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Biomedical subjects

A M van Loon

Publications and source records attributed to A M van Loon.

At least 37 records · Page 2Linked to original sources
PubMed2001

European proficiency testing program for molecular detection and quantitation of hepatitis B virus DNA.

External quality control of hepatitis B virus (HBV) DNA detection remains an important issue. This study reports and compares the results obtained from two different proficiency panels for both the qualitative and quantitative assessment of HBV DNA. The panels were designed by the European Union Quality Control Concerted Action, prepared by Boston Biomedica, Inc., and distributed in May 1999 (panel 1) and February 2000 (panel 2). Each contained two negative samples and six positive samples with 10(3) to 10(7) copies/ml (panel 1) or 10(3) to 2 x 10(6) copies of HBV DNA per ml (panel 2). For panel 1, 42 laboratories submitted 20 qualitative (all in-house PCRs) and 37 quantitative (87% commercial assays) data sets. For panel 2, 51 laboratories submitted 25 qualitative (all in-house PCRs) and 47 quantitative (94% commercial assays) data sets. Five data sets (8.8%) in panel 1 and two data sets (2.8%) in panel 2 contained totals of six and two false-positives, respectively, corresponding to false-positive result rates of 5.3% for panel 1 and 1.4% for panel 2. The false-negative result rates of 10.5% for panel 1 and 17.4% for panel 2 were dependent on the detection levels of the assays employed as well as panel composition. In the qualitative analysis of all data sets, 47.4% (panel 1) and 51.4% (panel 2) had all samples correct. An adequate or better score (all correct or only the weak-positive sample missed) was obtained with 77.2% of the panel 1 samples and 68.1% of the panel 2 samples. In the quantitative analysis, 57.1% (panel 1) and 42.6% (panel 2) of the data sets achieved an adequate or better score (positive results within the acceptable range of the geometric mean +/- 0.5 log(10) of all positive results). These results demonstrate that while the qualitative performance of HBV detection has considerably improved compared to that of a previously published HBV proficiency study, the detection levels of many commercial quantitative assays are still too high to allow adequate quantitation of all relevant clinical samples.

DNA, Viral↗
PubMed2001

Clinical diagnosis of influenza virus infection: evaluation of diagnostic tools in general practice.

BACKGROUND: With the development of new antiviral agents for influenza, the urge for rapid and reliable diagnosis of influenza becomes increasingly important. Respiratory virus infections are difficult to distinguish on clinical grounds. General practitioners (GPs) however, still depend on their clinical judgement. AIM: To evaluate the importance of clinical symptoms in the diagnosis of influenza virus infection. DESIGN OF STUDY: A multicentre questionnaire study. SETTING: Eighty-one patients from 14 general practices. METHOD: Patients with fever and at least one constitutional symptom and one respiratory symptom were included. A questionnaire with the medical history and clinical symptoms was completed and a combined nose-throat swab was taken. Virus culture, rapid culture, and polymerase chain reaction (PCR) amplification were performed on each specimen. Multivariate analysis was used to obtain the best predictive model. RESULTS: By using PCR, an increase was seen in the detection of the viral pathogens compared with the results of culture. In 42 out of 81 patients PCR was positive for influenza. A positive predictive value (PPV) of 75% was observed for the combination of headache at onset, feverishness at onset, cough, and vaccination status during the period of increase influenza activity. Criteria used by the ICHPPC-2 resulted in a PPV of 54%. The PPV for diagnosis made by the GP was 76%. CONCLUSION: Although influenza is difficult to diagnose on clinical grounds, the GPs in this study were able to diagnose influenza as such more accurately on their judgement than by the other criteria.

Adult↗
PubMed2000

The prevalence and incidence of hepatitis C virus infections among dialysis patients in the Netherlands: a nationwide prospective study.

A nationwide prospective survey on hepatitis C virus (HCV) infections among dialysis patients in The Netherlands was performed. Patients were recruited from 34 dialysis centers and were tested for antibodies and HCV RNA in 1995 and 1997. Seronegative serum samples were analyzed by reverse-transcriptase polymerase chain reaction in pools. HCV-RNA-positive serum samples were genotyped and were partly sequenced. In the first and second rounds, 67 (2.9%) of 2281 and 76 (3.4%) of 2286 patients were HCV positive, respectively. Of 960 patients with paired serum samples, 35 were HCV positive in both rounds, and 9 HCV-positive cases were newly identified in the second round. The incidence of HCV infection was 0.5 per 100 dialysis years. Phylogenetic analysis revealed clustered sequences that indicated nosocomial transmission. Sixty percent of HCV infections, however, can be attributed to 4 interdependent risk factors (i.e., hemodialysis before 1992, kidney transplantation before 1994, and birth or dialysis in a foreign country). In conclusion, the prevalence of HCV infections in The Netherlands does not decline, and transmission within dialysis units continues. Adequate screening of HCV infections and strict enforcement of universal infection control practices are required.

