The results of this study covering a period of two years showed that filamentous fungi were the main etiology in cases with fungal keratitis. Fusarium was the most isolated filamentous fungus, followed by Aspergillus. In addition, most cases had been associated with outdoor activities, where trauma with a herbal substance was the leading susceptibility factor, with structural materials in the second place. It has also been observed that men were significantly more affected than women.
Epidemiological studies have shown that the microorganisms that cause keratitis may vary according to the geographical features and climatic conditions of the countries. Filamentous fungi are the predominant pathogens that have been widely proven to be associated with fungal keratitis in humid and warm climates [1, 13–14]. Provinces of Southern Anatolia are located in the far east of the Mediterranean coast . The climate here is Mediterranean, characterized by hot and humid summers and humid subtropical climate ranging from cold to mild winters . The main pillars of the economy in this region are agriculture and industry .
Most of the patients in this study were agricultural workers, predominantly male, and corneal trauma with an herbal substance was the most common cause of keratitis. Studies have reported that ocular trauma is the predominant risk factor for fungal keratitis [18–21]. In a 10-year study by Gopinathan et al, it was found that males were affected 2.5 times more than females, and trauma was the etiological factor in more than 50% of infected eyes . Corneal trauma with an organic or herbal substance has been considered the predominant predisposing factor affecting 40–60% of patients with mycotic keratitis [7, 8, 22–24]. In line with these facts, Bharathi et al noted in a retrospective review that the highest prevalence of culture-proven cases of fungal keratitis was observed during the South Indian harvest season between June and September . They determined that 92% of patients with fungal keratitis had ocular trauma and 61% of cases were injured by a herbal substance.
In the etiology of corneal damage that causes keratomycosis, leaves, rice grain, cow tail, tree branch, soil and metal objects have been described in various studies [20–27]. Similarly, Ebadollahi-Natanzi et al found that corneal ulcers caused by fungal microorganisms are most common among farmers and construction workers in rural, structural, and roofless areas . In parallel with various studies in the literature, it has been reported that men over the age of 15, especially those working outdoors, are more frequently affected [13, 14, 21, 28–31]. Also, in regions where agriculture is the main economy, the highest fungal keratitis is analyzed to be associated with Fusarium and Aspergillus species .
Filamentous fungi, inhabitants of the environment, are widely associated with keratitis caused by ocular trauma, especially in topical areas containing organic matter [1, 13, 14]. In some countries with tropical or subtropical regions such as Singapore, Hong Kong, China, East India, South Florida, East Africa, and Northern Tanzania, the filamentous species were mostly isolated fungi and it was Fusarium sp. identified as the primary cause, followed by Aspergillus sp [19, 20, 30–37]. Similarly, studies from Ghana, Australia, Iran, Brazil, Tunisia, Thailand, Taiwan, Northern China and South India found Fusarium to be the most commonly identified species isolated from fungal keratitis cases. On the other hand, studies from India and the rest of Bangladesh showed that Aspergillus sp. was the major species detected in cases of fungal keratitis .
This study supports the existing data obtained from studies conducted in other regions of Anatolia where geographical and demographic factors are similar. In a study conducted in a province of Southern Anatolia, 11 out of 20 fungal keratitis cases had a history of trauma due to plant or soil material . In this 3-year retrospective study, there were five patients with a previous history of topical steroid use, but similarly, the cases were predominantly male, and filamentous pathogens were seen in the microscopy of all corneal scrapings.
According to the results of a 16-year retrospective study conducted in Western Anatolia where etiological factors and clinical features of microbial keratitis were investigated, almost half of the eyes had a history of ocular trauma with a herbal substance and the fungal pathogens isolated from these traumatized eyes were predominantly filamentous and 43.5% of fungal keratitis cases were agricultural workers or farmers . Fusarium sp were identified as the most isolated fungal species but differently they were followed by Candida sp. In addition, unlike our study, it was determined that corticosteroid therapy was the second most common risk factor for fungal keratitis.
It has been shown that fungal infections show a geographical distribution depending on climate and agricultural conditions . It has been reported that yeast infections causing fungal keratitis are more common in temperate climates and are less associated with vegetative matter and trauma, unlike filamentous fungi. In a large analysis conducted in New York, Candida sp. was found to be the most common fungal agent (48%) among 5083 cases with keratitis . Ocular surface diseases such as dry eye syndrome and corneal ulcer, systemic immunosuppressive diseases such as diabetes mellitus and the use of steroids and broad-spectrum antibiotics have been shown to be important predisposing factors for Candida-induced keratitis [1, 13, 14, 40]. In addition, previous ocular surgeries, especially penetrating keratoplasty, a pre-existing epithelial defect due to herpes keratitis and contact lens abrasions have been also found as risk factors for Candida keratitis [1, 40, 41]. In the present study, there were cases with diabetis mellitus, previous history of ocular surgery and contact lens use, however, Candida sp. was not isolated from any of them It may be because all cases had a history of corneal contact with an environmental agent.
There are extensive retrospective studies defining contact lens use as an important predisposing risk factor for fungal keratitis in studies where fungal etiologies differ by species [14, 32–35, 42, 43]. Filamentous fungus have been reported as one of these etiological factors for contact lens-associated keratitis [44–46]. In this study, Aspergillus sp. grew up in a corneal scraping culture of a case using contact lenses and she had a history of scratching her eye while working in a garden. Wong et al. reported that there were 2 patients using contact lenses among fungal keratitis cases. In this 5-year hospital-based retrospective study, the researchers determined the microbial and clinical characteristics of cases with fungal keratitis in Singapore, where the climate is warm and tropical. Similar to the current study, more than half of the patients had trauma and Fusarium sp. was the leading cause of fungal keratitis, followed by Aspergillus .
The most significant limitations of the present study were the retrospective design and relatively small number of patients. In addition, there were cases where subspecies could not be detected. Adding to this, the inclusion of only culture-positive cases of fungal keratitis may have led to a biased prevalence. That is, there may be some patients with high suspicion of fungal keratitis where fungal growth was not demonstrated in cultures of corneal specimens and microbiological studies were not repeated enough. Furthermore, although important information was provided to guide the treatment of fungal keratitis, the clinical picture, treatment methods and responses to these treatments were not included due to the lack of follow-up information of the patients . For his reason, the current study chose to focus more on the demographic features, epidemiological characteristics and etiological factors of the cases with fungal keratitis.
Our study, despite all its limitations, provides reliable preliminary information on this subject in Southern Anatolia, showing that agricultural activity and associated eye trauma are the main cause of fungal keratitis caused by filamentous fungi. The results of this retrospective review can be useful for both the prevention and early diagnosis of fungal keratitis, as corneal infections need urgent recognition to prevent permanent vision loss by facilitating a complete recovery . Furthermore these identified etiological factors may be useful in the selection of early empirical treatment of fungal keratitis cases encountered in Southern Anatolia.