EPIDEMIOLOGIC PARAMETERS OF WEST NILE VIRUS INFECTIONS IN HUMANS: A SCOPING REVIEW
To summarize the epidemiologic and clinical parameters related to West Nile virus (WNV) infections in North America. With the seasonal emergence of WNV that ranges from mild, febrile illness to severe neuroinvasive disease, accurate data on disease history are important for guiding patient care and healthcare decision-making.
We conducted a scoping review searching in MEDLINE, EMBASE, CINAHL and Scopus (January 1999 to December 2015) for primary human studies. Search terms related to WNV epidemiology and surveillance including prognosis, cause of death, comorbidity and functional status. We excluded case reports and non-English studies. Findings were summarized qualitatively by WNV syndrome: West Nile fever, meningitis, encephalitis, meningoencephalitis and acute flaccid paralysis.
We screened 2,336 articles and included 86 primary studies. Most studies (n=72) were from the United States, including Texas (n=11), Colorado (n=10), Louisiana (n=5) and Illinois (n=5). The remaining were from Canada (n=7) and Israel (n=7), which is the likely source of the New World WNV Lineage 1. The number of publications peaked in the years 2005 (n=12) and 2014 (n=7), corresponding to the timing of major outbreak years (2002, 2012). Mean patient ages were mainly >40 years or >50 years. Three studies (4%) focused on the pediatric population. Sample sizes ranged from under 25 patients (n=17) to over 400 patients (n=24). Five studies had long follow-up times (two to ten years) to examine mortality. Data were most limited for patients with acute flaccid paralysis and meningoencephalitis. Patients with encephalitis fared worse than patients with meningitis and West Nile fever in terms of proportion hospitalized, length of stay, proportion discharged home, proportion fully recovered and case-fatality. Age was consistently identified as a clinically and statistically significant risk factor for neuroinvasive disease and death. There was less agreement for other risk factors including sex, race, diabetes, hypertension and cancer.
Our review highlighted the heterogeneity in epidemiologic patterns across jurisdictions and outbreak seasons, even within North America. There was an overall lack of data specific to the WNV syndromes, despite having distinct clinical behaviors, indicating opportunities for future research areas.