Yeasts, mostly Candida species, can cause troublesome vulvovaginal infection. Approximately 75% of women have at least one episode of vaginal candidiasis in their lifetime.1 Some women experience recurrent disease, mainly in their childbearing years.1 Culture is recommended in cases of suspected vaginal candidiasis as symptoms are non-specific. Antifungal susceptibility testing is often requested/performed on genital isolates, especially in recurrent disease. We reviewed the disk susceptibility results for six antifungal agents against genital yeast isolates recovered over the 15-year period between 2001 and 2015. Our aim was to record current susceptibility to guide empirical treatment and to enable monitoring of antifungal susceptibility over time.

Only the first isolate of a species was included for each woman. Testing followed CLSI methods using Neo-Sensitab tablets (Rosco Diagnostica, Denmark).2–5 The six antifungal agents tested were: clotrimazole, CLO; fluconazole, FLC; itraconazole, ITC; ketoconazole, KTC; miconazole, MIC; and nystatin, NYS. Tablet potency and interpretive criteria are presented in Table 1.3,5 The clinical history and treatment details of the women are unknown. Forty women had sequential isolates and we compared their isolates’ susceptibility results to see if antifungal susceptibility had changed over time.

Table 1: Antifungal disk potency and interpretive criteria.

‍

Six hundred and fifty-six women had isolates tested; 26 had mixed infection, all with two species. Six hundred and eighty-two initial isolates were analysed. The most frequent isolates were C. albicans 55%, C. glabrata complex 24% and C. parapsilosis complex 10% (Table 2). Saccharomyces cerevisiae made up 3% of isolates. More than 90% of isolates were susceptible to all agents tested (with the exception of MIC) (Table 2). Only two isolates were resistant to nystatin (a C.albicans and a C. parapsilosis complex isolate); both susceptible to several azole agents. C. glabrata complex and Pichia kudriavzeii (previously C. krusei) were the least susceptible groups (Table 2).

Table 2: Susceptibility of vaginal yeast isolates to six antifungal agents.

‍

‍The susceptibility of azole non-susceptible isolates to other antifungals is shown in Table 3. Non-susceptibility to all azole agents was uncommon (Table 3). Forty women (6%) had sequential isolates of the same species; 29 had two sequential isolates, eight, two and one women had three, four and five sequential isolates respectively. Of the 40 sets of sequential isolates, 29 had identical susceptibility results, eight had a single antifungal result change from either S to SDD/I (n=4) or SDD/I to S (n=4) indicating biological variation within the limits of the test method, ie, 37 (93%) had no change in susceptibility between isolates. Two women had disc results suggesting increased resistance: one had three agents change from S or I to R, the isolate was still susceptible to three antifungals; the second had three agents change from S to SDD/I and one agent, ITR, move from S to R. This woman’s isolate was still susceptible to NYS. One woman had three or more agents change from R to S, suggesting strain replacement with a more susceptible strain. Overall only two patients (5%) had decreased susceptibility results in sequential isolates.

Table 3: Susceptibility of non-susceptible isolates to other antifungal agents.

‍

*Includes Susceptible-Dose Dependent, Intermediate and Resistant isolates.

Apart from miconazole, ≥92% of isolates were susceptible to antifungal agents commonly recommended and used for vaginal candidiasis.6,7 It was uncommon for an isolate non-susceptible to one azole agent to be non-susceptible to all azole agents (Table 3). Azole resistance was uncommon, even in repeat isolates from the same woman, supporting the observations of others.8–10 Sequential isolates from women, who probably had been treated and re-presented with symptoms, were unlikely to have developed resistance to antifungal agents (5%). Resistance to antifungal agents remains uncommon in genital isolates in New Zealand. These susceptibility results will allow monitoring of antifungal susceptibility over time. 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 failure of a stat dose or short course treatment does not indicate antifungal resistance and those women with recurrent vulvovaginal yeast infection can be reasonably treated empirically with a previously used agent while identification and susceptibility results are awaited.

‍