Onychomycosis to Fungal Superinfection: Prevention Strategies and Considerations

Onychomycosis is estimated to affect 12% of the United States population and represents 50% of all nail disorders. ^1,2 The incidence of skin dermatophyte infections is thought to be between 10% and 20% of the U.S. population. This translates to upwards of 59 million Americans experiencing at least one cutaneous fungal infection in any given year.³ While male gender and increasing age have been identified as predisposing factors, an equal proportion of men and women seek care for fungal infections. Moreover, according to Intercontinental Marketing Services (IMS) data, 63% of patients who filled prescriptions for oral terbinafine for onychomyosis were younger than 55 years.⁴

Onychomycosis is a fungal infection of the nail unit, which includes the nail plate itself along with the nail bed and periungual tissue. Clinically, the nail may become thick and discolored with separation from the nail bed. Onychomycosis is a progressive disease that, if left untreated, can lead to permanent nail damage and associated discomfort. In addition, local extension or spread to other body parts or to close contacts, as well as superinfections, may develop.^5,6,7 Finally, despite the best efforts in treatment, onychomycosis patients frequently relapse, with recurrence rates estimated to be between 40% and 70%.^8,9 For these reasons, early effective therapy is important.

It is estimated that one-third of patients with onychomycosis also have tinea pedis, most commonly the inter-digital subtype. ¹⁰ The infected nails serve as a fungal reservoir that infects the skin and causes the tinea pedis infection.^11,12 Because of this, it is important for onychomycosis patients to be evaluated for concurrent tinea pedis. Moreover, treating both conditions at the same time yields the best outcome in preventing a cyclical spread of fungus between the skin and the nails.⁴ The presence of tinea pedis has been shown to more than double the risk for subsequently developing onychomycosis or a recurrence once it has been cured.¹³

Several demographic, underlying medical, lifestyle, and climatic factors influence patients’ risk of developing both onychomycosis and tinea pedis. These infections have been shown to be more prevalent in men than in women, and in older compared with younger patients, as well as in smokers. Those with medical conditions such as poor peripheral circulation, diabetes, and immune deficiency are also at higher risk. Recent studies also suggest that there may be a genetic susceptibility to developing fungal infections. Finally, the incidence of dermatophyte infections has been linked to living in warmer, more humid environments as opposed to in areas that are arid and dry.^1,2,14

Lifestyle and hygiene also come into play in predisposing patients to dermatophyte infections. Wearing occlusive shoes, along with heavy perspiration and poor foot hygiene, create a moist environment that encourages invasion of fungi into the skin and nails. Moreover, exposing the feet to fungi by walking barefoot in public facilities such as gyms and swimming pools where humidity is high and fungi are prevalent also increases risk. Finally, frequent visits to nail salons has also been identified as a risk factor, as infection may be spread from dirty instruments or infected foot-soaking basins.^1,2,14

While many of these factors are unavoidable, extra attention should be paid to those that can be avoided. Patients with peripheral vascular disease, diabetes, or immunodeficiencies should regularly inspect their feet and visit their dermatologists