Silvia Blanco

Comparison of Two Commercially Available Gamma Interferon Blood Tests for Immunodiagnosis of Tuberculosis

ABSTRACT We evaluated the T-SPOT.TB and Quantiferon-TB Gold In tube (QFN-G-IT) tests for diagnosing Mycobacterium tuberculosis infection. T-SPOT.TB was more sensitive than QFN-G-IT in diagnosing both active and latent infection. Both gamma interferon tests were unaffected by prior Mycobacterium bovis BCG vaccination. Among children who were not BCG vaccinated but had a positive tuberculin skin test, QFN-G-IT was negative in 53.3% of cases, and T-SPOT.TB was negative in 50% of cases.

Usefulness of Urinary Antigen Detection by an Immunochromatographic Test for Diagnosis of Pneumococcal Pneumonia in Children

ABSTRACT We evaluated an immunochromatographic assay detecting pneumococcal antigen in urine samples from children diagnosed with pneumococcal pneumonia. The sensitivity and specificity of the immunochromatographic test with nonconcentrated urine (NCU) were 86.7 and 62.9%, respectively; with concentrated urine (CU), they were 100 and 11.7%, respectively. Pneumococcal antigen was also detected in 42.5% of NCU and 87.1% of CU samples from nasopharyngeal carriers. This is a nonspecific test for the diagnosis of pneumococcal pneumonia in children, particularly the very young.

T-cell responses to the Mycobacterium tuberculosis-specific antigens in active tuberculosis patients at the beginning, during, and after antituberculosis treatment.

The objectives of the study were to assess the performance of the QuantiFERON-TB Gold In-Tube (QFN-G-IT) and the T-SPOT.TB tests in the immunodiagnosis of active tuberculosis (TB) in adult patients, and to study the T-cell interferon gamma (IFN-gamma) responses during treatment and in patients who have recovered after curative treatment and self-healed TB patients. When only analyzing patients included at the beginning of treatment, the sensitivity was 83.3% for T-SPOT.TB and 69.4% for QFN-G-IT. In contrast, when evaluating patients during treatment, the sensitivity of the T-SPOT.TB and QFN-G-IT decreased to 69.8% and 48.8%, respectively. The response to the specific antigens increased after finishing the treatment compared with the values during the treatment. The T-SPOT.TB was more sensitive in diagnosing active TB than the QFN-G-IT. The IFN-gamma tests could be used as a complementary method in the diagnosis of active TB.

Use of Quantitative and Semiquantitative Procalcitonin Measurements to Identify Children with Sepsis and Meningitis

During infancy and childhood, clinical signs of infection and conventional laboratory markers are not specific in the early phase of disease [1]. The availability of a parameter that more rapidly identifies children suspected to have bacterial sepsis before microbiological results are available would minimize unnecessary treatments and hospitalization. Since its original description, the importance of procalcitonin (PCT) as an indicator of systemic bacterial infection has been demonstrated in many reports [2, 3, 4, 5]. The aim of our study was to evaluate the reliability of PCT measurement by quantitative luminometric immunoassay (LIA) in distinguishing between systemic bacterial infection (sepsis and/or meningitis), localized bacterial infection and aseptic meningitis in children, compared to leukocyte count and C-reactive protein (CRP) levels. We also evaluated the correlation of a rapid immunochromatographic test (ICT) for semiquantitative PCT measurement in comparison with quantitative test results. The study was carried out on selected children aged between 1 month and 12 years who were admitted to the pediatric emergency department of our hospital after presenting with fever of less than 12-h duration. At the time of admission, blood samples were collected for leukocyte count, CRP and PCT measurement. Clinical specimens were collected for microbiological testing in order to correctly establish the etiology. Serial serum samples for PCT and CRP assays were collected daily when possible. Patients were grouped retrospectively according to the type of illness. Group 1 included 25 children diagnosed with bacterial sepsis and/or meningitis by culture of blood and/or cerebrospinal fluid (CSF) samples: Neisseria meningitidis was isolated in 18 cases, Streptococcus pneumoniae in 6 and Haemophilus influenzae in 1. Bacteria were isolated from CSF culture only in 8 patients, blood culture only in 10 and both culture types in 7. Group 2 included 18 children diagnosed with aseptic meningitis by compatible clinical presentation, negative Gram stain, cultures and antigen tests for bacterial infection using blood and CSF samples, compatible CSF analysis (pleocytosis with a predominance of mononuclear cells) and successful recovery without antibiotic therapy. Viral cultures were not performed. Group 3 included 22 children presenting with localized bacterial infection such as purulent conjunctivitis, acute otitis media, streptococcal pharyngitis, cellulitis or sinusitis, confirmed by culture of the site of infection and negative blood cultures. The bacteria isolated were Staphylococcus aureus, Streptococcus pneumoniae and Streptococcus pyogenes. In order to establish normal PCT levels for comparison, serum samples were also collected from a control group of 25 similarly aged healthy children admitted to the hospital for elective surgery. PCT was measured using LIA (Lumitest PCT; Brahms Diagnostica, Germany) for quantitative detection and ICT (PCT-Q; Brahms Diagnostica) for semiquantitative detection following the manufacturer’s instructions. LIA requires 20 l of serum and 90–120 min to be performed. ICT requires 200 l of serum and results can be obtained in 30 min; samples can be measured individually. CRP was measured using a turbidimetric assay (C-Reactive Protein FlexT reagent cartridge, Dimension; Dade Behring, USA) and leukocyte count was measured with Coulter Counter Maxm (Coulter, USA). Comparison between groups for quantitative parameters was performed using the non-parametric MannWhitney U test for CRP, leukocyte count and PCT. Diagnostic accuracy and optimum cut-off points were determined using a receiver operating characteristic curve. Comparisons between the two methods were made C. Prat ()) · J. Dom nguez · M. Gim nez · S. Blanco · V. Ausina Servei de Microbiologia, Hospital Universitari Germans Trias i Pujol, C/Canyet s/n, 08916 Badalona, Spain e-mail: crisprat@ns.hugtip.scs.es Tel.: +34-93-4978894 Fax: +34-93-4978895

