Clinically Significant Fungal Pathogens Flashcards
What is a hospital aqcuired infection?
A hospital-acquired infection is usually one that first appears three days after a patient is admitted to a hospital or other health care facility.
- 5-10% of patients admitted to hospitals in the US develop a nosocomial infection.
- The CDC estimate > two million patients develop hospital-acquired infections yearly causing 99,000 deaths a year
Describe Candida auris- (Japanese fungus)
- First isolated in Japan in 2009
- It has been isolated from a range of body sites, resulting in invasive infections
- A more common “cousin” in this family is Candida albicans, which causes the yeast infection thrush.
- Hospital outbreaks have since been reported in the United States, India, Pakistan, Venezuela, Colombia, Israel, Oman, South Africa and Spain, as well as the UK
- 66% mortality rate
How do I know if someone has a Candida auris infection?
- Most people who get serious Candida infections are already sick from other medical conditions
- C. auris is still rare
- Invasive Candida infection causes fever and chills that don’t improve after antibiotic treatment for a suspected bacterial infection
- Only a laboratory test can diagnose C. auris infection
Describe drug resistance
- Highly transmissible between patients and from contaminated environments
- Highlighting the importance of instituting effective infection prevention and control practices.
- All isolates from the UK demonstrated reduced susceptibility to fluconazole, and variable susceptibility to other antifungals.
C.auris- UK data
- The first UK case emerged in 2013, infection rates have been going up - although it remains rare.
- End of July 2017- affected more than 200 patients in hospitals in England So far, no UK patient has died from it.
- Often misidentified
- Approximately ¼ of reported C. auris detections are clinical infections, including 27 candidaemias.
- Three large nosocomial intensive care unit outbreaks reported.
C.auris-investigation in clinical laboratories
• Indistinguishable from most other Candida species
purple
- Germ tube test negative budding yeast
- Some strains can form rudimentary pseudohyphae on cornmeal agar.
- Growth at 42 - 45⁰C
CHROMagar™ Candida
Incubate in aerobic conditions
30-37°C for 48 hours.
Typical Appearance of microrganisms:
Candida albicans → green
Candida tropicalis → metallic blue
Candida krusei / auris→ pink/purple, fuzzy
Other species → white to mauve
Sabouraud Dextrose agar (SDA)
30⁰C Atmosphere
Aerobic
Front line tests
- API AUX 20C
- VITEK-2 YST
- BD Phoenix
- MicroScan
- Misidentifed as a wide range of Candida species and other genera
Confirmation Testing -MALDITOF
Any Candida spp isolates associated with:
1) Invasive infections and isolates from superficial sites in patients from high intensity/augmented care settings
2) Transferred from an affected hospital (UK or abroad)
What further work should be undertaken to ensure that they are not C. auris?
- Molecular sequencing of the D1/D2 domain or MALDI-TOF Biotyper analysis with C. auris either already present or added to the database
- Pure isolates on Sabouraud slopes sent to PHE
Antifungal Susceptibility Testing
- There are no established minimum inhibitory concentration (MIC) breakpoints at present for C. auris.
- Using breakpoints for other Candida spp, CDC) demonstrated that, of the global outbreaks they investigated, nearly all of 54 isolates were highly resistant to fluconazole.
- More than half of C. auris isolates were resistant to voriconazole
- Some isolates have demonstrated elevated MICs to all three major antifungal classes, including azoles, echinocandins, and polyenes.
- WGS of the organism has found resistant determinants to a variety of antifungal agents.
- PHE Mycology Reference Laboratory indicates in the UK all isolates are resistant to fluconazole
Decribe treatment
- First-line therapy remains an echinocandin pending specific susceptibility testing which should be undertaken as soon as possible.
- Evidence that resistance can evolve quite rapidly in this species, ongoing vigilance for evolving resistance is advised in patients who are found to be infected or colonised
- No evidence to support combination therapy in bloodstream infections with this organism, although if the urinary tract or central nervous system (CNS) is involved dual therapy may be necessary.
- Currently UK strains remain susceptible to the topical agents nystatin and terbinafine
Describe Colonisation
Colonisation tends to persist and is difficult to eradicate making infection prevention and control strategies particularly important:
- Strict adherence to central and peripheral catheter care bundles, urinary catheter care bundle and care of the tracheostomy site
- Prompt removal of venous cannulas if there is any sign of infection
- High standards of aseptic technique when undertaking wound care
- Skin decontamination with chlorhexidine washes in critically ill patients.
Suggested screening sites, based on the predilection of Candida spp to colonise the skin and mucosal surfaces i.e. genitourinary tract, gastrointestinal, mouth and respiratory tract, are:
- Groin and axilla
- Urine
- Nose and throat
- Perineal swab
- Rectal swab or stool sample
Describe Infection control
- Effective handwashing
- Isolate the patient
- Waste disposal in clinical waste bins
What is ring worm?
- Ringworm is a common skin disorder otherwise known as “tinea” or “dermatophytosis.”
- First discovered in 1841 by Hungarian physician David Gruby
- 1934 Chester Emmons published study of several species of dermatophytes
- WWII, American servicemen contracted ringworm in the humid Pacific Theater
- Following which U.S. government launched an intensive study of fungal diseases.
How can you catch ringworm?
- From person to person
- Touching items which have been in contact with an infected person eg towels, clothes,
- From animals, such as dogs, cats, guinea pigs and cattle have fungal infections on their skin.
- Farm animals- Touching a farm gate where infected animals pass through may be enough to infect your skin.
- From soil- rare
Ring worm presentation: Tinea Capitis
- Scalp ringworm and is the most common ringworm infection in children.
- Causes the infected area to scale and may involve temporary hair loss.
Woods lamp examination
- Emits ultraviolet (UV) light in the 365 nanometer range
- The examination is performed in a dark room
- Wood’s light shines directly on the affected area for a few seconds and looking for any changes in colour or fluorescence.
- Normal skin does not fluoresce under the light of a Wood’s lamp.
- If a fungal or bacterial infection or pigment disorder is present, Wood’s lamp examination can strengthen or lessen the suspicion of a particular diagnosis, based on the colour of fluorescence of the affected skin being illuminated.
What are the targets for antifungal therapy?
Cell membrane: Fungi use principally ergosterol instead of cholesterol
DNA synthesis: Some compounds may be selectively activated by fungi, arresting DNA synthesis
Cell wall: Unlike mammalian cells, fungi have a cell wall
Describe Aspergillus Fumigatus
- Aspergillus is a group of moulds, of which about 200 species have been identified.
- 16 species of Aspergillus moulds are known to be dangerous to humans
- Aspergillus spp. distributed fungal moulds found in soil & other organic matter
- Human disease is caused by Aspergillus fumigatus or Aspergillus niger
- Inhalation of the fungal spores
- Respiratory tract
- Onychomycosis (fungal nail infection)
- Otomycosis (fungal infection of the external auditory canal)
- Implicated in sinus infection
Pathophysiology
- Immunocompetent individual, macrophages and neutrophils normally defend against the inhaled fungus.
- Toxic metabolites attack neutrophils and macrophages
- Underlying immunosuppression affects neutrophil numbers and function
Draw a table of the main approaches to laboratory diagnosis
