A 49-year-old man (taxi driver) sought treatment during the winter of 2009. He had a 7-day history of fever, chills, headache, nausea, vomiting, neck rigidity, generalized weakness, and paresthesias in his fingers. He denied recent travel or exposure to sick contacts. Medical history included a corneal transplant the previous year. His temperature when admitted was 37.5°C. Physical examination identified nuchal rigidity but was otherwise unremarkable. CSF showed leukocytes 871 cells/μL; erythrocytes 2 cells/μL, with 93% lymphocytes and 7% monocytes; glucose 32 mg/dL (serum glucose 93 mg/dL); and protein 185 mg/dL. Results of a computerized axial tomography scan of the brain and chest radiograph were unremarkable. A complete blood count and results of serum chemical tests and liver function tests were unremarkable. Blood cultures yielded no growth. CSF cultures for bacterial, fungal, and mycobacterial organisms were negative. Results for syphilis rapid plasma reagin, cryptococcal antigen, and HIV testing were negative.

Because of the patient’s hypoglycorrachia, pronounced CSF leukocytosis, and negative CSF cultures, acute infection with LCMV was considered. Serum tested at a commercial laboratory was positive for LCMV (immunoglobulin [Ig] G titer >256 (reference <16) and IgM titer 80 (reference <20) by immunofluorescence assay. CSF collected on day 1 and serum collected on days 7 and 15 was tested for LCM antibodies by the Centers for Disease Control and Prevention’s Special Pathogens Branch using ELISA. CSF and serum were both IgM and IgG positive and a 4-fold rise in acute-phase and convalescent-phase serum titers indicated the patient had a recent infection with LCMV (Table). The patient improved with supportive care, recovered fully, and was discharged on day 12.

The incidence rate of LCMV infection in New York City is unknown. The disease is likely underdiagnosed because only a limited number of commercial laboratories offer LCMV testing. Diagnosed cases of LCMV are often identified because they are part of a larger outbreak. Since 1960, only 7 cases have been reported in the literature (8,9); all but 2 had had contact with rodents. Several large outbreaks have been reported, often associated with pet hamsters or laboratory mice or hamsters; 1 outbreak had >236 human cases (8). A total of 54 cases of congenital LCMV are cited in the literature, 34 since 1993 (5).

Our patient denied both hamster and mouse exposure. His corneal transplant had occurred >1 year before, and was unlikely to be the source of infection. A definitive diagnosis was difficult, but testing by Centers for Disease Control and Prevention confirmed the diagnosis.

New York City Health Department officials attempted an investigation of the patient’s home and surroundings to look for evidence of rodents or rodent excreta, but were unable to do so due to the patient’s noncompliance. Several clues have assisted clinicians in the identification of patients with acute LCMV infection: 1) aseptic meningitis or encephalitis during the fall–winter season, 2) a febrile illness followed by brief remission before onset of neurologic illness, and 3) CSF with a lymphocytosis and hypoglycorrachia. Patients with suspected LCMV should be asked about potential rodent exposure (1). Patients with a history of organ transplantation within the preceding 3 months should be fully evaluated to determine whether infected organs were the source of LCMV.

We recommend enzyme immunoassay-based testing of CSF and serum when LCMV is considered. Public health surveillance, rodent control, healthcare provider education, and improved laboratory testing can enhance recognition of illness.

Health departments should consider making LCMV a reportable condition, and, if aseptic meningitis is reportable, questions should be added to case investigation forms regarding rodent exposure. LCMV was made reportable in New York City in 2009. Only with a better understanding of the true incidence of LCMV will authorities be able to enact measures to better prevent and control this disease in the vulnerable sections of our society.