Laboratory diagnosis of CNS infections by molecular amplification techniques

Laboratory diagnosis of CNS infections in children due to emerging and re-emerging neurotropic viruses

Recent decades have witnessed the emergence and re-emergence of numerous medically important viruses that cause central nervous system (CNS) infections in children, e.g., Zika, West Nile, and enterovirus/parechovirus. Children with immature immune defenses and blood-brain barrier are more vulnerable to viral CNS infections and meningitis than adults. Viral invasion into the CNS causes meningitis, encephalitis, brain imaging abnormalities, and long-term neurodevelopmental sequelae. Rapid and accurate detection of neurotropic viral infections is essential for diagnosing CNS diseases and setting up an appropriate patient management plan. The addition of new molecular assays and next-generation sequencing has broadened diagnostic capabilities for identifying infectious meningitis/encephalitis. However, the expansion of test menu has led to new challenges in selecting appropriate tests and making accurate interpretation of test results. There are unmet gaps in development of rapid, sensitive and specific molecular assays for a growing list of emerging and re-emerging neurotropic viruses. Herein we will discuss the advances and challenges in the laboratory diagnosis of viral CNS infections in children. This review not only sheds light on selection and interpretation of a suitable diagnostic test for emerging/re-emerging neurotropic viruses, but also calls for more research on development and clinical utility study of novel molecular assays. IMPACT: Children with immature immune defenses and blood-brain barrier, especially neonates and infants, are more vulnerable to viral central nervous system infections and meningitis than adults. The addition of new molecular assays and next-generation sequencing has broadened diagnostic capabilities for identifying infectious meningitis and encephalitis. There are unmet gaps in the development of rapid, sensitive and specific molecular assays for a growing list of emerging and re-emerging neurotropic viruses.

Herpes simplex viruses (1 and 2) and varicella-zoster virus infections in an adult population with aseptic meningitis or encephalitis: A nine-year retrospective clinical study

Three α-herpesviruses are known to be associated with central nervous system (CNS) infection; however, there are limited data on the incidence and clinical characteristics of α-herpesviruses CNS infections. This study aimed to assess the clinical manifestations, laboratory findings, and outcomes in patients with human herpes simplex virus 1 (HSV-1), human herpes simplex virus 2 (HSV-2), and varicella-zoster virus (VZV) CNS infections.We identified cases of HSV-1, HSV-2, and VZV CNS infections and reviewed their clinical and laboratory characteristics. The study population was drawn from patients with HSV-1, HSV-2, and VZV polymerase chain reaction positivity in cerebrospinal fluid (CSF) who visited Pusan National University Hospital between 2010 and 2018.During the 9-year study period, a total of 727 CSF samples were examined, with 72.2% (525/727) patients identified as having a CNS infection. Of 471 patients with aseptic meningitis and encephalitis, the causative virus was identified in 145 patients, and no virus was detected in 337 patients. A total of 15.2% (80/525) were diagnosed with one of the 3 herpesviruses as causative agents, 59 patients had meningitis, and 21 patients had encephalitis. Eleven patients with HSV-1, 27 patients with HSV-2, and 42 patients with VZV CNS infections were included. The distribution of cases by age showed different patterns depending on the type of herpesvirus infection. Compared with the HSV-1 group, the median age in the HSV-2 group was younger (HSV-1: 58 years; HSV-2: 38 years; P = .004), and patients with VZV infections showed a bimodal age distribution. Encephalitis was more common in the HSV-1 group, and HSV-1 infection was associated with a poor prognosis at discharge. CSF white blood cell counts were significantly lower in patients infected with HSV-1 (117 × 106 cells/L) than in patients infected with VZV (301 × 106 cells/L) (P = .008).These 3 herpesviruses are important causes of CNS infections regardless of immunologic status. HSV-1 infection was commonly associated with encephalitis and poor prognosis; HSV-2 and VZV CNS infections were associated with a low risk of mortality and neurological sequelae.

Central Nervous System Infections

This chapter provides an overview of infectious syndromes, pathogens, and diagnostic testing modalities for central nervous system infections in the immunocompromised host.