Usefulness of a new mycobacteriophage-based technique for rapid diagnosis of pulmonary tuberculosis.

ABSTRACT A new mycobacteriophage-based technique (PhageTek MB) was compared with standard culture and staining techniques for diagnosis of pulmonary tuberculosis. A total of 2,048 respiratory specimens from 1,466 patients collected from February 2000 to March 2001 were studied by both (i) conventional methods (direct microscopic examination [auramine-rhodamine fluorochrome], and culture in BacT/ALERT 3D and solid media) and (ii) the PhageTek MB assay. This phenotypic test utilizes specific mycobacteriophages to detect the presence of live Mycobacterium tuberculosis complex organisms within a decontaminated clinical sample. Overall, 205 (10%) specimens were positive for mycobacteria (134 patients): 144 (70.2%) M. tuberculosis isolates and 61 (29.8%) nontuberculous mycobacterium isolates (30 Mycobacterium kansasii, 12 Mycobacterium xenopi, 9 Mycobacterium gordonae, 7 Mycobacterium avium complex, 2 Mycobacterium chelonae, and 1 Mycobacterium fortuitum isolate). PhageTek MB was more likely to give a positive result with specimens in which high numbers of acid-fast bacilli were observed on the smear. The sensitivity, specificity, and positive and negative predictive values of this mycobacteriophage-based technique versus culture for M. tuberculosis were 58.3, 99.1, 83.2, and 96.9%, respectively. PhageTek MB is a rapid (48-h), specific, safe, and easy-to-perform test. According to the prevalence of the disease in the population studied, the test would require improved sensitivity in order to be used as a screening test for routine diagnosis of respiratory tuberculosis in our setting.

Serum Concentrations of Procalcitonin After Cardiac Surgery

Abstract  Background and Aim: Monitorization of complications in patients underlying cardiac surgery may be difficult because cardiopulmonary bypass (CPB) can lead to a systemic inflammatory response syndrome because of exposure of blood to nonphysiological surfaces. The purpose of the study was to establish the baseline levels of procalcitonin (PCT) after cardiac surgery in our population in order to analyze a possible induction of the inflammatory response that might interfere with the diagnosis of infection by PCT. Methods: Serum samples from patients undergoing coronary artery bypass grafting or valve replacement were collected at the time of admission to intensive care unit, after surgery as well as in the first and second postoperative days. Patients were followed for the development of postoperative complications. PCT levels were measured by immunoluminometric assay. Results: The mean PCT values were significantly higher in the first postoperative day in all the groups except the control group. No increased PCT levels were found related neither to duration of CPB, nor to time of aortic clamping. Only patients who presented complications had significantly increased PCT values immediately after surgery (p = 0.004), in the first postoperative day (p < 0.0001), and in the second postoperative day (p < 0.0001) with respect to those who recovered uneventfully. Conclusions: A slight and transient increase in PCT levels was observed in the first postoperative day after cardiac surgery. Significant elevation of PCT was only observed when complications were present.

Utility of an In-House Mycobacteriophage-Based Assay for Rapid Detection of Rifampin Resistance in Mycobacterium tuberculosis Clinical Isolates

ABSTRACT A rapid in-house mycobacteriophage-based assay to identify multidrug resistance by detecting the rifampin susceptibility of Mycobacterium tuberculosis in a microtiter plate format was evaluated. The sensitivity, specificity, and overall accuracy of the assay were 100%. This test is rapid to perform and suitable for widespread implementation.

