Evaluation of a commercial PCR kit for diagnosis of cytomegalovirus infection of the central nervous system

Clinical utility of viral load in management of cytomegalovirus infection after solid organ transplantation

The negative impact of cytomegalovirus (CMV) infection on transplant outcomes warrants efforts toward improving its prevention, diagnosis, and treatment. During the last 2 decades, significant breakthroughs in diagnostic virology have facilitated remarkable improvements in CMV disease management. During this period, CMV nucleic acid amplification testing (NAT) evolved to become one of the most commonly performed tests in clinical virology laboratories. NAT provides a means for rapid and sensitive diagnosis of CMV infection in transplant recipients. Viral quantification also introduced several principles of CMV disease management. Specifically, viral load has been utilized (i) for prognostication of CMV disease, (ii) to guide preemptive therapy, (iii) to assess the efficacy of antiviral treatment, (iv) to guide the duration of treatment, and (v) to indicate the risk of clinical relapse or antiviral drug resistance. However, there remain important limitations that require further optimization, including the interassay variability in viral load reporting, which has limited the generation of standardized viral load thresholds for various clinical indications. The recent introduction of an international reference standard should advance the major goal of uniform viral load reporting and interpretation. However, it has also become apparent that other aspects of NAT should be standardized, including sample selection, nucleic acid extraction, amplification, detection, and calibration, among others. This review article synthesizes the vast amount of information on CMV NAT and provides a timely review of the clinical utility of viral load testing in the management of CMV in solid organ transplant recipients. Current limitations are highlighted, and avenues for further research are suggested to optimize the clinical application of NAT in the management of CMV after transplantation.

Laboratory diagnosis of CNS infections by molecular amplification techniques

The initial presentation of symptoms and clinical manifestations of CNS infectious diseases often makes a specific diagnosis difficult and uncertain, and the emergence of polymerase chain reaction-led molecular techniques have been used in improving organism-specific diagnosis. These techniques have not only provided rapid, non-invasive detection of microorganisms causing CNS infections, but also demonstrated several neurologic disorders linked to infectious pathogens. Molecular methods performed on cerebrospinal fluid are recognized as the new 'gold standard' for some of these infections caused by microorganisms that are difficult to detect and identify. Although molecular techniques are predicted to be widely used in diagnosing and monitoring CNS infections, the limitations as well as strengths of these techniques must be clearly understood by both clinicians and laboratory personnel.

Comparative evaluation of published cytomegalovirus primers for rapid real-time PCR: which are the most sensitive?

Standardization of human cytomegalovirus (CMV) PCR is highly recommended. As primer design is essential for PCR sensitivity, this study evaluated all published CMV primer pairs to identify the most sensitive for single-round real-time PCR. PubMed (1993-2004) was searched for original papers aimed at CMV PCR. Fifty-seven papers were identified revealing 82 different primer pairs. Of these, 17 primer sets were selected for empirical study, as they were either used in real-time PCR or were evaluated comparatively by conventional PCR. After optimizing the PCR conditions, these primer sets were evaluated by real-time PCR using a SYBR Green format. Analytical sensitivities were assessed by testing the reference standard CMV strain AD169. A blast search was performed to identify mismatches with published sequences. Additionally, 60 clinical samples were tested with the three primer sets showing highest analytical sensitivity and the best match to all CMV strains. Three primer sets located in the glycoprotein B (UL55) gene region were found to be the most sensitive using strain AD169. However, two of these showed a considerable number of mismatches with clinical isolates in a blast search. Instead, two other pairs from the lower matrix phosphoprotein (UL83) gene and DNA polymerase (UL54) gene showed reasonable sensitivity and no mismatches with clinical isolates. These three pairs were further tested with clinical samples, which indicated that the two primer sets from UL55 and UL54 were the most sensitive. Interestingly, the analytical sensitivity of the PCR was inversely correlated with the size of the PCR product. In conclusion, these two primer pairs are recommended for a standardized, highly sensitive, real-time PCR.

Causes of death in hospitalized adults with a premortem diagnosis of tuberculosis: an autopsy study

OBJECTIVE

To ascertain the immediate and underlying causes of death in adults who died in hospital with a premortem diagnosis of tuberculosis.

DESIGN

Causes of death were assessed independently by internists and pathologists in 50 adults admitted to two Soweto hospitals who died 24 h or more after admission. Detailed record reviews and complete autopsies, including HIV tests when not performed premortem, were performed. In addition, a variety of postmortem microbiological tests were performed.

