HMA - Infections

Folliculitis

superficial infection of single hair follicles, usually causing small, red or pus-filled lesions.

Furuncles (boils)

deep infection of hair follicles extending to surrounding dermis, forming painful, pus-filled nodule.

Carbuncles

an aggregation of several furuncles, producing a larger, deeper area of infection with multiple draining points.

Non-bullous impetigo

superficial bacterial skin infection causing small vesicles/pustules that rupture and form characteristic honey-coloured crusts around mouth and nose.

Bullous impetigo

superficial infection, usually caused by S. aureus strains secreting exfoliative toxin A. producing large, fragile fluid-filled blisters (bullae) that rupture to form red, wet base and collarette.

Lymphadenopathy

swollen or enlarged lymph nodes.

Collarette

circular rim of fine, peeling scale that develops after a pustule, vesicle, or inflammatory lesion rupture.

Staphylococcus aureus

Most common causative agents for bacterial hair follicles.

Staphylococcus aureus

Most common causative agents for impetigo.

Exfoliative toxin A

secretion from some strains of staphylococcus aureus causing bullous impetigo.

Cellulitis

acute bacterial infection of the deep dermis and subcutaneous tissue often of the legs, causing spreading redness, warmth, swelling and pain with poorly defined borders, and systemic symptoms if severe (fever, chills, tachycardia, low BP).

Erysipelas

more superficial infection of the upper dermis and lymphatics of face or lower legs, typically producing a sharply demarcated, raised, bright-red area of inflammation, with fever chills, and malaise.

Necrotizing skin and soft tissue infection (NSTI)

rapidly progressive infection causing necrosis (tissue death) of skin and/or deeper soft tissues, often accompanied by severe systemic illness (high fever, tachycardia, confusion, unconscious, falling BP).

Necrotizing fasciitis

type of NSTI involving the fascia and surrounding soft tissues, causing rapidly progressive destruction of fat, subcutaneous tissues, and blood vessels and potentially life-threatening sepsis (30% mortality rate).

Gangrene

tissue death (necrosis) resulting from inadequate blood supply (dry), infection (wet), or both; may produce blackened tissue and can be associated with severe infection, common complication of diabetes.

Streptococcus pyogenes

Most common causative agent got monomicrobial necrotizing skin and soft tissue infection.

Acne

blocked hair follicles (comedomes) caused by accumulation of sebum and keratin presenting as blackheads, white heads, cysts, or nodules associated with pubertal hormonal changes and sometimes involving bacterial growth causing inflammation.

Comedomes

blocked hair follicles caused by accumulation of sebum and keratin associated with acne.

Oral herpes

HSV-1 infects and replicates in oral mucosa, travelling along sensory neurons to the trigeminal ganglion to remain dormant, reactivating in case of stress or illness.

Trigeminal ganglion

Where does HSV-1 remain dormant.

Genital herpes

a sexually transmitted infection caused mainly by HSV-2, but also commonly by HSV-1, producing painful genital or perianal vesicles/ulcers that can recur.

Warts

benign skin or mucosal growths caused by human papillomavirus (HPV), resulting from viral infection in basal epidermal cells, causing their proliferation; appearance varies by wart type and location (plantar, flat, plane).

Human papillomavirus

Causative agent for warts.

Dermatophytosis

superficial fungal infection of the skin, hair, or nails caused by dermatophytes (trichophyton, microsporum, epidermophyton), commonly presenting as tinea/ringworm.

Pityriasis versicolor

superficial fungal infection caused by overgrowth of Malassezia yeast, producing scaly, discoloured patches of skin, usually on the trunk and upper arms.

Malassezia yeast

Causative agent for pityriasis versicolor.

Scabies

contagious skin infestation caused by the mite Sarcoptes scabiei, which burrows into the stratum corneum, causing intense itching and a characteristic rash, often worse at night.

Mupirocin

topical antibiotic that inhibits bacterial protein synthesis, commonly used for localized impetigo and Staphylococcus aureus skin infections.

