Preventing Dermatophyte Reinfection
Whilst at a recent dermatology study day, there was some discussion around treating fungal foot infection – particularly what do you advise the patient to do after the fungal infection has been eradicated? Is there much evidence? As a result, I have put together the following points which may help podiatrists to distil this research into patient advice. At the end of this piece there is a patient advice sheet which can be downloaded.
Fungal foot infection (Tinea Pedis & Onychomycosis)
Fungal foot infection (both athletes foot and dermatophyte nail infection) is a very common problem with around a third of UK adults being infected (1). Fungal infection rates increase as we age. For example patients in their sixth decade have much higher rates of infection - nearly 50% (2). Patients with other co-morbidities such as diabetes and PVD are also likely to exhibit higher infection rates. Whatever the treatment that is used to treat and cure fungal foot infection (skin and nail) recurrence rates are very high. Essentially, patients should expect that reinfection will reoccur at some stage. Studies following patients after oral antifungals have shown relapse rates in onychomycosis as high as 87% within a few years (3). Therefore, measures to prevent reinfection are important. Nail infection virtually always follows skin infection (4), therefore preventative measures are best targeted at preventing tinea pedis and this will reduce the chances of nail reinfection too.
Recognition of fungal skin infection on the feet is notoriously difficult (for patients and healthcare professionals alike) owing to its subtlety and lack of symptoms (5) therefore patients should be educated on how to recognise re-infection. They should be advised to check the soles of their feet. Suspicion of reinfection should be raised when there is increased dryness or subtle redness with a white, chalky appearance accentuated in the skin creases anywhere on the plantar surface or fissuring between the toes.
Figure 1: Moccasin tinea pedis presenting as dry, white plantar creases
Preventing Skin Infection
The prophylactic use of topical antifungal cream is recommended for those who suffer recurrent skin infection (6). Topical imidazoles (clotrimazole and miconazole) and allylamines (terbinafine) creams are suitable for this purpose (7). Patients should be advised to use them one week a month (one week in four) during the winter months – ensuring all parts of the foot below the ankle are treated (including the interdigital areas and heels). As a reminder, topical miconazole nitrate should be avoided by those patients taking warfarin due to a small chance of interaction (8) (see my earlier blog - click here). Antifungal powders are less likely to be effective than creams in preventing recurrence (9).
Figure 2: Interdigital Infection
Where compliance is an issue for daily application of an antifungal, terbinafine film forming solution (Lamisil Once®) can be recommended. Applied once to clean and dry feet, the film containing terbinafine dries and adheres to the skin remaining active for up to a month. A study demonstrated a mycological cure of 72% at week 6 after a single application. Relapse rates at week 12, following a single application were equal to one week of terbinafine cream (10). In my clinical practice I generally recommend a single application of Lamisil Once® every 3 months to reduce reinfection rates.
It is important to check that the patient is not suffering with tinea elsewhere – typical sites include the groin and hands. If this is the case, these areas should be treated too, otherwise reinfection can arise from these areas.
Additional advice should be given to those patients who undertake sporting activities which require periods of time barefoot or using communal changing or bathing facilities where infection is more prevalent (11). Walking barefoot across areas where infected scales may be present can lead to adhesion of dermatophyte elements to the soles (12) and subsequent invasion of the epidermis can take place within hours. However, one study has highlighted how simple towel drying of the feet after exposure is adequate to physically remove adhered fungus from the skin (13). Therefore, patients should be advised to dry their feet thoroughly after undertaking any barefoot activities in communal areas before putting their shoes back on. If patients are unable to reach their feet fully to undertake this, rubbing their feet on a stiff mat has also been shown to be effective at removing any recently attached fungal elements.
Work conducted in 2006 looked at how fungal elements adhere to the skin when wearing contaminated footwear. The work concluded if shoes were worn, then socks should be too as this was shown to reduce the infection risk from the shoe to the skin (14).
Preventing Nail Infection
Figure 3: Established Sub-ungual Onychomycosis
Nail reinfection with fungus generally arises when skin infection exists, and therefore will be a later consequence of skin infection. Nails most at risk are those which have been previously traumatised – so may already be thickened or dystrophic. A recent study has shown that regular application of topical antifungal nail treatment (weekly) to be effective in reducing nail re-infection (15). In the UK, amorolfine 5% lacquer is currently the only licenced medicine and, on that basis, would be the recommended drug of choice.
Medical devices such as nail pens and treatment applications have no evidence of effectiveness in preventing recurrence so cannot be reliably recommended over amorolfine lacquer. Although formally untested, it is suggested that patients at risk of nail reinfection should also, regularly use a topical antifungal on their skin as suggested under “Preventing skin infection” above. Patients should be advised to return to their podiatrist if there is suspicion that nail infection is returning so an appropriate assessment and any required treatment can be conducted. As nail infection tends to be progressive and become more difficult to treat as the infection spreads throughout the nail, earlier attendance should always be encouraged.
Footwear and occlusion
The type of footwear worn probably has an influence on recurrence. FFI is most likely to strike when closed in footwear is being worn. Occlusion causes in-shoe temperature and humidity to rise. Levels above 95% humidity in the footwear promotes fungal growth. Consequently, well ventilated shoes may lessen that risk. In one study a typical casual shoe with leather uppers showed highest humidity levels when worn whilst wearing canvas shoes showed some reduction, footwear with ventilation holes within the upper design showed significantly lower humidity (16).
It has been observed that rates of fungal foot infection amongst the population correlates strongly to the length and severity of the winter. Therefore, wintertime probably presents as the greatest risk period for infection. When infection is suspected treatment should be undertaken as detailed below.
Disinfection of Footwear and Hosiery
Research has consistently demonstrated how the shoes and hosiery can be a ready source of fungal foot re-infection, following cure. Studies have demonstrated how fungal infection can remain viable in footwear for several weeks and beyond. The relative risk of each type of footwear has not be quantified although slippers are thought to particularly contribute to reinfection as they are often worn without socks and are rarely cleaned or replaced.
A recent review of the disinfection strategies employed to footwear and hosiery (17) highlights the research undertaken to determine the most satisfactory way to reduce fungal load. Although a number of options are explored: disposal of shoes and socks, washing of hosiery (at a range of temperatures), use of formaldehyde and other chemicals in-shoe and UV light devices there is not sufficient evidence to suggest any particular method (17). Empirically, the use of terbinafine 1% sprayed into footwear has been shown to be effective in reducing fungal presence in shoes (18). In addition, I have written in a blog previously how hypochlorous solution is effective in eradicating 99.9% of dermatophytes from sock fabrics in under 5 minutes (Read here).
The technique also has the benefit of being readily available and non-corrosive to footwear and so would seem an appropriate additional measure. Ultimately, footwear disinfection should be seen as secondary to prophylactic use of topical treatments as these are the main barriers to fungal reinfection.
Download the free patient advice sheet - Click Here
Please feel free to modify this leaflet for your own use, but please credit the original source.
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