Lecture 11

Question 1

Hospital-Acquired Infections (HAIs) / Nosocomial Infections

Answer 1

Infections acquired during hospital stay, which were not present or incubating at the time of admission

Infections can occur even after discharge

Affect 5–10% of hospitalized patients

Healthcare workers can rarely get infected too.

95% of HAIs are bacterial

5% are caused by viruses or parasites

Question 2

Most Common Types of HAI

Answer 2

Surgical site infection
Urinary tract infection (UTI)
Pneumonia
Sepsis
Other (e.g., bloodstream infections)

Question 3

Sources of Infection:

Answer 3

1. Exogenous (from external environment):

Direct inoculation (e.g., dirty tools) without colonization.
Now rare due to better hygiene.
Mostly occurs in ICUs if hygiene fails.

2. Endogenous (from the patient’s own microbiota):

Early endogenous: from flora already present before admission (e.g., E. coli, S. pneumoniae).

Late endogenous: hospital flora that first colonizes the patient, then causes infection (e.g., MRSA, P. aeruginosa).

Question 4

Factors Increasing HAI Risk:

Answer 4

🦠 Microorganism:
Often opportunistic pathogens, which take advantage when immunity is low.

Common ones: S. aureus, E. coli

🧍 Host (Patient):
Weakened immunity or barriers (e.g., wounds, catheters)

💉 Treatment:
Invasive procedures, prolonged catheter use, immunosuppressive drugs, antibiotic overuse

🏥 Environment:
Air, water, dust, surfaces, equipment—can all harbor pathogens

Question 5

High-Risk Patient Populations

Answer 5

Surgical patients: skin barrier breached

ICU patients: exposed to multiple invasive devices, on multiple antibiotics

Burn victims: large skin damage + suppressed immunity

Immunocompromised/Transplant patients: high antibiotic use + poor immunity

Question 6

Necrotizing Fasciitis (Flesh-eating Disease)

Answer 6

A rare but very serious soft tissue infection causing rapid tissue death.

🔍 Symptoms:
Severe pain, fever, swelling
Skin appears shiny, red, hard
Later stages:
Blisters (bullae)
Bleeding under skin
Gas formation in tissue
Skin numbness (dead nerves)

🧬 Risk Factors:
Diabetes, cancer, obesity
IV drug use
Peripheral artery disease
Trauma, recent surgery

Question 7

Types of Necrotizing Fasciitis: Type I – Polymicrobial (70–80%)

Answer 7

Caused by Mixed bacteria
Gram-positive cocci
Gram-negative rods
Anaerobes

Usually in abdominal or groin areas.

Clostridial Type (10% of Type I):
Gas gangrene caused by Clostridium species

Clostridium perfringens
Produces α-toxin and Θ-toxin:

α-toxin: Causes blood clotting, cuts oxygen to tissues, inhibits immune cells

Both toxins damage blood vessels and weaken the heart

Question 8

Types of Necrotizing Fasciitis: Type II – Monomicrobial (20–30%)

Answer 8

Caused by S. pyogenes, sometimes with S. aureus

Often affects young, healthy people after injury

Question 9

Types of Necrotizing Fasciitis: Type III – Vibrio vulnificus

Answer 9

Caused by Vibrio vulnificus
Rare, from saltwater through wounds

Question 10

Types of Necrotizing Fasciitis: Type IV

Answer 10

Fungal infections
Especially in immunocompromised patients

Question 11

Burn Units and Infections

Answer 11

Infection is the top killer in burn patients (61% of burn deaths are due to infection).

Burn wounds trigger inflammation and metabolic changes → easier for microbes to invade.

Question 12

ENVIRONMENTAL RISKS in HOSPITALS

Answer 12

Common sources:
Dust, water, antiseptics, fluids, air, food, IV medications, medical equipment

High-risk areas:
High: Operating rooms, ICUs, incubators
Medium: Patient and exam rooms
Low: Corridors, hospital cafés