Biomedical subjects
Publications and source records attributed to C Serrat.
We investigate propagation of light pulses in photonic crystals in the vicinity of the zero diffraction point. We show that Gaussian pulses due to nonzero width of their temporal spectrum spread weakly in space and time during the propagation. We also find the family of nonspreading pulses, propagating invariantly in the vicinity of the zero diffraction point of photonic crystals.
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BACKGROUND: We analyse whether the tuberculin skin test is a good survival marker in a cohort of pulmonary tuberculosis patients with HIV infection (PTB/HIV). In all, 494 PTB/HIV patients were enrolled in Barcelona (Spain) between January 1992 and December 1994 in the Tuberculosis Program of Barcelona. The main data problem was the large proportion of missing values in the covariates percentage of T CD4+ lymphocytes and the tuberculin test results: only 157 patients (31.8%) had both covariates recorded. METHODS: Patients were dichotomized into two groups according to their level of immunosuppression (< or = 14 and >14% T CD4+ cells). First, we carried out the semiparametric and parametric complete case analysis. After this, we analysed the data assuming a missing at random non-response pattern. We developed a bootstrap approach where missing data in the markers are imputed via a two-way linear model. Using Weibull regression estimation, we used a multiple imputation scheme to estimate the parameters of interest. RESULTS: We found significative differences for the most immunosuppressed group when comparing positive tuberculin patients with those who were tuberculin negative. From a complete case approach and through a multivariate Cox analysis, we obtained a significant relative hazard of 0.3657 (95% CI: 0.13-1.02; P = 0.054). When a Weibull model was fitted, we estimated a constant relative percentile value of pR = 4.1329 (95% CI: 0.97-17.59). From a missing data approach, we obtain a higher constant relative percentile 5.48 (P = 0.079). CONCLUSIONS: The imputation method allows us to assess the protective character of positivity for the tuberculin test for the lowest CD4+ level. These findings strongly suggest the value of the tuberculin skin test as a qualitative measure of the immunological response and its interest for developing countries where specific laboratory tests are not affordable.
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BACKGROUND: Cytomegalovirus (CMV) infection is common among HIV seropositive patients, being difficult to diagnose because it requires cell cultures not available in all hospitals. DNA amplification is being applied for diagnosis of infectious diseases with an increase in sensitivity and specificity with respect to previous laboratory methods. METHODS: Polymerase chain reaction (PCR) has been used in comparison with culture isolation, early antigen detection to diagnose CMV infection in 22 HIV infected patients, that suffered from symptoms compatible with CMV infection at the present time, and in other 5 patients suffering from Kaposi sarcoma. PCR was done with primer for CMV IE genomic region. The amplified sequences were detected after hybridization with a gamma-P-32 labelled probe, followed by electrophoresis in a 5% polyacrylamide gel and autoradiography. RESULTS: The PCR allows to detect CMV genome in cases in which other tests are negatives, in blood as well as in urine, included those patients suffering only from febrile symptoms or with other associated pathogen. CONCLUSIONS: PCR is a sensitive method to detect CMV, although it does not establish the responsibility of CMV in HIV infected patients.
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