Cutaneous abscess and recurrent staphylococcal infection

01OverviewDefinition, clinical context and the essential points that orientate the chapter.

Source control is the organising principle. Examine the whole lesion and regional nodes, assess observations and analgesia needs, and ask about onset, spontaneous drainage, previous antibiotics, diabetes, immune status, injecting, bites, water, travel and previous cultures. Palpation or ultrasound distinguishes a collection from induration. Obtain consent that covers pain control, scar, bleeding, incomplete drainage, packing or dressing and possible further surgery.

Drainage technique depends on anatomy and competence. Prepare aseptically, infiltrate local anaesthetic around rather than into the acidic cavity where possible, incise along safe skin lines at maximum fluctuance, break loculations gently, irrigate when appropriate and collect pus. Routine tight packing of every small cavity adds pain without assured benefit; follow local surgical practice and arrange wound review.

Recurrence is a separate diagnostic problem. Plot sites and look for tunnels, puncta and midline pits. Confirm staphylococcal disease microbiologically before decolonisation, then include relevant close contacts and environmental hygiene according to local or UKHSA advice. A child with unusually early, invasive recurrent abscesses may need immune assessment, but routine broad immunology is not justified after ordinary adult episodes.

Key points

A cutaneous abscess is a focal pus collection: look for fluctuance, pointing, focal pain or spontaneous drainage within or beside cellulitis.
Incision and drainage is the key treatment for an accessible uncomplicated collection; antibiotics cannot reliably sterilise an undrained cavity.
Use ultrasound when depth or fluctuance is uncertain, particularly with obesity, early infection or important nearby anatomy.
Send pus for culture in recurrent, severe, unusual, previously treated or MRSA-risk infection and whenever the result will alter ongoing care.
Add systemic antibiotics for systemic illness, significant surrounding cellulitis, immune compromise, multiple lesions, difficult sites or failed drainage-only care, following local susceptibility guidance.
Do not squeeze a facial, deep or perineal collection and do not incise near major vessels, nerves or tendon sheaths without appropriate expertise.
Recurrent abscesses require a site map and diagnostic review for hidradenitis, cyst, pilonidal disease, foreign body, diabetes and injection exposure.
Decolonisation is a time-limited household-aware protocol agreed with microbiology for recurrent confirmed staphylococcal disease, not a permanent antiseptic routine.

02AetiologyUnderlying causes, associations and risk factors, with why each one matters.

Staphylococcal follicular infection

Staphylococcus aureus, including community-associated MRSA in relevant settings, can extend from a follicle into dermis and form a walled collection.

Barrier inoculation

Shaving, eczema, wounds, injecting, foreign bodies and shared equipment introduce organisms, while household carriage can sustain recurrence.

Host susceptibility

Diabetes, neutrophil dysfunction, immune suppression, chronic skin disease and malnutrition increase severity or recurrence, though many patients have no systemic disorder.

Alternative recurrent anatomy

Hidradenitis, pilonidal sinus, infected epidermoid cyst and fistulating Crohn disease create repeated lesions that decolonisation cannot cure.

03PathophysiologyThe causal sequence from the underlying abnormality to symptoms and harm.

1
Liquefactive collection
Neutrophils, necrotic tissue and organisms accumulate within a cavity, creating pressure and limiting antibiotic penetration until source control occurs.
2
Local capsule and pointing
Inflammation walls off the focus and drives pus toward the surface, producing fluctuance, focal tenderness and eventual spontaneous drainage.
3
Surrounding cellulitis
Infection may extend beyond the cavity into dermis and subcutis, making systemic antibiotics more useful alongside drainage.
4
Colonisation-reinfection loop
Nasal, perineal, skin or household carriage and contaminated personal items can reintroduce a strain after an apparently successful episode.

04Clinical features and red flagsSymptoms, examination findings, patterns of presentation and time-critical warnings.

Fluctuant tender centre

A compressible fluid-like centre beneath taut tender skin supports a mature collection requiring drainage assessment.

Pointing or spontaneous pus

A thin pale apex or purulent discharge confirms cavity communication and provides a useful specimen before antibiotics.

