An entomologic index based on density estimates of
Lyme disease spirochete-infected nymphal deer ticks (lxodes scapularis) was developed to assess human risk of
Lyme disease. The authors used a standardized protocol to determine tick density and infection in numerous forested sites in six Rhode Island towns. An entomologic risk index calculated for each town was compared with the number of human
Lyme disease cases reported to the Rhode Island State Health Department for the same year. A strong positive relation between entomologic risk index and the
Lyme disease case rate for each town suggested that the entomologic index was predictive of
Lyme disease risk.