Lecture 11 - Healthcare Aquired Infections

Question 1

What are healthcare aquired infections.

Answer 1

5% - 10% of hospitalised patients acquire infection.
Hospital acquired infections are infections that are acquired in hospital, not being present in incubation at admission.
They can also occur after discharge such as post operation or after prosthesis. They most commonly occur in patients but can also occur in healthcare staff.
The most common HAIs are surgical site infections, UTIs and pneumonia

Question 2

What are the sources of healthcare aquired infections.

Answer 2

• Exogenous - Direct inoculation of organism into patients without colonisation, today they are relatively rare as they are easy to prevent with hygienic measures
• Endogenous - Infections that are caused by already colonising microorganisms
  ○ Early Endogenous - Colonising flora that patient had before hospitalisation
  Late Endogenous - Hospital flora which firstly colonises patients body and hen can cause infection flora.

Question 3

What factors affect HAI

Answer 3

Factors related to HAI
* Microorganism
* Host
* Treatment
* Environment
Most often HAIs are caused by opportunistic pathogens.

NCI infection possibilities
The patient is colonised by own flora but it is causing no harm
The patent is colonised by hospital flora but it causes no harm (nosocomially colonised)
The patent is nosocomially colonised and it leads to infection

Susceptible populations
* Surgical patients due to breach in skin integrity
* Patients in intensive care units due to increased intervention e.g. respirators
* Patients with burns - huge skin defects
* Immunocompromised patients; organ transplant, cancer, drugs, etc.
* Old people

Treatment related infections
* Antibiotics are overused which leads to antibiotic resistant bacteria
Immunosuppressive drugs lead to deficient immunity and higher susceptibility.

Question 4

Necrotizing fasciitis

Answer 4

An opportunistic infection that leads to skin decay
Symptoms include:
* Fever, swelling, excessive pain
* The initial skin changes are similar to cellulitis or abscess
* Hardening of skin- appears shiny and tense
Later stage symptoms
* Bullae
* Bleeding into the skin
* Gas in tissues - gas gangrene
* Absent sensation over skin
Risk factors include - poor immune function, obesity, cancer, intravenous drug use etc.
Its incidence is about 0.4/100,000 in USA and 1/100,000 in Europe. The incidence is equal in males and females but rare in children.

Question 5

What are the differences between the different types of necrotising fasciitis.

Answer 5

1. Type I - 70-80% of cases and is caused by a mixture of bacterial types (polymicrobial) it usually occurs in abdominal or groin areas. Clostridial infection accounts for 10% of type I infection and can cause gas gangrene. It has two deadly toxins a-toxin which causes excessive platelet aggregation which blocks blood vessels, allowing anaerobic bacteria to grow and preventing the access of WBCs. The a-toxin and Θ-toxin together cause the destruction of RBCs in blood vessels and cause damage to the integrity of the blood vessels, they also supress heart function.
2. Type II - 20-30% of cases, mainly involving the extremities. It mainly involves Streptococcus pyogenes alone or in combination with staphylococcal infections. It more commonly affects young healthy adults with a history of injury.
3. Type III - Vibrio Vulnificus a bacterium found in saltwater is a rare cause of this infection, which occurs through a break in the skin
4. Type IV - Possibly fungal in nature

Clostridial infection (associated with type II)
Clostridium sordelli can also produce two major toxins:
* Essential virulence factor lethal toxin
* Haemorrhagic toxin
The key virulence factor in Clostridium septicum is a pore forming toxin called alpha toxin.

Question 6

Why are burn units particularly succseptible to HAI

Answer 6

Burn Units
Burn wounds induce metabolic and inflammatory alterations that predispose the patient to various complications.
Infection is the most common cause of morbidity and mortality in this population.

Question 7

How does the environment affect HFI

Answer 7

Environment
The risk of HAI is different depending on the purpose of the hospital environment for example operation theatres have high risk whilst corridors have low risk.
* Dust
* Water - fluids and antiseptics
* Air - airborne microbes and air conditioning - prevented using strict regulations
* Food
* Medication - IV, drugs
* Devices
* Clean surfaces also important

Source
* Infected patient
* Contaminated environment
* Healthcare personnel
* Visitors (extremally rare)

Transmission
* Hands of healthcare staff
* Instruments not properly sterilised or disinfected
* Air
* Indirect contact with environment
* Food

Prevention - hand washing - education - appropriate antibiotic use