Surrounding cellulitis

Diffuse warmth, oedema and tenderness beyond the focal cavity increases the case for adjunctive systemic treatment.

Danger-site collectionRed flag

Periorbital, central facial, deep hand, breast, perineal or injection-related disease deserves lower specialist referral thresholds.

Necrotising warningRed flag

Pain out of proportion, rapidly spreading oedema, crepitus, haemorrhagic bullae, skin anaesthesia or shock requires immediate surgery.

Chronic tract pattern

Repeated flexural drainage from multiple openings with scars indicates hidradenitis or another sinus-forming disorder rather than isolated boils.

Red flags requiring action

Sepsis, necrotising features, facial or orbital danger triangle, deep hand or perineal disease, injection-related vascular compromise, severe immunosuppression, prosthetic material or inability to achieve safe analgesia and drainage requires urgent referral.

05InvestigationsWhat to request, why it matters and how to interpret it.

Investigation order

Read from the initial assessment onwards. Tests may run in parallel in urgent care; first-line, preferred, confirmatory, definitive and gold-standard labels appear only when the chapter explicitly states them.

01
Point-of-care ultrasoundFirst step
Why
Confirm fluid, measure depth and identify loculations or important adjacent structures.
Interpretation and limitations
Cobblestoning alone supports cellulitis; a hypoechoic cavity supports drainage, but operator skill and anatomy determine reliability.
02
Pus microscopy, culture and susceptibility
Why
Define pathogen and resistance in recurrent, severe, unusual or treatment-failed disease.
Interpretation and limitations
Collect directly from the cavity before antibiotics where feasible and provide exposure, MRSA and prior-treatment details.
03
Blood tests and cultures
Why
Assess sepsis, diabetes and organ dysfunction in systemic or high-risk presentations.
Interpretation and limitations
Routine bloods are unnecessary for a small well-patient abscess; normal markers cannot exclude a dangerous anatomical site.
04
Recurrent-site examination and carriage sampling
Why
Distinguish staphylococcal reinfection from hidradenitis, cyst, pilonidal sinus and fistula.
Interpretation and limitations
Use carriage swabs only as part of an agreed decolonisation assessment after the phenotype and cultured organism are established.
05
Targeted imaging or biopsy
Why
Evaluate deep extension, foreign body, osteomyelitis or a non-healing atypical cavity.
Interpretation and limitations
MRI or CT follows anatomical concern; biopsy an atypical edge with consent and warn pathology about pyoderma gangrenosum or malignancy.

06Differential diagnosisRealistic alternatives and the features that help distinguish them.

Cellulitis without collection

Diffuse warmth and tenderness without fluctuance or ultrasound fluid requires antimicrobial treatment but not a blind incision.

Hidradenitis suppurativa

Recurrent flexural nodules, double comedones, tunnels and rope-like scars indicate chronic follicular inflammation rather than repeated independent abscesses.

Inflamed epidermoid cyst

A longstanding lump with a punctum and keratinous contents may be sterile after rupture; definitive excision is considered after inflammation settles.

Necrotising infection

Disproportionate pain, systemic toxicity, crepitus, bullae, anaesthesia or necrosis demands immediate surgery rather than small-incision management.

Non-infective inflammatory nodule

Pyoderma gangrenosum, panniculitis and foreign-body reaction can mimic an abscess and may worsen after inappropriate debridement.

07ManagementImmediate care, first-line treatment, alternatives and escalation.

01Accessible uncomplicated abscessDrain and reviewFirst stepA superficial collection is confirmed in a stable patient at a site suitable for local drainage.

1Explain alternatives and obtain consent, provide adequate analgesia and asepsis, and collect pus as the cavity is opened.
2Drain loculations and dress according to local practice, avoiding routine antibiotic use when source control is complete and no risk modifier exists.
3Arrange wound review and safety-net fever, spreading inflammation, bleeding, recurrent collection and impaired function.

02Complicated collectionAdd systemic and specialist careSepsis, surrounding cellulitis, immune compromise, multiple lesions, difficult anatomy or incomplete source control is present.

