Antifungal susceptibility of genital yeast isolates, Auckland, 2016–2025

Yeasts, mostly Candida species, can cause troublesome vulvovaginal infection. Approximately 75% of women have at least one episode of vaginal candidiasis in their lifetime and 5–8% experience recurrent disease (≥four episodes a year), mainly in their childbearing years.¹ Culture is recommended in cases of suspected vaginal candidiasis as symptoms are non-specific and antifungal susceptibility testing is often requested/performed especially in recurrent disease.² We reviewed the disc susceptibility and broth microdilution minimum inhibitory concentration (MIC) results for genital yeast isolates tested over a 10-year period from 2016 to 2025. Our aim was to record current susceptibility results and to compare the results to the previous report covering 2001 to 2015.³

Only the first isolate of a species was included for each individual. Disc testing followed Clinical and Laboratory Standards Institute (CLSI) methods using Neo-Sensitabs tablets (Rosco Diagnostica, Denmark), as previously reported.³ The five antifungal agents tested were clotrimazole, fluconazole, itraconazole, miconazole and nystatin. Tablet potency and interpretive criteria for topical treatment are presented in Appendix Table 1. Nakaseomyces glabratus (N. glabratus) (previously Candida glabrata) and disc non-susceptible Candida albicans (C. albicans) isolates had MICs determined by the broth colorimetric microdilution method, Sensititre^® YeastOne^® (TREK Diagnostic Systems, West Sussex, England), as previously reported.⁴ The interpretive criteria for MIC testing are presented in Appendix Table 2. The clinical history and treatment details were unknown. There were 108 individuals, all women, with sequential isolates of the same yeast species where the initial isolate was susceptible by disc testing to two or more azole agents. We compared the initial and last susceptibility results to see if they had changed over time.

Disc testing was performed on 1,307 initial isolates; 17 (1.3%) were from males. There were 207 (16%) isolates from other hospitals, 675 (52%) from the regional community laboratory and 425 (33%) from Auckland City Hospital wards and clinics including 387 (27% overall) from sexual health clinics. Requests for susceptibility testing from the community and hospital clinics are often for isolates from women who have not responded to initial treatment or who have recurrent infections. For example, community referrals are based on clinical information being provided stating either recurrent infection or breakthrough symptoms on suppressive treatment. The most frequent isolates were C. albicans (64%), N. glabratus complex (17%) and Candida parapsilosis (C. parapsilosis) complex (7%) (Table 1). While 94% of isolates were susceptible to clotrimazole, susceptibility for other azoles ranged from 62–84%. All isolates were susceptible to nystatin. Pichia kudriavzevii (P. kudriavzevii) (previously Candida krusei) was the least susceptible group. For fluconazole, itraconazole and miconazole fewer isolates were susceptible than in the previous time period (Table 1). There was no difference in fluconazole resistance between hospital or community isolates, either for all species or for the most common isolate C. albicans.

The susceptibility of azole non-susceptible isolates to other antifungals is shown in Table 2. Pan-resistance was common in these isolates (Table 2). One hundred and eight women had sequential isolates, range 2–5, collected 1 week to 75 months apart, median 6 months. Of the 108 sets, 78 (72%) had identical susceptibility results and 26 had a single susceptibility change, e.g., susceptible to intermediate or intermediate to resistant, likely indicating biological variation within the limits of the test method. Four pairs (4%) had a change from susceptible to resistant, all for miconazole, suggesting increased resistance. All latter isolates were susceptible to at least two other azoles and nystatin.

After MIC testing for fluconazole, 26% of C. albicans and 90% of N. glabratus were susceptible-dose dependent with 60% and 10% being resistant, respectively (Table 3). The fluconazole results are in stark contrast to non-genital C. albicans isolates over the same period, where 635 of 652 (97%) were susceptible (unpublished laboratory data in: email, Arthur Morris, 1 February 2026). For itraconazole, almost all N. glabratus isolates were wild type, i.e., indicating the likely absence of acquired or mutational resistance. All species, for which criteria exist, were wild type for amphotericin (Table 3).

Apart from clotrimazole, with 94% being susceptible by disc testing, susceptibility to other azoles was variable, and as low as 62% for miconazole. This variability in commonly suggested agents for vulvovaginitis suggests susceptibility testing should be considered if initial treatment fails. That said, if a known active agent is used and symptoms return, it is uncommon for a subsequent isolate to have become resistant (4%). This is in keeping with the observations of others.^5–8 It was common for an isolate non-susceptible to one azole agent to be non-susceptible to all azole agents. Resistance to antifungal agents may have increased since the last reported period, and there was an increase in the number of pan-azole resistant isolates, 43 in this period vs only three previously.³ However, this is likely due to the selection of isolates for testing because clinician requests for susceptibility testing are usually triggered after previous azole exposure, for example following breakthrough symptoms on suppressive treatment or recurrent infection following azole exposure from self- or clinician-prescribed treatment. Our study is limited because without treatment information we are unable to evaluate its impact on isolate susceptibility. Changed referral patterns between the time periods may have also occurred which could have impacted the observed resistance rates.

The observation that all isolates were wild type to amphotericin is reassuring and would support its use for cases where azole agents are failing.

These susceptibility results will allow further monitoring of antifungal susceptibility over time. Given the recent change, the next review should probably be in 5 years rather than 10. Molecular testing for azole resistance mechanisms and to confirm strain identity would be useful additional information to give insight into the results observed in the low proportion of women with sequential isolates with apparent changes in susceptibility.

We conclude that, in this selected patient group, there appears to have been an increase in antifungal resistance to several topical agents used for genital yeast infections. However, susceptibility to clotrimazole has not changed. In a previously susceptible isolate treatment, failure after a stat dose or short-course treatment seldom indicates a change to antifungal resistance, and women with recurrent vulvovaginal yeast infection can be reasonably treated empirically while identification and susceptibility results are awaited.

Ethics: Under HDEC guidelines this audit of laboratory results is out of scope for HDEC review.

View Table 1–3.

View Appendix.