Control of Hepatitis A by Universal Vaccination of Adolescents, Puglia, Italy

documented evidence about the use of the specifi c milk replacers, we conservatively assumed that 12 of 13 case farms used the specifi c milk replacers. We estimated the odds ratio for this risk factor by using logistic regression analysis. Our results indicated that the use of the milk replacers produced by the specifi c factory was associated with BSE infection (odds ratio [OR] 39.3, 95% confi dence interval [CI] 4.9–312.9, p = 0.0005). The milk replacers produced by the specifi c factory contained tallow that was produced at domestic rendering factories and imported from the Netherlands. Milk replacers were fed to calves during a relatively short period after birth (an average of 79 and 68 days, for case and control farms, respectively). If 1 production lot of milk replacer became accidentally contaminated with BSE, the exposure would occur in newborn calves within a relatively short period. This contamination may explain why 11 of 13 BSE-infected calves were born within a 2-month period from February 10, 1996, to April 8, 1996. In Hokkaido, 9 of 10 BSE-infected calves were fed calf concentrates produced in the same feed factory. This proportion was higher than that of the 50 control farms in Hokkaido (22/50, Fisher exact test, p = 0.013). The calf concentrates might have become contaminated with meat-andbone meal (MBM) because this factory used MBM for other animal feed. Multivariate logistic regression analysis, including this factor and that for the specifi c milk replacers, did not indicate signifi cant association between the specifi c calf concentrates and occurrence of BSE (calf concentrates: OR 3.2 [CI 0.8–13.0], p = 0.14; milk replacers: OR 21.7 [CI 2.5–192.6], p = 0.006). The factory that provided the specifi c concentrates belonged to a company affi liated with the company that produced the milk replacers in question. Given the fact that farmers tend to use milk replacers and calf concentrates from the same company, association of the calf concentrates with the BSE infection may have been masked by the use of specifi c milk replacers. However, our study is limited by the small number of BSE cases and investigation of events that occurred 10 years ago. A possible causal association between the feeding of potentially contaminated milk replacers to calves and the occurrence of BSE has been suggested by several epidemiologic studies (2–5). However, no report shows experimental transmission of BSE by use of tallow or milk replacers (6). This lack of evidence in the literature may suggest that the risk of contracting BSE from processed tallow or milk replacers is low (7). If MBM is excluded as a source of infection, other transmission mechanisms, such as the feeding of animal fat, may become more important.