Impact of coagulation in the development of thromboembolic events in patients with spinal cord injury

STUDY DESIGN

Although the knowledge described about risk factors and venous thromboembolism (VT) in the general population, the impact of these factors in the development of thromboembolic events in patients with spinal injury (SI) caused by spinal cord injury (SCI) is poorly understood.

OBJECTIVE

Evaluate the impact of risk factors in the development of thromboembolic events in patients with SCI.

SETTING

Brazil, São Paulo.

METHODS

Observational, prospective and cross-study. Eligible patients (n=100) had SI by SCI, >18 years. The degree of motor and sensory lesion was evaluated based on American Spinal Injury Association (ASIA) Impairment Scale (AIS). Blood samples were collected for coagulation exams, hemogram, laboratory and biochemical analyses. Ultrasonography analyzes were performed from deep and superficial venous systems of lower limbs. Quantitative real-time PCR experiments were performed in order to investigate mutations in the prothrombin (G20210A) and Leiden factor V (G1691A) genes.

RESULTS

The main finding of this study was the higher occurrence of deep venous thrombosis (DVT) in patients with Leiden factor V and hyperhomocysteinemia. There was no association between SI for DVT, VT and thrombophilia. Also, there was no relation between lupus anticoagulant and anti-cardiolipin.

CONCLUSION

There is an important difference in the incidence of DVT in patients with SI by acute and chronic SCI. Therefore, the conduct of the investigation for thrombophilia should be based on clinical factors, risk factors for DVT and family history of thrombosis.

Estimation of R0 from the initial phase of an outbreak of a vector-borne infection

The magnitude of the basic reproduction ratio R(0) of an epidemic can be estimated in several ways, namely, from the final size of the epidemic, from the average age at first infection, or from the initial growth phase of the outbreak. In this paper, we discuss this last method for estimating R(0) for vector-borne infections. Implicit in these models is the assumption that there is an exponential phase of the outbreaks, which implies that in all cases R(0)>1. We demonstrate that an outbreak is possible, even in cases where R(0) is less than one, provided that the vector-to-human component of R(0) is greater than one and that a certain number of infected vectors are introduced into the affected population. This theory is applied to two real epidemiological dengue situations in the southeastern part of Brazil, one where R(0) is less than one, and other one where R(0) is greater than one. In both cases, the model mirrors the real situations with reasonable accuracy.

Threshold conditions for a non-autonomous epidemic system describing the population dynamics of dengue

A non-autonomous dynamical system, in which the seasonal variation of a mosquito vector population is modeled, is proposed to investigate dengue overwintering. A time-dependent threshold, R(t), is deduced such that when its yearly average, denoted by R, is less than 1, the disease does not invade the populations and when R is greater than 1 it does. By not invading the population we mean that the number of infected individuals always decrease in subsequent seasons of transmission. Using the same threshold, all the qualitative features of the resulting epidemic can be understood. Our model suggests that trans-ovarial infection in the mosquitoes facilitates dengue overwintering. We also explain the delay between the peak in the mosquitoes population and the peak in dengue cases.

The impact of imperfect vaccines on the evolution of HIV virulence

A theoretical framework is proposed on which some hypotheses related to the impact of imperfect vaccines on the evolution of HIV virulence can be tested. For this, a linear increase of risk behaviour with vaccine efficacy is assumed. This is based on the hypothesis that people are prone to relax preventive measures by knowing that they and their partners are vaccinated and that this effect is more intense the more effective the vaccine is known to be. An additional, and perhaps more important hypothesis is related to the theoretical possibility that increased risk behaviour of some vaccinated individuals in partially protected populations could act as a selective pressure toward more virulent HIV strains. Those hypotheses were tested by a mathematical model that considers three different HIV strains competing against each other in a population partially protected by imperfect vaccines of distinct efficacies. Simulations of the model demonstrated that, under the above hypotheses, there is a shift in HIV virulence towards more aggressive strains with increase in vaccine efficacy, associated with a marked reduction in the total amount of transmission and, consequently, in the prevalence of HIV. Potential ways for further testing the theory/model and the implications of the results are discussed.

