Streptoderma in a child: diagnosis

In the vast majority of cases, the diagnosis of impetigo is made clinically – based on the appearance and location of the rash and the course of the disease. Classic signs include superficial erosions with "honey-colored" (golden-yellow) crusts, most often around the nose and mouth, on the extremities, and other exposed areas; there may be itching or mild soreness. The bullous form produces flaccid blisters with clear contents that quickly burst; ecthyma goes deeper, forming painful scabs and may leave a scar after healing. It is important for the pediatrician to note the number of lesions, their prevalence, and the presence of systemic symptoms. [1]

It's not a concern if the child has no fever and their general condition is relatively unaffected—this is typical of superficial non-bullous impetigo. With ecthyma or massive lesions, pain, regional lymphadenopathy, and weakness are possible. Don't try to differentiate "streptococcal" from "staphylococcal" impetigo by eye: these forms overlap in appearance, and both pathogens often coexist. This is crucial because the initial treatment choice is made based on clinical findings, and microbiological clarification is determined based on the indications. [2]

The initial examination includes an assessment of blanching, the depth of the lesion (superficial erosion vs. ulceration), signs of cellulitis at the periphery, tenderness to palpation, and an examination of the nasal passage and nasal wings—children often scratch the entrance to their nostrils, which contributes to the lesion. Recent bites, abrasions, atopic dermatitis, and chickenpox are also noted—any barrier damage can become "impetiginized." Finding out if similar lesions exist in siblings or within a group helps to suspect an outbreak. [3]

The examination results in a preliminary clinical diagnosis: non-bullous impetigo, bullous impetigo, or ecthyma; an assessment of the prevalence ("local" or "widespread") and risk factors for complications. Treatment can usually begin at this stage; laboratory confirmation is not required for everyone, but only for clear indications (see below). [4]

When tests are needed and what exactly to take

Routine laboratory testing is not required: neither a complete blood count nor cultures improve outcomes in typical limited impetigo. Exceptions include severe or recurrent disease, failure of initial therapy, suspected methicillin-resistant Staphylococcus aureus (MRSA), outbreaks in children, as well as ecthyma and complications. In these situations, specimens from the lesion are sent for bacterial culture and antibacterial susceptibility testing; if possible, smear microscopy is also performed. [5]

Culture is also important when escalating therapy (for example, switching from topical to systemic therapy) or when systemic therapy is already in progress but lesions are spreading. A special case is bullous staph in children, multiple lesions associated with atopic dermatitis, diabetes, and immunodeficiency. Culture helps differentiate "normal" staph susceptibility from MRSA and identify the contribution of group A β-hemolytic streptococci (GAS), which is useful for adjusting the regimen. [6]

Serological tests (ASO titer, etc.) are not necessary for the diagnosis of impetigo: they do not determine treatment strategy or confirm a current skin infection. Blood tests (C-reactive protein, leukocyte formula) are reserved for complicated cases with cellulitis, fever, or systemic symptoms. Urine testing for post-streptococcal glomerulonephritis is performed only if there are appropriate clinical and laboratory signs following a previous infection; it is not indicated as part of the "diagnosis of impetigo." [7]

Repeat cultures are also not performed after clinical recovery; the dynamics of the lesions and the patient's overall well-being serve as a guide. The exception is persistent relapses, when decolonization measures are being considered and confirmation of staphylococcal carriage (e.g., from the nose) in a child or family member is desired; this is done as part of outbreak monitoring and frequent relapses, not as a routine practice. [8]

How to properly collect material for culture and what to ask the laboratory for

The best specimen is fresh exudate or pus from a ruptured vesicle/erosion before antibiotic therapy begins. If crusts have already formed, they are gently softened (with sterile saline), a thin fragment is removed, and a smear is taken from the moist surface beneath the crust. Dry crusts "on the surface" are of little information for microbiology. Indicate "suspected impetigo/ecthyma in a child" in the referral and request culture and susceptibility testing (including suspected MRSA using a local panel). [9]

Gram staining is not mandatory, but it can confirm that the material is indeed purulent (neutrophils) and sometimes provides an early indication of clusters (staphylococci) or chains (streptococci). This does not change the initial strategy, but is useful in severe cases. In outbreaks in children's groups, cultures from several patients are appropriate, and in some situations, screening for S. aureus in the nose of "key spreaders" (this decision is made by a physician with experience in infection control). [10]

If there are signs of cellulitis, abscess formation, or systemic infection, the priority is blood cultures as indicated and an examination to determine systemic therapy and, possibly, drainage. However, for classic superficial impetigo, blood cultures are not required. A skin biopsy is rarely necessary – in atypical, treatment-unresponsive lesions to rule out other dermatoses. [11]