RESULTS

Forty-seven patients had HIV infection; all were antiretroviral naive. Their median age was 34.5 years, median CD4 cell count was 48 cells/microl and median length of hospitalization before death was 6 days. Autopsy confirmed the premortem diagnosis of tuberculosis in 37 HIV-infected patients (79%), whereas 10 (21%) did not demonstrate tuberculosis. Bronchopneumonia and cytomegalovirus pneumonitis were the leading pathologies in these 10 patients. In 47 HIV-infected cadavers immediate or contributory causes of death were: extensive pulmonary tuberculosis, 32 (68%); disseminated tuberculosis, 28 (60%); bacterial pneumonia, 13 (26%); cytomegalovirus pneumonitis in seven (15%); cytomegalovirus DNA was found in 31 (66%) and Pneumocystis pneumonia was found in five cadavers (11%). The lung, followed by lymph nodes, liver and kidney, were the commonest sites of tuberculosis. Mycobacterium tuberculosis was cultured from 19 spleens, one of which was multidrug resistant, and Salmonella spp. was cultured from 11 splenic specimens.

CONCLUSION

We demonstrated disseminated, extensive tuberculosis associated with advanced HIV disease. Severe bacterial infections, including salmonellosis, were the leading co-morbidity, suggesting that hospitalized HIV-infected adults in whom tuberculosis is suspected may benefit from broad-spectrum antibiotic therapy.

Risk of transmission of herpesviruses through cord blood transplantation

Cord blood (CB) progenitor cells are increasingly used for transplantation in children because of the lower risk of graft-versus-host disease compared with unrelated bone marrow and comparable rates of disease-free survival. There is concern that CB might carry a higher risk of opportunistic infections. Human herpesviruses (HHV) are common pathogens in transplant recipients. CB donors are routinely tested for the presence of anti-cytomegalovirus (CMV) immunoglobulin M to reduce the risk of collecting CMV-infected CB. To assess the incidence of beta and gamma HHV infection of CB collected under standard procedures, we tested 362 CB samples for the presence of CMV; HHV-6, -7, and -8; and Epstein-Barr virus DNA by polymerase chain reaction. HHV-6 DNA was found in 2 samples, yielding an incidence of 0.55% (95% confidence interval, 0.1%-2%). None of the other viral DNAs was found, resulting in a 95% confidence interval of 0% to 1% for the incidence of CMV, Epstein-Barr virus, HHV-7, and HHV-8. Because the seroprevalence of HHV-8 among the CB donors in this study was only 4%, these findings cannot be extended to HHV-8-endemic areas. Our data show that screening prospective CB donors with anti-CMV immunoglobulin M practically eliminates the risk of CB CMV transmission, but HHV-6 warrants CB testing by polymerase chain reaction.

Molecular methods for diagnosis of viral encephalitis

Hundreds of viruses cause central nervous system (CNS) disease, including meningoencephalitis and postinfectious encephalomyelitis, in humans. The cerebrospinal fluid (CSF) is abnormal in >90% of cases; however, routine CSF studies only rarely lead to identification of a specific etiologic agent. Diagnosis of viral infections of the CNS has been revolutionized by the advent of new molecular diagnostic technologies to amplify viral nucleic acid from CSF, including PCR, nucleic acid sequence-based amplification, and branched-DNA assay. PCR is ideally suited for identifying fastidious organisms that may be difficult or impossible to culture and has been widely applied for detection of both DNA and RNA viruses in CSF. The technique can be performed rapidly and inexpensively and has become an integral component of diagnostic medical practice in the United States and other developed countries. In addition to its use for identification of etiologic agents of CNS disease in the clinical setting, PCR has also been used to quantitate viral load and monitor duration and adequacy of antiviral drug therapy. PCR has also been applied in the research setting to help discriminate active versus postinfectious immune-mediate disease, identify determinants of drug resistance, and investigate the etiology of neurologic disease of uncertain cause. This review discusses general principles of PCR and reverse transcription-PCR, including qualitative, quantitative, and multiplex techniques, with comment on issues of sensitivity, specificity, and positive and negative predictive values. The application of molecular diagnostic methods for diagnosis of specific infectious entities is reviewed in detail, including viruses for which PCR is of proven efficacy and is widely available, viruses for which PCR is less widely available or for which PCR has unproven sensitivity and specificity, and nonviral entities which can mimic viral CNS disease.

Human herpesviruses 6 and 7 and central nervous system infection in children

Human herpesviruses 6 and 7 were infrequently found in cerebrospinal fluid of children with central nervous system infection.

The role and frequency of human herpesviruses (HHV)-6 and -7 in central nervous system (CNS) diseases of children are unclear. Cerebrospinal fluid samples from 245 pediatric patients (median age 43 days), submitted for evaluations of possible sepsis or of neurologic symptoms, were tested for HHV-6 and HHV-7 DNA by polymerase chain reaction. HHV-6 DNA was found in 3 of 245 samples, and HHV-7 was found in 0 of 245 samples. The three patients with HHV-6 DNA were <2 months of age. HHV-6 was likely pathogenic in two patients with meningitis who lacked evidence of another microbiologic cause. HHV-6 and HHV-7 are uncommon causes of CNS infection in children. HHV-6 may occasionally cause meningitis in young infants.