The Eyam plague revisited: did the village isolation change transmission from fleas to pulmonary?

Back in the 17th century the Derbyshire village of Eyam fell victim to the Black Death, which is thought to have arrived from London in some old clothes brought by a travelling tailor. The village population was 350 at the commencement of plague, of which only 83 survived. Led by the church leaders, the village community realized that the whole surrounding region was at risk from the epidemic, and therefore decided to seal themselves off from the other surrounding villages. In the first 275 days of the outbreak, transmission was predominantly from infected fleas to susceptible humans. From then onward, mortality sharply increased, which indicates a changing in transmission pattern. We hypothesize that the confinement facilitated the spread of the infection by increasing the contact rate through direct transmission among humans. This would be more consistent with pulmonary plague, a deadlier form of the disease. In order to test the above hypothesis we designed a mathematical model for plague dynamics, incorporating both the indirect (fleas-rats-humans) and direct (human-to-human) transmissions of the infection. Our results show remarkable agreement between data and the model, lending support to our hypotheses. The Eyam plague episode is celebrated as a remarkable act of collective self-sacrifice. However, to the best of our knowledge, there were no evidence before that the confinement actually increased the burden payed by the commoners. In the light of our results, it can be said that the hypothesis that confinement facilitated the spread of the infection by increasing the contact rate through direct transmission is plausible.

Molecular characterization of van genes found in vancomycin-resistant Enterococcus spp. isolated from the Hospital das Clínicas, FMUSP, São Paulo, Brazil

Vancomycin-resistant enterococci strains (VRE) is an important pathogen related with hospital infections in many countries, presenting limited or no therapeutic options for treating serious infections. VRE has presented some different genotypes been VanA and VanB considered to be the most important in hospital environments. In the present study the authors investigated the prevalence of van genes (A, B an C) among clinical isolates of VRE in a five month period at a large tertiary hospital in Sao Paulo, Brazil. The results showed the presence of vanA, but not vanB or vanC in all 43 strains of E. faecalis and five E. faecium studied. The results bring an important issue, due to the possibility of resistance spread of vanA genes, to be monitored and solved by the hospital infection control team and the microbiology and molecular biology laboratories at tertiary Hospitals.

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.

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.

A mixed ectoparasite--microparasite model for bat-transmitted rabies

This paper considers the transmission of rabies to domestic livestock by vampire bats. Vampire bats act as ectoparasites on cattle both by ingesting a small amount of blood every night and by prolonging bleeding by the action of anticoagulant substances in their saliva. In addition to this parasitic action bats may also transmit rabies, inflicting important losses on affected herds by the inevitable mortality due to the infection. We modeled this complex interaction and we also demonstrate that bat control measures are more effective in reducing rabies prevalence and mortality by rabies than cattle vaccination.

Modelling the natural history of HIV infection in individuals and its epidemiological implications

The variation of viraemia in the natural course of HIV infection is expected to have major influence on the probability of transmission and, consequently, on the epidemiology of HIV/AIDS. In this paper we propose a model which takes into account the time evolution of HIV viraemia (measured as HIV-RNA copies per ml of blood) in an infected individual and its impact on the threshold for the establishment of an endemic level, and mainly on the relative contribution of each of the clinical phases of the infection to the total transmission of HIV per infected individual. We consider that an infected individual passes through three phases of viraemia. The first phase, which lasts for 6-7 weeks, is characterized by very high viraemia. In the second phase, which lasts about 10 years, the viraemia is much lower, increasing again in the last phase, which lasts up to two years, and ends in full-blown AIDS. We show that the relative contribution of each phase to the total transmission of HIV is very sensitive to the model we assume for the dependence of the transmissibility of HIV on the viral load. For instance, if we assume that transmissibility is proportional to the decimal logarithm of viraemia, then the second phase predominates always. Due to the epidemiological importance of this fact, it is clear that further improvement on virological research to better understand the dependence of HIV transmissibility on the viral concentration in biological fluids is necessary.

