Dermatophytoses are fungal infections caused by filamen- tous fungi that possess the ability to invade and proliferate within keratinized tissue (i.e., skin, nail, and hair). The fungal biota of superficial infections does not only vary geographically but also historically. For example, Epidermophyton floccosum, Microsporum audouinii, and Trichophyton schoenleinii were the major pathogens of superficial fungal diseases 100 years ago, but their frequency decreased dramatically since the middle of the twentieth century and they are limited to some less developed countries today1. Knowledge of the clinical features and changing epidemiology of dermatophytes helps in better managing them. E. floccosum causes a variety of clinical manifestations such as tinea cruris, tinea corporis, tinea pedis, and tinea unguium2. E. floccosum is more common in tropical and subtropical areas3,4. Moreover, E. floccosum can invade and cause deep fungal infections in immunocompro- mised patients5,6. Previously, our study group (Bang and Kim) reported the epidemiologic aspects of E. floccosum isolated from 71 patients between January 1998 and December 2007 in Korea7. In this study, the recent epidemiologic traits of E. floccosum between January 2008 and December 2019 were investigated and compared with previous studies.

The current study included 57 patients who visited our clinic and were diagnosed with E. floccosum infection via fungal culture between January 2008 and December 2019. Data on the date of visit, gender, age at onset, and site of infection were collected through a review of medical charts, and the findings were compared with that of previously reported studies7. KOH test was performed by collecting the scale and nail of the lesion and dissolving them in a 20% KOH solution. The mixture was then observed under a microscope. The culture was identified by inoculating the specimen into a Sabouraud dextrose agar medium and incubating it at 25℃ for 3~4 weeks. Colonies were identified based on the features, growth rate, color, and microscopic findings, and tests on pigment production, urease, and hair perforation were also conducted if necessary.

This study was conducted with the approval of the Institu- tional Review Board of Kyungpook National University Hospital (IRB No. 2020-08-001). Informed patient consent was waived by the board.

1. Isolation frequency of E. floccosum in der- matophytosis cases

Fifty-seven patients were diagnosed with E. floccosum infections among dermatophytes between 2008 and 2019, and only one case each was identified in 2018 and 2019. Therefore, the frequency of isolation of E. floccosum de- creased gradually (0.076% and 0.013% in 2008 and 2019, respectively) (Table 1).

2. Distribution of E. floccosum according to year and gender

The annual new cases of E. floccosum ranged from 1 to 10 between 2008 and 2019. The number of new cases was lowest in 2018 and 2019 and highest in 2010. The mean annual new cases of E. floccosum was 4.75. The distribution, divided by 2 years, showed a steadily decreasing tendency (Table 2). Patients most commonly visited the hospital in summer (19 cases) and fall (14 cases).

3. Distribution of E. floccosum according to infection site and gender

Fifty-two men (91.2%) and five women (8.8%) were diag- nosed with E. floccosum infections with a male to female ratio of 10.4:1 (Table 3). The inguinal area (33 cases) and the feet (tinea pedis, 19 cases) were the most common infection sites. Two cases each of tinea corporis and tinea unguium were identified.

4. Distribution of E. floccosum according to infection site and age groups

Most of the patients with tinea cruris were in their teens and 20s (28 out of 33, 84.8%), while those with tinea pedis were evenly identified in all age groups (Table 4). E. floccosum infections occurred in patients in their teens (22.8%) and 20s (35.1%). Two cases of tinea unguium occurred on the toenail while two cases of tinea corporis occurred on the chest and hip. In this study, tinea manus, tinea faciale, and tinea capitis were not identified.

It is difficult to identify the occurrence and distribution patterns of dermatomycosis, and many limitations are present in selecting and targeting the general study population. Consequently, many epidemiological studies have been con- ducted with patients visiting large hospitals in regional areas8. E. floccosum was previously the leading causative organism of tinea cruris infection worldwide9, and, in Korea, it has been known to be the fourth most common causative agent among dermatophytes after Trichophyton rubrum, Trichophyton mentagrophytes, and Microsporum canis10,11. Furthermore, epidemiological investigations of this species were reported in 1999 and 2008 in Korea7,12. In this study, the authors investigated the epidemiology of patients who had been diagnosed with E. floccosum infection during the recent 12 years (2008 to 2019) and sought to compare these with previous studies.

The frequency of isolation of E. floccosum in dermato- phytoses was found to be extremely low in this study. In combination with previous studies7,10,12, it can be concluded that E. floccosum infections in Korea have been decreasing rapidly since 1987. In Korea, the isolated proportion of E. floccosum was 3.87% from 1976 to 1980 but decreased sharply to 0.34% from 1986 to 199012. Zhan et al. reported that E. floccosum infections were disappearing in many areas other than Iran and Nigeria1. In this article1, E. floccosum accounted for 1% of isolated species in Denmark (2003) and 30~40% in Iran (2013~2014) and Nigeria (2011).

E. floccosum is generally known to cause superficial der- matomycosis, among which tinea cruris, tinea pedis, and tinea corporis are common2. In this study, the inguinal and feet area were the most commonly involved sites, indicating that the infection site remained unchanged even at a low incidence. Our previous study showed similar results among the 71 patients diagnosed with E. floccosum infection (62.0% for tinea cruris and 28.1% for tinea pedis)7. Likewise, a recent study in Iran showed similar results13. In Italy, similar results were published14 with a reported incidence of 4.5%. The infections caused by E. floccosum were classified as 83 cases of tinea cruris, 7 of tinea corporis, 3 of tinea pedis, and 1 each of tinea capitis and tinea unguium. Males were by far the most affected, and the majority are in the 21~30 year age group14.

A high male to female ratio was evident in patients with dermatophytosis, which tended to be similar to the reports from Korea and other countries8,12,13. In particular, some Korean and Italian studies reported the presence of extremely more male patients with E. floccosum infection. The male to female ratio was 6.6:1 and 4.28:1 according to Korean12 and Italian reports14. Similarly, the male to female ratio was 6.9:1 in our previous study7. However, the proportion of male patients increased further in this study.

Overall, dermatophytosis occurs most frequently in post- pubertal hosts. The most commonly infected age group in this study was the 10~29 year age group, showing similar results with our previous study7. Caretta et al.15 reported that 19.3% in their teens and 23.5% in their 20s were infected with E. floccosum, and Ahn et al.12 showed that 71.1% in their teens and 20s were affected by E. floccosum infection. This indicates that E. floccosum infections had a higher tendency to occur at younger ages than other causative fungi. Thus, more studies are needed to elucidate this.

In conclusion, the frequency of isolation of E. floccosum was found to decrease progressively, and the infections caused by E. floccosum were 33 cases of tinea cruris, 20 of tinea pedis, and 2 each of tinea corporis and tinea unguium. The male to female ratio was 10.4:1, and the majority was in the 10~29 year age group.