Relationship of Kaposi sarcoma (KS)-associated herpesvirus viremia and KS disease in Zimbabwe

The relationship between Kaposi sarcoma-associated herpesvirus (KSHV) viremia and KS disease was investigated in 500 subjects who received treatment in Harare, Zimbabwe. Subjects were grouped by results of human immunodeficiency virus (HIV) type 1 serological tests, KS diagnosis, and KS clinical stage. The plasma KSHV DNA concentration was associated with concomitant KS and HIV-1 infection (AIDS-KS; P<.001) and AIDS-KS clinical stage (P=.01). Plasma KSHV DNA levels were greater in AIDS-KS than in matched HIV-1-seronegative KS (P=.04). The plasma KSHV DNA level was not associated with age, sex, systemic symptoms, or CD4+ lymphocyte count. Plasma and peripheral blood mononuclear cell KSHV DNA concentrations were linearly related (r2=.44; P<.001), and the nucleotide sequence of the K1 gene highly variable region was identical in both compartments. These findings provide evidence that KSHV viremia is common in advanced AIDS-KS in Zimbabwe and suggest a relationship between KSHV lytic replication and untreated HIV-1 infection.

Molecular methods for cytomegalovirus surveillance in bone marrow transplant recipients

Two different methods for detection of cytomegalovirus (CMV), PCR and hybrid capture (HC), were compared by using plasma, peripheral blood leukocytes (PBLs), and whole blood (WB) from allogeneic bone marrow transplant recipients. One hundred specimens were obtained from nine children over an 18-month surveillance period. PCR of plasma for CMV was used for clinical management. The proportions of samples positive for CMV DNA by PCR with plasma, HC with WB, and PCR with PBLs were 21, 28, and 37%, respectively. Among 44 samples that were tested by all three methods, 68% had concordant results. By using a robust definition of true-positive samples (positivity by two or more methods or positivity of sequential samples by one method), the sensitivities of PCR with plasma, HC with WB, and PCR with PBLs were 50, 67, and 83%, respectively, and the specificities were 100, 96, and 96%, respectively. Two patients developed CMV-associated end-organ disease (one developed respiratory disease, and one developed gastrointestinal disease). CMV DNA was not detected in the plasma 1 week prior to the development of symptoms in either patient, whereas HC with WB was positive for both patients and PCR with PBLs was for one patient. These data suggest that WB or PBLs might be the preferred sample for use for surveillance for CMV in immunocompromised patients.

Quantitative CSF PCR in Epstein-Barr virus infections of the central nervous system

Acute Epstein-Barr virus (EBV) infection of the central nervous system (CNS) is associated with meningoencephalitis and other neurological syndromes and with CNS lymphomas (CNSLs). Diagnosis is based on serological studies and more recently on detection of EBV DNA in cerebrospinal fluid (CSF) by polymerase chain reaction (PCR). We measured EBV DNA by quantitative PCR and EBV mRNA by RT-PCR in the CSF in patients with EBV-associated neurological disorders. EBV was identified as the cause of CNS infection in 28 patients: 14 with CNSL, 10 with encephalitis, and 4 with postinfectious neurological complications. CSF analysis showed that patients with CNSL had high EBV load (mean +/- standard error of 4.8 +/- 0.2 log(10) DNA copies/ml) and low leukocyte counts (22 +/- 7 cells/microl); encephalitis was characterized by high EBV load (4.2 +/- 0.3 log(10) DNA copies/ml) and high leukocyte counts (143 +/- 62 cells/microl); and patients with postinfectious complications showed low EBV load (3.0 +/- 0.2 log(10) DNA copies/ml) with high leukocyte counts (88 +/- 57 cells/microl). Lytic cycle EBV mRNA, a marker of viral replication, was identified in 10 CSF samples from patients with CNSL and encephalitis. These studies demonstrate the utility of quantitative CSF PCR and establish the presence of lytic cycle EBV mRNA in CSF of patients with EBV-associated neurological disease.

Molecular Techniques in the Diagnosis of Central Nervous System Infections

Development of polymerase chain reaction (PCR)-based molecular techniques has initiated a revolution in the field of diagnostic microbiology. These techniques have not only provided rapid, noninvasive detection of microorganisms that cause central nervous system (CNS) infections, but have also demonstrated that several neurologic disorders are linked to infectious agents. While PCR-based techniques are predicted to be widely used in diagnosing and monitoring CNS infections, the limitations, as well as strengths, of these techniques must be clearly understood by both clinicians and laboratory personnel to ensure proper utilization.