Case-Control Studies↗
PubMed2000

Borna disease virus and schizophrenia in Surinamese immigrants to the Netherlands.

Borna disease virus (BDV) has been suggested to play a role in the etiology of schizophrenia. We tested the hypothesis that markers of BDV infection are more frequent in Surinamese immigrants to the Netherlands, diagnosed with schizophrenia, than in Dutch-born healthy subjects. For reasons that are poorly understood there is an increased incidence of schizophrenia in this immigrant group. Blood was obtained from 29 male schizophrenic patients (DSM-IV criteria) and from 26 healthy males. For detection of anti-BDV antibodies an indirect immunofluorescence assay (IFA) was performed. A nested, reverse-transcriptase-PCR, using primers specific for the p24 and p40 BDV genes, was used to determine BDV-RNA in peripheral blood mononuclear cells. Contrary to our expectations, the frequencies of BDV markers in the group of healthy subjects, as determined by IFA and both PCRs, exceeded that in the group of patients. The results do not support an association between markers of BDV infection in blood and schizophrenia. It is unlikely that the high incidence of schizophrenia in Surinamese immigrants is caused by BDV, but the small number of subjects examined do not warrant definitive conclusions.

Antibodies, Viral↗
PubMed2000

Infectious gastro-enteritis: an uncommon cause of diarrhoea in adult allogeneic and autologous stem cell transplant recipients.

The incidence and aetiology of acute diarrhoea in 60 adult allogeneic or autologous stem cell transplant (SCT) recipients was determined in a prospective study. Stool specimens were obtained prior to SCT and on days +20, +40, +60 and +100 post transplant. Microbiological evaluation was performed for pathogenic bacteria, fungi, parasites and viruses. Forty-seven patients were evaluable of whom 31 had a total of 48 acute diarrhoeal episodes. Diarrhoea occurred in 79% of allogeneic and 47% of autologous SCT recipients (P < 0.05). Intestinal infections were found in three of 48 (6%) diarrhoeal episodes. Clostridium difficile with positive toxin was cultured twice and one stool specimen was positive for cryptosporidium. Intestinal pathogens were identified in 13 out of 172 stool specimens from asymptomatic patients and included: rotavirus (4), adenovirus (3), C. difficile, toxin positive (2), and others (4). Graft-versus-host disease was confirmed by biopsy in two of 36 episodes of diarrhoea in allogeneic patients, and in three patients a relationship between reactivation of cytomegalovirus and diarrhoea was suspected. In 40 of 48 (83%) episodes of diarrhoea no clear aetiology could be found.

Adult↗
PubMed1999

Lessons from diagnostic investigations of patients with poliomyelitis and their direct contacts for the present surveillance of acute flaccid paralysis.

One of the key strategies for the global eradication of poliomyelitis is the virological investigation of stool samples in cases of acute flaccid paralysis (AFP) to exclude poliovirus as a possible cause. Clinical specimens from a serotype 3 outbreak provided an opportunity to examine the potential of newly developed methods for the diagnosis of poliomyelitis. The virus isolation rate was maximal (89.6%) during the first 2 weeks after the onset of paralysis and then dropped sharply to 18.6%. In contrast, a high percentage of patients tested positive for poliovirus-specific IgM (93.9%) in the early phase of the infection and remained positive for up to 8 weeks. Virus isolation would have correctly identified only 54.9% of the AFP cases. This rate would have been increased to 92% through the use of the poliovirus-specific IgM ELISA. The IgM ELISA could serve as an important additional tool for the rapid diagnosis of poliomyelitis.

Acute Disease↗
PubMed1999

Clinical evaluation of guidelines and two-test approach for lyme disease.

