A cutaneous abscess is a localized collection of pus, usually secondary to disruption of skin integrity. The organisms most often involved are methicillin-sensitive Staphylococcus aureus (MSSA), methicillin-resistant Staphylococcus aureus (MRSA), and Streptococcus pyogenes (GAS).
Clinical Presentation and Diagnosis
An abscess presents as a discrete, well-circumscribed swelling with central fluctuance. It is tender and is usually associated with erythema and warmth of the overlying skin. There may be an area of cellulitis adjacent to or surrounding the abscess. Lymphangitis and lymphadenitis are complications that can herald hematogenous dissemination and sepsis.
A patient with a significant abscess may exhibit signs of systemic disease such as temperature >38 °C, tachycardia, or tachypnea, and possibly an abnormal white blood count (>12,000/mm3 or < 4000/mm3).
The definitive treatment of an abscess is incision and drainage, which can usually be performed in the ED. When the abscess is in immediate proximity to neurovascular structures, first perform either a needle aspiration to confirm purulence or obtain an ultrasound to avoid incising a vascular aneurysm. This precaution applies to abscesses in the neck, supraclavicular fossa, antecubital fossa, popliteal fossa, and inguinal and axillary areas.
Maintain strict aseptic technique to prevent the spread of the infection; prepare the skin with a povidone-iodine solution. Although total anesthesia may be difficult to achieve, use a combination of a regional field block (a ring of 1% lidocaine outside the perimeter of the abscess and erythema) and a linear injection of 1% lidocaine into the roof of the abscess along the planned incision line. The maximum dose of lidocaine is 4–5 mg/kg without epinephrine and 7 mg/kg with epinephrine. If this technique is unsuccessful, provide sedation and analgesia (pp. 715–722).
Make the incision along the natural dynamic skin tension lines to prevent excessive scarring. In view of the increasing incidence of MRSA, after the incision, obtain a specimen for culture in case the patient subsequently requires antibiotic therapy. Explore the abscess cavity with a blunt instrument or sterile gloved finger to break up any loculated pockets of purulence. Copiously irrigate the cavity with NS under moderate pressure, pack it loosely with iodoform gauze to promote drainage and ensure hemostasis, and apply a sterile dressing.
Oral antibiotics are of no additional benefit after incision and drainage of uncomplicated abscesses <5 cm in otherwise healthy children. Antibiotics are indicated when the abscess is >5 cm or there is an area of surrounding cellulitis. Use cephalexin (40 mg/kg/day div qid) or cefadroxil (40 mg/kg/day div bid), but if MRSA is prevalent in the community, treat with clindamycin (20 mg/kg/day div qid) alone or add trimethoprim-sulfamethoxazole (which does not reliably cover group A Streptococcus) to one of the above regimens (8 mg/kg/day of trimethoprim div bid). Treat for 5–7 days. Arrange for follow-up in 24–48 hours to evaluate for complications, remove the packing, and repeat the irrigation. Loosely repack the cavity only if pus is found again. Usually, by 48 hours, the incision remains open without packing while the cavity heals from below. Instruct the family to irrigate the cavity under running warm water or to apply warm wet soaks three times daily at home for five days.
Refer breast, perirectal, fingertip (pulp), hand, and deep abscesses of the neck to an experienced surgeon.
After abscess drainage: daily for 2–3 days
Indications for Admission
Abscess associated with lymphangitic streaking, fever >38.9 °C (102 °F), or signs of toxicity
Abscess in an immunocompromised patient
Severe injuries and soft tissue infections
Infections that interfere with oral intake, urination, defecation
About 1% of all ED visits are for bites, the majority of which are caused by dogs. More than one-half of bite victims are children, most of them toddlers. While a patient may seek medical attention because of cosmetic concerns, bleeding, or fear of rabies, the most common complication is infection. An increased risk of infection occurs with puncture wounds, hand wounds, or when there has been a delay (>24 hours) in seeking medical attention.
Clinical Presentation and Diagnosis
Usually, the history of an animal bite is readily obtained, so the diagnosis is evident. The three major types of bite wounds are puncture wounds, lacerations, and closed-first injuries (CFIs). Puncture wounds are of particular concern, as the small break in the skin belies the significant risk of infection. Suspect that a laceration over the metacarpophalangeal joint of an adolescent represents a CFI, sustained when the patient punched another person in the mouth.
