Table 1 Definition of the variables and parameters used in the models to estimate true seroprevalence of Brucella spp. in a village of the Nile Delta, Egypt
Variable | Definition | Distribution, Value or Equation used | Data Source |
|---|---|---|---|
Se | Individual test sensitivity | Triangular: (0.952, 0.98, 0.996) | Manufacturer's estimates were used as the most likely values and minimum and maximum values were obtained from previous studies validating the ELISA test |
Sp | Individual test specificity | Triangular: (0.881, 0.985, 0.991) | Â |
S | Number of animals which tested seropositive for Brucella spp. | 22 | Results of serological tests |
N | Number of individual animals tested | 151 | Results of sampling |
AP | Apparent seroprevalence | Beta(23, 130) | Results of sampling/testing (α = s + 1, β = n - s + 1) |
h | Number of cattle and buffalo sampled within a household | 1, 2, 3 or 4 | Results of sampling |
I | Number of infected animals in a household | Discrete(h = 2;75,25) (h = 3;70,20,10) (h = 4;70,15,10,5) | Estimated from the number of test positive animals within households, can range from 1-h |
U | Number of uninfected animals in an infected household | U = h-I | Test results, could range from 1 to 3. |
P(+/+) | Probability that at least one infected animal within a household tests positive | P(+/+) = 1-(1-Se)^I | Outputs of previous distributions |
P(-/+) | Probability that, in an infected household, at least one uninfected animal tests positive | P(-/+) = 1-(1-Sp)^U | Outputs of previous distributions |
HSe | Probability that a positive household is correctly identified i.e. household sensitivity | HSe = P (+/+) + P(-/+) | Results of previous Equations |
HSp | Probability that a negative household is correctly classified i.e. household specificity | HSp = Sp^h | Results of previous Equations |
s h | Number of households of size h where at least one animal tested seropositive | 11(h = 2), 1(h = 3), 0(h = 4) | Results of serological tests |
n h | Total number of households of size h sampled | 40(h = 2), 2(h = 3), 1(h = 4) | Results of sampling |
AHP h | Apparent household seroprevalence of households of size h | Beta (s h + 1, n h - s + 1) | Results of sampling/tests |