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Abstract
LCMV, one of several human pathogenic arenaviruses, causes disease ranging from flu-like illness to meningitis. Recently, two studies (Childs, Glass, Ksiazek, Rossi, Barrera, & Leduc, 1991; Stephensen et al., 1992) reported that urban populations in the U.S., both Baltimore, MD and Birmingham, AL, have a 5% seroprevalence against LCMV. The genome of LCMV has been cloned molecularly and its nucleotide sequence determined by several investigators. This information was used to develop a diagnostic PCR assay for LCMV to determine the incidence of infection associated with CNS disease during a 1-year surveillance period in two Birmingham hospitals. An RT-PCR assay was developed by amplifying the S-RNA of LCMV. The amplified target was detected by staining after agarose gel electrophoresis. These PCR products were characterized further by either nested PCR or Southern blot analysis. This assay can detect LCMV-specific genomic RNA added to CSF specimens. RNA of LCMV was extracted from 10-100$\mu$l of CSF using guanidinium thiocyanate disruption and silica gel extraction. Under the optimal conditions described, this assay detected 5-50 copies of the target RNA.
To evaluate and measure the incidence of LCMV infection in a high LCMV seroprevalence area, CSF and serum samples were collected from patients with $>$10 inflammatory cells present in the CSF. None of the 405 patients at University Hospital nor the 408 patients at Children's Hospital had LCMV infection in CSF, based on PCR assay. These results were supported by an LCMV-specific IgM ELISA assay.
Although there was no acute LCMV infection, 4.0% (11/272) of sera from patients in University Hospital had LCMV-specific IgG. Seropositivity was higher in older subjects and those of lower socioeconomic status. These findings were confirmed in a follow-up sero-survey, in which an age-stratified sample was collected from the same hospitals. The overall seroprevalence in these sera was 3.5% (56/1600). Although seroprevalence was 5.4% (54/1000) among adults over 30 years of age, it was only 0.3% (2/600) in the younger age groups. Multiple logistic regression was used to identify risk factors for LCMV seropositivity. Among several variables tested, age ($p<0.0001$) and socioeconomic status ($p<0.03$) were statistically significant, confirming the results from the initial study.
