Economic Burden of West Nile Virus Disease

Quebec, Canada, 2012-2013

Najwa Ouhoummane; Eric Tchouaket; Anne-Marie Lowe; Ann Fortin; Dahlia Kairy; Anne Vibien; Jessica Kovitz-Lensch; Terry-Nan Tannenbaum; François Milord


Emerging Infectious Diseases. 2019;25(10):1943-1950. 

In This Article

Materials and Methods

Study Population

WNV infection is a reportable disease in Quebec. Physicians and laboratories must report all WNV-positive cases to regional public health boards, conduct which epidemiologic investigations to document the infection; determine the likely place of acquisition; and collect sociodemographic and clinical information, such as date of illness onset and clinical syndrome (i.e., uncomplicated fever, meningitis, encephalitis, and acute flaccid paralysis). The data are entered into the integrated system for public health monitoring of West Nile virus, a provincial electronic surveillance system for WNV disease that includes information on humans, mosquitoes, and animals.[12] During 2012–2013, a total of 155 symptomatic WNV cases were reported in Quebec.

We asked regional public health boards to contact each of the case-patients to see whether they were willing to participate in a study. A research nurse obtained written consent from all eligible case-patients to participate in a telephone interview and to enable access to their medical charts. Consent was obtained from parents or family of patients who were <18 years of age and for patients who had died. More details on the methods are available in a previous article.[6] The study protocol was submitted to the public health research ethics board of the Institut National de Santé Publique du Quebec, which provided a favorable recommendation for the study.[13]

Case Definitions

A WNV-positive case includes a laboratory diagnosis of WNV infection by IgM capture enzyme immunoassays for either serum or cerebrospinal fluid samples. In Quebec, after a first IgM-positive case has been confirmed by using a plaque reduction neutralization test, all other IgM-positive cases in the same season are considered to be laboratory confirmed. Cases are further classified according to their clinical manifestations: West Nile fever (WNF, an acute systemic febrile illness), West Nile meningitis (WNM, with stiff neck and cerebrospinal fluid pleocytosis), West Nile encephalitis (WNE, with altered mental status), West Nile meningoencephalitis, and acute flaccid paralysis (AFP, polio-like myelitis, or Guillain-Barré syndrome).[14]

Data Collection

For all eligible patients, we administered a telephone questionnaire 24 months after sign or symptom onset to document medical service, productivity losses, and expenses up to 2 years after the acute phase of WNV disease. We developed the questionnaire on the basis of the study by Staples et al..[8] Participants were asked to document the following items related to their WNV disease after initial hospitalization or consultation: subsequent hospitalization, stay in a rehabilitation center, physiotherapy, occupational therapy, speech therapy, home care, primary care physician consultations, neurologist consultations, medications, medical equipment, recruitment for household chores, and all other personal expenses incurred by the WNV disease. We also considered time off from work for the patient and for family members (to care for the patient). For hospitalized patients, we obtained data for hospital stay, intensive care unit admission, and inpatient rehabilitation from medical records.

Costs Estimation. We based the estimation of costs on the principle of human capital and a societal perspective (relevant costs regardless of who paid).[15] For their initial care, eligible patients either were hospitalized (n = 71), were seen in an emergency department but not hospitalized (n = 10), or consulted with doctor in a clinic (n = 12). For the third group, we did not collect any costs associated with their initial care.

Hospitalization. We obtained costs for initial hospitalization (no subsequent hospitalization was reported) by using the All Patient Refined–Diagnosis-Related Groups (APR-DRG) and the relative use of resources. The APR-DRG provides average costs incurred for inpatient services. These costs include all inpatient allied healthcare, surgical and medical procedures, medication, and laboratory tests. Because permission to access individual costs data was not obtained, we created 19 groups of patients on the basis of 4 criteria: the principal diagnosis of each patient (by using the International Classification of Diseases, 10th Revision), patient's age (<60 vs. ≥60 years of age), admission to intensive care unit (yes or no), and diagnostic year (2012 or 2013). Nearly 60% of hospitalized participants had specific principal International Classification of Diseases, 10th Revision, diagnosis code of WNV (A923) (Table 1). For other participants with no specific principal diagnosis code of WNV, WNV infection had to be coded as secondary diagnosis in the APR-DRG database to ensure specificity. The mean and median costs in the APR-DRG for each group were attributed to each patient in the group.

