Renal Abscesses Renal abscesses can occur as either a complication of pyelonephritis, where they typically are caused by gramnegative rods, or from hematogenous seeding from systemic bacteremia, in which case S aureus is the most common etiology Risk factors for renal abscesses due to pyelonephritis include anatomic obstruction (e.g., nephrolithiasis) or vesicoureteral reflux These abscesses can occur in either the renal cortex or medulla Risk factors for hematogenous spread include endocarditis or intravenous drug use; in some instances, children have had a preceding minor skin infection, with transient bacteremia seeding the kidneys These abscesses primarily are found in the renal cortex Symptoms include fever, malaise, back or abdominal pain, and weight loss The absence of dysuria does not exclude a renal abscess Costovertebral angle tenderness is found in a majority of adults, but is less sensitive in children Laboratory findings include leukocytosis with a left shift and elevated erythrocyte sedimentation rate (ESR) and CRP Patients whose abscesses connect with the collecting system may have urinalyses demonstrating pyuria, proteinuria, and bacteriuria For patients whose abscesses are due to hematogenous spread, initial urinalyses can be normal, but the organism will grow in culture Renal abscesses should always be suspected in a child with a presumed S aureus UTI Ultrasound often cannot distinguish a purulent collection from a hematoma, whereas a contrasted CT can help determine the extent of disease Medical management alone is usually sufficient for renal abscesses less than cm in diameter, whereas percutaneous drainage in addition to antibiotics is needed for larger abscesses Broad-spectrum antibiotics covering both gram-negative organisms (pseudomonal coverage should be considered for immunocompromised hosts or persons who previously have had pseudomonal UTIs) and S aureus should be started pending culture results Improvement is followed clinically (fever curve) and through laboratory parameters (normalization of white count and inflammatory markers) Standard precautions are indicated SKIN AND SOFT TISSUE INFECTIOUS EMERGENCIES The major infections of the skin, soft tissues, and bones include impetigo, cutaneous abscesses, cellulitis and superficial abscesses, fasciitis, septic arthritis, and osteomyelitis Additionally, mastitis and omphalitis occur in the neonate Among the disorders in this group, impetigo and cellulitis are both common complaints in the ED Although children with bone and joint infections are seen infrequently, the differential diagnosis of several common complaints (e.g., fever, limp) often includes these conditions Thus, the emergency clinician who cares for children should be familiar with such infections, particularly because a prolonged delay in the institution of therapy can result in appreciable morbidity Impetigo Impetigo is a superficial pustular infection of the epidermis In contrast, ecthyma involves the dermis Bullous impetigo is characterized by lesions greater than cm in diameter GAS is the most common cause of impetigo, while S aureus is the most common cause of bullous impetigo, but can also cause nonbullous impetigo Impetigo is predominantly a disease of the preschool-aged child, and is more common during summer months Children typically lack systemic signs and symptoms of infection Skin findings include honey-crusted or bullous lesions with minimal surrounding erythema or induration; regional adenopathy is not common Routine laboratory evaluation is unnecessary in the well-appearing, previously healthy child Complications may include cellulitis and glomerulonephritis if the child is infected with a nephritogenic strain The risk of renal disease is not decreased by treatment of local infection Mupirocin can eradicate most cases of impetigo, especially if the disease is limited in distribution, and may decrease selection for antibiotic resistance Systemic therapy may be indicated for bullous impetigo or if use of topical antibiotics is impractical due to extent of disease Oral treatment options include cephalexin, or clindamycin TMP-SMZ offers coverage for the vast majority of staphylococcal isolates (both MRSA and MSSA), but does not cover GAS Knowledge of the rates of MRSA in your area can help optimize empiric antibiotic therapy Contact precautions should be used Cellulitis Cellulitis is an infection of the skin and subcutaneous tissues A related disease is erysipelas, which involves the more superficial skin layers Erysipelas lesions are beefy red, raised above the skin surface, and have very welldemarcated borders; the most common cause is GAS The most common causes of cellulitis by location and exposure type are listed in e-Table 94.12 Clinical manifestations include erythema, edema, warmth, and pain; only 10% to 20% develop fever Regional adenopathy is common Blood cultures rarely are positive in wellappearing immunocompetent hosts, except in children with pneumococcal, H influenzae, or group B streptococcal