Hospital Acquired Infections and Microbiology Control Measures

Definition and Scope of Hospital Acquired Infections

• Nosocomial infections, also known as Hospital Acquired Infections (HAI) or Health care-associated infections (HCAI), are defined as infections acquired while patients receive treatment for other conditions within a healthcare facility, such as hospitals or clinics.

• To be classified as an HAI, the infection must not be present at the time of admission but rather develop after a period of $48 \text{ hours}$ or more following admission.

Consequences of HAIs

• HAIs lead to prolonged hospital stays, resulting in increased financial costs to both the individual patients and the broader healthcare system.

• These infections can result in serious illness or death.

• There is an increased usage of antibiotics to treat HAIs, which subsequently increases the selective pressure for antimicrobial resistance to emerge among hospital-bound pathogens.

• Infected patients can become a source of infection, transmitting the pathogen to others within the facility.

National and Global Prevalence Statistics

• United States (USA):

  • Approximately $1.7 \text{ million}$ HAIs occur each year.

  • About $4.5 \,\%$ of hospitalized patients contract an HAI.

  • Estimated deaths reach $99,000$ annually.

  • Costs associated with these infections total approximately $\$5 \text{ billion}$.

  • Data according to the Centers for Disease Control and Prevention (CDC).

• Australia:

  • Approximately $165,000$ Australians contract HAIs every year.

  • About $6 \,\%$ of hospitalized patients contract an HAI.

  • There is currently no nationally collected data; however, studies analyzed by Mitchell BG et al. (Infection, Disease \& Health 2017) between $2010$ and $2016$ provide these estimates.

• Intensive Care Unit (ICU) Specifics:

  • Patients in the ICU experience higher rates of HAI, estimated at approximately $30 \,\%$.

  • The risk of acquiring an HAI increases the longer a patient remains in the ICU.

• International Prevalence Rates (WHO 2010 Systematic Review):

  • Australia: $6.0 \,\%$

  • USA: $4.5 \,\%$

  • Canada: $11.6 \,\%$

  • Norway: $5.1 \,\%$

  • UK: $7.6 \,\%$

  • France: $6.7 \,\%$

  • Italy: $8.3 \,\%$

  • Finland: $9.1 \,\%$

  • Greece: $9.3 \,\%$

  • Cyprus: $7.9 \,\%$

  • Scotland: $9.5 \,\%$

  • Korea: $3.7 \,\%$

  • Albania: $19.10 \,\%$

  • Brazil: $14.0 \,\%$

  • Latvia: $5.7 \,\%$

  • Lebanon: $6.8 \,\%$

  • Lithuania: $9.2 \,\%$

  • Malaysia: $13.9 \,\%$

  • Mali: $18.7 \,\%$

  • Tanzania: $14.8 \,\%$

  • Thailand: $7.3 \,\%$

  • Tunisia: $17.8 \,\%$

  • Turkey: $13.4 \,\%$

Common Types of Hospital Acquired Infections

• Urinary tract infection (UTI): $42 \,\%$ (primarily catheter-associated UTI).

• Surgical wound infection: $24 \,\%$

• Lower respiratory tract infection: $11 \,\%$

• Bloodstream infections: $5 \,\%$ (primarily catheter-related bloodstream infections).

• Others: $18 \,\%$ (including Clostridioides difficile infections, skin infections, and gastrointestinal infections).

Microorganisms Associated with HAIs

• Escherichia coli (Gram negative rods): Common cause of UTI, surgical wound infections, and bacteremia.

• Staphylococcus aureus (Gram positive cocci): Commonly associated with surgical wound infections, bacteremia, and pneumonia.

  • MRSA: Methicillin Resistant Staph aureus.

  • MSSA: Methicillin Sensitive Staph aureus.

  • VSSA: Vancomycin Sensitive Staph aureus, with a Minimum Inhibitory Concentration (MIC) of < 2 \,\mu\text{g/ml}.

  • VISA: Vancomycin-intermediate Staph aureus, with an MIC of $4-8 \,\mu\text{g/ml}$.

  • VRSA: Vancomycin-resistant Staph aureus, with an MIC of $\ge 16 \,\mu\text{g/ml}$.

• Pseudomonas aeruginosa (Gram negative rods): Widely present in the environment; causes pneumonia, bacteremia, and surgical wound infections.

• Clostridioides (Clostridium) difficile (Gram positive rods, anaerobes): Causes colitis, typically following antibiotic use for unrelated conditions.

• Bacteroides fragilis (Gram negative rods, anaerobes): Associated with surgical wound infections and bacteremia.