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.

The risk of yellow fever in a dengue-infested area

Yellow fever and dengue are viral infections that in urban centres are transmitted by the same arthropod vector, a mosquito of the genus Aedes. In order to estimate the risk of an epidemic of urban yellow fever in a dengue-infested area we calculated the threshold in the basic reproduction number, R0, of dengue, above which any single sylvatic yellow fever-infected individual will trigger an urban yellow fever epidemic. Specifically, we analysed the relationship between the extrinsic incubation period and the duration of viraemia, from which it is possible to define the R0 for dengue that would also suggest an outbreak potential for yellow fever. We also calculated the critical proportion of people to vaccinate against yellow fever in order to prevent an epidemic in a dengue-endemic area. The theory proposed is illustrated by the case of São Paulo State in southern Brazil, where dengue is endemic and the risk of urban yellow fever is already imminent.

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.

Comparative study of agar diffusion test and the NCCLS macrobroth method for in vitro susceptibility testing of Candida spp

We performed a prospective double-blind study to evaluate the correlation between inhibition zones obtained by a disk-diffusion test, using Neo-sensitabs of fluconazole (Rosco Diagnostica), and the MICs generated by the NCCLS macrobroth dilution assay. Eighty clinical isolates, representing 5 of the clinically relevant species of Candida, were tested simultaneously by both methods. A clear inverse correlation was found between the results obtained by both tests (r = -0.69). In addition, there was high degree of agreement between methods in the identification of susceptible isolates. However, the resistance definition by disk-diffusion test had a positive predictive value of only 17%. Our data support the hypothesis that Rosco Fluconazole Neo-sensitabs have potential as a screening test for the identification of Candida isolates susceptible to fluconazole. Resistant isolates should be further investigated by standardized broth procedures.

Relationship between human papillomavirus (HPV) genotyping and genital neoplasia in HIV-positive patients of Santos City, São Paulo, Brazil

Among HIV-positive women, infection with multiple human papillomavirus (HPV) types is known to be more frequent and persistent, as well as a greater prevalence of high-grade genital lesions. This study aims to characterize, for the first time in Brazil, HPV presence and types among HIV-positive women of a high-risk population for genital intraepithelial neoplasia (GIN) development. A non-anonymous, voluntary, cross-sectional epidemiological survey was conducted, from June 1996 to April 1997, among 141 HIV-positive women followed at the Center of Reference in AIDS (CRAIDS). They were submitted to gynaecological examination, cytological screening and biopsies whenever necessary, for GIN and HPV DNA detection through polymerase chain reaction (PCR) technique. Positive HPV DNA were found in 80.8% patients. Two or more HPV types were detected in 45% of the samples. The most frequent HPV types detected were 16, 18 (30.5%); 61, 53 (24.4%), and non-identified types (18.7%). According to the oncogenic potential, 34.8% were considered of high-risk types. Among these HIV-positive patients, a great variety of HPV types, including high-risk types, was found in anogenital environment, as well as among young women, a great prevalence of high-grade genital lesions. Thus, it should strengthen the need for a periodical careful gynaecological examination among those women.

Fuzzy logic and measles vaccination: designing a control strategy

BACKGROUND

The State of São Paulo, the most populous in Brazil, was virtually free of measles from 1987 until the end of 1996 when the number of cases started to rise. It reached alarming numbers in the middle of 1997 and local health authorities decided to implement a mass vaccination campaign.

METHODS

Fuzzy Decision Making techniques are applied to the design of the vaccination campaign.

RESULTS

The mass vaccination strategy chosen changed the natural course of the epidemic. It had a significant impact on the epidemic in the metropolitan area of São Paulo city, but a second epidemic in the State's interior forced the public health authorities to implement a second mass vaccination campaign 2 months after the first.

