Reporting of suspect cases of foot-and-mouth-disease during the 2001 epidemic in the UK, and the herd sensitivity and herd specificity of clinical diagnosis

Abstract

We described the clinical diagnostic process utilized during the 2001 epidemic of foot-and-mouth-disease in the United Kingdom (UK), and considered it as a series of diagnostic tests. Premises were classified according to these diagnostic-test results and actual disease status, determined by the reference test, which in this case was one or more internationally accepted laboratory tests. The herd-level sensitivity (HSe) and herd-level specificity (HSp) of the clinical diagnostic process were calculated directly, relative to these internationally accepted reference tests. In this process, the first diagnostic test was ‘routine monitoring’, which resulted in the identification of suspect cases based solely on the clinical observations of farmers or veterinarians. 6762 suspect cases were identified, and the test had a HSe of 97.6% (95% C.I.: 96.7, 98.3) and a HSp of 95.2% (95% C.I.: 95.0, 95.3). Suspect cases were then subject to the second diagnostic test, termed ‘declaration’, which consisted of a review of a description of the clinical signs by government veterinarians. Premises that tested positive became ‘clinical cases’. The HSe of this test was 97.1% (95% C.I.: 96.2, 97.9), and the HSp was 90.9% (95% C.I.: 90.1, 91.6). During the epidemic, these tests were combined and applied in series, with an overall HSe of 94.7% (95% C.I.: 93.5, 95.7) and an overall HSp of 99.6% (95% C.I.: 99.5, 99.6). We also examined the effect of a policy shift that prohibited delaying the diagnosis pending laboratory testing where the animals exhibited equivocal clinical signs.