ESTIMATION OF THE INCIDENCE OF LYME-DISEASE

The incidence of Lyme disease in most endemic areas is unknown but wil l be an important factor in determining the cost-effectiveness of Lyme disease vaccines in those areas. The authors developed a deterministi c model with nine components to estimate the frequency of Ixodes scapu laris tick bites and the resulting incidence of Lyme disease in reside nts of endemic areas. For each component, best point estimates and pla usible ranges of values were based on the published literature, unpubl ished data, expert opinion, or a combination of the above. By using th e mean, crude, annual total of 3,827 Lyme disease cases reported from the endemic county of Westchester, New York, in 1991-1994, a mean of 1 78,889 I. scapularis bites (20.4 per 100 person-years) and a mean of 1 0,632 incident Lyme disease cases (1.2 per 100 person-years) were esti mated to have occurred per year. Results of a sensitivity analysis tha t used two different methods suggested that this deterministic model i s reasonably robust. In conclusion, according to this model, the incid ence of Lyme disease in Westchester County is several-fold higher than suggested by the current passive reporting system.