CONCLUSIONS

Fuzzy Logic techniques are a powerful tool for the design of control strategies against epidemics of infectious diseases.

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.

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.

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.

Azole resistance among oral Candida species isolates from AIDS patients under ketoconazole exposure

This is a prospective study designed to investigate species distribution and azole susceptibility profile among Candida spp. isolated from the oral cavities of AIDS patients. One hundred thirty-two AIDS patients sequentially admitted at a teaching tertiary care hospital were enrolled in this study. Samples were obtained by swabbing the oral cavities of the patients. Yeast isolates were identified by classical methods and the antifungal susceptibility profile was further determined according to the NCCLS microbroth assay. Among all patients with prescriptions of systemic antifungal drugs, ketoconazole had been elected to treat 56% of patients. We found 82% of oral yeast carriage, 22% of them harboring non-albicans species. Overall rates of susceptibility dose dependent/resistance to azoles was 16% for itraconazole, 13% for ketoconazole, and 10% for fluconazole with a high agreement rate among the susceptibility profiles of all isolates tested against the triazoles.

[Comparative study of American tegumentary leishmaniasis between childhood and teenagers from the endemic areas Buriticupu, Maranhao and Corte de Pedra, Bahia, Brazil]

A comparative study on children aged 0-15 years, with American tegumentary leishmaniasis (ATL), in the endemic regions of Buriticupu (MA) and Corte de Pedra (BA), whereby 214 cases were detected between 1982 and 1993, 78 (36.4%) of them originated from Corte de Pedra and 136 (63.6%) from Buriticupu. In Corte de Pedra, most cases were observed in patients aged between 0-5 years. Twenty nine (37.2%) cases; 62% of those were male. In the Buriticupu region, 88 (64.7%) cases occurred in patients of 11-15 years of age, where in 73.8% consisted of male. In both researched regions, brunetts were predominant, with a ratio of 65.4% in Corte de Pedra and 75% in Buriticupu. Twenty six (33.3%) children in the village of Corte de Pedra were farmers, predominantly male (57.7%), generating statistical significance (chi 2 = 11.21). Twenty one (80.8%) farmers were aged 11-15 years. Thirty seven and a half per cent of the children from Buriticupu were students, however, 41 (30.2%) were farmers, representing 39 (44.3%) cases; all of them male. Both in Buriticupu and Corte de Pedra, the unique wound was predominant, corresponding to 57.7% and 53.7%, respectively. The wounding time stood out from one to three months, with 45 (69.2%) cases in Corte de Pedra and 73 (61%) in Buriticupu (chi 2 = 11.82). As to the wound locations, it has been observed that they were most constantly present on the lower limbs, with 77.2% in Corte de Pedra and 58.9% in Buriticupu (chi 2 = 27.9). The cutaneous case mostly found in Corte de Pedra was the ulcerous one (91%). IDRM was positive in 61 (78.2%) children originated from Corte de Pedra, wherein no statistical difference was detected between age ratio and positivity of the test (chi 2 = 0.0669).

[The epidemiological determinant aspects in the maintenance of visceral leishmaniasis in the state of Maranhão, Brazil]

The authors analysed the visceral leishmaniasis (VL) aspects in the state of Maranhão, Brazil, from 1982 to 1993. The disease happens to occur predominantly in São Luís Island (MA) and during the epidemic period, town of São Luís was pointed out as the main endemic area. The greatest frequency of cases occurred in 1993, despite the use of insecticide and dogs control. There was predominance of age between 0- to 4-year-old population with 58.04% of cases. Neither the human disease nor the rainfall index had significant seasonal variation. However they were correlated moderately, with high number of cases after the period of great precipitation of rain. After this study, the data obtained will allow a better control of the disease, despite some factors such as: the urbanization, localization and dynamic of transmission in endemic areas in the Maranhão state.

