Methods of rapid diagnosis for the etiology of meningitis in adults

Mass spectrometry-based metabolomics for tuberculosis meningitis

Tuberculosis meningitis (TBM) is a prevalent form of extra-pulmonary tuberculosis that causes substantial morbidity and mortality. Diagnosis of TBM is difficult because of the limited sensitivity of existing laboratory techniques. A metabolomics approach can be used to investigate the sets of metabolites of both bacteria and host, and has been used to clarify the mechanisms underlying disease development, and identify metabolic changes, leadings to improved methods for diagnosis, treatment, and prognostication. Mass spectrometry (MS) is a major analysis platform used in metabolomics, and MS-based metabolomics provides wide metabolite coverage, because of its high sensitivity, and is useful for the investigation of Mycobacterium tuberculosis (Mtb) and related diseases. It has been used to investigate TBM diagnosis; however, the processes involved in the MS-based metabolomics approach are complex and flexible, and often consist of several steps, and small changes in the methods used can have a huge impact on the final results. Here, the process of MS-based metabolomics is summarized and its applications in Mtb and Mtb-related diseases discussed. Moreover, the current status of TBM metabolomics is described.

Non-culture based assays for the detection of fungal pathogens

Traditional, culture based methods for the diagnosis of fungal infections are still considered as gold standard, but they are time consuming and low sensitive. Therefore, in order to overcome the limitations, many researchers have focused on the development of new immunological and molecular based rapid assays that could enable early diagnosis of infection and accurate identification of fungal pathogens causing superficial and invasive infection. In this brief review, we highlighted the advantages and disadvantages of conventional diagnostic methods and possibility of non-culture based assays in diagnosis of superficial fungal infections and presented the overview on currently available immunochromatographic assays as well as availability of biomarkers detection by immunodiagnostic procedures in prompt and accurate diagnosis of invasive fungal infections. In addition, we presented diagnostic efficiency of currently available molecular panels and researches in this area.

Practice Guidelines for Clinical Microbiology Laboratories: Mycobacteria

Mycobacteria are the causative organisms for diseases such as tuberculosis (TB), leprosy, Buruli ulcer, and pulmonary nontuberculous mycobacterial disease, to name the most important ones. In 2015, globally, almost 10 million people developed TB, and almost half a million patients suffered from its multidrug-resistant form. In 2016, a total of 9,287 new TB cases were reported in the United States. In 2015, there were 174,608 new case of leprosy worldwide. India, Brazil, and Indonesia reported the most leprosy cases. In 2015, the World Health Organization reported 2,037 new cases of Buruli ulcer, with most cases being reported in Africa. Pulmonary nontuberculous mycobacterial disease is an emerging public health challenge. The U.S. National Institutes of Health reported an increase from 20 to 47 cases/100,000 persons (or 8.2% per year) of pulmonary nontuberculous mycobacterial disease among adults aged 65 years or older throughout the United States, with 181,037 national annual cases estimated in 2014. This review describes contemporary methods for the laboratory diagnosis of mycobacterial diseases. Furthermore, the review considers the ever-changing health care delivery system and stresses the laboratory's need to adjust and embrace molecular technologies to provide shorter turnaround times and a higher quality of care for the patients who we serve.

Economic analysis of rapid multiplex polymerase chain reaction testing for meningitis/encephalitis in pediatric patients

AIM

We assessed the possible economic impact of a rapid test in pediatric patients with suspected community-acquired meningitis/encephalitis.

MATERIALS & METHODS

Modeling simulated diagnosis, clinical decisions, resource use/costs of standard of care (SOC) and two cerebrospinal fluid testing strategies using FilmArray^® (FA), a US FDA-cleared system that provides results in approximately 1 h.

RESULTS

Pathogens detected by FA caused approximately 75% of cases, 97% of which would be accurately diagnosed with FA.  Mean cost/case ranged from $17,599 to $22,025.  Syndromic testing is less expensive than SOC. Testing all suspected cases yielded greater savings ($3481/case) than testing only those with abnormal cerebrospinal fluid ($2157/case).

