Epidemiology and Antifungal susceptibility profiles of clinical Aspergillus species in Singapore 

Yen Ee Tan, Mei Gie Tan, Ai Ling Tan

Objectives:
Aspergillosis causes a wide range of diseases and is a major cause of morbidity and mortality in immunocompromised patients. Early diagnosis and appropriate antifungal treatment are important for patient survival. Increasing antifungal resistance has been reported from various geographic areas and this may lead to treatment failure.  Such data is not available in Singapore to date and there is a need to understand the epidemiology and susceptibility profiles of Aspergillus species in Singapore. This study aims to study species distribution and antifungal susceptibility profiles of Aspergillus species isolated from a large tertiary hospital in Singapore. 

Methods:
Data on Aspergillus species and anti-fungal susceptibility testing of Aspergillus species cultured from clinical specimens received from January to December 2017 was obtained from the Laboratory Information System. The antifungal susceptibility testing was performed upon clinicians’ request using the Sensititre® YeastOneR YO10 (TREK Diagnostic Systems Ltd.). Minimum inhibitory concentration (MIC) or minimum effective concentration (MEC) range was obtained for each species/drug combination and interpreted using the epidemiological cut-off values (ECVs) provided by the Clinical and Laboratory Standards Institute (CLSI) where applicable. Geometric mean (GM) MICs and MECs were calculated for genera with more than 4 strains. The clinical isolates were identified by a combination of phenotypic methods and/or sequencing and the site of isolation and species distributions were analyzed.



Results:
A total of 326 clinical Aspergillus species were isolated from 320 patients in 2017. The sites of isolation were: Respiratory tract (n=140; 42.9%), nail, skin and soft tissues (n=126; 38.7%), ear (n=38; 11.7%), sinus-related (n=15; 4.6%), eye (n=5; 1.5%) and others (n=2; 6.1%). Two hundred and fifty-two isolates were identified to the species level. Aspergillus niger complex (n=140; 42.9%) was the most frequently isolated species followed by Aspergillus flavus complex (n=55; 16.9%) and Aspergillus fumigatus complex (n=47; 14.4%).  Other species isolated included: Aspergillus terreus complex (n=7; 2.1%), Aspergillus nidulans complex (n=2; 0.6%) and Aspergillus glaucus (n=1; 0.3%). Antifungal susceptibility testing was requested for 17 Aspergillus isolates by the clinicians. These were Aspergillus flavus complex (n=8), Aspergillus fumigatus complex (n=6), Aspergillus niger complex (n=2) and Aspergillus versicolor complex (n=1). Most tested strains were wild-type isolates except for 2 Aspergillus fumigatus complex (33.3%; MIC 4 µg/mL, GM MIC 2.52 µg/mL) and 1 Aspergillus versicolor complex (MIC 4 µg/mL) strains which displayed non wild-type MICs for amphotericin.  All the isolates were susceptible to the mould-active azole antifungal agents itraconazole, voriconazole, and posaconazole. 

Conclusions:
Respiratory system was the most frequently involved site. The most commonly isolated Aspergillus species was Aspergillus niger complex (42.8%) followed by Aspergillus flavus complex (16.8%) and Aspergillus fumigatus complex (14.4%). However, the most commonly tested for antifungal susceptibility were Aspergillus flavus complex and Aspergillus fumigatus complex, indicating that these 2 species caused most concern for clinicians to warrant request for antifungal susceptibility testing. All the tested Aspergillus strains were susceptible to mould-active azoles, while 3 isolates displayed non wild-type MICs for amphotericin. Although the number tested is small, it is reassuring that the mould active azoles remain useful for treating Aspergillosis in our institution.