OBJECTIVE: The diagnosis of Lyme disease should be based on objective clinical signs and symptoms. In a clinical study, we have evaluated whether the recommended two-step approach for serodiagnosis of Lyme disease is useful in daily clinical practice and can influence clinical decision making. METHODS: The signs and symptoms of patients with ongoing musculoskeletal complaints, assumed by their referring physician or themselves to be attributable to active or chronic Lyme disease, and of patients diagnosed as having Lyme disease, were evaluated. On the basis of clinical evaluation only, patients were classified into three groups: previous Lyme disease, active Lyme disease and no Lyme disease. Antibodies to Borrelia burgdorferi were determined by means of an enzyme-linked immunosorbent assay (ELISA), followed, when positive, by immunoblotting. RESULTS: One hundred and three patients (41 males and 62 females, mean age 48.7 yr) participated in the study. Of the 49 patients classified as previous Lyme disease, 25 (51%) had antibodies to B. burgdorferi. All 10 patients with active Lyme disease had positive antibodies and 12 of the 44 patients (27%) classified as no Lyme disease had positive antibodies. No statistically significant differences were found between the percentage of positive immunoblots from patients with previous Lyme disease (72%) and patients with active Lyme disease (100%). In the group of no Lyme disease, five out of 12 patients had a negative immunoblot. Concerning serological testing, immunoblotting could have added additional information. However, immunoblotting did not influence clinical decision making in this group of patients. CONCLUSION: Immunoblotting did not influence clinical decision making for the 47 patients with antibodies to B. burgdorferi in this study.

Adolescent↗
PubMed1999

Multicenter quality assessment of PCR methods for detection of enteroviruses.

We conducted a multicenter evaluation of commercial and in-house PCR methods for the detection of enteroviruses. Three coded panels of test and control RNA samples, artificial clinical specimens, and representative enterovirus serotypes were used to assess amplification methods, RNA extraction methods, and reactivities with different enterovirus serotypes. Despite several differences between PCR methods, there was good agreement, although some variation in sensitivity was observed. Most PCR methods were able to detect enterovirus RNA derived from 0.01 50% tissue culture infective dose (TCID50) and were able to detect at least 1 TCID50 of enterovirus in cerebrospinal fluid, stool, or throat swab specimens. Most were also able to detect a wide range of enterovirus serotypes, although serotypic identification was not possible. Some laboratories experienced false-positive results due to PCR contamination, which appeared to result mainly from cross-contamination of specimens during RNA extraction. Provided that this problem is overcome, these PCR methods will prove to be a sensitive and rapid alternative to cell culture for the diagnosis of enterovirus infection.

Base Sequence↗
PubMed1999

Genetic basis for immunological aberrations in poliovirus Sabin serotype 3 strains imported in the netherlands.

During the characterization of poliovirus type 3 strains imported in The Netherlands, Sabin serotype 3 strains that reacted with both specific antisera against Sabin-like (vaccine) and non-Sabin-like (wild-type) strains by the intratypic strain differentiation assay have been found. The present study was done to determine the pathogenic potential of these virus strains for humans. Characterization of these so-called double-reactive strains with neutralizing monoclonal antibodies (MAbs) against the major antigenic sites of serotype 3 Sabin virus led to the identification of two groups with different antigenic properties. Six of the seven strains were resistant to neutralization with MAbs against sites 2B and 3B and one strain was neutralized by all the MAbs in a manner similar to that for the Sabin serotype 3 virus. Partial sequencing of the coding regions confirmed the antigenic changes for all six antigenically distinct strains. By inoculation of these viruses into transgenic mice which express the human poliovirus receptor, one strain was identified as highly neurovirulent, three were identified as intermediate, and three were identified as attenuated. Sera from vaccinated persons efficiently neutralized the mutants. Our data suggest that some double-reactive strains are a potential risk to the unvaccinated community but not to the vaccinated population.

Animals↗
PubMed1999

External quality assessment of enterovirus detection and typing. European Union Concerted Action on Virus Meningitis and Encephalitis.

Reported are the results of a study of an enterovirus proficiency panel for use in isolation and serotyping and/or the polymerase chain reaction (PCR) carried out by 12 laboratories in nine European countries. Eleven laboratories reported results of virus isolation and serotyping. In addition, four laboratories reported results of a PCR for enterovirus detection. Correct virus isolation results were obtained for 105 of 110 samples (95.5%, four false-negatives, one false-positive), and correct PCR results for 39 of 40 (97.5%, one false-negative). The highest isolation rate (87.5%) was observed in primary and tertiary monkey kidney cells; on monkey kidney cell lines, human diploid fibroblasts or human heteroploid cells the isolation rate varied between 64% and 71.4%. Serotyping results were less satisfactory. Only 63 of 106 (59.4%) isolated viruses were typed correctly. Major problems were seen with samples containing mixtures of enteroviruses and with enterovirus 71 or echovirus 4, with 9%, 50%, and 55% correct results, respectively. These results underline the need for improvement of enterovirus typing, especially in view of the poliomyelitis eradication initiative.

