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Journal of Clinical Microbiology, August 2007, p. 2516-2520, Vol. 45, No. 8
0095-1137/07/$08.00+0 doi:10.1128/JCM.00141-07
Copyright © 2007, American Society for Microbiology. All Rights Reserved.

Infectious Diseases Unit, Department of Medicine, Solna, Karolinska University Hospital, SE-171 76 Stockholm, Sweden,1 Department of Clinical Microbiology, Karolinska University Hospital, SE-171 76 Stockholm, Sweden,2 Department of Clinical Microbiology, Tumour and Cell Biology, Karolinska Institutet, SE-171 77 Stockholm, Sweden3
Received 19 January 2007/ Returned for modification 3 April 2007/ Accepted 4 June 2007
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The overall incidence of aseptic meningitis is estimated to be 20 cases/100,000/year. The incidence of meningitis is probably underestimated due to unawareness and to previous limitations of diagnostic methods. HSV was previously detected by isolation from the cerebrospinal fluid (CSF) of between 0.5 and 3% of patients with aseptic meningitis. With detection of the viral genome in CSF by PCR, additional cases were identified (1, 3, 9, 21a, 27, 30). Using nested PCR, 5 to 17% of patients tested positive for HSV-2 DNA (13, 18, 20, 23). Since PCR assays were introduced, they have undergone further development. Real-time PCR has proved to be an efficient and reliable means for the detection and quantification of viral genomes (19, 26).
Aseptic meningitis and meningoencephalitis may be caused by varicella-zoster virus (VZV) infection, frequently without the zoster rash. In studies using nested PCR, it is suggested that VZV is an important etiological agent in acute aseptic meningitis (AAM) (11, 17, 18).
An evaluation of the sensitivity of PCR in early diagnosis by using CSF from patients with primary and recurrent HSV-2 aseptic meningitis is hitherto lacking. In this study, we evaluated the real-time PCR method for the detection of HSV-2 and VZV DNA in CSF from clinically well-characterized patients with aseptic meningitis.
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Patients >15 years of age with clinical signs of meningitis and CSF pleocytosis (>5 x 106 mononuclear leukocytes/liter) and cultures negative for bacteria and fungi and belonging to one of two main groups, as described below, were included.
Patients with HSV-2 meningitis (HSM) or meningitis with strongly suspected HSV-2 infection etiology who met one or more of the study criteria (n = 65) comprised one group. This group was further subdivided into those with primary infection (i.e., infection appearing clinically for the first time) and those with recurrent infection. Inclusion criteria were as follows: (i) HSV-2 DNA in CSF, detected with nested PCR; (ii) present seroconversion against HSV-2; (iii) concurrent herpetic genital lesions and negative differential diagnosis; (iv) recurrent meningitis and earlier, verified HSV-2 meningitis; and (v) recurrent meningitis and a history of meningitis of unknown origin and HSV-2 antibodies in acute-phase serum and negative differential diagnosis.
Patients with AAM, i.e., those who were negative in diagnostic tests for enteroviruses, Borrelia burgdorferi, tick-borne encephalitis (TBE) and HSV-1 and who did not meet the above criteria for HSV-2 meningitis (n = 45) comprised the second group. Demographic and clinical data were collected from medical records.
Viral DNA preparation. CSF specimens were analyzed for HSV-1 and HSV-2 by nested PCR upon arrival at the laboratory. Viral DNA was prepared by freeze-boiling for 10 min prior to amplification by nested PCR. Thereafter, the CSF samples were stored at –70°C. For real-time PCR, viral DNA was extracted from 200 µl of CSF with a Biorobot M48 using a MagAttract virus M48 mini-kit and eluted in 100 µl of buffer.
Nested PCR. Routine diagnostics for HSV-1 and HSV-2 were performed with all material, using a previously described, qualitative, nested PCR assay (1a, 2).