Inpatient Rehabilitation. Cost for inpatient rehabilitation was based on the average daily cost of services in a rehabilitation center for physical disabilities in 2012–2013. This factor was multiplied by the number of days spent in a center, which was obtained from the medical record.

Emergency Department Consultations. For patients seen in an emergency department, the physician service claims database was used to estimate the cost of medical consultations in the emergency department (Canadian $109.90).[16] This rate includes only the physician remuneration. Costs associated with emergency department stays and laboratory examinations and accommodations were not included.

Medical and Paramedical Care up to 2 Years after Sign/Symptom Onset. During the telephone interview, patients were asked to provide information on types and numbers and duration of outpatient medical and paramedical services that they sought after the acute-care period. We obtained estimated costs for these services by multiplying type-specific cost estimates by the number of visits reported (Table 2).[16] The number of follow-up physician visits was missing for 2 participants; a minimum of 1 visit was used for those case-patients.

Medical Equipment. Patients were asked about the acquisition of specific equipment and associated costs. Costs were assigned a value of 0 if the equipment was provided by government or was borrowed.

Recruitment for Household Chores. We obtained information for patients who needed aids for household chores. We also asked them to provide associated costs.

Absence from Work. We obtained information about missed workdays by patients or family members to care for a patient. Patients or family members having a job at their time of their WNV infection were asked to provide the occupation, the number of days they worked per week, and the number of days they missed work (including hospital stay). Income data for each patient or family member were obtained from the wage guide by occupation in Quebec according to their occupation. Productivity losses were estimated by multiplying the time taken off work by a weekly wage.

Occupation data were missing for 2 patients and 2 family members. For these 4 persons, we used the minimum wage. One patient reported stopping work because of his WNV infection. For this patient, we estimated the associated cost as the number of potential years of lost employment (65 minus age at infection). All persons (n = 11) who died during their initial hospitalization were ≥65 years of age. Therefore, productivity losses caused by death were not taken into account.

Other Personal Expenses. Patients were asked about other costs that they had to assume. For ambulance transportation, the basic cost of Canadian $125 was used.

Data Analysis

For data analysis, we combined West Nile meningoencephalitis cases (n = 18) and AFP cases (n = 2) with WNE cases (n = 28) because of similar clinical manifestations; 1 case with missing information about clinical syndrome was excluded. All analyses were performed according to 3 clinical categories (WNF, WNM, and WNE). We compared proportions by using the χ 2 test or Fisher exact test when appropriate. We compared distributions of age and hospital stay by using nonparametric tests (Wilcoxon rank-sum or Kruskal-Wallis tests).

Because cost distributions were not normal, we calculated mean and median values with the interquartile range (IQR). In this study, participants and nonparticipants were comparable with regard to demographic and illness severity (see Results). Thus, we assumed that participants were representative of the total number of WNV cases during 2012 and 2013, and we extrapolated estimated costs to all reported WNV cases according to clinical syndrome, cost category, and year. For each category, we estimated total number of cases (except for hospitalization, for which the exact number of cases was known) and total cost. For example, the total number of WNE case-patients admitted to inpatient rehabilitation (Nt) = total number of WNE case-patients × proportion of WNE case-patients admitted to inpatient rehabilitation. The total cost for this category = Nt × Cp, in which Cp is the inpatient rehabilitation median costs per WNE case-patient.

We performed analyses by using SAS version 9.1 (SAS Institute Inc., A 2-sided p<0.05 was considered statistically significant.