Bacterial Typing Techniques↗
PubMed1998

[Vertical HIV-I-transmission. I. Risk and prevention in pregnancy].

Without anti-HIV treatment, mother to child HIV-I transmission occurs in 15-30% of HIV positive pregnancies. Transmission occurs mostly in the last trimester or at birth. The maternal virus load in the last trimester and around birth is strongly related to the risk of HIV transmission to the child. This risk can be reduced during pregnancy by anti-HIV treatment and in certain cases by performing a caesarean section. It is recommended to determine the plasma virus load several times during pregnancy. If the virus load is found to be high, measurement of plasma anti-HIV drug concentrations and anti-HIV drug resistance may prompt modification of the anti-HIV drug regimen with the objective of achieving maximal suppression of virus replication in the last trimester.

Adolescent↗
PubMed1998

[Vertical HIV-I-transmission. II. HIV-diagnosis in a child].

In newborn children from HIV-infected women early establishment of HIV infection is of importance for optimal therapy of HIV-infected children and avoidance of unnecessary medication in uninfected children. A more than 95% reliable diagnosis of HIV infection can now be obtained at the age of four weeks by polymerase chain reaction (PCR) technology. Before this age a positive PCR result is relevant since it necessitates additional investigation such as measuring anti-HIV drug resistance and may lead to modification of anti-HIV treatment. Prophylaxis against Pneumocystis carinii is not needed if HIV infection can not be demonstrated by PCR after the age of four weeks.

AIDS-Related Opportunistic Infections↗
PubMed1998

Molecular typing of enteroviruses: current status and future requirements. The European Union Concerted Action on Virus Meningitis and Encephalitis.

Human enteroviruses have traditionally been typed according to neutralization serotype. This procedure is limited by the difficulty in culturing some enteroviruses, the availability of antisera for serotyping, and the cost and technical complexity of serotyping procedures. Furthermore, the impact of information derived from enterovirus serotyping is generally perceived to be low. Enteroviruses are now increasingly being detected by PCR rather than by culture. Classical typing methods will therefore no longer be possible in most instances. An alternative means of enterovirus typing, employing PCR in conjunction with molecular genetic techniques such as nucleotide sequencing or nucleic acid hybridization, would complement molecular diagnosis, may overcome some of the problems associated with serotyping, and would provide additional information regarding the epidemiology and biological properties of enteroviruses. We argue the case for developing a molecular typing system, discuss the genetic basis of such a system, review the literature describing attempts to identify or classify enteroviruses by molecular methods, and suggest ways in which the goal of molecular typing may be realized.

Encephalitis, Viral↗
PubMed1998

Hepatitis C virus infections in dialysis centers in The Netherlands: a national survey by serological and molecular methods.

A national survey of hepatitis C virus (HCV) infections among dialysis patients in The Netherlands was performed. The study involved 2,653 patients (2,108 hemodialysis patients and 545 chronic ambulatory peritoneal dialysis [CAPD] patients) from 39 of the 49 dialysis centers in the country. Patient sera were analyzed by both serological and molecular methods. Screening by a third-generation enzyme immunoassay (EIA) yielded 79 reactive sera. The presence of anti-HCV antibodies was confirmed in 70 patients by a line immunoassay. All seropositive samples were tested by reverse transcriptase PCR, and 57 samples were found to contain HCV RNA. Of the nine EIA-positive and line immunoassay-negative or indeterminate samples, four were HCV RNA positive. All seronegative samples were screened for the presence of HCV RNA in pools of five sera. Of 2,576 antibody-negative samples, 6 contained HCV RNA. All antibody-positive and RNA-positive samples were also tested by a second serological assay. The prevalence of HCV infections among Dutch dialysis patients as determined by serology or the presence of HCV RNA was 3% (80 of 2,653), i.e., 3.5% (73 of 2,108) in patients treated on hemodialysis and 1.3% (7 of 545) in patients on CAPD. Of these 80 HCV-infected dialysis patients, 67 (84%) were HCV RNA positive. Serological screening alone would have diagnosed only 70 infected patients. Therefore, antibody screening combined with detection of HCV RNA should be considered as the "gold standard" for diagnosing HCV infection in dialysis patients. The prevalence of HCV-infected patients in Dutch dialysis centers ranged from 0 to 8%, suggesting the existence of local risk factors for acquiring HCV infection. Genotyping analysis by reverse hybridization line probe assay revealed the presence of genotypes la (23%), 1b (46%), 2 (3%), 2a (13%), 2b (1%), 3a (7%), and 4a (4%). In four (6%) samples multiple genotypes were detected. The genotype distribution of HCV isolates among Dutch dialysis patients was similar to the distribution among nondialysis patients from the Benelux, except for subtype 1a, which was significantly more prevalent among dialysis patients. In only one center, a high prevalence of an uncommon genotype was suggestive of infection from a common source.