Laboratory Diagnosis of Central Nervous System Infection

Central nervous system (CNS) infections are potentially life threatening if not diagnosed and treated early. The initial clinical presentations of many CNS infections are non-specific, making a definitive etiologic diagnosis challenging. Nucleic acid in vitro amplification-based molecular methods are increasingly being applied for routine microbial detection. These methods are a vast improvement over conventional techniques with the advantage of rapid turnaround and higher sensitivity and specificity. Additionally, molecular methods performed on cerebrospinal fluid samples are considered the new gold standard for diagnosis of CNS infection caused by pathogens, which are otherwise difficult to detect. Commercial diagnostic platforms offer various monoplex and multiplex PCR assays for convenient testing of targets that cause similar clinical illness. Pan-omic molecular platforms possess potential for use in this area. Although molecular methods are predicted to be widely used in diagnosing and monitoring CNS infections, results generated by these methods need to be carefully interpreted in combination with clinical findings. This review summarizes the currently available armamentarium of molecular assays for diagnosis of central nervous system infections, their application, and future approaches.

Improved detection of bacterial central nervous system infections by use of a broad-range PCR assay

A universal PCR assay for bacteria and fungi detected meningitis pathogens in 65% of 20 cerebrospinal fluid (CSF) samples from patients with suspected central nervous system (CNS) infections compared to a 35% detection rate by culture and/or microscopy methods. Thus, the PCR assay can improve the diagnosis rate of infective meningitis when standard methods provide a negative result.

Incidence and clinical features of herpes simplex viruses (1 and 2) and varicella-zoster virus infections in an adult Korean population with aseptic meningitis or encephalitis

Since there are limited data on the incidence and clinical findings of central nervous system (CNS) infection by three α-herpesviruses including human herpes simplex virus 1 (HSV-1), HSV-2 and varicella-zoster virus (VZV) in Korea, a retrospective analysis of clinical data and polymerase chain reaction (PCR) results was performed in patients who presented with suspicion of acute viral meningitis and/or encephalitis at the emergency department of a tertiary referral hospital in Seoul, Korea. During the 3-year study period, a total of 224 cerebrospinal fluid (CSF) samples from 224 patients were examined. Among the 224 patients, 135 (60.3%) patients were identified as having aseptic meningitis (n = 70, 51.9%), encephalitis (n = 41, 30.4%) or meningoencephalitis (n = 24, 17.8%) at discharge. Twenty-four (17.8%) patients were identified as having VZV meningitis (n = 16, 11.9%), VZV meningoencephalitis (n = 2, 1.5%), HSV-2 meningitis (n = 4, 3.0%), or HSV-1 encephalitis (n = 2, 1.5%). Of the 24 patients infected with the three herpesviruses, immunocompromised patients accounted for 33.3% (n = 8). Skin rashes were observed in half (n = 9) of the patients with VZV, and none with HSV-1 or HSV-2. One patient with VZV meningitis and four patients with brain parenchymal involvement had neurologic sequelae. In conclusion, three herpesviruses are important causative agents of CNS infectious disease with significant morbidity in adults, regardless of the immunologic status. Therefore, CSF should be examined for HSV-1, HSV-2, and VZV using sensitive diagnostic methods in all cases of adult patients with clinical manifestations of CNS disease in order to identify the correct etiology and to determine appropriate therapy.

Interpretation and Relevance of Advanced Technique Results

Advanced techniques in the field of diagnostic microbiology have made amazing progress over the past two decades due largely to a technological revolution in the molecular aspects of microbiology [1, 2]. In particular, rapid molecular methods for nucleic acid amplification and characterization combined with automation and user-friendly software have significantly broadened the diagnostic capabilities of modern clinical microbiology laboratories. Molecular methods such as nucleic acid amplification tests (NAATs) rapidly are being developed and introduced in the clinical laboratory setting. Indeed, every section of the clinical microbiology laboratory, including bacteriology, mycology, mycobacteriology, parasitology, and virology, have benefited from these advanced techniques. Because of the rapid development and adaptation of these molecular techniques, the interpretation and relevance of the results produced by such molecular methods has lagged somewhat behind. The purpose of this chapter is to review and discuss the interpretation and relevance of results produced by these advanced molecular techniques. Moreover, this chapter will address the “myths” of NAATs, as these myths can markedly influence the interpretation and relevance of these results.