Staphylococcus aureus

Staphylococcus aureus is a Gram-positive bacterium. 15–40% of healthy people carry it harmlessly in the nose and skin folds (DermNet). It can only invade through broken skin, which is why eczema suits it so well. Colonisation in Atopic Dermatitis is very common. The Totté et al. meta-analysis (BJD 2016; 95 observational studies) found S. aureus on 70% of eczema lesions, 39% of non-lesional skin and 62% of noses in people with AD. People with AD were about 20 times more likely than controls to be colonised on lesional skin (OR 19.74). In children with AD, studies report colonisation in 57–100%, and more than 40% carry it on both lesions and nose. The nose is a likely source of recolonisation (Ogonowska et al., Front Microbiol 2021). Colonisation rises with eczema severity. MRSA makes up a 4–13 times larger share of AD isolates than in healthy people, especially in children (MRSA).

Staphylococcus aureus [part-of] Skin Microbiome Skin Barrier Dysfunction [causes] Staphylococcus aureus Staphylococcus aureus [worsens] Atopic Dermatitis Filaggrin [relates] Staphylococcus aureus

Colonised versus infected. Colonisation and infection are different, and the difference matters for treatment. S. aureus makes toxins, including superantigens such as enterotoxin B and TSST-1, which fuel itch and Th2 inflammation even in eczema that does not look infected. Toxin-producing strains were found on 31.5–80% of lesions (Ogonowska 2021). When the bacteria cause clinical infection, eczema becomes impetiginised. It turns weepy, develops golden-yellow crusts or pus spots, gets worse quickly or stops responding to treatment, and the child may have a fever or seem unwell (NICE NG190; NICE CKS). See Infected Eczema and Impetigo. NICE warns that “eczema is often colonised with bacteria but may not be clinically infected”, and that not every weepy, crusted flare is bacterial. Under-5s are also the main group affected by staphylococcal scalded skin syndrome, a toxin-driven blistering illness (DermNet).

Staphylococcus aureus [causes] Infected Eczema Staphylococcus aureus [causes] Impetigo Staphylococcus aureus [triggers] Th2 Immune Response

Antibiotics: flucloxacillin and fusidic acid, but not by default. NICE NG190 (2021) applies to children from 72 hours old. It says: do not routinely offer a topical or oral antibiotic to a child who is not systemically unwell, because the benefit over Topical Corticosteroids alone is limited and repeat courses breed resistance. Emollients and steroid creams should carry on either way. If an antibiotic is used, the options are:

• Fusidic Acid 2% cream three times a day for 5–7 days, for small, localised patches only.
• Oral Flucloxacillin for widespread or severe infection, or for a child who is systemically unwell. NG190 gives 125–250 mg four times a day for 5–7 days for ages 2–9, and 62.5–125 mg for infants. The prescriber fixes the dose for each child using BNFC.
• Clarithromycin if the child is penicillin-allergic.
• For suspected MRSA, the doctor consults a microbiologist.

DermNet explains why flucloxacillin is first choice: S. aureus makes beta-lactamase (penicillinase), and flucloxacillin resists it. NG190 also says not to swab routinely at the first visit. Swabs are for infection that is not improving or keeps coming back. For frequent recurrences, a nasal swab and decolonisation (for example nasal mupirocin or fusidic acid) can be considered.

