Assessment of Immunoglobulin M Enzyme-Linked Immunosorbent Assay Ratios to Identify West Nile Virus and St. Louis Encephalitis Virus Infections During Concurrent Outbreaks of West Nile Virus and St. Louis Encephalitis Virus Diseases, Arizona 2015.

West Nile virus (WNV) and St. Louis encephalitis virus (SLEV) are closely related mosquito-borne flaviviruses that cause clinical disease ranging from febrile illness to encephalitis. The standard for serological diagnosis is immunoglobulin M (IgM) testing followed by confirmatory plaque reduction neutralization test (PRNT) to differentiate the infecting virus. However, the PRNT is time-consuming and requires manipulation of live virus. During concurrent WNV and SLEV outbreaks in Arizona in 2015, we assessed use of a diagnostic algorithm to simplify testing. It incorporated WNV and SLEV ratios based on positive-to-negative (P/N) values derived from the IgM antibody-capture enzyme-linked immunosorbent assay. We compared each sample's ratio-based result with the confirmed WNV or SLEV sample result indicated by PRNT or PCR testing. We analyzed data from 70 patients with 77 serum and cerebrospinal fluid samples, including 53 patients with confirmed WNV infection and 17 patients with confirmed SLEV infection. Both WNV and SLEV ratios had specificity ≥95%, indicating a high likelihood that each ratio was correctly identifying the infecting virus. The SLEV ratio sensitivity of 30% was much lower than the WNV ratio sensitivity of 91%, likely because of higher cross-reactivity of SLEV antibodies and generation of lower P/N values. The standard for serological diagnosis of WNV and SLEV infections remains IgM testing followed by PRNT. However, these results suggest the ratios could potentially be used as part of a diagnostic algorithm in outbreaks to substantially reduce the need for PRNTs.

Cost Analysis of 3 Concurrent Public Health Response Events: Financial Impact of Measles Outbreak, Super Bowl Surveillance, and Ebola Surveillance in Maricopa County.

OBJECTIVE: To generate estimates of the direct costs of mounting simultaneous emergency preparedness and response activities to respond to 3 major public health events. DESIGN: A cost analysis was performed from the perspective of the public health department using real-time activity diaries and retrospective time and activity self-reporting, wage and fringe benefit data, and financial records to track costs. SETTING: Maricopa County Department of Public Health (MCDPH) in Arizona. The nation's third largest local public health jurisdiction, MCDPH is the only local health agency serving Maricopa's more than 4 000 000 residents. Responses analyzed included activities related to a measles outbreak with 2 confirmed cases, enhanced surveillance activities surrounding Super Bowl XLIX, and ongoing Ebola monitoring, all between January 22, 2015, and March 4, 2015. PARTICIPANTS: Time data were sought from all MCDPH staff who participated in activities related to any of the 3 relevant responses. In addition, time data were sought from partners at the state health department and a community hospital involved in response activities. Time estimates were received from 128 individuals (response rate 88%). MAIN OUTCOME MEASURE: Time and cost to MCDPH for each response and overall. RESULTS: Total MCDPH costs for measles-, Super Bowl-, and Ebola-related activities from January 22, 2015, through March 4, 2015, were $224 484 (>5800 hours). The majority was for personnel ($203 743) and the costliest response was measles ($122 626 in personnel costs). In addition, partners reported working more than 700 hours for these 3 responses during this period. CONCLUSIONS: Funding for public health departments remains limited, yet public health responses can be cost- and time-intensive. To effectively plan for future public health responses, it may be necessary to share experiences and financial lessons learned from similar public health responses. External partnerships represent a key contribution for responses such as those examined. It can be expensive for local public health departments to mount effective responses, especially when multiple responses occur simultaneously.