S6: blood bourne viruses & hospital acquired infections

Question 1

Describe the characteristics of Clostridioides difficile

Answer 1

Gram-positive, anaerobic, spore-forming bacillus – responsible for the development of antibiotics-associated diarrhoea & colitis
Presence of oxygen is inhibitory to its growth
Infection mostly occurs as a result of spore transmission – via hands of healthcare professionals

Question 2

What is the main protective barrier against Clostridioides difficile & what toxins does Clostridioides difficile produce?

Answer 2

Main protective barrier = normal intestinal flora (when balance of gut microorganisms is disrupted, Clostridioides difficile starts to dominate & colonise the large intestine)
Toxins: A & B
-toxin A: enterotoxin that causes excessive fluid secretion, but also stimulates an inflammatory response & has some effect on damaging cell structure
-toxin B: cytotoxin & damages protein synthesis and cell structure

Question 3

What are main risk factors associated with CDI?

Answer 3

1) Antibiotic exposure = alter & supress normal flora -> allows proliferation of CD & toxin production
2) Older age
3) Hospitalisation

Question 4

What are the clinical signs of Clostridioides difficile infection?

Answer 4

Asymptomatic
Mild/moderate CDI = diarrhoea, presence of mucus or blood in stools, fever & abdominal pain
Severe CDI = leucocytosis, elevated serum creatinine levels & pseudomembranous colitis
Severe, complicated CDI = ileus, hypotension/shock/sepsis, abdominal perforation & very rarely death

Question 5

How do you diagnose CDI?

Answer 5

Aim to identify Clostridioides difficile bacteria & presence of toxins
Stool samples
-enzyme immunoassay
-real time PCR
-EIA for detecting toxins A & B

Question 6

Describe the treatment for the different stages of CDI

Answer 6

1) Mild, antibiotic-associated diarrhoea = cessation of antibiotics may be only treatment necessary
2) Mild to moderate diarrhoea/colitis = metronidazole or vancomycin
3) Severe or complicated disease = vancomycin

Question 7

Describe the pathogenesis of Clostridioides difficile

Answer 7

1) Transmission – patients excrete Clostridioides difficile, faecal-oral transmission (most probably via the hands of health-care workers, patients and friends/family)
2) Host susceptibility – bowel colonisation resistance is diminished (by reduction in diversity of normal flora)
3) Germination – spores interact with germinants (eg. bile acids), triggering germination into toxin-producing bacteria that multiple & adhere to host epithelium; sporulation provides vectors for onward transmission

Question 8

What is MRSA? How is it spread?

Answer 8

MRSA is a type of Staphylococcus aureus that is resistant to most beta-lactam antibiotics, antistaphylococcal penicillins (e.g., methicillin, oxacillin), and cephalosporins
Usually spread through skin-to-skin contact & through contact with objects infected person has touched

Question 9

What is norovirus? How is it spread?

Answer 9

Small, non-enveloped single stranded RNA virus = major cause of gastroenteritis outbreaks
No specific treatment available
Transmission is mainly faecal-oral & thought to also be respiratory
-can be spread following ingestion of contaminated food, direct person-to-person contact or contact with contaminated surfaces

Question 10

Describe the structure of HIV

Answer 10

Single-stranded RNA retrovirus
Specifically affects cells of the immune system specifically CD4 cell
After hijacking the cell’s machinery to replicate the cells are destroyed
Extent of the infection is estimated by the patient’s CD4 T-cell count

Question 11

What is AIDs?

Answer 11

Acquired immunodeficiency syndrome = describe the most advanced stage of HIV infection when the patient has become immunocompromised
Susceptible to serious complications from opportunistic pathogens
-pneumocystis pneumonia
-candidiasis
-protozoal infections

Question 12

List the main symptoms of acute HIV infection & AIDs

Answer 12

Acute HIV infection = fever, weight loss, rash, nausea, vomiting, myalgia, pharyngitis
AIDs = meningitis, pneumocystis pneumonia, TB, skin tumours, chronic diarrhoea

Question 13

List the 7 steps of the HIV life cycle

Answer 13

1) Binding
2) Fusion
3) Reverse transcription
4) Integration
5) Replication
6) Assembly
7) Budding

Question 14

How is HIV transmitted?

Answer 14

Contact of infected bodily fluids with mucosal tissue/blood/broken skin

• sexual contact
• contaminated needles
• vertical transmission to fetus during delivery

Question 15

List the different HIV tests

Answer 15

1) Serology – detects both antigens & antibodies to HIV in the blood
2) PCR – detects the viral nucleic acid
3) Rapid testing – picks up antibodies to HIV in either blood or saliva

Question 16

List HIV treatments & prevention strategies

Answer 16

Treated as soon as possible with anti-retroviral drugs – ensure an undetectable HIV viral load allowing CD4 count to recover
Three ARVs are given = less chance to develop resistance
Prevention: increase condom usage, wide-spread testing/screening, PEP & PrEP

Question 17

Describe the structure of hepatitis B virus & how it is transmitted

Answer 17

Double-stranded enveloped DNA virus
Transmission: blood, sexual intercourse & vertical transmission (predominately)
50% will clear the infection themselves in around 6 months

Question 18

What are the main symptoms of hepatitis B infection?

Answer 18

Jaundice
Fatigue
Abdominal pain
Anorexia/nausea/vomiting 
Joint pain

Question 19

List which antibodies are used to determine hep B status

Answer 19

HBsAg & HBsAb
HBeAg & HBeAb
HBcAb
Chronic hep B infection = persistence of HBsAg after 6 months

Question 20

When is the hepatitis B vaccine given?

Answer 20

Given to babies at 8, 12 & 16 weeks old

Consists of part of surface antigen to induce immune response

Question 21

Describe the structure of hepatitis C virus & how it is transmitted

Answer 21

Single-stranded RNA virus that is enveloped & icosahedral in shape
Transmission of HCV is through sex and blood (IV drug users & needlestick injuries)

Question 22

List symptoms of hepatitis C infection

Answer 22

Around 80% of acute HCV infections are asymptomatic

Symptoms: fatigue, decreased appetite, nausea, vomiting, abdominal pain & jaundice

Question 23

List the tests for hepatitis C

Answer 23

1) Anti-hepatitis C antibody = detects whether people have been infected or if they have been infected before (not protective – only diagnostic value)
2) Viral PCR – look for HCV RNA to confirm if patient has chronic infection

Question 24

Is there a cure for hepatitis B and C?

Answer 24

Hepatitis B = chronic HBV cannot be cured so those infected will spend the rest of their life taking antivirals to try & supress viral replication
Hepatitis C = no vaccine but there is a cure – antiviral combination