Be sure to record recent antibiotic use, chronic dermatoses (atopic dermatitis), visits to the pool/sports section, insect bites, and injuries in your chart - this helps explain relapses and plan prevention (fomite control, equipment treatment, etc.). If episodes recur in the same location, consider microtrauma/itching (e.g., the nose) rather than a "rare microbe." [12]

How to distinguish impetigo from "similar" conditions (differential minimum)

The most common "mimickers" are: herpes infection (clusters of painful blisters on an erythematous base, rapid erosions; confirmed by PCR of scrapings if in doubt), contact dermatitis (clear connection with an allergen/irritant, no pus, gray-yellow crusts, itching is dominant), impetigo-like dermatitis around the mouth in children, contagious molluscum with impetiginization around the papules. In impetigo, "honey-colored" crusts and mild soreness/itching are clues, but always consider the context. [13]

It's important to distinguish ecthyma from ulcerative pyoderma and necrotizing cellulitis: ecthyma is characterized by a painful, eschar-like ulcer similar to impetigo, without severe intoxication; necrotizing infections cause disproportionately severe pain, rapid spread, fever, and systemic symptoms—these are not outpatient situations. Furuncles and carbuncles are deeper, originate from a follicle, and require a different approach (often drainage). [14]

In children, bullous impetigo is sometimes mistaken for burns/steam burns or staphylococcal scalded skin syndrome (SSSS). SSSSS lacks localized purulent crusts, but presents painful, diffuse erythema and epidermal detachment with a positive Nikolsky sign, and cultures from the lesion are often sterile. The diagnosis and management are different and usually inpatient. If in doubt, refer immediately. [15]

Finally, in children with atopic dermatitis, it's easy to confuse an exacerbation with impetigo. Clues to impetigo include the appearance of a "honey-colored" crust over the eczema, localized painful erosions, worsening with scratching, and the lack of response to anti-inflammatory topical therapy alone. In questionable cases, taking a swab from the surface of the erosion before starting antibiotics is sufficient. [16]

Special situations: outbreaks, MRSA, relapses

If several children in a group are diagnosed with impetigo in rapid succession, it's considered an outbreak. Laboratory confirmation isn't necessary for everyone, but it's advisable for some patients to guide treatment and identify any unusual resistance. Hygiene measures are discussed alongside treatment: separate towels, cleaning toys and surfaces, covering lesions with bandages, and temporarily limiting close contact until clinical improvement occurs. [17]

MRSA is suspected when initial therapy is ineffective, when similar episodes occur in family members, or when local epidemiological data are available. In these cases, culture is essential: it will allow for adjustment of the regimen and, if necessary, discussion of decolonization measures (intranasal mupirocin, antiseptic baths) for the child and close contacts. The decision is always individualized and aligned with antimicrobial policy guidelines. [18]

Recurrent impetigo is often associated with chronic microtrauma (nose picking, scratching due to itching), atopic dermatitis, and shared towels and equipment at sports clubs. The diagnostic approach here is pragmatic: confirm the microbiology at least once and develop a "prevention plan" with the family (skin care, itching treatment, fomite removal). Without this, simply changing the antibiotic will not solve the problem. [19]

For ecthyma and in children with risk factors (immunodeficiency, diabetes, extensive lesions), the threshold for laboratory confirmation is lower—take a culture before starting systemic therapy. This isn't just a matter of academic research: susceptibility data will help more quickly establish an effective regimen and reduce the risk of complications (cellulitis, abscess). [20]

Common diagnostic errors and how to avoid them

The first mistake is trying to "identify the pathogen by its appearance" and then base treatment decisions on that. Non-bullous impetigo caused by streptococci and staphylococci is visually indistinguishable; rely on clinical presentation, local recommendations, and culture indications. The second is excessive testing "just in case" for typical, limited impetigo: it doesn't speed recovery or change treatment strategies. [21]

The third is improper sample collection: dry crusts without exudate are uninformative. Soak the crust, take a swab from the wet surface, send it before starting antibiotics, and be sure to request a sensitivity test if you anticipate the need for systemic therapy. The fourth is a neglected focus on sources of recurrence: the nose, hands, shared towels, and sports equipment. Diagnosis also involves finding out "why it keeps coming back." [22]

Fifth, confusion with differential diagnosis: herpes, SSSS, contact dermatitis, and furunculosis require different solutions. Rule: if the diagnosis doesn't fit or there's no response to therapy within the expected timeframe, revisit the diagnosis – review the clinical presentation, take a culture, and, if necessary, take photographs documenting the progress. [23]

And finally, underestimating outbreaks. If there is a cluster of cases in a group, formulate a clinical diagnosis, but confirm the microbiology of at least some of the children, communicate hygiene recommendations to the institution, and provide parents with clear criteria for re-entry (usually after treatment has begun and in closed outbreaks). This is also part of a competent diagnosis—it doesn't end in a "test tube" but in the right organizational conclusions. [24]