Family now out of the country. Reported to our physician that child is in hospital there with possible encephalitis 8/23/05 and is in coma. Follow-up report states: The case paitent is a 9 year old boy with no significant past medical history, who developed encephalitis after receiving the yellow fever vaccine on 8/9/05 in another state. He received YF vaccinatin (Aventis Lot#EU 347 AA) prior to departing for out of the country on 8/13, where his immediate family was moving to work. He arrived on 8/14. He was in good health until 8/16 when he developed a severe headache. He was evaluated in an emergency room, where a head CT was normal, and he was treated with acetaminophen and discharged. The following day, he continued to have headache and developed fever to 39 degrees C and vomiting. He worsened and was reevaluated at another hospital on 8/18, where he was diagnosed with pharyngitis and given benzathine penicillin G IM. Over the next two days, he became somnolent, and was admitted to a third hospital on 8/20 for further evaluation. On admission, he had miotic, minimmally reactive pupils, nystagmus and ataxia, but had no nuchal rigidity, and good strength throughtout. Fundoscopic exam was normal. His CSF protein was 66 and glucose 83; it had 230 wbc, with 35% PMNs, 40% lymphocytes, and 25% mononuclear cells. CBC showed WBC 9.5K (75% segs,20% lymps, 5% monons, 2% eos), H/H 12.6/38.6, Plts 348K. An MRI of the brain revealed no abnormalities. He was empirically started on acylovir 30mg/kg/d. By 8/25, he was alert, but complained of myalgias, and low back pain in particular. He was discharged in 8/27. On 8/30 he was seen at an outpatient clinic with symptoms of fatigue and irritability. His exam revealed horizontal nystagmus and lumbar tenderness. The remainder of his exam was normal. Blood was drawn for testing of convalescent serums; but the mother refused a repeat lumbar puncture. His symptoms completely resolved by 9/9. The working diagnois was encephalitiis/cerebellitis seconday to West Nile virus, vs YF vaccine adverse event (considered less likely by his physicians and the local MH). The boy had no prior history of arboviral infection, including dengue, had no allergies, and was taking no medications at the time of his illness onset. A native of a foreign and had been living out of the country for the past three years. From 7/11-7/21 he visited a foreign country and then from 7/22-8-13, visited his family in the US. While in the US, he traveled by car with his parents and grandmother throught many states, ultimately returning to his grandmother's house. He spent most of the time on his trip doing outdoor activites, and he and his grandmother reportedly had many mosquito bites after walking along the river on approximately 8/8. His grandmother also had an illness consisting of headache and severe nausea from 8/26-8/29, which resolved on its own. She was evaluated at a clinic where peripheral blood serology for WNV was performed on 8/29 and 9/9; in both instances the WNV IgM and IgG were negative. The results of serolgoy for SLE performed on 10/14 are pending. The boy's mother called the ID physician after the boy was admitted; he informed her that WNV was a possibility, BMH was alerted by the boy's physicians. Serum and CSF collected on 8/21 and 8/20, respectively, were sent on 8/23 to the arboviral reference lab at IEC. The serum and CSF tested negative by HI for DEN 1-4 YF, Ileus fever, SLE and Rocio encephalitis. Serum and CSF were also negative by IgM ELISA for DEN 1-4, YF, SLE, and WNV. In addition there was reportedly a positive HSV IgM titer in CSF; it is unknown whether HSV PCR was done. The CSF had been frozen and was deemed an "inadequate" specimen. A second and third serum collected 8/25 and 8/30 were pending on 8/30, the last day that the BMH communicated findings to CDC. Viral culture on C6/36 and Vero cells, and inoculation in suckling mice, were pending. RT-OCR (unclear for which viruses) was also pending.