Thoroughly clean every bite wound with soap and water. Moderate-pressure irrigation in the ED is indicated for lacerations and CFIs, but it is probably ineffective for punctures. Use an 18 or 20 gauge IV catheter attached to a 1 L bag of NS, around which a blood transfusion cuff is inflated to 300 mm Hg. If the irrigation is not tolerated, anesthetize the intact skin margins of the wound with 1% lidocaine and then irrigate. Debride devitalized tissue, which is an excellent culture medium. This is particularly important with dog bites, which are, in part, crush injuries.
Do not suture puncture wounds; hand, forearm, or foot lacerations; wounds more than eight hours old (except the face in children over one year old); wounds over a joint; crush wounds that cannot be debrided; or if the patient is immunosuppressed. In these circumstances, if the wound appears clean and cosmesis is a concern, close the wound in approximately four days (delayed primary closure). Alternatively, allow the wound to granulate (secondary closure). Low-risk dog bite wounds can be sutured, but avoid deep closure to minimize the possibility of infection.
Because the infection rate is high, leave cat bite wounds open. Exceptions are easily cleaned wounds that are not on the hand, forearm, or foot. Once again, avoid deep closure to minimize the possibility of infection.
Consult with a pediatric infectious disease expert to determine the risk of infection.
Organisms causing infections include Pasteurella multocida, Staphylococcus aureus, and Streptococcus species. Give antibiotics for puncture wounds, hand and forearm wounds, injuries that are considered deep or have penetrated the joint capsule, and lacerations that are sutured. Also give antibiotics to a patient who is immunocompromised, asplenic, or has moderate to severe injuries to the hand and/or face. Use amoxicillin-clavulanate (875/125 formulation; 45 mg/kg/day of amoxicillin div bid). If MRSA is a concern, use either clindamycin (20 mg/kg/day div qid) alone or add trimethoprim-sulfamethoxazole (which does not reliably cover group A Streptococcus) as described for an abscess (p. 763).
Etiologies of infections include Eikenella corrodens, Staphylococcus aureus, Streptococcus spp., Haemophilus spp., Fusobacterium spp., Veillonella spp., and Pervotella spp. Use the same guidelines as for dog and cat bites (above).
Consult a pediatric infectious diseases expert (as above).
Clostridia can be present in the mouths of coprophagic animals. Give tetanus toxoid unless it is certain that a booster was received in the previous five years. For patients under seven years of age, use 0.5 mL of DTaP, unless pertussis vaccination is contraindicated, in which case use DT. For patients 7–10 years old, use 0.5 mL of dT. If the patient is ≥11 years old, use 0.5 mL of Tdap.
Decisions regarding rabies treatment depend on the prevalence of the disease in the species in the area where the animal lives. See pp. 771–772 for the indications for prophylaxis. Give post-exposure prophylaxis (PEP) for any patient with a bite, scratch, or mucous membrane exposure to a bat, unless the bat is available for testing and is negative for evidence of rabies. Also give PEP when direct contact between a child and a bat has occurred, unless the exposed person can be certain that there was no bite, scratch, or mucous membrane exposure. If a bat is found indoors and there is no history of bat–human contact, the likely effectiveness of PEP must be balanced against the low risk of such an exposure. PEP may also be indicated for a patient who was in the same room as a bat and might be unaware that a bite or direct contact had occurred (e.g., a sleeping person awakens to find a bat in the room or an adult witnesses a bat in the room with a previously unattended child, mentally disabled person, or intoxicated person) and rabies cannot be ruled out by testing the bat.
Indications for Admission
Infected bite wounds in patients who initially seek attention >24 hours after the bite
Bite wounds in immunocompromised patients
Foreign Body Removal
A fresh wound is usually tender, and the foreign body is often seen or palpated just below the skin surface. Delayed presentations are associated with induration and tenderness, often with purulent or serosanguinous drainage.
Fishhooks embedded in the skin merit special consideration, as there may be more than one barb. The barb may completely penetrate a finger or earlobe, emerging from the other side, leaving the hook shaft still embedded.
Radiographs can be helpful in identifying and locating foreign bodies. Use a radiopaque marker, such as a bent paperclip taped to the overlying skin, as a reference point for estimating the exact location of the object. A radiograph is also indicated when the presence of a foreign body cannot be ruled out, as when an old wound does not heal, continues to drain serosanguinous or purulent material, or remains tender. Virtually all glass is radiopaque, and wooden splinters can occasionally be seen if they are covered with dirt particles. Obtain an ultrasound to locate a nonradiopaque foreign body such as a thorn or piece of plastic.