CONCLUSION

Greater economic benefits are achievable with syndromic testing of all cases, rather than SOC or targeted syndromic testing.

Diagnostic accuracy of Xpert MTB/RIF Ultra for tuberculous meningitis in HIV-infected adults: a prospective cohort study

BACKGROUND

WHO recommends Xpert MTB/RIF as initial diagnostic testing for tuberculous meningitis. However, diagnosis remains difficult, with Xpert sensitivity of about 50-70% and culture sensitivity of about 60%. We evaluated the diagnostic performance of the new Xpert MTB/RIF Ultra (Xpert Ultra) for tuberculous meningitis.

METHODS

We prospectively obtained diagnostic cerebrospinal fluid (CSF) specimens during screening for a trial on the treatment of HIV-associated cryptococcal meningitis in Mbarara, Uganda. HIV-infected adults with suspected meningitis (eg, headache, nuchal rigidity, altered mental status) were screened consecutively at Mbarara Regional Referral Hospital. We centrifuged CSF, resuspended the pellet in 2 mL of CSF, and tested 0·5 mL with mycobacteria growth indicator tube culture, 1 mL with Xpert, and cryopreserved 0·5 mL, later tested with Xpert Ultra. We assessed diagnostic performance against uniform clinical case definition or a composite reference standard of any positive CSF tuberculous test.

FINDINGS

From Feb 27, 2015, to Nov 7, 2016, we prospectively evaluated 129 HIV-infected adults with suspected meningitis for tuberculosis. 23 participants were classified as probable or definite tuberculous meningitis by uniform case definition, excluding Xpert Ultra results. Xpert Ultra sensitivity was 70% (95% CI 47-87; 16 of 23 cases) for probable or definite tuberculous meningitis compared with 43% (23-66; 10/23) for Xpert and 43% (23-66; 10/23) for culture. With composite standard, we detected tuberculous meningitis in 22 (17%) of 129 participants. Xpert Ultra had 95% sensitivity (95% CI 77-99; 21 of 22 cases) for tuberculous meningitis, which was higher than either Xpert (45% [24-68]; 10/22; p=0·0010) or culture (45% [24-68]; 10/22; p=0·0034). Of 21 participants positive by Xpert Ultra, 13 were positive by culture, Xpert, or both, and eight were only positive by Xpert Ultra. Of those eight, three were categorised as probable tuberculous meningitis, three as possible tuberculous meningitis, and two as not tuberculous meningitis. Testing 6 mL or more of CSF was associated with more frequent detection of tuberculosis than with less than 6 mL (26% vs 7%; p=0·014).

INTERPRETATION

Xpert Ultra detected significantly more tuberculous meningitis than did either Xpert or culture. WHO now recommends the use of Xpert Ultra as the initial diagnostic test for suspected tuberculous meningitis.

FUNDING

National Institute of Neurologic Diseases and Stroke, Fogarty International Center, National Institute of Allergy and Infectious Disease, UK Medical Research Council/DfID/Wellcome Trust Global Health Trials, Doris Duke Charitable Foundation.

Diagnostic usefulness of Xpert MTB/RIF assay for detection of tuberculous meningitis using cerebrospinal fluid

OBJECTIVE

Tuberculous meningitis (TBM) is the most severe form of extra-pulmonary tuberculosis (TB) due to association of diseases with high rates of mortality and morbidity. Diagnosis continues to be a clinical challenge as microbiological confirmation is rare and time consuming resulting in delayed treatment. Xpert MTB/RIF assay is a rapid and simple test, which has been endorsed by World Health Organization as an initial diagnostic test for the diagnosis of TBM. However, evidence still lacks for its performance on cerebrospinal fluid (CSF) for the diagnosis of TBM especially from India.

METHODS

A total of 267 CSF samples from patients with high clinico-radiological suspicion of TBM were included in this study. Ziehl-Neelsen (ZN) staining, BACTEC Mycobacterial Growth Indicator Tube (MGIT-960) culture system, and Xpert MTB/RIF assay (using cartridge version G4) were tested on all samples.

