Cystic echinococcosis in slaughtered cattle in Sardinia: a retrospective epidemiological study and spatial analysis

Cystic echinococcosis (CE) in cattle was found in 246 out of all 377 municipalities in Sardinia, Italy. Out of 32,685 bovines slaughtered in Sardinia in 2009, 1,360 were found to be positive for CE with a registered average prevalence of 4.2%. Of these animals, 896 (66%) had lived on the same farm from birth to slaughter, thus linking the infection to the farm with certainty, while 413 (30%) had lived on two different farms (one transfer) and 51 (4%) on three (two transfers). As it was not possible to assess in which farm the animals acquired the infection, all farms having kept infected cattle were considered as suspected sources of CE infection. Based on this classification, 534 farms were listed as definitely infected with a further 495 suspected to also be infected. Scan statistics was used with the Bernoulli model to detect and evaluate clusters of infected farms and also clusters of non-cases. For the spatial analysis, 1,029 farms (534 + 495) were considered as positive with the number of non-infected farms from which negative results were available (8,457) as controls. A most likely cluster was detected at latitude 39.47861 N and longitude 8.58216 E in a centroid of 97.92 km radius and a secondary cluster was detected at latitude 40.58890 N and longitude 8.98400 E in a centroid of 15.44 km radius. To address the issue of sensitivity and consistency of the results, we ran multiple scans with various max-sizes as this allowed us to achieve more valid, consistent results and to highlight the core clusters.