P-04 Retrospective Study of the Introduction and Establishment of West Nile Virus in San Bernardino County, California in 2004-2006: Lessons Learned

Background: West Nile Virus was first reported in the US in 1999 by 2001 it had spread in parts of San Bernardino County California. This study will evaluate the 2004-2006 WNV outbreak in in San Bernardino county California in order to identify the best surveillance strategies and outline lessons learned from the outbreak. Objectives: To describe the introduction and distribution of West Nile Virus and West Nile Encephalitis in San Bernardino County and the county’s preparedness for the outbreak. To determine the association between WNV trends in animal, mosquitoes and birds and Human in order to identify the host that is most appropriate for early detection of WNV outbreak. Methods: This retrospective study was part of the routing surveillance activities of the Vector control unit of San Bernardino County Health department. Surveillance records were obtained from collection of data through the surveillance activities for WNV hosts, namely chickens, dead birds, and mosquito pools. Presence of WNV was documented by bleeding chicken and testing for WNV; recording reports of dead birds and collecting and testing for WNV; collection of mosquitoes (NJ Traps and Co2 traps), species identification and mosquitoes testing for WNV. Records of human cases from hospital admission and asymptomatic cases from blood tests were also collected. Data analysis: spatial maps for disease distribution was created using GIS Arc 9.2 maps and charts for trends and time lines of index case for each host were determined. Associations of disease in various hosts was done using Pearson and Spearman correlation. A 6 week time lag was introduced to verify the relationship through visual inspection. Results: West Nile virus was concentrated in the south west of San Bernardino County. The reports of dead birds was highly associated with human cases of WNV(r=0.85). Similarly, abundance of mosquito and temperature were also positively correlated with human cases. (r=0.7) and r=0.75 respectively). Conclusion: WNV was possibly introduced in San Bernardino through migrating birds. Dead bird provide six weeks early warning for infection by West Nile Virus to humans. The aggressive and effective surveillance and operation activities in the Vector control unit in SBC managed to put the disease under control. WNV is a self-limiting disease hence immunity might have contributed to the diminishing of the disease. Increasing dead birds particularly American crow coupled with positive mosquitoes and temperature changes in a warm season is an important early warning indicator for WNV outbreak.