RESULTS

Of total 267 samples, all were negative for smear AFB and 52 (19.5%) were culture positive by MGIT-960 culture system. However, out of 52 (19.5%) cultures detected positive by MGIT-960, 5 (9.6%) were detected as resistant to rifampicin. Xpert MTB/RIF assay was positive in 38 (14.2%) samples and negative in 223 (83.5%) samples. Cartridge error was detected in 6 (2.2%) samples, which could not be repeated due to insufficient sample volume. The sensitivity and specificity of Xpert MTB/RIF assay in comparison to MGIT-960 was 55.1% (95%, CI: 40.2-69.3) and 94.8% (95%, CI: 90.9-97.4) respectively. Overall, Xpert MTB/RIF assay detected 38 (14.2%) as positive for MTB of which 4 (10.5%), 31 (81.6%) and 3 (7.9%) were found to be rifampicin resistant, sensitive and indeterminate respectively.

CONCLUSION

Xpert MTB/RIF assay showed lower sensitivity as compared to MGIT 960 culture for the diagnosis of TBM from CSF samples.

Comparative Diagnostic Utility of IS6110 PCR Assay in CSF and Peripheral Blood Samples of Tuberculous Meningitis Patients: A Pilot Study from Central India

INTRODUCTION

Tuberculous Meningitis (TBM) is the most severe form of Central Nervous System Tuberculosis (CNS-TB) and constitutes about 6% of all Extrapulmonary TB (EPTB) cases. Most guidelines for the diagnosis and management of TBM agree on the use of simple Cerebrospinal Fluid (CSF) analysis using molecular tools like Polymerase Chain Reaction (PCR). However, the sensitivity of PCR varies while using a CSF sample. In the present study, we have compared the diagnostic utility of PCR assay in both peripheral blood and CSF sample collected from TBM cases.

AIM

To evaluate the application of the peripheral blood PCR assay as an alternate tool for TBM diagnosis compared to conventional CSF-PCR based system.

MATERIALS AND METHODS

A total of 50 TBM patients were prospectively recruited from in patient department wards of Central India Institute of Medical Sciences (CIIMS) between January 2014 - Feburary 2015. Mycobacterium tuberculosis (MTB) specific IS6110 PCR and BactT liquid culture were performed in 20 of recruited cases classified as Stage 1, 2 and 3 based on British Medical Research Council (BMRC) contemporary clinical criteria for the severity of TBM. Clinical characteristics were summarised in terms of percentages for categorical variables, i.e., age groups, gender, signs and symptoms. All statistical analysis was carried out using MedCalc software version 11.6.

RESULTS

Overall IS6110 PCR positivity in CSF was around 80% (16/20), which was higher than culture (29.3%) and peripheral blood (39%). Out of 8 positive cases, stage wise positivity of peripheral blood PCR assay in three TBM stages was 0% (stage1) 50% (stage 2) and 67% (Stage 3) respectively. Positivity of peripheral blood PCR was significantly more (86%) in patients with CSF culture/ IS6110 PCR positive for MTB infection with sensitivity and specificity of 50 and 100% respectively. Increased positivity rates of peripheral blood PCR was observed with decreased CSF/Blood sugar ratio in stage 3 cases, suggesting enhanced probability of mycobacterial blood dissemination in cases of TBM severity.

CONCLUSION

Our results suggest that although the molecular diagnosis of TBM infection in CSF remains the method of choice, peripheral blood based PCR can be used as a good alternative to CSF in case of TBM severity where the repeated CSF collection may be needed. However, study demands further validation in large cohorts to justify the present hypothesis.

Is it possible to differentiate tuberculous and cryptococcal meningitis in HIV-infected patients using only clinical and basic cerebrospinal fluid characteristics?

BACKGROUND

Tuberculous and cryptococcal meningitis (TBM and CM) are the most common causes of opportunistic meningitis in HIVinfected patients from resource-limited settings, and the differential diagnosis is challenging.