Ambulatory Care Facilities↗
PubMed1998

Multicenter evaluation of the Amplicor Enterovirus PCR test with cerebrospinal fluid from patients with aseptic meningitis. The European Union Concerted Action on Viral Meningitis and Encephalitis.

The Amplicor Enterovirus PCR test was compared with viral culture for the detection of enteroviruses in cerebrospinal fluid (CSF) specimens. In a multicenter study in which nine laboratories participated, a total of 476 CSF specimens were collected from patients with suspected aseptic meningitis. Sixty-eight samples were positive by PCR (14.4%), whereas 49 samples were positive by culture (10.4%), demonstrating that the Amplicor Enterovirus PCR test was significantly more sensitive than culture (P < 0.001). After discrepancy analysis the sensitivity and specificity of the Amplicor Enterovirus PCR test obtained by using viral culture as the "gold standard" were 85.7 and 93.9%, respectively. Our results with the CSF specimens collected in different countries demonstrate that the Amplicor test is capable of detecting a large variety of enterovirus serotypes and epidemiologically unrelated isolates in CSF specimens from patients with aseptic meningitis. The Amplicor Enterovirus PCR test is a rapid assay which can be routinely performed with CSF samples and is an important improvement for the rapid diagnosis of enteroviral meningitis.

Cerebrospinal Fluid↗
PubMed1998

Diagnosis and clinical management of neurological disorders caused by cytomegalovirus in AIDS patients. European Union Concerted Action on Virus Meningitis and Encephalitis.

Cytomegalovirus (CMV) infections are common and severe complications of HIV infection. The virus involves the nervous system, causing encephalitis, polyradiculomyelitis and peripheral neuropathies. Due to their limited sensitivity, traditional virological approaches, such as virus isolation or antigen detection in the CSF are useful only in limited instances, e.g. CMV polyradiculopathy. The aetiological diagnosis of these disorders relies on the analysis of cerebrospinal fluid by PCR and quantitative PCR may be important to establish the extent of CNS lesions and to monitor the efficacy of antiviral treatments. CMV is susceptible to various antivirals, including ganciclovir, foscarnet and cidofovir. CMV infections of the nervous system, in particular encephalitis, however, show only a poor response to standard treatments. Drug combination treatments i.e. ganciclovir plus foscarnet, are currently under evaluation in clinical trials.

Acquired Immunodeficiency Syndrome↗
PubMed1998

Surveillance of acute flaccid paralysis in The Netherlands, 1992-94.

Detection and investigation of all cases of acute flaccid paralysis (AFP) in children below 15 years of age are among the criteria for poliomyelitis-free certification. In the absence of poliomyelitis the incidence of AFP is around 1 per 100,000 children aged < 15 years. In the Netherlands, surveillance of AFP began in October 1992 under the supervision of the Dutch Paediatric Surveillance System (NSCK). Over 90% of clinically active paediatricians participated in the monthly reporting of new cases of AFP. From October 1992 to December 1994 (27 months), 52 cases of AFP were reported. The incidence was 0.7 per 100,000 over the period, and reported cases were evenly distributed throughout the country. The main cause of AFP was Guillain-Barré syndrome. The average time between onset of symptoms and visiting a doctor was less than 3 days. The median reporting delay was 29 days, although the system was not intended as surveillance for action. Virological examination of faeces was carried out for only 40.4% of AFP patients. The start of the NSCK surveillance system coincided with the 1992-93 outbreak of poliomyelitis in the Netherlands, but only 7 of the 18 children with paralytic poliomyelitis were reported through the AFP surveillance system. For certification purposes, the present AFP surveillance system in the Netherlands needs to be improved with respect to coverage by including neurologists, rapidity of reporting, and completeness of laboratory investigations.

Adolescent↗