• Klebsiella pneumoniae \& Proteus mirabilis (Gram negative facultative anaerobes, rods): Cause pneumonia, UTI, and bacteremia.

• Enterococcus faecalis \& Enterococcus faecium (Gram positive cocci): Cause UTI, surgical wound infections, and bacteremia; some strains are Vancomycin-resistant.

• Acinetobacter baumannii (Gram negative coccobacillus): Outbreaks typically occur in the ICU; causes pneumonia, bacteremia, meningitis, and infections of the surgical sites and urinary tract.

• Enterobacter cloacae \& Enterobacter aerogenes (Gram negative rods): Affect ICU patients, particularly those on mechanical ventilation.

• Burkholderia cepacia (Gram negative rods): Low risk to healthy people but can cause serious respiratory infections in hospitalized patients.

• Candida albicans: Opportunistic fungal pathogen causing candidiasis; systemic candidiasis carries a mortality rate of $40 \,\%$

• Viruses:

  • Hepatitis C, Hepatitis B, and Human Immunodeficiency Virus (HIV) are considered rare sources.

  • Influenza virus and Norovirus usually circulate in the community but can occur in hospitals.

ESKAPE Pathogens

• ESKAPE is an acronym for a group of pathogens with high antibiotic resistance rates responsible for many HAIs.

• The group includes: Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa, and Enterobacter species.

• They are characterized by their ability to "escape" the effects of standard antibiotics.

Sources and Predisposing Factors for HAI

• Endogenous Sources: Microorganisms derived from the patient's own normal microbiota (e.g., skin, gastrointestinal tract, or respiratory tract).

• Exogenous Sources:

  • Other persons within the hospital, such as healthcare workers.

  • Invasive medical devices like urinary catheters, ventilators, or IV catheters.

  • Common hospital items such as blankets, sheets, sinks, telephones, or the air.

• Predisposing Factors:

  • Patient host factors: Underlying disease, age, and suppressed immune systems.

  • Invasive Devices: Exposure to venous catheters, mechanical ventilation, and urinary catheters.

  • Medical Procedures: Surgical wounds and the use of antibiotics.

  • Environment: Inadequate cleaning, overcrowding, lack of isolation for infectious sources, and poor sterilization of equipment.

  • Healthcare Workers: Inadequate application of standard precautions.

Catheter-Associated Urinary Tract Infections (UTI)

• Urinary catheters inoculate bacteria into the bladder.

• Catheters provide a surface for adhesion and the formation of bacterial biofilms.

• Biofilms: Slime-enclosed aggregates where bacterial cells stick to each other on a surface within an extracellular matrix. They exhibit extreme resistance to antibiotics and can evade host defenses.

• The daily incidence of bacteriuria (asymptomatic bacteria in urine) is $3-10 \,\%$ once a catheter is placed.

• UTI is defined when symptoms accompany bacteriuria.

• Catheter obstruction further increases the risk of infection.

• Causative Agents for Catheter-Associated UTI:

  • Uropathogenic E. coli (UPEC): $40 \,\%$

  • Candida spp.: $16 \,\%$

  • Other Gram negatives: $11 \,\%$

  • Proteus mirabilis: $3 \,\%$ (Produces urease, which hydrolyzes urea to ammonia, $NH_3$).

  • Coagulase-negative Staph: $5 \,\%$

  • Other Gram positives: $25 \,\%$

• Prevention: Avoid unnecessary catheterization, use aseptic insertion techniques, maintain unobstructed flow, and remove catheters promptly when no longer needed.

Surgical Site Infections (SSI)

• Risk depends on the specific procedure and tissue levels involved.

• Incidence Factors: Complexity and duration of surgery, surgical skill, intrinsic patient risk, presence of a prosthesis, and surgery on heavily colonized sites.

• Presentation: Infections may appear in the hospital, but $50 \,\%$ become apparent after discharge due to shorter post-op stays. Deep surgery (e.g., Coronary artery bypass graft) may present up to $4 \text{ weeks}$ after surgery.

• Causative Agents: Primarily Staphylococcus aureus (MSSA or MRSA). Others include Klebsiella spp., Enterobacter spp., E. coli, P. aeruginosa, Streptococcal spp., and Enterococcus spp.

• Prevention: Controlling patient diabetes, short pre-operative stays, appropriate antimicrobial prophylaxis, avoiding razors for hair removal, and rigorous cleaning/sterilization of equipment.

Hospital Acquired Pneumonia (HAP) and VAP

• HAP: Pneumonia developing $48 \text{ hours}$ after hospital admission, occurring in $0.5-2 \,\%$ of patients.

