Bacterial nail infections are caused by microorganisms such as Staphylococcus aureus (S. aureus). It is an infection of the nail fold which may involve the nail plate.
Structure of the Nail
The nail is actually a plate of keratin formed by the germinal tissue called the nail matrix, under the proximal part of the nail (where it starts growing from the underlying finger tissue). The nail matrix is part of the nail bed which adds thickness to the nail plate. The nail protects the tip of the finger from accidental trauma.
The nail joins the finger at the proximal and lateral nail folds. This tissue actually splits to enclose the nail at its boundaries. The upper part of the proximal nail plate forms the cuticle which joins the nail plate to the skin behind it. This is a tight seal which keeps the nail free of infection.
The nail fold is infected in cases of paronychia. This may be the result of injury, infections or allergic reactions.
Types of Bacterial Paronychia
Acute paronychia is usually preceded by finger trauma in the form of biting the nails, manicuring too deep, a hangnail or sucking the fingers. The most common organism involved is S. aureus. Other causative microorganisms include streptococcus and pseudomonas species.
Chronic paronychia is caused by many factors acting together, including infective and inflammatory agents. It occurs mostly in people who have their hands constantly exposed to agents which are chemically or immunologically irritant, or in a wet environment.
Acute paronychia presents with localized pain and tenderness of the skin around the nail. The skin appears reddened and swollen, and the infection may discolor the nail or lead to distortion of its shape.
In more severe cases, pus may collect and form an abscess at the base or sides of the nail. In such cases the skin feels fluctuant and looks whitish. In more severe infections, the nail is lifted off the nail bed by the extension of the infection beneath the margin of the nail.
Chronic paronychia is usually not very red, but the nail folds are puffy and painful. The characteristic boggy look and feel gives away the diagnosis. In such cases the symptoms will have been present for at least 6 weeks, either constantly or from time to time.
These episodes may be triggered by exposure to wet surroundings. Fluctuance is not usually seen in these cases. However, the nail plates become chronically thickened and the color may change. The cuticles appear to be widely separated from the underlying nail plate, leaving a gap through which microbes may penetrate and cause infection.
Diagnosis and Management
With early paronychia, the finger should be fomented in hot water 3-4 times a day. This relieves pain and swelling while the infection resolves. With persistent infection, oral antibiotics should be started. The finger may be splinted to alleviate the symptoms and prevent further trauma.
Antibiotics are usually selected to treat staphylococci. In cases which follow finger-sucking or nail biting, anerobes may be present, and thus appropriately general antibiotics should be prescribed.
The commonly used antibiotics are penicillin and ampicillin. If resistant staphylococci are present, amoxicillin with clavulanic acid may be used, as may clindamycin. Another option is to take specimens for cultures before starting antibiotic therapy.
If a collection of pus has formed, surgical drainage should be considered. Otherwise the pus may form a run-around abscess by extending under the nail fold to reach the other side.
Other routes of extension are under the nail plate to the nail bed, elevating the nail. In such cases incisions may have to be made, and the nail may require to be removed, for proper drainage to occur.
When the skin is yellow or white over the abscess, it is dead and direct incision is all that is necessary.
The wound should be pressed gently to drain the pus and packed for open drainage, along with an appropriate oral antibiotic. Dressings should be removed after 48 hours, and warm soaks will help continue drainage and promote healing.
In chronic bacterial paronychia, it is necessary to keep the hands clean and dry, and to protect them from chemicals and trauma. Cotton-lined gloves are useful for this.
Topical steroids, antibiotics and antifungals are effective in treating the infection which is often complicated by fungal infection. Acetic acid soaks are also used. Oral antibiotics may be started if required. Surgical management involves removing the nail, or marsupialization of the eponychium.
Reviewed by Afsaneh Khetrapal, BSc (Hons)