Chronic vulvovaginitis caused by Candida dubliniensis in an immunologically competent adult female

Introduction

Opportunistic fungal infections, especially those caused by various Candida species, lead to significant morbidity and mortality. The newly-emergent species Candida dubliniensis resembles Candida albicans phenotypically and hence can be easily misdiagnosed. C. dubliniensis has been found to develop resistance rapidly to fluconazole in vitro, a phenomenon which may have resulted in its emergence. ¹

Case history

A 30-year-old married woman presented with a complaint of vaginal discharge associated with itching of two months’ duration. On inquiry, the patient gave history of lower abdominal pain. In the past, the patient was treated with various antibiotics for lower abdominal pain at multiple peripheral centres without significant improvement. Her speculum examination revealed copious, non-foul smelling curdy white discharge and erythema of the vaginal walls (Figure 1(a)).

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Figure 1.

(a) Curdy white copious vaginal discharge with erythema. (b) KOH mount of vaginal discharge showing budding yeast cells and pseudohyphae.

Potassium hydroxide (KOH) mount of vaginal swab showed budding yeast cells with pseudohyphae (Figure 1(b)). On further investigation, the patient’s venereal disease research laboratory (titre 1:8) and Treponema pallidum hemagglutination tests were positive. HIV ELISA and viral markers for hepatitis B and C were non-reactive.

The patient was treated with injected benzathine penicillin 2.4 million units three doses one week apart along with oral fluconazole 150 mg single dose. The patient returned after a month with similar symptoms and she was treated with oral fluconazole 150 mg single dose and clotrimazole vaginal pessaries for seven days and was continued on a maintenance regimen of fluconazole 150 mg once a week for three months. However, the patient continued to develop recurrent episodes of vaginal discharge over a period of eight months. At the latest visit, microscopic examination of the vaginal smear showed budding yeast cells with pseudohyphae; Gram stain showed Gram-positive cocci in clusters. Nugent score was 2.

Culture on Sabouraud dextrose agar at 37°C after 48 h showed growth of creamy white colonies (Figure 2(a)). Candida species were further identified as C. dubliniensis using the VITEK 2 system (bioMérieux, Inc, Hazelwood, Mo. USA). Antifungal susceptibility studies revealed susceptibility to fluconazole, voriconazole, caspofungin, micafungin, amphotericin with intermediate susceptibility to flucytosine. Sheep blood agar and MacConkey agar grew Staphylococcus aureus (coagulase positive) that was resistant to both methicillin and vancomycin.

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Figure 2.

(a) Creamy white colonies of C. dubliniensis on Sabouraud dextrose agar following 48 h of incubation at 37°C (credit: Dr Miskeen Autar, Central Clinical Microbiology Labs). (b) Clinical improvement after eight weeks of treatment.

In accordance with drug susceptibility reports, the patient was treated with higher doses of fluconazole (400 mg/week for eight weeks) and oral linezolid (600 mg BD) for two weeks with complete remission (Figure 2(b)).

Discussion

Candidal vulvovaginitis is a common fungal infection affecting healthy women of all ages, but more commonly in the reproductive age group. At least 75% of women develop one or more genital candidal infections once during their lifetime with 5% of those developing recurrent infections. ²

The disease is seldom life threatening but is associated with considerable morbidity, healthcare cost, discomfort, pain and sexual dysfunction. Presenting symptoms are vulvovaginal pruritus, irritation and burning micturition with signs such as oedema, erythema, fissures and curdy white discharge.

In our patient, multiple antibiotic courses given for lower abdominal pain may have been responsible for recurrent vulvovaginitis along with acquisition of vancomycin-resistant S. aureus. Lactobacilli compete with Candida species for nutrients and interfere with adherence to vaginal epithelium. Antibiotic agents are thought to facilitate candidal infection by eliminating Lactobacilli, thereby enabling Candida species to grow, adhere and germinate. ³

Several studies show that C. albicans, a commensal dimorphic fungus, is the most common microorganism that causes vaginal candidiasis, accounting for 75–90% of all cases, followed by Candida glabrata, Candida tropicalis, Candida krusei and Candida parapsilosis. ⁴ C. dubliniensis is a new species that was first reported in 1995 from AIDS patients in Dublin, Ireland, and hence the name. The incidence of C. dubliniensis varies between different studies – from 0.17 to 29.52%.^5,6 In a recent study of vulvovaginal candidiasis in pregnant women in Argentina, C. albicans species were isolated in 80.7% of cases and C. dubliniensis was isolated in 3.8% of cases. ⁷ C. dubliniensis has been implicated in oral candidiasis in HIV-infected individuals but has also been recovered from HIV non-infected individuals with clinical signs of oral candidiasis and rarely from the genital tract of some immunocompetent women with vaginitis. ⁸

C. albicans and C. dubliniensis share extensive phenotypic characteristics making it impossible to distinguish between the colonies on conventional solid media. C. dubliniensis isolates continue to be misidentified as C. albicans. ¹ As C. dubliniensis is gaining importance as a significant opportunistic pathogen and considering its predisposition for fluconazole resistance, it has become important for laboratories to screen for this species in clinical specimens.

Both C. albicans and C. dubliniensis are germ tube test positive and form creamy white colonies on Sabouraud’s dextrose agar at 37°C. Dark green colonies on CHROM agar, inability to grow at 45°C and production of abundant chlamydoconidia and pseudohyphae after 48 h are characteristics that differentiate C. dubliniensis from C. albicans. ⁴ Commercially available yeast identification kits based on the ability of Candida to assimilate carbohydrates, and automated systems such as VITEK 2 successfully identify yeast isolates from clinical specimens.^9,10

VITEK 2 system, which was used in our patient, is a rapid automated microbiological system used for bacteria and yeast identification, and antimicrobial susceptibility testing allows clinical laboratories to perform both fungal identification and antifungal susceptibility testing simultaneously using a fully automated and completely standardized format. ¹¹

Some studies have mentioned the limitations of the VITEK 2 system for the identification of Candida. In these studies, some species were misidentified and identified with low discrimination requiring additional help of conventional methods. ¹² Failure to correctly diagnose and treat accordingly has led to recurrent vulvovaginitis, defined as four or more proven infections per year, causing prolonged distress. In recurrent vulvovaginal candidiasis (VVC) usually caused by fluconazole-susceptible strains of Candida, remission can be induced by more intensive prolonged induction therapy for 14 days. The fungistatic nature of the available agents along with persistence of the underlying defect is responsible for relapse within three months unless a maintenance antifungal regimen is employed. ¹³

As C. dubliniensis is known to develop rapid resistance to fluconazole, our patient also did not respond to standard doses of fluconazole, but antifungal susceptibility test indicated sensitivity to fluconazole. ¹³ Therefore, we treated the patient with higher doses for a longer duration leading to complete resolution.

In VVC, non-albicans Candida species are emerging as a significant cause of morbidity. Culture and newer diagnostic methods are valuable not only for the accurate diagnosis of these species but also to determine antifungal resistance. Surveillance of antifungal susceptibility profiles is considered a useful tool to validate empiric treatment regimens. Antifungal resistance may be due to incomplete therapeutic regimens or self-prescribed, indiscriminate use of anti-fungal agents. Identification of rare pathogens like C. dubliniensis is necessary not only for therapeutic purposes but also to determine their incidence and role in systemic and invasive disease.