Here are three concepts regarding yeasts which challenge the dogma and traditional practice of most clinical microbiology labs.

• Vaginal candidiasis is best diagnosed by microscopy as opposed to culture. I daren’t think how many vaginal swabs have been cultured for yeasts by microbiology labs over the years. Millions probably. Yet we know that yeasts in small numbers colonise the female genital tract in about 10% of the (asymptomatic) population. Thus there is a very poor correlation between the culture of yeasts and symptoms caused by vaginal candidiasis. A better approach is to just look for the presence of yeasts/candida on microscopy. This will miss very small numbers of yeasts but will pick up the patients with larger numbers, i.e. the patients in whom the yeasts are more likely to be causing symptoms. In essence one is decreasing sensitivity in order to improve specificity. This may be a bit unpopular with some people, “We are missing them“, but that is the whole point….

• For the vast majority of swabs all we need to know about the yeast is that it is a yeast. When we do culture a yeast, then sure it is nice to show exactly what type of yeast it is, but is it really necessary? Identification of yeasts, although usually straightforward, is not labour or consumable free, and it may delay a report going out to the clinicians. In the vast majority of cases, who actually cares if the yeast is a Candida albicans, parapsilosis or a glabrata? For non-critical swabs a better approach might be to put out a report such as “Yeast isolated. Identification +/- susceptibilities on request if clinically indicated.” 99 times out a 100, they won’t be needed.

• Candida infection of the mouth is best diagnosed without the help of the microbiology laboratory. Oral candidiasis is very much a clinical diagnosis and usually very easily treated with either topical applications or a stat dose of oral anti-fungals. In all but the most exceptional cases, the lab should not be getting involved in the diagnosis of this condition. The sensitivity and specificity of the clinical diagnosis should more than match anything that the laboratory can offer here.

Have a think about what is done with regards to yeast processing at your lab or institution. You may not follow any of the processes above, or you might do all of them, but query and discuss what you have been doing nevertheless. Is it the best way?

Always question dogma. Just because something has been done at your lab for decades, it doesn’t mean it is right. Don’t be scared to be the person to suggest a change, and don’t be afraid to be the first lab to make the change.

Michael