Miscellaneous infections Flashcards
Joint infections
Usually only occurs in one joint (monoarticular) and usually occurs in the knees and hips. There is direct extension of infected bone and is secondary to hematogenous spread. Can be used by an inflammatory response
Laboratory tests of joint fluids (3)
- Increased white blood cells
- Decreased glucose
- Increased protein
Specimen collection and processing of joint infections
Aspirate by needle and syringe. Inject specimen into anaerobic transport vial. If clotted, must grind, then prepare direct smear Can inoculate blood culture bottle, in addition to solid media. Includes nonselective media, enriched media (thioglycollate broth), and anaerobic media
Infection of prosthetic joints
Infection often occurs over a year after surgery- biofilms. Usually occurs due to normal skin flora
Specimen collection of bone marrow
- Cleanse puncture site
- Aspirate bone marrow
- If clotted, homogenize specimen in BSC
- Inoculate blood culture bottles and nonselective media
- Centrifuge lysis procedure (Isolator system) is recommend
Osteomyelitis
Due to hematogenous spread of the infectious agent and invasion of bone tissue, can occur from trauma or surgery. This often becomes a chronic infection. Underlying conditions put patients at risk- diabetes, bites, hospitalized patient, medical devices
Specimen collection and processing- osteomyelitis
Bone is removed at surgery or percutaneous biopsy- the infected bone is generally soft and necrotic. In BSC, grind specimen in sterile saline before inoculation of media. Place small bits of bone into solid media and enrichment broth
Selection of skin/tissue specimens
This depends on the extent and character of infection. A closed abscess is the specimen site of choice, culture is not recommended for dry, encrusted lesions. Tissues- specimens are usually sterile sites, collected from surgery, needle biopsy, and autopsy
Specimen collection from skin and tissue (6)
- Decontaminate skin, aspirate abscess contents with syringe
- Collect specimen from the advancing margin of the lesion.
- Burns must be extensively cleaned and debrided before collection.
- Place tissue sample into sterile container
- Swabs & aspirates use transport medium
- Labeling - give specific anatomic site; do not label specimen only as “wound.”
Aerobic transport of skin or tissue specimens
For aerobic only, submit in aerobic transport medium. This includes exudates from superficial lesions, open wounds, lacerations, or open abscesses
Anaerobic transport of skin and tissue samples
For anaerobic and aerobic requests- submit in anaerobic transport medium. Includes surgical aspirates, closed-abscess aspirates, and tissue biopsies
Processing of skin and tissue samples (5)
- Direct Gram stain
- Histological stain—helps determine tissue invasion
- Process sample in biological safety cabinet
- Enriched and selective solid media, as dictated by anatomical site of lesion. Broth media aid in isolation of facultative and anaerobic organisms.
- Quantitative tissue samples- primarily for infected burns
Direct Gram stain of skin and tissue samples
Determines quality of specimen. Look for bacteria. Neutrophils indicate presence of infection. Epithelial cells indicate contamination with skin flora
Skin infections (6)
- Pyoderma
- Cellulitis
- Impetigo
- Furuncle
- Carbuncle
- Erysipelas
Pyoderma
Skin infection, presence of pus (WBC)
Cellulitis
A bacterial infection, affects the deeper layer of skin and soft tissue
Impetigo
A highly contagious skin infection associated with children. Forms red, itchy lesions around the nose and mouth, which develop into vesicles that burst forming yellow crusted areas. Commonly caused by Staphylococcus or Streptococcus
Furuncle
Infection of the hair follicle; common name = boil
Carbuncle
A painful collection of furuncles that is connected under the skin.
Erysipelas
A bacterial infection that is commonly caused by group A strep. It is a superficial form of cellulitis (in the upper dermis layer of the skin). Symptoms0 large red patches, swelling, pain
Vesicles
small fluid filled blisters (sac, cyst)
Bullae
large blisters, usually >5mm
Draining Sinuses
Channel or passage way, abnormal passage from inside of the body to the outside
Fistulas
Resulting from surgery or injury, an abnormal connection between organs or other tissues. Formation between hollow area and an organ.
