Should I trust this strangles test result?

Diagnostic tests are at the heart of decision making at all stages in the strangles outbreak timeline from initial confirmation of disease, containing the outbreak within the affected premises and, in particular, deciding when the outbreak is over. To obtain results that can be trusted: 1) appropriate samples and diagnostic tests must be selected at different stages of the outbreak to address the clinical or management question being asked; 2) the strengths and weaknesses of the tests used (sensitivity and specificity) and the likelihood and impact of false negative and positive results must be understood.

Key points

• Understand the pathogenesis of strangles, especially duration of bacterial shedding and of seroconversion • Understand which samples are appropriate at different stages of the outbreak
• Understand the tests you are requesting, especially their limitations
• Be confident about sensitivity and specificity and explain to your clients: no test is 100% sensitive and 100% specific
• Recognise when single tests are adequate and when multiple testing is required; avoid false economies and don’t waste money
• Carry out enough tests to be confident of the result but don’t carry out unnecessary tests: once a diagnosis is obtained don’t waste money on further testing (keep budget for carrier screening at the end of the outbreak)
• Recognise the importance of PCR positives
• Take advice – there is plenty of help available
[…]