Clinical use
Investigation of hair, skin and nails for superficial mycoses.
Background
Dermatophytes can be divided into three groups:
- anthropophilic dermatophytes are passed from human to human and are the most common in the community.
- zoophilic or animal acquired infections are usually sporadic.
- geophilic dermatophytes are most often acquired following a close association with soil or from an animal itself infected by soil contact.
Infection is usually diagnosed by observing the presence of fungal hyphae in skin, hair or nail specimens. However, it is important to culture the material to determine the infecting genus and species. This is done to ensure selection of the most appropriate therapy and in order to trace its likely epidemiology which may help in the management of infection. Dermatophyte infections (commonly known as ringworm) are usually referred to as tinea followed by the Latin name of the body area involved. The most common dermatophyte infections are tinea pedis in adults (athlete’s foot) which may also include tinea unguium (nail infection), and tinea capitis (scalp ringworm) in children.
Infection by dermatophytes is cutaneous and generally restricted to the non-living cornified layers in patients who are immunocompetent. This is because the dermatophyte group of fungi are generally unable to penetrate tissues which are not fully keratinised (ie deeper tissues and organs). However, reactions to such infections can range from mild to severe depending upon the host’s immune response, the virulence of the infecting species, the site of infection and environmental factors.
Patient preparation
Skin
Patients’ skin and nails can be swabbed with 70% alcohol prior to collection of the specimen, this is especially important if creams, lotions or powders have been applied. The edges of skin lesions yield the greatest quantities of viable fungus. Lesions should be scraped with a blunt scalpel blade. If insufficient material can be obtained by scraping and being placed in a container, then a swab or sticky tape can be pressed on the lesion and transferred to a clean glass slide for transport to the laboratory (‘stripping’). Samples in containers achieve the optimum results.
Nail
Good nail samples are difficult to obtain. It should be specified whether the sample is from the fingernails or toenails. Material should be taken from any discoloured, dystrophic or brittle parts of the nail. The affected nail should be cut as far back as possible through the entire thickness and should include any crumbly material. Nail drills, scalpels and nail elevators may be helpful but must be sterilized between patients. When there is superficial involvement (as in white superficial onychomycosis) nail scrapings may be taken with a curette. If associated skin lesions are present samples from these are likely to be infected with the same organism and are more likely to give a positive culture. Sample from associated sites should be sent in separate packets.
Hair
Samples from the scalp should include skin scales and hair stumps. Cut hairs are not suitable for direct examination as the infected area is usually close to the scalp surface. Scraping for direct examination is the preferable sample collection method, however plastic hairbrushes, scalp massage pads, swabs or plastic toothbrushes may be used to sample scalps for culture where there is little obvious scaling. If sufficiently long, hairs should be plucked with forceps and wrapped in black paper or commercial transport packs together with flakes of skin. Collect specimens other than swabs into appropriate CE marked leak-proof containers and place in sealed plastic bags.
Specimen requirements
Dermapak
Specimens should be kept at room temperature and transported and processed as soon as possible although, provided the samples are kept dry, the fungus will remain viable for several months.
Samples should be allowed to dry out and kept at room temperature.
Limitations & restrictions
Avoid the use of plastic containers.
Do not refrigerate samples if there is a delay in transport to the laboratory. Keep at room temperature.
Turnaround time
3 weeks
Analysing laboratory
Microbiology Lab, James Cook University Hospital, Marton Road, TS4 3BW