Use of internal standard RNA molecules for the RT-PCR amplification of the faeces-borne RNA viruses

The diagnostic system based on reverse transcription (RT)-PCR has been used widely for the detection of viral genomes of faecal-borne RNA viruses. However, faecal specimens often produce both false positive and false negative results. Therefore, there is a need for a diagnosis procedure that can control for 'false-results'. In this study, an internal standard RNA that can serve as a non-competitive positive template was developed and used directly to detect faecal-borne RNA viruses without noticeable competitive inhibition of the target viral genome. These results suggest that the internal standard RNA is a useful standard molecule when undertaking diagnostic qualitative RT-PCR procedures for enteroviruses and related faecal-borne RNA viruses.

Recurrences of cytomegalovirus retinitis in a human immunodeficiency virus-infected patient, despite potent antiretroviral therapy and apparent immune reconstitution

We describe a 42-year-old man with human immunodeficiency virus infection who developed multiple recurrences of cytomegalovirus (CMV) retinitis despite receiving highly active antiretroviral therapy and having apparent immune reconstitution as evidenced by CD4(+) T lymphocyte counts of > 200 cells/mm(3). Laboratory investigation during one recurrence of retinitis confirmed that there was active CMV replication in the plasma and vitreous fluid. In addition, lymphoproliferative responses to CMV antigens were absent despite evidence of reactivity to Candida antigen and pokeweed mitogen. The clinical significance of this case and of other recently reported cases is discussed.

Comparison of three nucleic acid amplification assays of cerebrospinal fluid for diagnosis of cytomegalovirus encephalitis

The diagnostic reliabilities of three cytomegalovirus (CMV) nucleic acid amplification assays of cerebrospinal fluid (CSF) were compared by using CSF samples from human immunodeficiency virus-infected patients with a postmortem histopathological diagnosis of CMV encephalitis (n = 15) or other central nervous system conditions (n = 16). By using a nested PCR assay, the quantitative COBAS AMPLICOR CMV MONITOR PCR, and the NucliSens CMV pp67 nucleic acid sequence-based amplification assay, sensitivities were 93.3, 86.6, and 93.3%, respectively, and specificities were 93.7, 93.7, and 87.5%, respectively. The COBAS AMPLICOR assay revealed significantly higher CMV DNA levels in patients with diffuse ventriculoencephalitis than in patients with focal periventricular lesions.

Comparison of PCR, antigenemia assay, and rapid blood culture for detection and prevention of cytomegalovirus disease after lung transplantation

The goal of this study was to evaluate serial cytomegalovirus (CMV) blood culture, antigenemia testing, and qualitative and quantitative plasma CMV PCR for their ability to predict CMV disease and thus to direct preemptive therapy after lung transplantation. Forty-one patients provided 414 samples for blood culture, 290 samples for antigenemia testing, and 432 samples for PCR. Seven patients developed 11 episodes of CMV disease. CMV PCR had sensitivity, specificity, and positive predictive and negative predictive values of 79, 99, 84, and 99%, respectively, compared with 48, 99, 85, and 98%, respectively, for antigenemia testing, and 8, 100, 100, and 97%, respectively, for culture. Only quantitative CMV PCR correlated with disease stage: asymptomatic patients had a mean of 1,500 CMV DNA copies/ml, whereas patients who developed CMV disease had 5,087 copies/ml 12 to 4 weeks before symptoms and 32,000 copies/ml at diagnosis. Furthermore, CMV PCR-measured DNA increased 5- to 10-fold immediately preceding symptoms. PCR and antigenemia test values decreased with anti-CMV therapy. CMV DNA (as detected by PCR), but not antigenemia, persisted in patients who later developed recurrent CMV disease. The data indicate that lung transplant recipients will benefit from monitoring of CMV disease by plasma CMV PCR.

New strategies for prevention and therapy of cytomegalovirus infection and disease in solid-organ transplant recipients

In the past three decades since the inception of human organ transplantation, cytomegalovirus (CMV) has gained increasing clinical import because it is a common pathogen in the immunocompromised transplant recipient. Patients may suffer from severe manifestations of this infection along with the threat of potential fatality. Additionally, the dynamic evolution of immunosuppressive and antiviral agents has brought forth changes in the natural history of CMV infection and disease. Transplant physicians now face the daunting task of recognizing and managing the changing spectrum of CMV infection and its consequences in the organ recipient. For the microbiology laboratory, the emphasis has been geared toward the development of more sophisticated detection assays, including methods to detect emerging antiviral resistance. The discovery of novel antiviral chemotherapy is an important theme of clinical research. Investigations have also focused on preventative measures for CMV disease in the solid-organ transplant population. In all, while much has been achieved in the overall management of CMV infection, the current understanding of CMV pathogenesis and therapy still leaves much to be learned before success can be claimed.