HIV and infections of similar transmission patterns in a drug injectors community of Santos, Brazil

To study the prevalence of HIV and infections with related transmission patterns, we interviewed and obtained blood samples from 220 injecting drug users (IDUs), sampled by snowballing, from the city of Santos in the state of São Paulo, Brazil, where the estimated number of IDUs (10,000) comprises approximately 2% of the entire population. Seroprevalence of HIV, hepatitis B and C, syphilis, and HTLV (1 and 2) was assessed and compared with that in 197 blood donors from the same city, matched for age and gender. Risk behavior related to HIV was assessed by a standard questionnaire applied to the IDU sample. Univariate and multivariate analyses of the risk factors were performed. Seroprevalences found were 62% for HIV, 75% for HCV, 75% for HBV, 34% for syphilis, and 25% for HTLV (1 and 2) among IDUs, which compare with 0.0%, 2%, 23%, 12%, and 1% for blood donors, respectively. The risk for parenterally transmitted infections in this IDU community was higher than that for sexually transmitted infections (odds ratio for syphilis, 3.57; hepatitis B, 10.0; and hepatitis C, 100). The results of the mutivariate risk analysis showed that daily rate of ID use >5 times/day (OR = 6.73), not changing behavior to avoid AIDS (OR= 3.28), ID use >15 days/month (OR = 2.72), and ID use in the last 2 months (OR = 2.23) were the risk behaviors significantly associated with HIV infection.

Diabetes mellitus associated with pentamidine isethionate in diffuse cutaneous leishmaniasis

The authors report a case of a male patient from Bacabal, MA with diffuse cutaneous leishmaniasis (DCL), for at least nine years, with 168 lesions on his body. These were tumour-like nodules with some ulceration. He used pentavalent antimonial (glucantime) and an association of gamma interferon plus glucantime with improvement of the lesions but relapsed later. Recently, pentamidine isethionate (pentacarinat) was given a dosage of 4mg/kg/weight/day on alternate days for 20 applications. After 3 months a similar course of 10 application was given 2 times. Later he developed diabetic signs with weight loss of 10kg, polydypsia, polyuria and xerostomia. The lower limbs lesions showed signs of activity. Blood glucose levels normalised and remain like this at moment. Attention is drawn to the fact that pentamidine isethionate should be used as a therapy option with care, obeying rigorous laboratory controls including a glucose tolerance test.

Assessing the efficacy of a mixed vaccination strategy against rubella in São Paulo, Brazil

BACKGROUND

In 1992 a major vaccination strategy against measles-mumps-rubella was introduced in the State of Saão Paulo, Brazil. This strategy was based on mathematical models and comprised a pulse vaccination covering all children aged 1-10 years, followed by the inclusion of this vaccine in the routine calendar at 15 months of age. The present work reports the evaluation of the efficacy of this mixed vaccination strategy.

METHODS

A rubella seroprevalence survey was carried out immediately and one year after the campaign, comprising 4953 children aged 1-15 years.

RESULTS

We show that average rubella seroprevalence increased from 0.40 to 0.97 and that the reported number of congenital rubella syndrome (CRS) cases dropped dramatically.

CONCLUSIONS

The mixed vaccination strategy adopted against rubella has proved to be very effective in reducing the number of CRS cases in São Paulo.

Leishmaniose visceral no estado do Maranhão, Brasil: a evolução de uma epidemia

Os autores fazem um breve relato da evolução histórica da leishmaniose visceral no Estado do Maranhão, Brasil, avaliando as possíveis causas da expansão da referida doença no Estado, assim como as medidas de controle adotadas pelo Ministério da Saúde objetivando a diminuição da incidência da mesma.

