Biomedical subjects
Publications and source records attributed to M Schechter.
The magnetization of an ensemble of isolated lead grains of sizes ranging from 4 to 1000 nm is measured. A sharp disappearance of the Meissner effect with a lowering of the grain size is observed for the smaller grains. This is a direct observation by magnetization measurement of the occurrence of a critical particle size for superconductivity, which is consistent with Anderson's criterion.
We calculate the orbital linear magnetic response of disordered metallic rings to an Aharonov-Bohm flux using the BCS model for attractive electron-electron interaction. The contribution of all levels including those up to a high energy cutoff results in a much larger value than previously obtained using the local interaction model. The possible relevance of our results to the resolution of the discrepancy between the experimental and theoretical values for the ensemble-averaged persistent currents in these systems is discussed.
OBJECTIVE: To study the impact of chemoprophylaxis for tuberculosis on the survival of HIV-infected patients with a positive tuberculin skin test. DESIGN: Prospective observational cohort study. SETTING: Outpatient clinic of a university hospital, in Rio de Janeiro, Brazil. PATIENTS: Two-hundred and ninety-seven patients with a positive tuberculin skin test (reaction > or = 5mm) who were admitted to the cohort between January 1991 and December 1994. Follow-up ended on September 30, 1998. INTERVENTION: The use of chemoprophylaxis for tuberculosis. MAIN OUTCOME MEASURES: Death was the primary outcome variable. The occurrence of tuberculosis was studied as a secondary outcome. Cox regression models were used in these analyses. RESULTS: The median follow-up time was 43.6 months. Chemoprophylaxis was used by 128 (43%) of the patients. The use of chemoprophylaxis was associated with a reduction in risk for tuberculosis (hazard ratio, 0.38; 95% confidence interval, 0.14-1.04; P = 0.05). In a regression model adjusted for baseline CD4 cell count, chemoprophylaxis was associated with longer survival (hazard ratio, 0.24; 95% confidence interval, 0.09-0.65; P = 0.002). CONCLUSIONS: Anti-tuberculosis chemoprophylaxis was associated with a substantially prolonged survival among purified protein derivative-positive HIV-infected patients in Brazil. These data have important implications for the clinical care of patients with HIV infection in areas of the world with a high prevalence of Mycobacterium tuberculosis infection.
Evaluation of HIV vaccines requires high-risk individuals willing to participate in a vaccine trial. We investigated the willingness to participate in HIV vaccine trials of initially HIV-seronegative homosexual men enrolled in an HIV seroincidence cohort study. Of 815 initially HIV-seronegative participants, 569 (69.8%) reported willingness to participate in an HIV vaccine trial. Altruism was the primary reason given for wanting to participate. Fear of HIV infection from the study's immunizations and a vaccine-induced positive HIV test result were the main reasons for not wanting to participate. Of the 34 study subjects who eventually had HIV seroconversion, 29 (85%) had indicated a willingness to participate. In a univariate analysis, factors associated with willingness to participate included HIV seroconversion during follow-up (odds ratio [OR]. 2.6; p =.04), low educational level (OR, 1.6; p =.005), low family income (p =.02), and exchanging sex for housing, food, or clothing (OR 6.1; p =.005). Students were less likely to be willing to participate in a trial (OR, 0.7; p = .03), as well as those who reported sex at the first encounter (OR, 0.7; p = .05). In a multivariate analysis, low education level, infection with Condyloma, and exchanging sex for housing, food, or clothing were positively associated with willingness to participate, whereas being a student and reporting sex at first encounter were negatively associated. In general, factors indicative of high-risk of HIV infection were associated with a higher willingness. These data demonstrate that this high-risk homosexual male cohort has a high willingness to participate in HIV vaccine trials.