Comparison of a monoclonal with a polyclonal antibody-based enzyme immunoassay stool test in diagnosing Helicobacter pylori infection before and after eradication therapy.

Detection of Helicobacter pylori antigen in stool samples has been a subject of controversy. However, it has been included in several clinical guidelines as a recommended non‐invasive testing procedure in dyspeptic patients.

Noninvasive Method for Diagnosis of Visceral Leishmaniasis by a Latex Agglutination Test for Detection of Antigens in Urine Samples

Since the appearance of human immunodeficiency virus (HIV), visceral leishmaniasis (VL) has emerged as an opportunistic infection in developed countries (1, 3, 10). It appears in advanced stages of HIV infection and is supposed to accelerate the progression of AIDS (3, 5, 8). Therapeutic failures and relapses are common. Accurate diagnosis is usually difficult in HIV-coinfected patients because VL has atypical clinical expressions and because serological diagnosis becomes unreliable (1). Demonstration of the parasite in cultured samples or in stained preparations is considered the “gold standard” (GS) for diagnosis but requires invasive techniques. A noninvasive and accurate test is needed in order to improve diagnosis of VL, especially in individuals with an increased risk of suffering complications after invasive methods (2, 6). We have evaluated the effectiveness of a rapid latex agglutination test (LAT) (KATEX; Kalon Biological Ltd., Aldershot, Hants, United Kingdom) in the detection of a leishmanial antigen (9) in urine from patients with VL and its usefulness in treatment monitoring. A bone marrow aspirate and a fresh urine specimen were collected from 85 patients with suggestive clinical symptoms and signs of VL. The demonstration of the parasite by culture or Giemsa stain in bone marrow aspirate was considered the GS. In 16 out of 89 cases the VL clinical diagnosis was confirmed by the GS (group 1), while in 73 it was not (group 2). Urine samples from 73 patients without any suspicion of VL were collected as negative controls (group 3). The percentages of HIV-infected individuals were as follows: 100% in group 1, 91% in group 2, and 21% in group 3. The LAT was performed in previously boiled urine specimens according to the manufacturers instructions. A clear agglutination was recorded as positive. All specimens from group 1, three from group 2, and none from group 3 were positive by the LAT (Table ​(Table1).1). One of the three patients from group 2 who tested positive had been diagnosed with VL 1 year before. The sensitivity was 100%, and specificity was 96% (Table ​(Table11). TABLE 1. Leishmanial urinary antigen detection in different patient groups We followed up the cases of 13 of the 16 patients from group 1. A urine specimen was collected each time they came to the hospital, and a bone marrow aspirate was also collected if a VL relapse was suspected. The LAT was performed for all urine samples obtained. The leishmanial antigen could be detected in urine up to 1 year after VL diagnosis in HIV-coinfected patients, probably due to their inability to control the parasitosis (4, 7). Therefore, this technique does not seem very helpful in monitoring treatment and predicting relapses. However, our results show that the test is a sensitive and specific noninvasive tool for diagnosing VL. It is easy to perform and interpret, so it could be used as a screening test in developing areas and among susceptible populations. However, due to the low number of patients with VL included in our evaluation, further studies are needed to confirm these data.

ASSESSMENT OF A NEW TEST TO DETECT LEGIONELLA URINARY ANTIGEN FOR THE DIAGNOSIS OF LEGIONNAIRES' DISEASE

Given that the rate of mortality by Legionella pneumonia increases in incorrectly treated patients, rapid diagnosis and early antibiotic treatment are needed. We have assessed the performance of a new enzyme immunoassay (EIA) test (Bartels Inc. Trinity Biotech Company, Wicklow, Ireland) to detect Legionella pneumophila antigen in urine comparing it to Binax EIA (Binax, Portland, Maine). We also evaluated the capability of both EIAs to detect extracted soluble antigens of Legionella strains. Using nonconcentrated urine samples (NCU) the sensitivity of Bartels EIA was 74.1% (66/89) and the sensitivity of Binax EIA was 51.7% (46/89). The sensitivity of both EIA tests were 91.5% (54/59) using concentrated urine samples (CU). Specificity of both EIA tests was 100% in NCU and CU. Bartels EIA was able to detect all serogroup L. pneumophila antigens, achieving a higher sensitivity in the case of L. pneumophila serogroup 1 soluble antigen. The new EIA was found to be a useful test for the rapid diagnosis of Legionella pneumonia, being a better alternative to the Binax EIA if NCU is used.