Healthcare-Associated Infections Overview Summary & Study Notes

🏥 Introduction to HCAI

HealthCare-Associated Infections (HCAI) are infections that patients acquire while receiving health care. They were originally called nosocomial infections and are defined as infections that appear 48 hours or more after admission or within 30 days after receiving health care. Understanding where microbes come from helps target prevention efforts.

Exogenous sources come from the environment and equipment, and are potentially preventable. Endogenous sources come from the patient’s own flora and can be more difficult to control. Infections can also be transmitted via staff and other patients, all of which are potentially preventable with proper practices.

🧭 Importance of HCAI

HCAIs increase mortality, morbidity and costs. For example, about 25% of patients with a bloodstream infection due to Staphylococcus aureus die. They also prolong hospital stays and lead to extra treatments and investigations. HCAIs raise public concern and are closely linked to antimicrobial resistance.

🌍 Epidemiology & risk factors

HCAIs affect millions of people worldwide and place a heavy burden on health systems. In the EU/EEA, more than 3.5 million HCAI cases occur each year with over 90,000 deaths and millions of disability-adjusted life years (DALYs). Up to half of HAIs are estimated to be preventable, and HAIs account for a large share of antibiotic-resistant infections.

Across 204 countries, antimicrobial resistance is estimated to have caused around 1.27 million deaths and contributed to about 4.95 million deaths overall.

🧩 Most prevalent HCAIs (2022-2023 point prevalence in acute hospitals)

Surgical site infection (SSI or wound infection), Hospital-acquired pneumonia (HAP), Urinary tract infection (UTI), Bloodstream infection (BSI), and others. About 80–90% of HCAIs involve roughly 15–20 microorganisms, with around 20% of these being multidrug-resistant (MDR) phenotypes.

🧬 Factors affecting HCAI risk

• Environment factors: overcrowding, shared toilet facilities, equipment and facility upkeep.
• Patient factors: extremes of age, LTC residency, chronic disease, immunosuppression, invasive devices, prior antibiotic use.
• Microorganism factors: certain pathogens have higher virulence or resistance.

PPS 2017: patient demographics (illustrative data)

• Mean age: Beaumont tertiary hospitals and national data show a predominantly older population; a large proportion were ≥65 years.
• High dependency markers: a notable percentage were intubated, with urinary catheter use and central venous catheters reported in various cohorts.

🧪 Specific HCAIs: what to know

1) Surgical Site Infection (SSI)

SSI can be superficial or deep and may be implant-associated (e.g., prosthetic joints).

SSI risk factors

• Pre-op: Skin flora colonisation (MSSA/MRSA); comorbidities such as diabetes, obesity, malnutrition, smoking, steroid use.
• Intra-op: Contaminated procedure (e.g., bowel surgery); foreign body implantation; contamination from surgeon, instruments, dressings; airborne spread via staff clothing or theatre air flow.
• Post-op: Poor wound care; drains or catheters increasing contamination.

Causative pathogens

• Staphylococcus aureus (including MRSA) is the most common; β-hemolytic streptococci Group A; anaerobes (e.g., Bacteroides spp., Clostridium perfringens); Gram-negative bacilli (e.g., Escherichia coli, Klebsiella spp., Enterobacter cloacae, Pseudomonas aeruginosa); Enterococci. Many wounds are colonised rather than infected by some organisms.

2) Hospital-Acquired Pneumonia (HAP)

Predisposing factors include postoperative state with reduced breathing effort, antibiotic-altered flora, endotracheal intubation, and aspiration risk (e.g., after stroke or poor swallow).

Pathogens include Pseudomonas aeruginosa and other Gram-negative bacilli. In critical care, ventilator-associated pneumonia (VAP) is a major concern. Moist environments (sinks, drains) can harbour organisms and contribute to transmission via splash or hand contamination.

3) Urinary Tract Infection (UTI)

Predisposing factors include catheterisation and prolonged instrumentation. Common pathogens often reflect the catheter-associated flora.

