TABLE 3.

Application of LR to the interpretation and use of ELISA results in M. paratuberculosis-infected dairy herdsa,b

S/P ratioc	Interpretation	Explanation and recommendation
0-0.09	Negative	Antibodies to M. paratuberculosis were not detected. The animal is either not infected or in a very early, undetectable stage of infection. Retesting in 6 to 12 months will increase confidence that the animal is free of paratuberculosis.
0.10-0.24	Suspect	Evidence of serum antibodies above normal background levels. The cow may be in the early stages of infection. Cows with this level of ELISA are roughly 5 to 15 times more likely to be M. paratuberculosis infected than the ELISA-negative cows. Cows with this result should give birth to their calves in a separate pen, and their colostrum should not be fed to calves.
0.25-0.39	Weak positive	Low level of serum antibodies to M. paratuberculosis but above the standard cutoff for a positive test. Odds are 16:1 or higher that this cow is infected. However, cows with weak-positive ELISA results may remain in good health for another lactation and are of limited infection transmission risk to the herd, provided colostrum, milk, and manure from these, animals are kept away from calves.
0.40-0.99	Positive	Moderate level of serum antibodies to M. paratuberculosis. The odds that this cow is infected are at least 30:1. This cow is likely to be shedding the bacterium in its feces and milk and so should be culled from the herd soon and sold for slaughter only.
1.00-10.00	Strong positive	High level of serum antibodies to M. paratuberculosis. The odds that this cow is infected are over 200:1, and the animal is likely in the advanced stages of infection, shedding large numbers of the bacterium in feces and milk. It probably will soon develop clinical signs of the disease. The animal should be culled immediately and sold for slaughter only.

^aThis interpretation scheme only is valid for herds of dairy cattle proven to be M. paratuberculosis infected by having at least one culture-confirmed case in an animal born and raised in the herd (herd prevalence above zero).

^bAn earlier version of this table, based on preliminary data, appears on the Cornell website describing the New York State Cattle Health Assurance Program (http://nyschap.vet.cornell.edu/).

^cAn ELISA S/P ratio of 0 indicates an antibody level equal to that of the negative control provided with the diagnostic kit. ELISA S/P ratio of 1 indicates an antibody level equal to that of the positive control provided with the diagnostic kit.