Estimation of prevalence of disease, including construction of confidence intervals, is essential in surveys for screening as well as in monitoring disease status. In most analyses of survey data it is implicitly assumed that the diagnostic test has a sensitivity and specificity of 100%. However, this assumption is invalid in most cases. Furthermore, asymptotic methods using the normal distribution as an approximation of the true sampling distribution may not preserve the desired nominal confidence level. Here we proposed exact two-sided confidence intervals for the prevalence of disease, taking into account sensitivity and specificity of the diagnostic test. We illustrated the advantage of the methods with results of an extensive simulation study and real-life examples.

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The performance of a live marker vaccine for bovine herpesvirus type 1 (bhv-1) was studied in the field in three European Union countries with different farming conditions. The progress in the eradication of the virus was followed in a large herd in Germany and one in Italy, and a major serological survey involving 147 farms was conducted in Hungary. Commercial batches of the same vaccine were used in all three studies. The herds were vaccinated according to agreed protocols and the animals' bhv-1 antibody status was determined at local institutes by using commercial glycoprotein B (gB)- and glycoprotein E (gE)-elisas. In all three studies, the seroprevalence of bhv-1 gE decreased progressively. Given the starting conditions and the long duration of the studies, reactivation events and virus circulation would have been more likely to have occurred if the herds had not been vaccinated.

A study was performed to survey the virological prevalence of bovine viral diarrhoea (BVD) virus (BVDV) in cattle herds in Hungary between 2008 and 2012. A total of 40,413 samples for BVDV detection and 24,547 samples for antibody testing were collected from 3,247 herds (570,524 animals), thus representing approximately 75% of the cattle population in Hungary. Retrospective Bayesian analysis demonstrated that (1) the herd-level true virus prevalence was 12.4%, (2) the mean individual (within-herd) true virus prevalence was 7.2% in the herds having at least one virus-positive animal and 0.89% for all investigated herds with a mean apparent prevalence of 1.15% for the same population. This is the first study about BVDV prevalence in Hungary.