a human case-patient. The sequence data from the virus directly detected in the CSF and from the WNV isolate from cell cultures are identical. Hindiyeh et al. (10) reported the iso- lation of WNV from the blood of viremic patients who were not immunocompromised and who seroconverted later. In con- trast, the patient in this case was elderly and was undergoing treatment for lymphoma. She was unable to mount an immune response as shown by the fact that the results of serologic tests on both CSF and serum specimens were negative. To our knowledge, all previous attempts to recover WNV from human patients associated with the North American out- break have been unsuccessful. The ability to recover an infec- tious isolate in this report may have been contingent on the fact that the patient was immunologically impaired. She had lymphoma and had been undergoing treatment with CHOP plus rituximab for 2 months at the time the WNV infection RESEARCH Figure 2. West Nile virus copy numbers in clinical samples and clinical. WBC, leukocytes. Detailed sample information is listed in Table 2; day 1 is date the patient was hospitalized, 9/18/2001. Sequence Analysis Since only a very small amount of CSF remained after the diagnostic work-up, we carefully designed a protocol to gener- ate PCR bands with sizes ranging from 500 to 1000 bp. This protocol allowed the complete genome sequence of the virus in the CSF to be determined by sequencing overlapping PCR bands (GenBank accession no. AF533540). We used a similar protocol to obtain the genome sequence of the isolate adapted from cell culture and found that the sequence data from the virus in the CSF and from the WNV isolate were identical. A 1648-bp fragment encoding the PreM, M, and part of the 5′-E gene was used for phylogenetic studies (Figure 3). The analy- sis showed that the sequence data from this case are similar to the sequence data obtained from human (7) (GenBank acces- sion no. AF202541), horse (8) GenBank accession no. AF260967), and bird (9) (GenBank accession no. AF196835) WNV isolates in New York in 1999. Discussion This case is important for several reasons. It represents the first instance in which WNV was recovered from a person in the United States. It is also the first time that the entire genomic sequence of WNV has been obtained from CSF from Figure 3. Phylogenetic relationships among West Nile virus strains. Sequence data from the present case are shown in italics. The tree is based on the 1,648-bp fragment encoding the preM, M, and part of the 5′-E gene. Numbers at the nodes are bootstrap confidence estimates based on 1,000 replicates. 1370 Emerging Infectious Diseases • Vol. 8, No. 12, December 2002