developed. The relative role of immunosuppression caused by the lymphoma itself compared with the immunosuppression due to treatment of the lymphoma is unclear. At the time of the WNV infection, the patient’s serum IgG levels were moder- ately suppressed. This was most likely the result of lymphoma, because a reduction in immunoglobulins, secondary to impaired B-cell function from rituximab, usually occurs after 3 months of therapy (11). In a previous randomized study, eld- erly patients receiving CHOP chemotherapy and rituximab had increased their overall survival and had not experienced an increase in toxic clinical effects compared with effects from CHOP treatment alone (12). However, rituximab used as a sin- gle agent has been reported to lead to excessive bacterial and viral infections, including respiratory tract infections and her- pes (13). Rituximab is also implicated as a risk factor for unusual viral infections when used as an immunotherapy agent in the peritransplant period of autologous stem cell transplant in non-Hodgkin lymphoma patients (14). Another consider- ation is the fact that the patient was neutropenic. The relation- ship between neutrophil function and the severity of WNV infection is unknown. The virus may be cleared by neutro- phils, and the severity of the viral infection may have been due to the fact that the patient was neutropenic at the time of the acute infection. What lends credence to this hypothesis is the observation that the highest viral titer as determined by PCR coincided with the recovery of the WBC count. Following the resolution of the myelosuppression, the RNA copy number of the WNV in blood samples declined rapidly (from 1.1 x 106 to 5.4 x 104 copies/mL). In summary, this report is the first of WN encephalopathy in an immunocompromised patient undergoing treatment for lymphoma. The patient’s serologic tests remained negative, and the diagnosis was made by RT-PCR from both CSF and peripheral blood, and by in vitro cultivation of the virus from blood. WNV infection should therefore be considered in the differential diagnosis of patients with lymphoma who exhibit encephalopathy, even if serologic tests are negative for WNV. Extra care should be taken to prevent patients with lymphoma, especially those undergoing treatment, from being exposed to WNV. Acknowledgments The authors thank Blair Rosen for performing the Taqman RT- PCR, Rocco Ferrera for his technical support, the Diagnostic Immu- nology Laboratory at the Wadsworth Center for conducting serologic testing, R. Lanciotti for performing all arbovirus serologic tests, and the Molecular Genetics Core at the Wadsworth Center for providing the oligonucleotides and for automated sequencing. This work was supported in part by the Epidemiology and Labo- ratory Capacity for Infectious Diseases cooperative agreement (U50/ CCU212415-04) and the Emerging Infections Program cooperative agreement (U50/CCU213698-03) with the Centers for Disease Con- trol and Prevention. Its contents are solely the responsibility of the authors and do not necessarily represent the official views of CDC. RESEARCH Dr. Huang is director of the Encephalitis PCR Laboratory, Wad- sworth Center, New York State Department of Health. Her scientific interests include molecular characterization of several arboviruses of public health importance. References 1. Calisher CH, Karabatsos N, Dalrymple JM, Shope RE, Porterfield JS, Westaway EG, et al. Antigenic relationships between flaviviruses as determined by cross-neutralization tests with polyclonal antisera. J Gen Virol 1989;70:37–43. 2. Smithburn KC, Hughes TP, Burke AW, Paul JH. A neurotropic virus iso- lated from the blood of a native of Uganda. 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Address for correspondence: Cinnia Huang, Wadsworth Center, New York State Department of Health, Box 509, Albany, NY 12201-0509, USA; fax: 518- 869-6487; e-mail: Cinnia.huang@wadsworth.org Use of trade names is for identification only and does not imply endorse- ment by the Public Health Service or by the U.S. Department of Health and Human Services. Emerging Infectious Diseases • Vol. 8, No. 12, December 2002 1371