Real-time PCR. The design of the real-time PCR assays was based on a previously published paper (26), with some modifications. Primers were selected from glycoprotein D for HSV-1, glycoprotein G for HSV-2, and open reading frame (ORF) 29 for VZV (29) (Table 1). The HSV primers were optimized to work in a duplex format where HSV-1 and HSV-2 present melting temperatures of approximately 81°C ± 0.5°C and 87°C ± 0.5°C, respectively. The assays were performed in a LightCycler 1.2 (Roche). Amplifications were carried out in a 20-µl volume containing 5 µl of sample, 10 µl of 2x Quantitect SYBR Green PCR master mix (QIAGEN), 1 µM of primer HSV 1:2 and HSV 1:3, and 0.5 µM of HSV 2:1 and HSV 2:4. Solutions of 1.0 µM primers were used in the VZV real-time PCR. Both HSV and VZV real-time PCR assays used the same amplification profile. The cycling conditions were 15 min at 95°C and 45 cycles at 95°C for 5 s, 60°C for 15 s, and 72°C for 20 s, followed by a melting curve analysis. In this study, however, the HSV-1 primers were omitted to eliminate any possible interaction of the HSV-1 primers with the quantification of HSV-2.
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TABLE 1. Real-time PCR primers
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TABLE 2. Detection limits of HSV-2 by real-time PCR compared to those of nested PCR
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Statistics.
Comparisons were made using the t test and the
2 test.
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TABLE 3. CSF findings in patients with primary and recurrent HSM and AAM of unknown origina
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Comparison of nested PCR and real-time PCR. The detection sensitivities of nested PCR and real-time PCR were compared by testing serial dilutions of an HSV-2 DNA standard as well as by serial dilutions of HSV-2 isolates in cerebrospinal fluid. Real-time PCR and nested PCR detected DNA standard and HSV-2 dilutions equally well in CSF down to 55 to 60 copies per reaction. Below this level, real-time PCR gave more positive reactions than nested PCR. When 2.5 to 12 copies/reaction were tested, 7/16 (44%) patients tested positive by real-time PCR compared to 1/12 (8%) patients by nested PCR (P < 0.05), combining the results of a standard and HSV-2 in CSF (Table 2).
Using real-time PCR, HSV-2 DNA was detected in 53 out of 110 (48%) patients compared with 47 out of 110 (42%) by nested PCR (Table 4). Only one patient in the AAM group was positive for HSV-2 DNA by real-time PCR but negative by nested PCR. HSV-2 DNA was found in CSF from 52 out of 65 (80%) patients with clinical HSV-2 meningitis compared to 47 out of 65 (72%) with nested PCR. The detection rate of HSV-2 by real-time PCR was increased in the group of patients with recurrent HSM, 70% compared to 52%, although the difference was not statistically significant. In the primary meningitis group, 87% of patients were positive by both methods.
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TABLE 4. Results of quantitative real-time PCR and qualitative nested PCR for detection of HSV-2 in CSF in two groups of patients with acute aseptic meningitis
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Among the 10 samples that were positive by real-time PCR only, five had <1,000 copies/ml, and five had between 1,000 and 10,000 copies/ml.
Viral load in primary versus recurrent HSV-2 meningitis and correlation with inflammatory changes. The number of viral copies found in patients with primary versus recurrent HSV-2 meningitis is shown in Fig. 1. The viral load reached significantly higher levels in primary meningitis than in recurrent meningitis (P < 0.05). Viral loads of >10,000 copies were found exclusively in patients with primary HSV-2 meningitis, while viral loads of <1,000 or between 1,000 and 10,000 copies were found in all patients with recurrent HSV-2 meningitis. Correlation was found between the viral load and the amount of leukocytes, monocytes, protein, and albumin in CSF.
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FIG. 1. Box and whisker plot showing viral loads (log copies/ml) in patients with primary (32 patients) and recurrent (19 patients) HSV-2 meningitis.
