Guidelines for oral fluid-based surveillance of viral pathogens in swine

Table 4 Probability of PRRSV detection as a function of within pen prevalence

Within pen prevalence	Probability (%) of detection with one oral fluid sample (95% CI)^a		Serum samples to match oral fluid probability^b
Within pen prevalence	RT-PCR	ELISA	RT-PCR	ELISA
5%	31% (9, 67)	17% (6, 38)	8	5
10%	79% (48, 94)	59% (37, 77)	11	5
20%	98% (88, 100)	94% (82, 98)	13	10
30%	100% (96, 100)	99% (93, 100)	12	10
40%	100% (98, 100)	100% (97, 100)	10	9
50%	100% (99, 100)	100% (98, 100)	9	8

^aProbability of detection in oral fluids estimated by logistic regression (pen as random effect) from data reported in Olsen et al. (2013b). Within pen prevalence established by placing PRRSV-positive pigs (14 days after MLV vaccination) in pens of PRRSV-negative pigs to achieve 25 pigs per pen [89]
^bNumber of serum samples required to match the probability of detection for one oral fluid sample was estimated using a hypergeometric distribution

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