OBJECTIVE

To compare clinical and basic cerebrospinal fluid (CSF) characteristics between TBM and CM in HIV-infected patients.

METHODS

A retrospective analysis was conducted of clinical, radiological and laboratory records of 108 and 98 HIV-infected patients with culture-proven diagnosis of TBM and CM, respectively. The patients were admitted at a tertiary centre in São Paulo, Brazil. A logistic regression model was used to distinguish TBM from CM and derive a diagnostic index based on the adjusted odds ratio (OR) to differentiate these two diseases.

RESULTS

In multivariate analysis, TBM was independently associated with: CSF with neutrophil predominance (odds ratio (OR) 35.81, 95% confidence interval (CI) 3.80 - 341.30, p=0.002), CSF pleocytosis (OR 9.43, 95% CI 1.30 - 68.70, p=0.027), CSF protein >1.0 g/L (OR 5.13, 95% CI 1.38 - 19.04, p=0.032) and Glasgow Coma Scale <15 (OR 3.10, 95% CI 1.03 - 9.34, p=0.044). Nausea and vomiting (OR 0.27, 95% CI 0.08 - 0.90, p=0.033) were associated with CM. Algorithm-related area under the receiver operating characteristics curve was 0.815 (95% CI 0.758 - 0.873, p<0.0001), but an accurate cut-off was not derived.

CONCLUSION

Although some clinical and basic CSF characteristics appear useful in the differential diagnosis of TBM and CM in HIVinfected patients, an accurate algorithm was not identified. Optimised access to rapid, sensitive and specific laboratory tests is essential.

Mediators and Biomarkers of Inflammation in Meningitis: Cytokine and Peptidome Profiling of Cerebrospinal Fluid

Differential diagnosis of bacterial and viral meningitis is an urgent problem of the modern clinical medicine. Early and accurate detection of meningitis etiology largely determines the strategy of its treatment and significantly increases the likelihood of a favorable outcome for the patient. In the present work, we analyzed the peptidome and cytokine profiles of cerebrospinal fluid (CSF) of 17 patients with meningitis of bacterial and viral etiology and of 20 neurologically healthy controls. In addition to the identified peptides (potential biomarkers), we found significant differences in the cytokine status of the CSF of the patients. We found that cut-off of 100 pg/ml of IL-1β, TNF, and GM-CSF levels discriminates bacterial and viral meningitis with 100% specificity and selectivity. We demonstrated for the first time the reduction in the level of two cytokines, IL-13 and GM-CSF, in the CSF of patients with viral meningitis in comparison with the controls. The decrease in GM-CSF level in the CSF of patients with viral meningitis can be explained by a disproportionate increase in the levels of cytokines IL-10, IFN-γ, and IL-4, which inhibit the GM-CSF expression, whereas IL-1, IL-6, and TNF activate it. These observations suggest an additional approach for differential diagnosis of bacterial and viral meningitis based on the normalized ratio IL-10/IL-1β and IL-10/TNF > 1, as well as on the ratio IFN-γ/IL-1β and IFN-γ/TNF < 0.1. Our findings extend the panel of promising clinical and diagnostic biomarkers of viral and bacterial meningitis and reveal opposite changes in the cytokine expression in meningitis due to compensatory action of pro- and antiinflammatory factors.

Cerebrospinal fluid metabolomic profiling in tuberculous and viral meningitis: Screening potential markers for differential diagnosis

BACKGROUND

Tuberculous meningitis (TBM) is the most severe and frequent form of central nervous system tuberculosis. The current lack of efficient diagnostic tests makes it difficult to differentiate TBM from other common types of meningitis, especially viral meningitis (VM). Metabolomics is an important tool to identify disease-specific biomarkers. However, little metabolomic information is available on adult TBM.

METHODS

We used ¹H nuclear magnetic resonance-based metabolomics to investigate the metabolic features of the CSF from 18 TBM and 20 VM patients. Principal component analysis and orthogonal signal correction-partial least squares-discriminant analysis (OSC-PLS-DA) were applied to analyze profiling data. Metabolites were identified using the Human Metabolome Database and pathway analysis was performed with MetaboAnalyst 3.0.