Attempt to remove a foreign body in the ED only if it is close enough to the surface to be seen or palpated. Cleanse the skin with povidone-iodine, and anesthetize the area by local infiltration, field block, or regional nerve block. Using the paperclip marker and x-rays for reference, make a stab incision with a No. 11 blade directed at the foreign body. Carefully explore the wound with a small hemostat to find and remove the object. Then gently palpate over the wound with a gloved finger to identify any remaining fragments.
When removal attempts are prolonged or unsuccessful, consult with a surgeon to plan for a definitive operative procedure under fluoroscopic or sonographic guidance. Foreign bodies in the plantar surface of the foot are especially difficult to remove in the ED. Refer patients with foreign bodies in the face or hand to a surgeon, and consult with a surgeon before attempting to remove a foreign body from the neck, unless it is clearly superficial.
When the foreign body is small or cannot be palpated, probing the wound is usually fruitless. If the wound is tender and crusted over, however, unroof it with the point of an 18 gauge needle to facilitate the drainage of any pus; the object may emerge over the next several days. Continue with warm soaks at home, and reevaluate the wound in 48 hours.
To remove a fishhook, advance the barbed end until the skin is tented and anesthetize that area with 1% lidocaine. Then advance the point until the barb leaves the skin, sever the barbed point with wire cutters, and pull the shaft of the hook back out through the original entrance wound. Small-barb hooks may be removed in a retrograde fashion through the original wound site. If the fishhook has several barbs, separate them with wire cutters and remove each one individually. If the barb is already through the skin, cut it off and pull the shaft out without using any anesthetic.
Give tetanus toxoid unless it is certain that a booster was received in the previous five years. For patients under seven years of age, use 0.5 mL of DTaP, unless pertussis vaccination is contraindicated, in which case use DT. For patients 7–10 years old, use 0.5 mL of dT. If the patient is ≥11 years old, use 0.5 mL of Tdap.
Small or nonpalpable foreign body: 48 hours
Insect Bites and Stings
Insect bites and stings usually cause a local reaction. Systemic anaphylactic reactions occur after 1–3% of Hymenoptera stings (honeybees, wasps, hornets, yellow jackets, harvester and fire ants) in susceptible patients.
Reactions can be classified as immediate (within two hours) or, rarely, delayed (after two hours). Immediate reactions may be local or systemic.
Immediate Local Reactions
These include local pain, erythema, swelling, tingling, warmth, and pruritus at the sting site. Local reactions usually last 24–48 hours; they can be extensive, although all affected skin is contiguous with the sting site.
These can occur after a 1–2-week interval. They present as large local reactions, serum sickness (fever, arthralgia, urticaria, lymphadenopathy), and rarely, peripheral neuritis, vasculitis, nephritis, or encephalitis.
Immediate Systemic Reactions
The hallmark of a systemic reaction is swelling that occurs at locations not contiguous with the sting site. The reaction may be mild, with itching and urticaria. More severe anaphylactic reactions can occur with hypotension, wheezing, laryngeal edema, and shock. Eighty-five percent of sensitive patients manifest symptoms within five minutes; all have symptoms within 1–2 hours.
The diagnosis is suggested by the history of a sting or by the typical appearance of a local reaction in the warm-weather months. Stings, as opposed to insect bites, are always painful. Cellulitis may look similar, but a bacterial infection usually does not develop abruptly. A cellulitis may be associated with fever, lymphangitic streaking, and local lymphadenopathy.
Consider other causes of systemic allergic reactions, such as drugs (penicillins, sulfonamides, contrast dyes) and foods (shellfish, eggs). Try to ascertain whether the insect was a member of the Hymenoptera order, and inquire about a history of allergies and any previous systemic reactions to insect stings.
Among the Hymenoptera, only honeybees lose their stingers, which may remain at the sting site. Remove the stinger (if it is still in place) by grasping as close to the puncture site as possible with a small forceps. Cleanse the site, apply ice or cool compresses to the area, and give oral diphenhydramine (5 mg/kg/day div qid, 50 mg/dose maximum) or hydroxyzine (2 mg/kg/day div tid, 50 mg/dose maximum). If the erythema continues to spread during the 24 hours after the bite or sting, consider the wound to be infected. Treat with 40 mg/kg/day of cephalexin (div qid) or cefadroxil (div bid), warm compresses every two hours, and elevation. If MRSA is a concern, use either clindamycin (20 mg/kg/day div qid) alone or add trimethoprim-sulfamethoxazole (which does not reliably cover group A Streptococcus), to one of the above regimens (8 mg/kg/day of trimethoprim div bid).
Local reaction: 24 hours, if the erythema is spreading
Systemic reaction (not anaphylaxis): 2–3 days