-long dataset with 134 taxa. The phylogenetic analysis indicated that all samples were of DENV-3 and related to strains circulating on the isle of Martinique in 2000–2001. Sixty DENV-3 from São José do Rio Preto formed a monophyletic group (lineage 1), closely related to the remaining 22 isolates (lineage 2). We assumed that these lineages appeared before 2006 in different occasions. By transforming the inferred exponential growth rates into the basic reproductive rate, we obtained values for lineage 1 of R₀ = 1.53 and values for lineage 2 of R₀ = 1.13. Under the exponential model, TMRCA of lineage 1 dated 1 year and lineage 2 dated 3.4 years before the last sampling. The possibility of inferring the spatio-temporal dynamics from genetic data has been generally little explored, and it may shed light on DENV circulation. The use of both geographic and temporally structured phylogenetic data provided a detailed view on the spread of at least two dengue viral strains in a populated urban area.

Most of the molecular phylogeny studies of dengue fever, an important public health problem, use convenience samples for their analysis, and they do not evaluate the spatial and temporal features involved in the spread of the different serotypes (and genotypes) circulating in urban settings during an outbreak. Our study describes the patterns of spread of different lineages of dengue 3 virus circulating in a medium-sized city from Brazil, and we also analyzed the dynamics and microevolution of the disease during the 2006 outbreak. We used both geographic and temporally structured phylogenetic data, which provided a relatively detailed view on the spread of at least two dengue viral lineages circulating in an urban area. The pattern of dengue virus circulation might be similar to many other settings all over the world, and the information provided by our study can help a better understanding of dengue outbreaks, providing important information for public-health systems. We could identify at least two lineages, which were introduced in different occasions. They circulated and spread at different rates within the city, and this differential spread and the role of socioeconomic features in this phenomenon are discussed.

Seroprevalence of rubella antibodies in the State of São Paulo, Brazil, 8 years after the introduction of vaccine

Rubella vaccine was introduced in the official immunization calendar of the State of São Paulo, in 1992, at 15 months of age, following a mass vaccination targeting all children between 1 and 10 years of age. This mixed strategy was designed taking into account serological data and mathematical models to estimate the optimal ages for vaccination. To evaluate the efficacy of routine vaccination on rubella infection in São José do Rio Preto, State of São Paulo, 8 years after the introduction of vaccine, a seroprevalence survey was carried out in December 2000, comprising 1,536 subjects aging from 6 months to 25 years. Rubella specific IgG was detected in blood samples by enzyme-linked immunosorbent assay (ELISA). From 18 months to 5 years of age (covered by a mass vaccination campaign 6 months before the study) the seroprevalence was above 90%. From 6 to 8 years of age (vaccinated by routine schedule at 15 months), the seroprevalence was 76%. From 9 to 18 years of age (vaccinated at the mass campaign that introduced the vaccine 8 years before) the seroprevalence was about 85%. After 20 years of age, protection was acquired by previous infection, as they were not covered by any vaccine program. From 20 to 25 years of age, the seroprevalence was 70%. As the seroprevalence remains low at ages not vaccinated, it should be expected low infection rates at this age window. Despite this, the present situation deserves care, as routine vaccination is given a protection below the minimum level necessary (80%). The efficacy of the proposed strategy depends on better routine vaccination coverage. A second dose of vaccine should also be considered.

Immunogenicity of measles and rubella vaccines in Oman: a prospective clinical trial

A prospective immunogenicity trial of measles and rubella vaccines was conducted in Oman. Children received measles vaccine at age 9 months and measles-rubella vaccine at age 15 months. Serum specimens were tested for measles-specific IgG and rubella-specific IgG. Of 1025 eligible infants, 881 (86.0%) returned for all five visits and had adequate serum samples for testing. Seroconversion to measles after vaccination at 9 months was 98.1%. At 15 months, 47 (5.3%) of the 881 children were seronegative for measles; of these, 44 (93.6%) seroconverted. At 16 months, 99% of the children seronegative at age 9 months seroconverted after receiving two doses of measles vaccine. At age 15 months, 684 (77.6%) children were seronegative for rubella. Of these, 676 (98.8%) seroconverted by age 16 months. One dose of measles vaccine at age 9 months was highly immunogenic. One dose of measles-rubella vaccine at age 15 months closed the remaining measles immunogenicity gap and resulted in a high rate of rubella seroconversion.

