HEALTH-RELATED QUALITY OF LIFE IN PERSONS WITH WEST NILE VIRUS INFECTION

Purpose:

   To describe the long-term impact of West Nile virus (WNv) infection on patient health-related quality of life (HRQOL).West Nile virus symptoms present predominately as mild febrile illness. However, <1% of infections become neuroinvasive, which is associated with debilitating physical and cognitive impairments.  

Method:

   Our study uses data from a Canadian longitudinal cohort study (Loeb 2008) where physical and mental functioning was assessed using the SF-36 in 156 persons with WNv infection over a follow-up of up to three years.

   We generated health utilities from SF-36 responses using the University of Sheffield SF-6D classification, where preference weights of the general population in the United Kingdom were derived from standard gamble. Utility scores range on a scale from 0 (equivalent to death) to 1 (equivalent to perfect health). We summarized utility scores into (i) episode scores (mean from one-year study visit and thereafter) and (ii) area under the curve (AUC), i.e. the time-weighted average HRQOL. Utilities scores are reported for the entire cohort and stratified by neuroinvasive/nonneuroinvase disease, comorbidity status, age and sex. We used bootstrapping techniques to determine 95% bootstrap percentile confidence intervals (CI). 

Result:

   Mean utility score improved from 0.59 (CI: 0.38, 0.93) at baseline to 0.77 (CI: 0.53, 1) at six months, before plateauing for the remaining two years. At six months, patients with nonneuroinvasive disease had higher mean scores than those with neuroinvasive disease (0.79 (CI: 0.53, 0.96) versus 0.73 (CI: 0.51, 1)). Patients without comorbidities had higher mean scores than those with one and those with more (0.82 (CI: 0.59, 1) vs 0.78 (CI: 0.54, 1) vs 0.67 (CI: 0.45, 0.96), respectively). Younger patients fared better than patients ≥65 years (0.77 (CI: 0.54, 1) versus 0.73 (CI: 0.51, 0.89)) whereas males fared better than females (0.80 (CI: 0.53, 1) versus 0.74 (CI: 0.54, 0.93). Over the long-term, patients had a mean episode score of 0.81 (CI: 0.77, 0.84) and mean AUC of 0.73 (CI: 0.68, 0.79). 

Conclusion:

    WNv infection is associated with low HRQOL during acute illness. While improving over time, HRQOL is reduced from baseline for at least six months post-index date, particularly for those with neuroinvasive disease. To our knowledge this is the first study reporting health utilities for WNv infection, providing fundamental evidence to inform cost-utility analyses.