BACKGROUND: Symptoms associated with HIV infection are common among HIV seroconverters, but the acute retroviral syndrome (ARS) is a diagnostic challenge because of the absence of a sensitive and specific case definition. We conducted an analysis of HIV seroconverters in Projeto Praça Onze, a HIVNET HIV seroincidence study among homosexual men in Rio de Janeiro. METHODS: Information from study subjects enrolled in Projeto Praça Onze who were documented HIV seroconverters were compared with nonseroconverters. At each semiannual study visit, participants were asked about HIV seroconversion symptoms and sexually transmitted diseases (STDs) during the preceding 6 months. All information was collected before the laboratory evaluation. A classification tree analysis was used to identify an ARS case definition, first using clinical information and then after including risk factor data for seroconversion in our cohort. RESULTS: As of July 1998, 674 volunteers were enrolled and 34 of these seroconverted; information was available for 33 of these. Among the seroconverters, 11 (34%) denied any symptoms, and 22 (66%) reported one or more symptoms, the most common of which were fever (25% of seroconverters versus 7% of nonseroconverters; p <.01), night sweats (9% versus 2%, respectively; p =.05), incapacitating disease (ID) for >/=3 days (27% versus 7%, respectively; p <.001), and weight loss of >/=2 kg (21% versus 9%, respectively; p =.05). STDs were more common in seroconverters (gonorrhea: 9% versus 1%, respectively; p <.01 and condyloma: 9% versus 3%, respectively; p =. 08). The first case definition was ID for >3 days, fever, pharyngitis, and myalgia (seroconverters, 3 of 32, versus nonseroconverters, 2 of 640). The second case definition was was ID for >3 days, anti-core hepatitis b-positive, and age <21 years (seroconverters: 6 of 32 versus nonseroconverters 4 of 640). The sensitivity and specificity for the first and second case definitions were: 9.4%, 99.4%, and 18.8%, 99.8%, respectively. CONCLUSIONS: Among HIV seroconverters, symptoms consistent with ARS were common. We were unable to identify a sensitive case definition that could be used as a screening tool. Although the clinical case definition was not validated, the specificity of our case definitions was high, suggesting that subjects within this HIV risk group who fulfill the case definition should be tested for HIV.
BACKGROUND: The effect of antiretroviral therapy on seminal HIV shedding in the community remains unknown. OBJECTIVE: To evaluate the effect of antiretroviral therapy on HIV shedding in semen. DESIGN: Prospective cohort study. SETTING: University hospital in Rio de Janeiro, Brazil. PATIENTS: 93 HIV-infected men. INTERVENTION: Antiretroviral therapy as prescribed by each patient's physician. MEASUREMENT: HIV RNA in semen and blood plasma before and after introduction of therapy. RESULTS: At baseline, HIV RNA was detected in 69 semen samples (74%) and 89 blood samples (96%). Six months after introduction of therapy, HIV RNA was detected in 29 semen samples (33%) and 33 blood samples (38%). The mean reduction in levels of HIV RNA in semen at 6 months was 1.65 log10 units. CONCLUSIONS: Antiretroviral therapy reduces shedding of HIV in semen, which probably in tum reduces HIV transmissibility. However, a substantial proportion of patients may still be infectious and may have drug-resistant strains of the virus.
HIV-1 serotype B-Br (GWGR) is rare in the United States but predominates in Brazil. Differences in prognosis for patients infected with serotype B-Br or serotype B (GPGR) have not been addressed previously. In this prospective cohort study, we compared the rate of disease progression between patients infected with the HIV-1 V3 serotype B or B-Br in Brazil. Progression to AIDS or death was studied by the Kaplan-Meier and Cox proportional hazard methods. Among 445 HIV-infected patients who were tested with a specific enzyme immune assay, 204 (46%) had serotype B-Br infection and 127 (28%) had serotype B infection. Both groups were similar with regard to baseline CD4+ cell count, serum HIV RNA viral load, initial clinical stage, and the proportions who were treated with antiretroviral drugs. Patients with serotype B infection were significantly younger (p = 0.005) and tended to report homosexual behavior more frequently (p = 0.08). Mean follow-up was 30 +/- 13.5 months. During the study period, 41 (32%) patients infected with serotype B and 44 (22%) infected with serotype B-Br developed AIDS (p = 0.03). In a regression model adjusted for age and risk factor for HIV infection, progression to AIDS was faster in patients infected with serotype B (hazard ratio [HR] 1.59; 95% CI, 1.03-2.43; p = 0.03). A similar trend was observed in a model that considered AIDS or death as the outcome (HR, 1.43; 95% CI, 0.95-2.0; p = 0.09). These results suggest that patients infected with closely related HIV-1 serotypes may differ in the rate of progression to AIDS and indicate that serotype should be taken into account in HIV vaccine studies in Brazil.
The study of interventions to prevent HIV transmission requires access to populations with a high rate of HIV transmission. We estimated HIV incidence among heterosexual males and females who were seen at an HIV testing site in Rio de Janeiro, Brazil. Stored sera from individuals who visited the site between March and December 1998 were analyzed using the sensitive/less sensitive (S/LS) assay and a chart abstraction was performed. During the study period, 6353 serum samples were tested. Of those tested, 1203 were found to be HIV-seropositive or indeterminate, of which 1050 (87%) remained available for further testing. In addition, 84 serum samples, representing 63 adults, were found to produce results suggesting early HIV infection. Of these, 14 were heterosexual and female (median age, 38 years), and 19 were heterosexual and male (median age, 25 years). The estimated HIV seroincidence was 1.9 (95% confidence limits (CL), 0.9%-3.9%) and 2.8 (95% CL, 1.4%-5.3%) per 100 person-years among heterosexual women and men, respectively. A survey on willingness to participate in future placebo-controlled HIV vaccine trials in this population indicated that 54.5% and 53.9% of heterosexual women and men, respectively, indicated that they would definitely be willing to participate. We have identified a heterosexual population in Rio de Janeiro with a high rate of HIV transmission willing to participate in placebo-controlled vaccine trials. This study demonstrates the usefulness of the newly described S/LS assay, which allows one to estimate HIV incidence from single serum specimens.
