63% of the New York City patients (22 of 35 patients who participated in a follow-up interview) and 37.5% of the Tennessee patients (nine of 24) suffered persistent cognitive, physical, or functional impairment 12 months after the onset of severe WNV infection (Box 5.2).

BOX 5.2

Persistent Signs and Symptoms of WNV Illness 1 year After Onset

New York cohort (p ≤ 0.002 relative to baseline function):

  • Muscle weakness

  • Difficulty in walking

  • Fatigue

  • Loss of concentration

  • Lightheadedness

  • Memory loss

  • Need for assistance with meal preparation, light housekeeping, and shopping

Tennessee cohort (five most commonly reported symptoms):

  • Fatigue

  • Muscle weakness

  • Difficulty in walking

  • Joint weakness

  • Headaches

Klee and colleagues followed the New York cohort for 18 months. At that time, 30% of the patients continued to report persistent memory loss, confusion, depression, irritability, and the need for assistance with activities of daily living (mostly those requiring increased strength). Many patients continued to report difficulty in walking, muscle weakness, fatigue, and insomnia; more than 40% reported some combination of these symptoms.

The most important risk factor for long-term morbidity in both cohorts was advanced age, defined as over 50 years by Gottfried et al and at least 65 years by Klee et al. Neither the clinical manifestation of acute WN illness nor the prior presence of underlying disease was predictive of physical or cognitive recovery, Klee et al. found, even after adjusting for age. In the Gottfried et al. study, two of the five patients whose acute illness lacked neurologic involvement reported a full recovery during the 1-year followup interview; the degree of recovery of the other three patients, who moved to nursing facilities after their WNV infection, was not ascertained.

Unlike the retrospective case-series studies based on self-reported symptoms, a prospective, clinical case series of long-term morbidity associated with WNND was conducted with 39 suspect cases of acute WNV infection in Louisiana (Sejvar et al. 2003). The patients all resided in the same parish and presented from August 1 to September 2, 2002.

Hospitalized for their acute conditions, the 39 patients were examined by a neurologist and underwent neuroimaging and electrophysiologic and serologic tests. A second neurologist verified the findings in seven patients. Sixteen subjects tested positive for WNV: five had a diagnosis of WNM, eight WNE, AFP, and one classified AFP and WNE. One subject with WNE died after 2.5 months of hospitalization in a comatose state. Five patients—three with AFP and two with WNE—were discharged to long-term rehabilitation facilities. The other 10 subjects who tested positive went home on discharge.

Eight months later, a neurologist re-examined the 15 surviving patients with WNND, who also answered a standardized questionnaire about their symptoms and functional status. The most commonly reported adverse health outcomes were fatigue, tremor, and mild parkinsonism. Eleven subjects were home and functioning independently; three were home but dependent, and

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