West Nile Virus & St. Louis Encephalitis End of Year Report, 2019 West Nile virus (WNV) arrived in Arizona in 2003 and is now endemic in Maricopa County. St. Louis encephalitis virus (SLE) is a rare mosquito-borne disease in Maricopa County. Maricopa County Department of Public Health Office of Epidemiology collaborates with the Maricopa County Department of Environmental Services Office of Vector Control to identify and monitor areas of WNV and SLE activity. This report describes trends in human infections during 2019. Maricopa County saw the most WNV cases this year since the initial outbreak year in 2004 (n=355). Some data has been suppressed to protect confidentiality. Year Total WNV 155 Non-neuroinvasive Neuroinvasive Hospitalized Deaths Gender M/F Median Age (Min, Max) 35 Fever 73 Encephalitis 41 Meningitis 111 Neuroinvasive 15 Non-neuroinvasive 17 90/65 64 (6, 92) 127 White, Non-Hispanic 11 Hispanic/Latino 14 Unknown <5 69 (48, 85) 5 White, Non-Hispanic Encephalitis 17 SLE 8 <5 6 Encephalitis Median Age† (Min, Max) 70 (48, 92) Gender M/F 10/7 <5 0 †The difference in the mean age of WNV survivors (61 yrs) vs deaths (71 yrs) was statistically significant (α=0.05). WNV Viremic donors who did not become symptomatic (n=16) are not included in year total 80 Race/Ethnicity 14 White, Non-Hispanic Race/Ethnicity Human Infections of WNV by Month Onset* WNV Deaths 2015–2019* 20 60 15 40 10 5 Year Average 5 20 0 Jan 3 * * Feb Mar Apr * * May Jun Jul Aug Sep Oct Nov 0 Dec Human Infections of SLE by Month Onset* * 2015 2016 2017 2 2018 2019 SLE Deaths 2015–2019* 2 5 Year Average 1 1 0 Jan Feb Mar Apr * * * * May Jun Jul Aug 0 Sep Oct Nov Dec * 2015 *Data are suppressed to prevent identification of cases due to small number (< 5) of cases in each figure 2016 2017 2018 2019 West Nile Virus & St. Louis Encephalitis End of Year Report, 2019 Human Infections of WNV1,3,* and WNV Positive Mosquito Pools by MMWR Week 70 60 20 50 15 40 10 30 5 Human 20 Mosquito 10 0 Number of Mosquito Pools2 Number of Human Cases1 25 Rates of Human Illness per 100,000 Population Maricopa County Overall Rate and Cities with Highest Rates WNV 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 MARICOPA COUNTY OVERALL MMWR Week3 3.5 GILBERT 4.7 GLENDALE Human Infections of SLE1,3,* and SLE Positive Mosquito Pools by MMWR Week SCOTTSDALE 25 15 10 5 0 MMWR Week3 1 A human case is an individual infected with WNV or SLE and with a clinically compatible illness 2 Mosquito pools are a collection of mosquitoes collected by MCDES from a county trap and tested positive for WNV and SLE 3 Human data are based on date of symptom onset, mosquito data are based on date of mosquito collection *Data are suppressed to prevent identification of cases due to small number (< 5) of cases in each figure 8.1 0 Number of Mosquito Pools2 20 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 5.2 2 4 6 8 10 SLE** MARICOPA COUNTY OVERALL 0.2 0 1 **Due to the low number of cases in 2019, rates of human SLE illness by cities is not shown.