1Refer urgently for threatened anatomy or necrotising features and begin resuscitation and exposure-appropriate antimicrobial treatment.
2Use ultrasound or surgical imaging without delaying emergency source control, and send cavity plus blood cultures when indicated.
3Tailor antibiotics to culture and clinical response, shorten exposure appropriately and reassess for retained foreign material or deeper focus.

03Recurrent staphylococcal diseaseConfirm before decolonisingCultured or clinically convincing abscesses recur in the patient or household.

1Map lesions and exclude hidradenitis, cyst, pilonidal disease, injecting and untreated eczema; assess HbA1c or immunity only when indicated.
2Culture an active lesion and discuss carriage sites, household cases, towels, razors, sport equipment and wound coverage.
3Use a single time-limited decolonisation protocol for patient and relevant contacts with microbiology advice, then audit recurrence rather than repeating indefinitely.

Key medicines and prescribing safety2 treatments · regimens, roles and cautions

Narrow adjunctive therapy after source control for susceptible staphylococcal and streptococcal infection.

Flucloxacillin capsules

Take 500 mg to 1 g orally four times daily for five to seven days when significant surrounding cellulitis warrants adjunctive treatment and MSSA is likely.

Not a substitute for drainage; check penicillin allergy, liver history, renal status and culture, and use local MRSA guidance when risk is credible.

Reduces skin carriage temporarily when recurrent confirmed infection justifies coordinated decolonisation.

Chlorhexidine 4% wash

Use once daily for five days only as one component of a locally agreed staphylococcal decolonisation protocol, avoiding face, ears and mucosa.

Rare serious allergy and chemical burns can occur; do not use indefinitely, follow exact product instructions and combine with nasal treatment only under protocol.

08ComplicationsImportant consequences, why they occur and why they matter clinically.

Sepsis and bacteraemia

An uncontrolled collection can seed blood, joints, bone or endocardium, particularly in immune compromise or injection-related infection.

Local structural injury

Delayed drainage, deep anatomy or poorly planned incision can damage nerves, vessels, tendon sheaths or cosmetically important structures.

Persistent sinus or scar

Incomplete source control, foreign material or an alternative chronic diagnosis can leave drainage, hypertrophic scarring and recurrent pain.

Antimicrobial resistance

Repeated empirical antibiotics and unsupervised decolonisation select resistance while failing to remove a closed cavity or diseased tract.

09Monitoring and follow-upTreatment response, safety checks and longer-term review.

Review the wound for residual collection, spreading cellulitis, bleeding, pain, function and dressing tolerance within the locally agreed interval.
Check culture and narrow, change or stop antibiotics according to source control, susceptibility and clinical response.
Escalate fever, hypotension, rapid spread, disproportionate pain, crepitus, new neurological deficit or perineal change immediately.
For recurrence, record site, organism, susceptibility, contact involvement and whether the complete decolonisation protocol was followed.
Assess scar, sinus and repeated same-site disease after inflammation settles, when an underlying cyst or tract is easier to identify.

10Special situationsVariants, exceptions and circumstances that change the usual approach.

Pus needs an exit

A walled cavity has impaired antimicrobial penetration, making adequate drainage more decisive than broader antibiotic spectrum.

Ultrasound prevents blind incision

A fluid scan can distinguish drainable pus from cellulitic induration and reveal depth near vulnerable anatomy.

Same site suggests structure

A repeatedly inflamed identical point should prompt a search for cyst wall, sinus, foreign body or fistula.

Packing is not automatic

Small uncomplicated cavities may heal without painful packing; follow cavity size, haemostasis and local surgical guidance.

Decolonisation is coordinated

Treating only one household member or repeating single agents haphazardly encourages recolonisation and resistance.

11Common pitfallsFrequent interpretation and management errors.

01
Prescribing antibiotics repeatedly for a fluctuant abscess without arranging drainage.
02
Incising indurated cellulitis blindly when ultrasound shows no collection.
03
Attempting office drainage of a deep hand, orbital, central facial or perineal collection without expertise.
04
Calling recurrent axillary tunnels boils and missing hidradenitis suppurativa.
05
Using permanent chlorhexidine and nasal antibiotic treatment without cultured recurrence or microbiology oversight.