Investigation of a rubella outbreak in Kyrgyzstan in 2001: implications for an integrated approach to measles elimination and prevention of congenital rubella syndrome

In 1999, the Ministry of Health of Kyrgyzstan adopted the goal of measles elimination. This opportunity was used to launch a rubella and congenital rubella syndrome prevention program. Between January and August 2001, a rubella outbreak occurred in Bishkek City and Chui Oblast. Rubella surveillance data were reviewed for Kyrgyzstan (1981-2000) and rubella case-patient and laboratory information from Bishkek City and Chui Oblast during the outbreak. The data suggest that rubella is endemic in Kyrgyzstan with periodic epidemics every 3-5 years. From January to August 2001, 1936 rubella case-patients were reported from Bishkek City and Chui Oblast; 242 were tested and 176 (73%) were laboratory confirmed. Most case-patients were 3-14 years old. However, the incidence rate per 100,000 among persons aged 15-35 years increased >/=40-fold from 1 in 2000 to 41 in 2001. These findings highlight the importance of introducing rubella-containing vaccine in conjunction with measles elimination activities.

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.

Burden of congenital rubella syndrome after a community-wide rubella outbreak, Rio Branco, Acre, Brazil, 2000 to 2001

BACKGROUND

During 1999 and 2000 rubella outbreaks were reported in 20 of 27 states in Brazil, many among young adults. We investigated a large rubella outbreak in Rio Branco, Acre, in northwestern Brazil, where rubella vaccination targeting children 1 to 11 years old had been introduced in April 2000. Surveillance for congenital rubella syndrome (CRS) was initiated after the outbreak.

METHODS

Suspected rubella cases were detected through active and passive surveillance. Confirmed rubella cases were patients with fever, rash and rubella-specific IgM antibodies. Suspected CRS cases were infants born with CRS-compatible defects or born to mothers with a history of rubella during pregnancy. Confirmed cases were infants with CRS-compatible defects and rubella-specific IgM antibodies.

RESULTS

From April 1 to December 31, 2000, 391 confirmed rubella cases were reported. The incidence among persons ages 12 to 19 years (3.3 per 1000 population) was increased 3.7-fold relative to children ages 1 to 4 years (95% confidence interval, 2.4 to 5.8). Of 21 infants with suspected CRS cases, 17 (91%) were tested for rubella-specific antibodies, of whom 7 were IgM-positive and 5 had confirmed CRS. The peak incidence of confirmed CRS (4.3 per 1000) was in March 2001, 7 months after the outbreak peak, with an annualized incidence of 0.6 per 1000.

CONCLUSIONS

Vaccination among school age children was insufficient to prevent a rubella outbreak among young adults that resulted in the occurrence of at least 5 cases of CRS. To prevent further cases of CRS, outbreak vaccination of young adults was conducted in November 2000 and among women ages 12 to 39 years in 2001 as part of a national campaign, with a coverage of 98% statewide.

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.

Maternal rubella-specific antibody prevalence in Ethiopian infants

In countries with a high transmission rate of rubella the optimal age for universal rubella vaccination of infants is critically dependent upon the rate of loss of maternal antibodies. Few studies have investigated the decay characteristics of such antibodies. Mother:infant pairs were recruited at the Ethio-Swedish Children's Hospital, Addis Ababa, in 1994/95. Rubella antibody levels, determined by radial haemolysis, were available for analysis from 1542 infants aged 0-12 months, with 942 repeat measures, and from 846 mothers. Decay in seropositivity was well described by a delayed exponential function. The proportion seropositive at age 6, 9, or 12 months was 6-13%, 1-4%, or 0-1%, respectively, dependent upon assay cutoff level. Only infant age and mother's antibody level were important predictors of seropositivity. Results suggest that the success of vaccination at age 9 months or above would be little affected by residual maternal antibodies.

Rubella seroprevalence in an unvaccinated population in Izmir: recommendations for rubella vaccination in Turkey

BACKGROUND

The European Advisory Group on the Expanded Program on Immunization of WHO has recommended that by 2010 or earlier congenital rubella should be well-controlled or eliminated in all countries in Europe. Debate on the introduction of rubella vaccine into national immunization schedules continues to occur, and data on rubella and congenital rubella syndrome in Turkey are insufficient.

OBJECTIVE

To determine age-specific rubella seroprevalence in the 1- to 29-year-old unvaccinated population in Izmir, Turkey.