RESULTS

The OSC-PLS-DA model could distinguish TBM from VM with high reliability. A total of 25 key metabolites that contributed to their discrimination were identified, including some, such as betaine and cyclohexane, rarely reported before in TBM. Pathway analysis indicated that amino acid and energy metabolism was significantly different in the CSF of TBM compared with VM.

CONCLUSIONS

Twenty-five key metabolites identified in our study may be potential biomarkers for TBM differential diagnosis and are worthy of further investigation.

Serum uric acid levels in patients with infections of central nervous system

The lower levels of serum uric acid (UA) correlated with meningitis have been reported. However, comparison of UA levels among different kinds of infections of central nervous system (CNS) and changes of UA levels before and after treatment are unknown. Our study aimed to investigate the antioxidant status of serum UA in five common types of CNS infections. We retrospectively evaluated serum UA levels of 399 patients with different types of CNS infections including viral meningitis or meningoencephalitis (VM), brain cysticercosis (BC), tuberculous meningitis or meningoencephalitis (TM), cryptococcus meningitis or meningoencephalitis (CM) and bacterial meningitis or meningoencephalitis (BM), and 119 healthy controls. The changes of serum UA were examined and analyzed. The serum levels of UA in patients with CNS infections were significantly lower than those in normal subjects and among in TM, CM and BM groups were apparently lower when compared with VM and BC groups; otherwise, after effective therapy, serum UA levels were obviously higher than before. Our findings showed that patients with CNS infections had lower serum UA levels, which was independent of the classification and the serum UA levels increased obviously after valid treatment, the variation of UA levels might be considered as an indicator of clinical curative effect in patients with CNS infections.

Improved diagnostic sensitivity for tuberculous meningitis with Xpert(®) MTB/RIF of centrifuged CSF

BACKGROUND

TB meningitis (TBM) diagnosis is difficult and novel diagnostic methods are needed. The World Health Organization recommends Xpert(®) MTB/RIF as the initial TBM diagnostic test based on two studies reporting suboptimal sensitivity (~50-60%).

OBJECTIVE

To study the effect of cerebrospinal fluid (CSF) centrifugation on Xpert performance for TBM detection.

DESIGN

A total of 107 predominantly human immunodeficiency virus (HIV) infected adults with presumed meningitis were screened prospectively in Kampala, Uganda. CSF was tested using 1) microscopy for acid-fast bacilli; 2) MGIT™ culture; 3) Xpert of 2 ml of unprocessed CSF; and 4) Xpert of centrifuged CSF. Diagnostic performance was measured against an a priori composite reference standard of any positive CSF tuberculosis test.

RESULTS

Of 107 participants, 18 (17%) had definite TBM. When CSF was centrifuged, Xpert had better sensitivity (13/18, 72%) than when using 2 ml of unprocessed CSF (5/18, 28%; P = 0.008). The median centrifuged CSF volume was 6 ml (IQR 4-10). Mycobacterial culture yielded 71% (12/17) sensitivity at a median delay of 27 days. Only 39% were positive by both culture and centrifuged Xpert, with additional cases detected by Xpert and culture.

CONCLUSIONS

CSF centrifugation optimizes the diagnostic performance of Xpert in the detection of TBM. A combination of culture and Xpert detected the largest number of cases.

State-of-the-Art Microbiologic Testing for Community-Acquired Meningitis and Encephalitis

Meningitis and encephalitis are potentially life-threatening diseases with a wide array of infectious, postinfectious, and noninfectious causes. Diagnostic testing is central to determining the underlying etiology, treatment, and prognosis, but many patients remain undiagnosed due to suboptimal testing and lack of tests for all pathogens. In this article, we summarize the epidemiology, barriers to diagnosis, and current best tests for meningitis and encephalitis in developed countries. We end with a brief discussion of new test methods, such as multiplex panel-based tests and metagenomic sequencing, which are likely to alter diagnostic strategies for these conditions in the near future.