Impetigo is a relatively common, contagious, superficial skin infection caused by either Staphylococcus aureus or beta-hemolytic streptococci. At times, both microorganisms may be isolated. Impetigo mainly affects children and young adults. The disease is more prevalent in hot, humid weather. Two diverse forms are recognized on the basis of clinical, bacteriological, and histological findings: impetigo contagiosa and bullous impetigo. The diagnosis is primarily clinical and the appearance of thick, dirty looking, honey coloured crust is characteristic of impetigo. It may be supplemented by Gram-stained smear examination of the pus and also its culture on suitable bacteriologic media. Adequate treatment with topical and/or systemic antibiotics terminates impetigo.
No known genetic pattern
Primary infections are more common in children. Secondary infections in any age.
Males = Females
SIGNS AND SYMPTOMS
- It begins as a small reddish macule which soon turns into a vesicle/vesiculopustule
- The vesicle has a thin roof that ruptures to expose a red moist base
- The serous and purulent fluid dries to form a reddish brown/honey colored, firmly adherent crust. The crust may thicken and has a “stuck on” appearance, a hallmark of impetigo.
- A slight erosion is revealed on removal of the crust
- Satellite lesions may appear in the vicinity resulting in annular, circinate and/or gyrate patterns
- Face, hands, feet, and legs are the usual sites of involvement. However, the lesions may appear anywhere on the body
- Most lesions heal without scarring or other sequelae. Glomerulonephritis is an uncommon but feared complication.
- It erupts as a small, erythematous macule that turns into a vesicle. However, the developing vesicles do not rupture but enlarge to form flacid bullae.
- The contents of the bullae, initially clear, turn cloudy
- The centre of the thin roofed bulla collapses, collecting the seropurulent contents into its folds
- Eventually the roof desiccates to form a thin honey colored, “varnish like” crust
- Removal of crust reveals an inflamed, erythematous base that oozes serum
- Untreated, the lesions may extend radially and attain a size of 2 to 4 cm and subsequently undergo spontaneous healing in a few weeks
- Staphylococcus aureus most commonly causes impetigo contagiosa. Also group A beta-hemolytic Streptococcus pyogenes (GAS) or mixed organisms cause impetigo contagiosa
- Bullous impetigo is caused by phage group 2, type 71 S. aureus
- Warm ambient temperature
- High humidity
- Presence of skin diseases favouring secondary impetiginization
- Poor hygiene
- Crowded living condition
- Neglected minor trauma
- Insect bites
- Gram stained smear of exudate reveals Gram-positive cocci, in chains or clusters, within the neutrophils
- Culture, S. aureus, commonly:GAS (especially from older lesions). Failure of oral antibiotic may be indication of infection by methicillin—resistant S. aureus (MRSA)
- Hematology: Leukocytosis
- Serology: Anti-DNAse beta detects prior GAS infection
Drugs that may alter lab results
Disorders that may alter lab results
- The histologic examination may reveal
- Vesicle formation in the subcorneal or granular region, acantholytic cells, spongiosis, dermal perivascular infiltrate of lymphocytes and neutrophils
- Gram-positive cocci in blister fluid and within neutrophils.
Anti DNAse beta detects prior GAS infection
- Pemphigus vulgaris
- Subcorneal pustular dermatosis
- Stevens—Johnson syndrome
- Herpes zoster
- Herpes simplex
Non bullous impetigo
- Insect bites
- Infectious eczematoid dermatitis (IED)
- Allergic contact dermatitis
APPROPRIATE HEALTH CARE
Bland compresses and use of soap and water to remove bacteria laden crust. Saline solution or boric acid or aluminium acetate, or potassium permanganate compresses are useful.
No special diet
The importance of good hygiene must be emphasised to the patient
DRUG(S) OF CHOICE
- Cloxacillin, 250 to 500 mg, 6 hourly, for 10 days
- Cephalexin, 250 to 500 mg, 6 hourly, for 10 days
- Amoxicillin plus clavulanic acid, 20 mg/kg/day, given tid, for 10 days
- * Erythromycin, 250 mg to 500 mg, 6 hourly, for 10 days
- * Clarithromycin, 250 mg to 500mg, 12 hourly, for 10 days
- * Azithromycin, 500 mg, once a day, for 3 days
- Methicillin resistant S. aureus may be managed by
- * Minocycline, 100 mg, every 12 hours, for 10 days
- * Ciprofloxacin, 500 mg, twice day for 10 days
Mupirocin ointment for application twice a day
Sensitivity to drugs
See manufacturer's profile for each drug
Significant possible interactions
See manufacturer's profile for each drug
Patient must be monitored for healing of the lesions. If the pyoderma does not clear in 7 to 10 days, culture and antibiotic sensitivity testing is essential
PREVENTION / AVOIDANCE
Mupirocin may be applied thrice a day to the sites of minor skin trauma. It is effective as a preventive treatment.
Patients with recurrent impetigo should be evaluated for carriage of S. aureus. Nares and perineum are the commonest sites for microbial carriage. Mupirocin ointment applied to the nares and perineun twice a day for 5 to 7 days significantly reduces S. aureus carriage. Rifampicin may also be administered orally for the same purpose.
- Cellulitis and erysipelas
- Guttate psoriasis
- Scarlet fever
- Post-streptococcal glomerulonephritis
EXPECTED COURSE AND PROGNOSIS
Impetigo usually resolves in 5 to 7 days with adequate antibiotic treatment
Systemic antibiotics appear no more capable of preventing the renal lesion in this disease than they do in the streptococcal pharyngitis leading to rheumatic fever.3
- Anaemia and malnutrition
- Poor hygiene and sanitation
- Preexisting dermatoses
AGE RELATED FACTORS
- Barton LL, Friedman AD. Impetigo: a reassessment of etiology and therapy. Pediatr Dermatol 1987; 4: 185–188.
- Degan R. Impetigo in childhood: Changing epidemiology and new treatments. Pediatric Annuals 1993; 22: 235–240.
- Demidovich CW, Wittler RR et al. Impetigo. Current etiology and comparison of penicillin, erythromycin, and cephalexin therapies. Am J Dis Child 1990; 144: 1313–1315.
- Doebbeling BN. Long term efficacy of intranasal mupirocin ointment. A prospective cohort study of Staphylococcus aureus carriage. Arch Intern Med 1994; 154: 1505–1508.
- Sehgal VN and Jain S. Pyoderma. JIMA 1991; 89: 175–176.