METHODS

A total of 600 unvaccinated persons 1 to 29 years old were selected for the study with cluster sampling in Izmir, Turkey. The information on sociodemographic characteristics and disease history was gathered for each participant, and in 580 of them rubella-specific IgG antibodies were assayed quantitatively by the micro-enzyme immunoassay.

RESULTS

Of the 580 participants tested for rubella antibodies, 135 (23.3%) were seronegative. The proportions of susceptible individuals were 61.7, 29.5, 12.4, 10.3 and 8.4% in the age groups of 1 to 4, 5 to 9, 10 to 14, 15 to 19 and 20 to 29 years, respectively. Of the young women 15 to 19 years of age, 13.5% were susceptible to rubella infection.

CONCLUSIONS

Because a substantial proportion of women in their childbearing years are susceptible to rubella, immunization efforts should be directed at infants or prepubertal children.

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.

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.

A comparison of oral fluid and serum for the detection of rubella-specific antibodies in a community study in Addis Ababa, Ethiopia

OBJECTIVE

To assess the utility of oral fluid compared with serum for the determination of age-prevalence of rubella-specific antibodies in an urban African community setting.

METHOD

Paired serum and oral fluid samples were collected from 439 individuals aged 0-49 years in Addis Ababa, Ethiopia, as part of a larger seroepidemiological survey in 1994. Oral fluid was sampled using a simple sponge device that was well accepted by subjects of all ages; venous blood was collected by Vacutainer system. We measured rubella-specific antibodies in serum by the Radial Haemolysis (RH) test, supported by two confirmatory assays, and in oral fluid by IgG antibody-capture radioimmunoassay (GACRIA).

RESULTS

Sensitivity and specificity of oral fluid results compared to serum were 89% and 76%, respectively. Sensitivity declined from 96% in age group 0-19 years to 90% in age group 20-29 and 78% in age group 30-49. Specificity was 86% in 0-9 year olds contrasting with 61% in older groups (10-49 years). The positive predictive value of an oral fluid sample was high in all age groups (range 92-100%), while the negative predictive value declined from > or =80% in those aged <10 years to <10% in those aged > or =30 years. Serum confirmatory tests suggested a proportion of false serum RH negatives, increasing with age, indicating a need to standardize serum as well as oral fluid tests.

CONCLUSION

In the community setting of a developing country, oral fluid surveys could be useful to estimate age-prevalence of rubella immunity and identify rubella-susceptible children for follow-up. Further work is required to simplify assays and sample processing, improve assay sensitivity and estimate assay specificity more precisely, and compare and standardise collection methods suitable for surveillance of a variety of childhood viral infections.

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.

Population biology, evolution, and immunology of vaccination and vaccination programs

The purpose of prophylactic vaccination is to reduce morbidity and mortality in a population. Many questions related to the design of vaccines and vaccination programs require a population standpoint for their sharp formulation and laboratory and field studies to understand their immunologic background. Practical suggestions of the workshop included increased studies of age-specific immunity, better immunoepidemiologic surveillance, better design of efficacy studies, and more systematic sampling of parasite strains to study the evolutionary pressure exerted by vaccines. Theoretical immunology has much to contribute. One of the realizations of the workshop was the value of a strong interdisciplinary approach in vaccine development, utilizing relevant contributions from immunology, population biology, mathematical modeling, epidemiology, molecular biology, and virology.

Control of rubella and congenital rubella syndrome (CRS) in developing countries, Part 2: Vaccination against rubella

In 1995-96 we conducted a review of rubella immunization strategies. Worldwide, 78 countries (more than one-third) reported a national policy of using rubella vaccine. This was closely related to country economic status. Based on the United Nations country classification, rubella vaccine is used in 92% of industrialized countries, 36% of those with economies-in-transition, and 28% of developing countries. Cases of congenital rubella syndrome (CRS) may be prevented as follows: by providing direct protection to women and/or schoolgirls (a selective vaccination strategy); by vaccinating boys and girls to provide indirect protection by reducing the transmission of rubella virus (a childhood vaccination strategy); or by a combination of these approaches (a combined strategy). A combined strategy was most commonly reported (60% of countries); seven countries (9%) reported a selective strategy; and 24 countries (31%) reported only childhood immunization. Experience has shown that it is essential to include vaccination of women of childbearing age in any rubella control strategy. Childhood vaccination alone may pose a risk of an increase in CRS cases. Although many countries have introduced rubella vaccine, few report any data on the impact of vaccination. Countries using rubella vaccine need to establish surveillance for rubella and CRS and monitor coverage in each of the target groups.