The basic reproduction ratio of HIV among intravenous drug users

A new approach for the estimation of the Basic Reproduction Ratio R0 for HIV among intravenous drug users (IVDU) is proposed. This approach is based in an adaptation of the models proposed by Ross and Macdonald for vector-borne infections. A straightforward adaptation of Macdonald's model is presented first: biological vectors are replaced by needles and syringes and we consider a homogeneous population of IVDUs; next we present a modified model where several heterogeneities are considered. Some of those heterogeneities are due to intrinsic differences between needles and syringes and biological vectors; others, such as those related to movements of individuals between communities, should apply to both biological vectors and injection apparatuses. An example of the calculations of R0 for a real IVDUs community is presented.

A model-based design of a vaccination strategy against rubella in a non-immunized community of São Paulo State, Brazil

A mixed vaccination strategy against rubella is proposed. We describe how the vaccination strategy was designed with the help of mathematical techniques. The strategy was designed for application in a non-immunized community of the State of São Paulo, Brazil, and was implemented by local health authorities in 1992. This strategy comprises a pulse vaccination campaign, covering the age interval between 1 and 10 years, followed by the introduction of the vaccine in the immunization calendar at 15 months of age. The expected impact of the proposed strategy is discussed.

New arenavirus isolated in Brazil

A new arenavirus, called Sabiá, was isolated in Brazil from a fatal case of haemorrhagic fever initially thought to be yellow fever. Antigenic and molecular characterisation indicated that Sabiá virus is a new member of the Tacaribe complex. A laboratory technician working with the agent was also infected and developed a prolonged, non-fatal influenza-like illness. Sabiá virus is yet another arenavirus causing human disease in South America.

Malaria prevalence amongst Brazilian Indians assessed by a new mathematical model

An alternative way to estimate the endemic level of malaria amongst Brazilian indians is proposed. This is achieved by estimating the age-related 'force of infection' of malaria (the effective inoculation rate), applying a mathematical model, described elsewhere, to serological data. In addition we present a way to estimate the Basic Reproductive Rate of malaria in the same area. The results have shown a good degree of accuracy in describing the endemic pattern of malaria in the area, and also indicate some relevant aspects of its age distribution related to the design of control strategies.

Malaria transmission rates estimated from serological data

A mathematical model was used to estimate malaria transmission rates based on serological data. The model is minimally stochastic and assumes an age-dependent force of infection for malaria. The transmission rates estimated were applied to a simple compartmental model in order to mimic the malaria transmission. The model has shown a good retrieving capacity for serological and parasite prevalence data.

Epidemiologic typing of multiply drug-resistant Pseudomonas aeruginosa isolated from an outbreak in an intensive care unit

From June to August 1991, there was an outbreak of Pseudomonas aeruginosa infections in an intensive care unit in a general hospital in Sao Paulo, Brazil. We obtained 14 isolates from 14 patients, 11 from tracheal aspirate, and 3 from surgical wound exudates. These strains were typed by serotyping, pyocin typing, and pulsed-field electrophoresis (CHEF) of chromosomal DNA (chrDNA), and the different typing methods were analyzed. These three methods demonstrated seven identical strains. We also performed an extensive antibiogram (33 drugs) in all 14 isolates. The incidence of resistance to aminoglycosides, extended-spectrum beta-lactams, and quinolones was very high among the seven identical isolates; however, the antibiogram profile differed significantly among the isolates. Our results suggest that a unique strain caused several cross-transmitted infections during this period of time, and the emergence of antimicrobial resistance has been occurring before and after the establishment of the epidemic strain by selective drug use. The chrDNA fingerprinting proved to be versatile and precise for epidemiologic investigations of P. aeruginosa infections.

Effects of vaccination programmes on transmission rates of infections and related threshold conditions for control

This study addresses the problem of the existence of conditions for persistence or eradication of age-dependent directly transmitted infections. The usual system of differential equations describing the dynamics of the disease is transformed into integral equations. The authors show how to solve these equations and, by applying the contraction mapping theorem, give conditions for the persistence or eradication of the infection. A practical illustration of the application of the methods proposed is sketched, using data for rubella collected from a small Brazilian community.