How do we diagnose Candidaemia? - Part 1

Part of the challenge that fungal infections pose is that confirming a diagnosis can be difficult.

If candidaemia is suspected empirical treatment is indicated. This principle is based on the absence of rapid sensitive and specific diagnostic tests and on the knowledge that every 24-hours of delay in starting effective treatment increases the mortality to candidaemia by up to 15%. It is not appropriate to wait for the blood culture to turn positive 24-36 hours later.

What antifungal stewardship approaches could be used to prevent overuse of antifungals in the ICUs? What diagnostics are available and how should these be used?

Blood Culture

candida seen under the microscope using a blue stain

Blood culture remains the gold standard for the diagnosis of candidaemia but its sensitivity is considerably lower than in common bacteraemia due to low concentration of Candida in blood (up to 65% of positive blood cultures have <1 CFU/mL)

  • A total of 60mL of blood needs to be collected within a 30-min period (three sets of 2x10mL) to achieve sensitivity of 50–75%

  • Often takes 2-3 days to turn positive, final report available in 4-5 days

  • Identification of Candida to species level is usually possible by using the standard platforms used for identification of bacteria (VITEK, MALDI-TOF, API).

Antifungal Susceptibility Testing

antifungal susceptibility testing of candida on an agar plate. Zones of inhibition seen around diffusion disc and MIC strip

Antifungal susceptibility testing of Candida species may be done using standard platforms used for antibiotic susceptibility testing (VITEK).

  • Antifungal susceptibility testing is available at the two national mycology reference laboratories (PHE and NHS), results are available in 3-4 days

Candida Score

Recording the number of body sites colonised with Candida has been used to assess the risk for candidaemia (Candida score). However, it is important to understand that colonisation as such should not be treated with antifungals. Instead, it should trigger infection prevention measures such as changing urinary caterers (in case of high Candida counts in urine), change of lines (in case of heavy Candida growth around peripheral line) or improvement of oral hygiene/change of endotracheal tube (in case of heavy Candida growth in respiratory samples).

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This article is from the free online course:

The Role of Antifungal Stewardship

BSAC