Necrotizing Fasciitis or Necrotizing Subcutaneous Infection (NSI)
Infection of the fascia – tissue lining under the skin that separate muscle and internal organs. Introduction by ulceration, infection (infected pox, blister) or trauma. 30% mortality when not diagnosed early
Myonecrosis
Deep muscle tissue, leading to pain, cell death, gas gangrene= necrosis, sepsis, organ failure leading to death
Myositis
Inflammation of the muscle, resulting from infection, injury, or autoimmune conditions.
Clostridial Myonecrosis
- Clostridium perfringens (traumatic form, most common), 2. C. septicum (spontaneous form, most common),
- C.histolyticum, C. sordelli, C. sporogenes, etc.
Traumatic – injury or trauma limiting blood supply. Spontaneous – Associated with immune dysfunction, colon cancer, rectal cancer other cancers
Erythema Chronicum Migrans
Bull’s eye rash associated with Lyme disease. Lyme disease is the most common arthropod-borne (i.e., Ixodes tick) disease in the US. Causative agent - Borrelia burgdorferi
Erythema Infectiosum
Slapped cheek rash associated with Fifth disease
Erythema Infectiosum causative agents (4)
- Parvovirus B-19 – most commonly associated with 5th Disease
- S. pyogenes
- Syphilis
- Measles
Bone marrow bacterial infections (2)
- Brucella abortus
- Mycobacterium tuberculosis
Bone marrow fungal infections (2)
- Histoplasma capsulatum
- Blastomyces dermatitidis
Necrotizing fasciitis causative agents (4)
- Group A streptococci
- Staphylococcus aureus
- Bacteroides sp.
- Clostridium sp.
Why plate postmortem cultures?
Cultures must be taken no longer than 48hrs postmortem, best <24hr. Blood culture and sterile tissue are most helpful.
A single organism, typical pathogen, suggests true infection. Recovering skin flora suggests contamination from procedure
Autopsy samples
Most internal organs (other than lungs) are previously uninfected and remain sterile for approximately 20 hours after death. 75% of all tissues obtained at autopsy should be sterile. >10^5 organisms/gram tissue indicates infection, While <10^5 organisms/gram tissue indicates colonization
Optimal growth for mycobacteria
optimal growth for these is 30 degrees C
Causes of wounds and abscesses (3)
- Bowel- lower GI flora
- Colon cancer
- Hospital-acquired infections (HAI, nosocomial)
Types of wound infections (3)
- Tetanus- Clostridium tetani
- Wound botulism- Clostridium botulinum
- Fungal infections-Sporotrichosis, Phaeohyphomycosis, chromoblastomycosis, mycetoma, coccidiomycosis, & blastomycosis
Surgical wound infection
Due to breakdown of skin barrier or the organism is introduced during surgery
Main risk of intraabdominal abscess
Leads to secondary bacteremia
Risk of bites
Infection with human or animal oral flora. Includes aerobic and facultative bacteria and anaerobes
Infection of prosthetic devices
Infection occurs within 1 week to several years due to biofilm formation
Infections in drug abusers
Source of infection includes contaminated materials or needles, or endogenous normal flora. There are factors contributing to increased risk of infection: malnourished, poor hygiene, lapses of consciousness, or aspiration. The most common infectious agent is S. aureus
Complications of infection in drug abusers (2)
- Endocarditis: S. aureus, streptococci, enterococci, P. aeruginosa, Serratia marcescens
- Pneumonia: Prevotella sp., other anaerobic GNR, Peptostreptococcus sp., streptococci, S. aureus, aerobic GNR
Predisposing factors of infection in diabetes patients (3)
- Peripheral neuropathy and decreased peripheral vascular circulation
- Acidosis predisposes patient to fungal infection
- Increased glucose levels can be immunosuppressive
Types of infection in diabetes patients (6)
- Diabetic foot ulcer
- Chronic soft tissue infection
- Anaerobic cellulitis and fasciitis
- Necrotizing cellulitis
- Malignant otitis externa
- Fungal infections: Rhinocerebral mucormycosis, candidiasis