CONTEXT: Because of problems with adherence, toxicity, and increasing resistance associated with 6- to 12-month isoniazid regimens, an alternative short-course tuberculosis preventive regimen is needed. OBJECTIVE: To compare a 2-month regimen of daily rifampin and pyrazinamide with a 12-month regimen of daily isoniazid in preventing tuberculosis in persons with human immunodeficiency virus (HIV) infection. DESIGN: Randomized, open-label controlled trial conducted from September 1991 to May 1996, with follow-up through October 1997. SETTING: Outpatient clinics in the United States, Mexico, Haiti, and Brazil. PARTICIPANTS: A total of 1583 HIV-positive persons aged 13 years or older with a positive tuberculin skin test result. INTERVENTIONS: Patients were randomized to isoniazid, 300 mg/d, with pyridoxine hydrochloride for 12 months (n = 792) or rifampin, 600 mg/d, and pyrazinamide, 20 mg/kg per day, for 2 months (n = 791). MAIN OUTCOME MEASURES: The primary end point was culture-confirmed tuberculosis; secondary end points were proven or probable tuberculosis, adverse events, and death, compared by treatment group. RESULTS: Of patients assigned to rifampin and pyrazinamide, 80% completed the regimen compared with 69% assigned to isoniazid (P<.001). After a mean follow-up of 37 months, 19 patients (2.4%) assigned to rifampin and pyrazinamide and 26 (3.3%) assigned to isoniazid developed confirmed tuberculosis at rates of 0.8 and 1.1 per 100 person-years, respectively (risk ratio, 0.72 [95% confidence interval, 0.40-1.31]; P = .28). In multivariate analysis, there were no significant differences in rates for confirmed or probable tuberculosis (P = .83), HIV progression and/or death (P = .09), or overall adverse events (P = .27), although drug discontinuation was slightly higher in the rifampin and pyrazinamide group (P = .01). Neither regimen appeared to lead to the development of drug-resistant tuberculosis. CONCLUSIONS: Our data suggest that for preventing tuberculosis in HIV-infected patients, a daily 2-month regimen of rifampin and pyrazinamide is similar in safety and efficacy to a daily 12-month regimen of isoniazid. This shorter regimen offers practical advantages to both patients and tuberculosis control programs.
OBJECTIVE: To update recommendations for antiretroviral therapy for adult human immunodeficiency virus type 1 (HIV-1) infection, based on new information and drugs that are available. PARTICIPANTS: A 17-member international physician panel with antiretroviral research and HIV patient care experience initially convened by the International AIDS Society-USA in December 1995. EVIDENCE: Available clinical and basic science data including phase 3 controlled trials; data on clinical, virologic, and immunologic end points; research conference reports; HIV pathogenesis data; and panel expert opinion. Recommendations were limited to therapies available (US Food and Drug Administration approved) in 1999. CONSENSUS PROCESS: The panel assesses new research reports and interim results and regularly meets to consider how the new data affect therapy recommendations. Recommendations are updated via full-panel consensus. Guidelines are presented as recommendations if the supporting evidence warrants routine use in the particular situation and as considerations if data are preliminary or incomplete but suggestive. CONCLUSIONS: The availability of new antiretroviral drugs has expanded treatment choices. The importance of adherence, emerging long-term complications of therapy, recognition and management of antiretroviral failure, and new monitoring tools are addressed. Optimal care requires individualized management and ongoing attention to relevant scientific and clinical information in the field.
An HIV seroincidence study was conducted to identify a high-risk population for HIV prevention trials. Inclusion criteria were male gender, homosexual behavior, age between 18 and 50 years, and negative HIV serostatus; 862 study subjects were screened and 753 were enrolled and observed during follow-up for a mean of 1.5 years. In this population, 34 people had HIV seroconversions for an overall annual seroincidence of 3.1% (95% confidence interval [CI], 2.1%-4.1%). Among study subjects <20 years old, annual incidence was 8.4% (95% CI, 1.7%-15%). Independent risk factors for seroconversion were age <25 years (p = .01), hepatitis B core antibody seropositivity (p > .01), sex at first encounter in the preceding 6 months (p = .11), and a history of gonorrhea or condyloma in the 6 months before seroconversion (p = .04 and p = .08, respectively). At enrollment, 85% of the eventual seroconverters said they would participate in a vaccine trial; all agreed to participate when told there would be a placebo arm. Follow-up rates were 97%, 91%, and 88% at 6, 12, and 18 months, respectively. The HIV-1 subtype was B for each of the first 17 seroconverters. These data demonstrate the suitability of this cohort for HIV prevention trials, based on high HIV incidence and retention rates, and a willingness to participate in such trials.