• Ventilator-Associated Pneumonia (VAP): Develops in ICU patients mechanically ventilated for at least $48 \text{ hours}$.

  • Risk increases by $1-3 \,\%$ per day of intubation.

  • VAP risk is $6-20 \text{ times}$ higher than in non-ventilated ICU patients.

  • VAP mechanisms include damaged salivary flow, poor oral hygiene, and the endotracheal tube (ET) surface providing a base for bacterial colonization.

• Causative Agents: S. aureus, Klebsiella spp., P. aeruginosa, Enterobacter spp., Streptococcus spp., and various viruses.

• Prevention for VAP: Oral care, routine assessment for extubation readiness, and proper sterilization of respiratory equipment.

Hospital Acquired Bloodstream Infections

• These infections carry a mortality rate of approximately $20 \,\%$

• Sources:

  • Peripheral catheters ($0.36 \text{ per } 1000 \text{ uses}$).

  • Central vein catheters ($23 \text{ per } 1000 \text{ uses}$ in Australian studies).

  • Infections elsewhere in the body (e.g., lungs, wounds).

• Mechanisms: Bacteria adhere to cannulas to gain entry to tissues. Signs include localized phlebitis with pain, redness, or pus.

• Prevention: Hand hygiene, correct insertion procedures, clean/dry dressings, and prompt removal of unnecessary catheters.

Staph aureus Bacteremia (SAB) in Australia

• Data from the 2024-2025 AIHW report for public hospitals:

  • $1,745 \text{ reported cases}$ of SAB bacteremia.

  • The rate is $0.74 / 10,000 \text{ patient days}$.

  • $12.8 \,\%$ of these cases are MRSA.

• Risk Factors: Open wounds, invasive devices, weakened immune systems (cancer, transplants, the very young/elderly), chronic diseases like diabetes, and prolonged antibiotic exposure.

MRSA Screening and Decolonization

• Universal admission screening combined with decolonization resulted in a $77 \,\%$ reduction in MRSA infections over $10 \text{ years}$.

• Screening only high-risk ICU patients yielded a $66 \,\%$ reduction.

• Decolonization Protocol:

  • Body wash: Daily for $5 \text{ days}$ using Triclosan $1 \,\%$ or Chlorhexidine gluconate $4 \,\%$

  • Nasal ointment: Twice daily for $5 \text{ days}$ using Mupirocin $2 \,\%$

  • Dentures: Soak overnight in a denture cleaning product.

The Chain of Infection and Prevention

• The foundation of prevention is breaking the links in the chain of infection.

• Links and Intervention Points:

  • Infectious Agents: Bacteria, Viruses, Fungi. Prevention: Decontamination, rapid identification, prompt treatment.

  • Habitats (Reservoirs): People, equipment, water. Prevention: Environmental sanitation, disinfection, sterilization.

  • Portals of Exit: Excretions, secretions, droplets. Prevention: Hand hygiene, airflow control.

  • Mode of Transmission: Contact, droplets, airborne, vector-borne. Prevention: Isolation precautions, proper food handling.

  • Portals of Entry: Respiratory tract, GI tract, mucous membranes, skin. Prevention: Aseptic technique, wound care, catheter care.

  • Susceptible Hosts: Patients with cancer, burns, diabetes, or the elderly. Prevention: Good health and hygiene.

Five Moments of Hand Hygiene (WHO)

1. Before touching a patient: To protect the patient from germs on hands.

2. Before a clean/aseptic procedure: To protect the patient from germs (including their own) entering their body.

3. After body fluid exposure risk: To protect self and environment from harmful germs.

4. After touching a patient: To protect self and environment after leaving the patient's side.

5. After touching patient surroundings: To protect self and environment from germs on furniture or objects.

Protective Clothing and Isolation

• Protective Clothing: Sterile gowns, gloves, headgear, and face masks are used in theaters to minimize bacterial shedding.

• Barrier Nursing: Used for communicable diseases.

• Isolating or Cohorting:

  • Isolation: Single room with private bathroom for patients with multi-resistant organisms.

  • Cohorting: Placing all patients carrying the same organism (e.g., MRSA) in the same ward.

Outbreak Investigation

• Infection Control Team Role: Determines the number of people infected, admission dates, timing of infection, ward location, medical team involvement, and common treatment exposures.

• Microbiology Laboratory Role:

  • Isolates the causative agent to confirm it is consistent across all patients.

  • Identifies the organism to provide clues about the source (e.g., MRSA in wounds suggests contact spread from staff).

  • Performs epidemiological typing to distinguish the outbreak strain from common environmental strains or normal flora.