Table 7.

The results of the case-control study

SP: Seropositive flocks (Cases), SN: Seronegative flocks (Controls). ^*Active meant that an owner had one social activity less than 3 d. Social activity means that an owner participated in a meeting or meets farmers for the poultry society, ^†High degree meant that an owner usually works together with employees every day, Low was defined when an owner almost did no work with employees, ^‡If employees go out several times a day or once less than 2 d, it was described as frequent, ^§Frequent meant that employees take some instructions,like sanitary education or explanation from owner, at least once per 2 d, ^∥If employee changed or refreshed disinfectants in front of the chicken house or entrance to the farm at least once per 3-4 d, it was designated as frequent.