04/11/23

SKIN AND WOUND INFECTIONS

Dr. Lakmini Yapa, Senior Registrar ( Medical Microbiology),

T/H Kurunegala

1. Describe the risk factors for infections of the skin

2. Describe the principles of classifying post operative wound infections

3. Describe the methods of collection and transport of samples for microbiological diagnosis

4. Outline principles of treatment and prevention

Be able to

Factors controlling skin microbial load

Dry skinFew organisms

Mainly staphylococci /diphtheroids

Moist skinMany organisms

Including staphylococci /Diphtheroids/

Gram negatives etc

pustule

papilloma

macule

vesicleulcer

Wound Depth can Result in Different Diseases

S. aureus infections

S. aureus infections

Folliculitis

Carbuncle

•CA MRSA•Near nares / upper lips -

S. aureus infections

Group A Streptococcal

infections

cellulitis

Rash of scarlet fever

lymphadenitisNecrotizing fasciitis

erysepalas

Necrotizing fasciitis

• Clinical features– Early – pain, cellulitis, fever,

swelling, induration, skin anaesthesia

– Late – severe pain, blistering, skin discolouratin, dishwater discharge, crepitus, multi-organ failure

• Diagnosis– Clinical and needs high index

of suspicion

• Microbiology• Management

Necrotizing fasciitis

• Microbiology– Group A streptococci – 15% of cases

• M types 1 & 3• Produce exotoxin A and streptolysin O which act as

super-antigens

– Often polymicrobial• Other Gram positive cocci• Gram negative bacilli – aeobic and anaerobic

– Occasionally fungi and vibrio

• Management– Early diagnosis and adequate surgical

debridement– Appropriate antibiotics

Cutaneous infections

Cutaneous anthrax

ErythrasmaCorynebacterium minutissimum

Mycobacterial infections

Atypical mycobacterial infections

M ulcerans

M.marinum

Buruli ulcer

Viral infections of skin

fungal infections of the skin

Tinea versicolor onychomycosis

Candida infection

Serious infections associated with

skin manifestations

Post operative wound infections

• Increases morbidity / mortality

• Increases cost

• Varying risk– Type of operation– Elective / emergency– Experience of surgeon– Patient co-morbidities

Classification of operative wounds by level of bacterial

contamination

Classification of operative wounds by level of bacterial

contamination

• Clean wound – in which no inflammation was encountered– a non traumatic wound – no break in technique occurred – respiratory/ GU and alimentary tracts not opened

I. Vascular surgery

II. mastectomy

infection rate: without prophylaxis 5.1% with prophylaxis 0.8%

• Clean-contaminated wound – non traumatic

– GI/GU/Respiratory tract entered without spillageI. Appendectomy

II. Abdominal and Vaginal Hysterectomy

Classification of operative wounds by level of bacterial

contamination

Classification of operative wounds by level of bacterial

contamination

Infection rate: without prophylaxis 10.1% with prophylaxis 1. 3%

• Contaminated wound– fresh traumatic wound from a relatively clean source– operative wound with major breach in technique– gross spillage from GI tract– entry into biliary or urinary tract with infected bile or urine

• incisions encountering acute non purulent inflammation• dirty wounds (dirty source/delayed)• faecal contamination / foreign bodies / devitalized viscus• pus from any source encountered

Classification of operative wounds by level of bacterial

contamination

Classification of operative wounds by level of bacterial

contamination

Infection rate: without prophylaxis 21.9% with prophylaxis

10.2%

Classification of operative wounds by level of bacterial contamination

• Dirty wound– Operative wound dirty – Traumatic wound from dirty source – Traumatic wound with delayed treatment – Fecal contamination – Foreign body – Retained devitalized tissue – Operative wound w/ acute bacterial inflammation or perforated viscus – Operative wound where clean tissue is transected to gain access to a

collection of pus

Major pathogens

• Clean surgery - S aureus• gut related surgery - mixed flora including

anaerobes

•Specific pathogen not reliably predictable

•Sensitivities also not reliably predictable

•Differentiate between colonization and pathogen necessary

•multiple pathogens common in many situations (gut)

•antibiotic cover for major pathogen(s) adequate - both for prophylaxis and treatment)

Route of bacterial contamination of surgical wounds

Prevention of surgical infections

• Surgical technique

• Asepsis

• Antibiotic prophylaxis

Microbial concentration and virulence

+Injury to wound tissue

+Foreign material

Resistance to perioperative antibiotics

+

=

Risk of wound infections

General and host immunity

+ Peri-operative antibiotics

Interventions of benefit in reducing risk of surgical wound infections

• Reduce inoculation of virulent or antimicrobial resistant bacteria into wound

Interventions of benefit in reducing risk of surgical wound infections (cont.)

• Reduce inoculation of virulent or antimicrobial resistant bacteria into wound– Intra-operative and post-operative

• careful preparation of skin with povidone-iodine or chlorhexidine containing solution

• rigorous adherence to aseptic technique

• high flow of filtered air*

• consider laminar flow environment*

• consider irrigation of wound with antibiotic containing solution

• isolate clean from contaminated surgical fields

• minimize drains (drains through separate stab wound)

• minimize catheters and IV lines post-operatively

Peri-operative antibiotic prophylaxis• Efficacy - unquestioned• Selection of appropriate antibiotic(s)

– based on clinical trials (usually under powered)– likely pathogen(s) and ABST– safety / cost

• Timing and duration of prophylaxis– with induction (exception-colonic surgery)– operations>4 hours - repeat dose intra-operatively every 4 hours– duration -contentious issue (single vs multiple)

Peri-operative antibiotic prophylaxis (cont.)

• Recommendation for prophylaxis– see current literature

• Side effects of prophylaxis– antibiotic associated colitis– vancomycin related hypotension– selection of resistant ‘hospital’ flora

• Cost-benefit of prophylaxis– difficult

Aetiological diagnosis in skin infections

Specimens• Macules / papules - usually no direct examination

• Vesicles / ulcers – aspirate / scraping from base

• Pustules/boils / carbuncles – pus (by aspiration or incision and drainage)

• Wound infections – aspirate / tissues removed at surgery (surface swabs often taken but often reflect colonizing flora)

Request from microbiology laboratory

• Microscopy - Gram stain / Zeihl Neelsen / wet prep

• Culture – bacterial / fungal / viral

• Particularly viral infections – antigen detection / PCR

Interpretation of results

Culture of wounds :• Surface of wounds colonized with many organisms• Surface swab reflects this colonization

– miss true pathogen– lead to overuse of antibiotics

http://jdfc.org/spotlight/diabetic-foot-infections-current-diagnosis-and-treatment/

The Journal of Diabetic Foot Complications, 2012; Volume 4, Issue 2, No. 1, Pages 26-45