RESEARCH Sampling and Analyses of Fox Fecal Samples Fox fecal samples were collected at least once per month in bait and control areas and their immediate vicin- ity during the following periods: winter 1999/2000 (November 1999 to February 2000), spring 2000 (April to June 2000), summer/autumn 2000 (July to October 2000), winter 2000/01 (November 2000 to February 2001), and summer/autumn 2001 (July to October 2001). Several cri- teria, such as size, shape, homogeneity, and smell of the droppings, were used to distinguish fox fecal samples from other fecal samples (22). For each of the 1,537 collected fecal samples, we recorded the exact position to an accura- cy of 20 m. E. multilocularis coproantigen was detected by a sand- wich–enzyme-linked immunosorbent assay (EM–ELISA) (25), which was recently validated for testing field fecal samples in eastern France (26) and our study area (22). Coproantigen-positive fecal samples, collected in bait and control areas during 2001, were further evaluated to check whether infected foxes in bait areas had predominantly fresh, prepatent infections and did not excrete E. multiloc- ularis eggs. Therefore, we isolated taeniid eggs from the fecal samples followed by E. multilocularis–specific poly- merase chain reaction (PCR) as described previously (27). Sampling and Analyses of A. terrestris In Zürich, we found the highest prevalence of E. multi- locularis coproantigen in the intermediate host A. terrestris (22). Therefore, we focused on this species to evaluate the effect of bait distribution on intermediate host populations. A. terrestris were trapped with unbaited tong traps (Hauptner Instrumente GmbH, Dietlikon, Switzerland) and Topcat traps (TOPCAT GmbH, Wintersingen, Switzerland). Traps were set in intervals of 1 to 2 months in each bait and control area from April to November 2000 and from July to October 2001. Additionally, in the 6–km2 bait area, traps were regularly set from July 1999 to February 2000. All 1,229 dissected rodents were carefully examined macroscopically for lesions in their livers and other organs. Lesions >2 mm in diameter were investigat- ed for E. multilocularis metacestode tissue either by exam- ining morphologic features or by DNA detection by using modified PCR (28). Statistical Analysis Statistical analyses were performed with SPSS–PC ver- sion 10.0. Stepwise backward logistic regression was used to test the effect of baiting on the proportion of coproanti- gen-positive fecal samples and on its prevalence in A. ter- restris. The influence of baiting was represented by the interaction between the two factors: area type (baited vs. nonbaited areas) and period (temporal progress of the experiment). The area type and period variables were added as blocking variables to the initial model. In addi- tion, season (spring: March to June, summer/autumn: July to October, winter: November to February) and urban area variables (urban zone, border zone, and periurban zone) were included in the initial model since these factors were known to affect the prevalence of E. multilocularis (17). Deviations from expected frequencies were tested by chi square tests. P values are given two-tailed if not other- wise stated. If the minimum entry in the table of expecta- tion was <5, p values were calculated with Actus (George F. Estabrook, New Hampshire, USA), which performs ran- domized contingency tables and gives probabilities for deviations from expected values (29). Critical significance levels were Bonferroni-corrected according to Rice, taking into account multiple tests on the same data (30). We cal- culated exact binomial 95% confidence intervals (CI) for means of binomial variables, according to the method of Clopper and Pearson (31). Results Baiting and Environmental Contamination To evaluate the effect of the experimental baiting, we analyzed 682 fox fecal samples collected in the six 1-km2 bait areas and 523 fecal samples from the six control areas. The stepwise logistic regression indicated a significant final model (model χ2=139.4, df=11, p<0.001) with a high- ly significant influence of anthelmintic baiting, expressed by the interaction between the area type and period vari- ables on the proportion of coproantigen-positive fecal samples (Wald Statistics 20.5, df=4, p<0.001). The propor- tion of coproantigen-positive fecal samples in bait areas decreased from 38.6% (95% CI 26.0% to 52.4%) during winter 1999 to 5.5% (95% CI 3.1% to 8.9%) in summer/autumn 2001. In the control areas, the initial pro- portion of coproantigen-positive fecal samples was 47.1% (95% CI 35.1% to 59.4%) in winter 1999; it decreased to 25.4% (95% CI 15.3% to 37.9%) in the initial phase of baiting (spring 2000) but thereafter remained stable during the baiting experiment (Figure 2). The two blocking fac- tors, period (Wald Statistics=60.9, df=4, p<0.001) (Figure 2) and urban area (Wald Statistics=6.0, df=2, p=0.05), also entered the final model. In the urban zone, 1 of 33 fecal samples was coproantigen positive (mean 3.0%; 95% CI 0.0% to 15.8%), whereas within the border zone and in the periurban zone, the proportion of coproantigen-positive fecal samples was significantly higher with similar per- centages of 19.1% (95% CI 16.3% to 22.0%) and 18.5% (95% CI 14.8% to 22.6%). A strong decrease in the proportion of coproantigen- positive fecal samples was also recorded in the 332 fecal samples collected in the 6–km2 bait area. Before baiting started in winter 1999/2000, the proportion of coproanti- 1268 Emerging Infectious Diseases • Vol. 9, No. 10, October 2003