Fusidic acid

topical antibiotic that inhibits bacterial protein synthesis, commonly used for localized staphylococcal skin infections, particularly impetigo.

Floxacillin

oral β-lactam antibiotic resistant to staphylococcal β-lactamases, commonly used for cellulitis, infected wounds, folliculitis and other MSSA skin infections.

Dicloxacillin

oral anti-staphylococcal penicillin that inhibits bacterial cell-wall synthesis and is resistant to β-lactamases, commonly used for MSSA skin and soft-tissue infections, including cellulitis and infected wounds.

Doxycycline

tetracycline antibiotic that inhibits bacterial protein synthesis, commonly used orally for acne.

Escherichia coli

gram(-) rod in intestinal/perineal microbiota, causes urinary catheter associated UTIs, surgical wound infections, and bacteremia.

Clostridioides difficile

gram(+) anaerobic, spore-forming rod producing toxins; causes antibiotic-associated diarrhoea and colitis when antibiotics disrupt intestinal microbiota, allowing acquired spores to proliferate.

Bacteroides fragilis

gram(-) anaerobic rod in intestinal microbiota; causes intra-abdominal infections and abscesses in surgical wounds, and causing bacteremia.

Proteus mirabilis

gram(-) rod in intestinal microbiota; causes UTIs, pneumonia and bacteraemia.

Burkholderia cepacia

gram(-) aerobic rod; can cause severe respiratory infections in vulnerable patients, from contaminated water, medications or medical equipment.

Candida albicans

fungus in skin/GI/genital microbiota; causes systemic candidiasis, commonly associated with central venous catheters, surgery, antibiotics or immunosuppression.

Enterococcus faecalis/faecium

gram(+) cocci in intestinal microbiota; causes UTIs, bacteraemia and surgical-site infections, often arising from patient GI flora and associated with medical devices; E. faecium commonly develops vancomycin resistance (VRE).

Staphylococcus aureus

gram(+) cocci in in skin/nasal microbiota; commonly causing surgical wound infections, also bacteremia or pneumonia via transmission or invasive medical device MRSA is resistant to most β-lactams.

Klebsiella pneumoniae

gram(-) rod commonly in intestinal microbiota; causes UTIs, pneumonia and bacteraemia often from urinary/vascular devices; important ESBL and carbapenem-resistant pathogen.

Acinetobacter baumannii

gram(-) short coccobacillus; pneumonia, bacteremia, meningitis surgical wound infection, UTIs spread between ICU patients, and from contaminated hospital environment; often multidrug-resistant.

Pseudomonas aeruginosa

gram(-) rod causing pneumonia, bacteremia, and surgical wound infections from contaminated water, equipment or respiratory devices; often multidrug-resistant.

Enterobacter species

gram(-) rods in intestinal microbiota; cause UTIs, pneumonia and bacteraemia for ICU patients and those on mechanical ventilation; often multidrug-resistance.

Urinary tract infections

usually catheter-associated; ascend from microbiota or hospital environment along urinary catheter where biofilm forms, promoting persistent infection.

Bacterial biofilm

aggregated bacteria adhering to a surface encased in a sticky extracellular substance they produce that creates extreme immune and antibiotic resistance.

E coli, Klebsiella pneumoniae, Proteus mirabilis

List 3 key causative agents for hospital acquired UTIs.

Surgical wound infections

microorganisms enter surgical site from skin/mucosal microbiota, contaminated environment, or healthcare workers, with location, complexity, or length of surgery affecting incidence.

Staphylococcus aureus

Most common causative agent for surgical wound infections.

Hospital acquired pneumonia (HAP)

caused by aspiration of colonised oropharyngeal/GI secretions into the lower respiratory tract; endotracheal tube facilitate biofilm formation and bacterial entry causing ventilator-associated pneumonia (VAP).

Bloodstream infections

commonly associated with central venous catheters from skin microbiota, healthcare workers, or contaminated equipment; also spread from surgical wound or respiratory infection.