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Viral meningitis remains an important cause of morbidity and financial burden and merits efforts to improve diagnostic, treatment, and prevention options (15, 22). The etiological diagnosis of HSV-2 meningitis is of particular importance as this condition carries a considerable risk of future neurological morbidity. HSV-2 proved to be the major cause of benign recurrent lymphocytic meningitis (30). A retrospective study (3) showed that during the year following the acute phase of HSV-2 meningitis, more than 30% of 40 patients suffered from recurrent neurological symptoms (one or several episodes of recurrent meningitis or myelitis or distinct attacks of severe headache). With HSV-2 diagnosis, accurate information about diagnosis, prognosis, and treatment options, i.e., early episodic treatment or suppressive prophylaxis in cases with frequent recurrences, is possible.
Isolation of HSV from CSF has been reported in cases of primary meningitis caused by both types of virus, i.e., HSV-1 and HSV-2 (5, 21, 23, 27, 28). In recurrent meningitis, attempts to isolate HSV in the CSF have been unsuccessful (5). The implementation of PCR for the detection of viral DNA in spinal fluid has resulted in considerable improvement. HSV-2 DNA has been detected by PCR in several patients with primary as well as recurrent aseptic meningitis, both with and without mucocutaneous lesions (3, 9, 25 and 30). However, an evaluation of the diagnostic sensitivity has not been documented in larger sized series. In a number of cases where an HSV-2 etiology is suspected on clinical grounds, e.g., in patients with previous genital blisters or recurrent episodes with a confirmed HSV-2 etiology, nested PCR assays fail to detect HSV-2 DNA.
In our study, real-time PCR verified a larger number of cases of HSV-2 meningitis than the previously used nested PCR. In the absence of a gold standard, using the above-stated criteria for HSV-2 meningitis, the sensitivities of real-time PCR for the detection of HSV-2 DNA in CSF were 87% (33/38) and 70% (19/27) in primary and recurrent meningitis.
However, 4 out of 47 patients were found to be negative by real-time PCR but positive by nested PCR. The missing cases as well as the discrepancy between the nested PCR and the real-time PCR results may be explained by the fact that the DNA in the investigated samples may be around the level of detection and may be unevenly distributed, as shown by analyses of portions of CSF drawn on the same occasion (2). Consequently, discordant results were noticed mainly for samples with low copy numbers.
Real-time PCR makes it possible to evaluate quantitative data in relation to the clinical course and antiviral treatment. The clinical symptoms of recurrent HSM are generally milder and of shorter duration than those of primary meningitis (4, 5). Accordingly, the viral loads in primary meningitis were significantly larger, and the inflammatory changes in the CSF were more pronounced in primary meningitis than in recurrent episodes.
Patients with first-time meningitis came to the clinic, on average, 1 day later than the patients with recurrent meningitis. This could be due to unawareness and misinterpretation of the clinical symptoms. In previous investigations of series of CSF samples, the viral load has been shown to decrease over time (unpublished data). In the present study, viral loads in the group of patients with recurrent HSM were lower than those in the primary group, although their samples were taken earlier, suggesting even greater differences in viral loads in primary versus recurrent meningitis.
Hypoglycorrhachia has previously been reported in HSM (4, 7, 8, 14). In our study, slightly increased lactate levels and lowered CSF/serum glucose ratios were found with a small proportion of HSM patients, in agreement with previous reports. This should be kept in mind in the clinical interpretation of acute meningitis.
With regard to VZV, our findings underline the fact that VZV should be considered in the etiological diagnosis of aseptic meningitis among adults with or without vesicular rash (6, 10).
In conclusion, the sensitivity of real-time PCR for the diagnosis of HSV-2 meningitis was evaluated and found to be high, though somewhat lower in recurrent infection than primary infection. Real-time PCR for the detection of HSV-2 and VZV DNA in CSF is a quick and efficient tool for the etiological diagnosis of aseptic meningitis and should be used in the first-line routine diagnosis. With doctors' increased awareness of the diagnosis, a thorough history taking, and the consistent use of novel diagnostic methods, HSV-2 and VZV etiologies will be revealed in an even higher percentage of cases.
Published ahead of print on 13 June 2007. ![]()
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