OBJECTIVE: To compare three possible therapeutic strategies for the treatment of patients with an intermediate risk of HIV disease progression. DESIGN: Mathematical modeling based on assumptions derived from published data. METHODS: A parametric survival model was fitted to empirical data to describe the survival trajectory of untreated individuals. It was assumed that successful treatment decreases the risk of disease progression curing the first year after its introduction by a constant that is dependent on the magnitude of the initial drop in HIV viral load. Thereafter, individual members of the treatment cohort follow different pathways, depending on the duration of the initial response or, in case of virologic failure, the response to a new drug regimen. RESULTS: Sub-groups of patients starting therapy with two nucleoside reverse transcriptase inhibitors (NRTI) or two NRTI and a protease inhibitor had the highest instantaneous risk of disease progression at the end of the 5-year follow-up period. Patients who started therapy with two NRTI and a non-NRTI had the lowest likelihood of progression to AIDS or death at 5 years of follow-up. This is because, in the case of the subgroup whose initial treatment included a protease inhibitor, failure rates due to non-adherence to therapy are high and response to salvage therapy is limited by past protease inhibitor experience. CONCLUSIONS: Despite the superior virologic potency of the protease inhibitor-containing regimens, in this analysis other strategies performed equally well or even better. In the absence of solid empirical data and until the advent of antiretroviral regimens that are shown to be safe, simple to take, and maximally suppress viral load, caution may be required in selecting the long-term therapy for patients with less advanced HIV disease.
The genetic variation of the human immunodeficiency virus type 1 (HIV-1) protease gene (prt) permits the classification of HIV-1 strains into five distinct protease subtypes, which follow the gag subtyping patterns. The susceptibilities of non-B-subtype strains to protease inhibitors (PIs) and other antiretroviral drugs remain largely unknown. Subtype F is the main non-B strain contributing to the Brazilian epidemic, accounting for 15 to 20% of these infections. In this work, we report the findings on 81 isolates from PI-naive Brazilian patients collected between 1993 and 1997. In addition, the relevant PI resistance mutations and their phenotypes were determined in vitro for 15 of these patients (B = 9 and F = 6). Among these, the subtype F samples evidenced high sensitivities in vitro to ritonavir and indinavir, with MICs at which 50 and 90% of the isolates are inhibited similar to those of both the Brazilian and the U.S. subtype B isolates. Analysis of the 81 Brazilian prt sequences demonstrated that the subtype F consensus sequence differs from the U.S. and Brazilian subtype B consensus in eight positions (I15V, E35D, M36I, R41K, R57K, Q61N, L63P, and L89M). The frequency of critical PI resistance substitutions (amino acid changes D30N, V82A/F/T, I84V, N88D, and L90M) among Brazilian isolates is very low (mean, 2.5%), and the associated secondary substitutions (amino acid positions 10L, 20K, 36M, 46M, 48G, 54I, 63P, 71A, and 77A) are infrequent. These observations document the relative rarity of resistance to PIs in the treatment of patients infected with HIV-1 subtype F in South America.
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The relation between gender and survival after a diagnosis of AIDS was studied in a cohort of patients with HIV infection in Rio de Janeiro, Brazil. During the study period, 124 of 617 patients (20%) developed AIDS. Of this group, 91 patients were men and 33 were women. There were no gender related differences regarding the access to antiretroviral therapy or to prophylaxis for Pneumocystis carinii pneumonia. Survival was shorter among women (hazard ratio [HR] = 4.43; p < .001) after adjustment for age and AIDS-defining condition. Adjusting for CD4+ and CD8+ counts reduced the difference between genders (HR = 3.33; p = .017). These results suggest that survival after an AIDS diagnosis may be shorter among women than men in Brazil. Further studies are needed to determine the factors that may be negatively influencing the prognosis of women with AIDS in Brazil.
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The prevalence of human herpesvirus 8 (HHV-8; Kaposi's sarcoma [KS] herpesvirus) infection was determined by IFA in 297 persons living in Brazil and Colorado. The prevalence of antibody to HHV-8 in human immunodeficiency virus (HIV) type 1-seropositive gay men with and without KS was similar in Brazil and Colorado. In Brazil, the prevalence of HHV-8 antibody was significantly greater in HIV-1-seronegative gay men than in HIV-1-seronegative male intravenous drug users. HHV-8-seropositive Brazilian gay men who had a clinical diagnosis of KS or who were infected with HIV-1 had significantly higher titers of HHV-8 antibody than did HHV-8-seropositive, HIV-1-seronegative Brazilian gay men. These findings provide further support for the association between HHV-8 infection and KS and suggest that, as in the United States, HHV-8 infection is transmitted sexually in Brazil.