Flucloxacillin [treats] Staphylococcus aureus Fusidic Acid [treats] Staphylococcus aureus NICE NG190 [regulates] Flucloxacillin Staphylococcus aureus [relates] MRSA

What the Cochrane review found (George et al. 2019). “Interventions to reduce Staphylococcus aureus in the management of eczema” (Cochrane CD003871.pub3, updating Birnie 2008) pooled 41 RCTs with 1,753 participants. Twelve trials recruited only children, and mean ages ranged from 1.1 to 34.6 years. The review found insufficient evidence that anti-staphylococcal treatments help either infected or uninfected eczema:

• Steroid/antibiotic combination creams may give slightly more “good/excellent” improvement than steroid alone (RR 1.10, 95% CI 1.00–1.21; 3 studies; low quality). Quality of life in children probably did not differ (moderate quality).
• Oral antibiotics versus placebo in infants and children may make no difference (RR 0.80, 95% CI 0.18–3.50; low quality).
• Bleach Baths versus water or placebo may make no difference (RR 0.78; low quality). Burning, stinging and dry skin were similar in both groups.
• Antibacterial soaps, bath additives and topical antiseptics showed no clear benefit.
• Data on antibiotic resistance were very low quality.

33 of the 41 studies were at high risk of bias. The authors call for larger trials and for non-antibiotic strategies, given rising resistance. So the overall evidence level for treating the bacteria is weak, even though the bacteria’s role is well established.

Cochrane [contradicts] Bleach Baths Cochrane [relates] Staphylococcus aureus

Antiseptics and prevention at home. NICE CG57 advises teaching parents to recognise infection and to replace emollient tubs and steroid creams after an infection, because opened products can become contaminated. Scooping emollient out with a clean spoon or using a pump dispenser also helps (Emollient Therapy). DermNet (2015) recommends handwashing, nasal decolonisation and “twice-weekly bleach baths may be useful”. The Cochrane review did not find a benefit from bleach baths.

Conflict: [DermNet, 2015] says twice-weekly dilute bleach baths “may be useful” to prevent staph infection in eczema. [Cochrane, George et al., 2019] says bleach baths may make no difference to eczema improvement versus water (low-quality evidence) and no anti-staph intervention has clear benefit. Unresolved — add to open_questions.

Home bleach baths and "antibacterial" products on toddler skin

Dilute bleach baths are only worth considering on a clinician’s instructions with exact dilution. Mixing them by guesswork risks chemical irritation of broken skin. Antibacterial soaps and bath additives showed no benefit in Cochrane 2019, and fragranced antiseptic products can sting or sensitise eczematous skin.

Emollient Therapy [relates] Staphylococcus aureus Bleach Baths [relates] Staphylococcus aureus

Connections

• Atopic Dermatitis — infective complication, source: DermNet; NICE CG57
• Skin Barrier Dysfunction — overgrows on barrier-impaired, filaggrin-poor skin (>40% of bacteria in paediatric flares) and worsens it, source: Edslev, Acta Derm Venereol 2020
• Th2 Immune Response — superantigens drive IgE/Th2; Th2 cytokines suppress antimicrobial peptides, source: Agrawal & Woodfolk 2014
• Filaggrin — FLG mutations raise colonisation risk, source: Edslev 2020
• Infected Eczema — main cause of impetiginised eczema, source: NICE NG190
• Eczema Herpeticum — co-infection in 30.3% of hospitalised EH children, source: Aronson, Pediatrics 2011
• Flucloxacillin — first-choice oral antibiotic when one is needed, source: NICE NG190; DermNet
• Fusidic Acid — first-choice topical for localised infection, source: NICE NG190
• MRSA — 4–13× more common among AD isolates, source: Ogonowska, Front Microbiol 2021
• Bleach Baths — no clear benefit in RCTs, source: Cochrane 2019
• Cochrane — George 2019 review: insufficient evidence for anti-staph interventions, source: Cochrane CD003871
• Skin Microbiome — dominates dysbiotic eczema skin, source: Ogonowska 2021
• Impetigo — staph skin infection presenting as crusts/blisters, source: NHS
• NICE NG190 — antibiotic prescribing guideline, source: NICE
• Coconut Oil — VCO decolonised SA in adult AD RCT (unreplicated in children), source: Verallo-Rowell 2008
• Skin pH — grows better at neutral pH; dermcidin killing drops from >90% (pH 5.5) to 60% (pH 6.5), source: Kumar & Das 2023