4) Bloodstream Infection (BSI)

Pathogens vary by source:

• Central lines: Staphylococcus aureus, coagulase-negative staphylococci (e.g., S. epidermidis), enterococci, Candida albicans (especially ICU/immunocompromised).
• Urinary/abdominal sources: Escherichia coli and other Gram-negative bacilli (e.g., Pseudomonas aeruginosa).
• Surgical site infections can seed the bloodstream with S. aureus and other organisms.

HCAI in the ICU

ICUs have high HCAI incidence due to very ill patients, frequent invasive devices, emergencies and close contact care, with notable antibiotic resistance concerns (e.g., MRSA, VRE).

Device/implant-related infections

Common device-related infections include PVC- and CVC-associated BSI, catheter-associated UTI, ventilator-associated pneumonia (VAP), and prosthetic joint infections.

5) Others

Hospital-acquired influenza, norovirus, Clostridioides difficile, and other pathogens can cause outbreaks in care settings.

🛡 Prevention of HCAI

HCAIs are a major safety concern. The World Health Organization (WHO) emphasises hand hygiene as a key intervention, with the aim of reducing transmission by reducing pathogen load on hands.

Hand hygiene: what and when

• Transient organisms are picked up easily from the environment and patients and can be transferred to others.
• Resident organisms live on skin and are less easily transferred.
• Cleaning hands before and after patient contact is one of the most effective measures to prevent spread.

Hand hygiene: how and barriers

• Use alcohol-based hand rubs or soap and water; both are effective in most situations.
• Follow the WHO 5 Moments for hand hygiene to maximise protection.
• Areas frequently missed include the thumbs, fingertips, and nails; ensure hands are clean between patient contacts.
• Bare below the elbows: remove rings, watches; sleeves should be clean and short.

Standard precautions: PPE and basics

• Use gloves and aprons when dealing with uncontrolled secretions; change gloves and apron between patients.
• Hand hygiene must be performed after removing gloves.

Transmission-based precautions

Apply in addition to Standard Precautions for patients with specific pathogens:

• Contact precautions (gloves, gown) for direct/indirect contact.
• Droplet precautions (surgical mask) for large droplets.
• Airborne precautions (FFP2/3 mask, N95 equivalent) for airborne pathogens.
• Contact “plus” precautions may include long-sleeve gowns and eye protection where appropriate.

Visitor management

Before entering, visitors should seek information from nursing staff. Follow entry/exit steps that include hand hygiene and appropriate PPE as needed.

Negative-pressure isolation room

Used for airborne infections (e.g., TB). The room has higher outside pressure to keep air from escaping; door opening allows air to flow in but not out.

Antibiotic prophylaxis and surgical-site care

• Prophylaxis: use the right drug, at the right time (often within 60 minutes before incision), and for the correct duration.
• Skin preparation: chlorhexidine/alcohol combinations are commonly recommended.
• Wound care: apply a sterile dressing and avoid touching the wound for at least 48 hours; maintain asepsis during inspection.

Preventing device-related infections

• Minimise use of invasive devices where possible and remove when no longer needed.
• Adhere to sterile technique during insertion and maintenance.
• Regularly review the need for lines and catheters to reduce infection risk.

Cleaning, disinfection and sterilisation of the environment

• Cleaning removes dirt and reduces microbial load.
• Disinfection significantly reduces the number of organisms; sterilisation aims to eradicate all microbes including spores.
• The sequence is cleaning first, then disinfection, then sterilisation when appropriate (e.g., surgical instruments).

Safe patient placement and isolation decisions

• Isolation rooms provide single-patient containment with hand hygiene facilities.
• Cohorting groups patients with the same infection if isolation rooms are limited.

🔎 Surveillance: what it is and why it matters

Surveillance involves collecting local, national and international data to improve practices and anticipate problems. It supports outbreak investigations and, when needed, typing of microbes to track transmission.

What is an outbreak?

An outbreak is defined as two or more linked cases of the same illness or when observed cases exceed what is expected for a given setting and time period.

Summary

• HCAIs affect a sizable proportion of hospitalised patients but are largely preventable with standard practices.
• Microbial, host and environmental factors all contribute to susceptibility.
• Prevention hinges on standard precautions, timely use of transmission-based precautions, removal of unnecessary devices, and annual vaccinations where applicable.
• Surveillance data drives improvement and helps detect and control outbreaks.