West Nile virus serosurvey and assessment of personal prevention efforts in an area with intense epizootic activity: Connecticut, 2000

West Nile virus (WNV) can cause large outbreaks of febrile illness and severe neurologic disease. This study estimates the seroprevalence of WNV infection and assesses risk perception and practices regarding potential exposures to mosquitoes of persons in an area with intense epizootics in 1999 and 2000. A serosurvey of persons aged > or = 12 years was conducted in southwestern Connecticut during October 10-15, 2000, using household-based stratified cluster sampling. Participants completed a questionnaire regarding concern for and personal measures taken with respect to WNV and provided a blood sample for WNV testing. Seven hundred thirty persons from 645 households participated. No person tested positive for WNV (95% CI: 0-0.5%). Overall, 44% of persons used mosquito repellent, 56% practiced > or = two personal precautions to avoid mosquitoes, and 61% of households did > or = two mosquito-source reduction activities. In multivariate analyses, using mosquito repellent was associated with age < 50 years, using English as the primary language in the home, being worried about WNV, being a little worried about pesticides, and finding mosquitoes frequently in the home (P<0.05). Females (OR = 2.0; CI = 1.2-2.9) and persons very worried about WNV (OR = 3.8; CI = 2.2-6.5) were more likely to practice > or = two personal precautions. Taking > or = two mosquito source reductions was associated with persons with English as the primary language (OR = 2.0; CI = 1.1-3.5) and finding a dead bird on the property (OR = 1.8; CI = 1.1-2.8). An intense epizootic can occur in an area without having a high risk for infection to humans. A better understanding of why certain people do not take personal protective measures, especially among those aged > or = 50 years and those whose primary language is not English, might be needed if educational campaigns are to prevent future WNV outbreaks.

A phylogenetic approach to following West Nile virus in Connecticut

The 1999 outbreak of West Nile (WN) virus in the northeastern United States was the first known natural occurrence of this flavivirus in the Western Hemisphere. In 1999 and 2000, 82 independent Connecticut WN virus isolates were cultured from nine species of birds, five species of mosquitoes, and one striped skunk. Nucleotide sequences obtained from these isolates identified 30 genetic changes, compared with WN-NY99, in a 921-nt region of the viral genome beginning at nucleotide position 205 and ending at 1125. This region encodes portions of the nucleocapsid and envelope proteins and includes the entire coding regions for the premembrane and membrane proteins. Amino acid changes occurred at seven loci in six isolates relative to the WN-NY99 strain. Although 34 of the isolates showed sequences identical to the WN-NY99 isolate, we were able to show geographical-based clusters of mutations. In particular, 26 isolates were characterized by mutation of C to T at position 858. This group apparently originated in Stamford, CT and disseminated to sites located as far as 54 miles from Stamford. Sequences of WN virus isolated from both brain and heart tissues from the same avian host were identical in all 14 tested individual birds, suggesting that the mutations we have documented are real and not caused by culture, RNA extraction, or PCR procedures. We conclude that this portion of the viral genome will enable us to follow the geographical and temporal movement of variant WN virus strains as they adapt to North America.