Nosocomial Infections

Nosocomial (healthcare-associated) infections are infections acquired during healthcare delivery, appearing 48 hours or more after admission, within 3 days of discharge, or within 30 to 90 days of surgery (depending on the implant). They affect about 5 to 10% of hospitalised patients in high-income countries and up to 15 to 25% in low- and middle-income settings, with ICU rates higher still. They increase mortality, length of stay and cost, and drive antimicrobial resistance.

Major types (approximate shares of hospital-acquired infection):

• Urinary tract infection (about 30%): 75% catheter-associated.
• Surgical site infection (about 20%).
• Pneumonia (about 15%): hospital-acquired and ventilator-associated.
• Bloodstream infection (about 10%): central line-associated (CLABSI).
• Others: Clostridioides difficile infection, skin and soft tissue infection (pressure ulcers), gastroenteritis (norovirus), and device-related infections.

Key pathogens:

• Gram-positive: Staphylococcus aureus (including MRSA), coagulase-negative staphylococci, Enterococcus faecium (vancomycin-resistant, VRE), Clostridioides difficile.
• Gram-negative: E. coli, Klebsiella pneumoniae, Enterobacter, Pseudomonas aeruginosa, Acinetobacter baumannii, Serratia, Stenotrophomonas maltophilia, with extended-spectrum beta-lactamase (ESBL) and carbapenemase-producing (CPE, KPC, NDM, OXA-48) strains.
• Fungi: Candida species (C. albicans, C. glabrata, Candida auris, an emerging multidrug-resistant pathogen causing outbreaks), Aspergillus (construction work, immunocompromised).
• Viruses: norovirus, influenza, RSV, SARS-CoV-2, rotavirus, hepatitis B and C, and CMV.
• Others: Legionella (water systems), Mycobacterium abscessus and non-tuberculous mycobacteria (water and surgical devices), and tuberculosis.

Risk factors:

• Patient: extremes of age, malnutrition, diabetes, immunosuppression, malignancy, chronic organ failure, and previous antimicrobial exposure.
• Exposure: invasive devices (urinary catheters, central venous catheters, ventilators, drains), surgery, prolonged hospital or ICU stay, broad-spectrum antibiotics, proton pump inhibitors, and overcrowding or understaffing.
• Environment and organisation: poor hand hygiene, contaminated surfaces and equipment, water and ventilation system contamination, and poor adherence to bundles.

Transmission: contact (hands of healthcare workers, the most important route), droplet, airborne, common-source (contaminated water, solutions, devices), and endogenous (patient's own flora).

General: new fever, chills, hypotension, tachycardia, leukocytosis or leukopenia, altered mental status, new localising signs, and sepsis in a hospitalised patient. Infections may be atypical in older, ventilated or immunosuppressed patients.

By syndrome:

• Catheter-associated UTI: fever, suprapubic tenderness, flank pain, delirium, rigors, new haematuria (often few local symptoms).
• Surgical site infection: wound erythema, warmth, swelling, purulent discharge, dehiscence, fever 3 to 7 days after surgery (earlier within 48 hours suggests group A streptococcus or Clostridium). Deep or organ-space infection: abscess, peritonitis, persistent fever, and ileus.
• Hospital-acquired and ventilator-associated pneumonia: new infiltrate with fever, purulent secretions, worsening oxygenation, leukocytosis (after 48 hours in hospital, VAP after 48 hours of intubation).
• CLABSI: fever or hypotension without other source, erythema or purulence at the insertion site (may be absent), rigors with line flushing, and septic shock. Complications include endocarditis, septic thrombophlebitis, osteomyelitis.
• C. difficile infection: watery diarrhoea (3 or more loose stools in 24 hours), abdominal pain, fever, leukocytosis, and fulminant disease with ileus, toxic megacolon, and shock.
• Others: pressure ulcer infection, phlebitis from peripheral lines, nosocomial sinusitis, ventriculitis in neurosurgical patients, and outbreaks of viral gastroenteritis.

Red flags: sepsis, outbreaks (clusters of cases in a ward), unusual or resistant organisms (C. auris, CPE), and infections in the immunosuppressed.

Surveillance definitions (CDC/NHSN, ECDC) provide standardised criteria:

• CAUTI: catheter in place for more than 2 days, plus fever above 38 degrees or suprapubic tenderness or flank pain, and urine culture with 10^5 CFU/mL or more of no more than two organisms.
• CLABSI: a recognised pathogen from blood culture, or a common skin commensal in two or more cultures, with a central line in place for more than 2 days, not related to another site.
• VAP: mechanical ventilation for more than 2 days with worsening oxygenation (ventilator-associated condition), plus inflammatory signs and purulent secretions or positive microbiology.
• SSI: superficial incisional, deep incisional or organ-space infection occurring within 30 days of surgery (90 days with implants).

Investigations:

• Blood cultures: at least 2 sets from separate sites (peripheral and line) before antibiotics. Differential time to positivity (line positive at least 2 hours earlier than peripheral) supports CLABSI.
• Urine culture (from a freshly replaced catheter), sputum or endotracheal aspirate (quantitative culture, with threshold 10^5 to 10^6 CFU/mL), bronchoalveolar lavage (10^4 CFU/mL) or protected specimen brush (10^3 CFU/mL) in suspected VAP, wound swab or tissue/pus culture, and stool tests (C. difficile toxin and PCR, two-step algorithm).
• Biomarkers: white count, CRP, procalcitonin (guides discontinuation), and lactate.
• Imaging: chest radiograph or CT (infiltrate, effusion), ultrasound or CT for abdominal abscess, echocardiography in S. aureus or Candida bacteraemia, and venous imaging for line-associated thrombosis.
• Resistance testing: susceptibility testing, rapid molecular tests for resistance genes (mecA, vanA, carbapenemase genes), and screening swabs (MRSA, VRE, CPE) of high-risk patients on admission.
• Outbreak investigation: typing (whole genome sequencing) to detect clusters.

Prevention (the most effective strategy)

• Hand hygiene (WHO "5 moments") with alcohol-based hand rub (60 to 80%), soap and water for C. difficile and visibly soiled hands.
• Standard precautions for all patients, and transmission-based precautions: contact (gown and gloves for MRSA, VRE, CPE, C. difficile, with single rooms and dedicated equipment), droplet (surgical mask for influenza, meningococcus) and airborne (N95 respirator and negative-pressure room for tuberculosis, measles, varicella, and aerosol-generating COVID-19 procedures).
• Device bundles:
• Central line: hand hygiene, maximal barrier precautions, chlorhexidine 2% in 70% isopropyl alcohol skin preparation, avoid femoral site, ultrasound guidance, daily review of the need, chlorhexidine-impregnated dressings, and antimicrobial locks selectively.
• Urinary catheter: insert only for appropriate indications, aseptic technique, closed drainage, daily review, early removal, and alternatives (intermittent catheterisation, external catheters).
• Ventilator: head-of-bed elevation to 30 to 45 degrees, daily sedation interruption and spontaneous breathing trials, subglottic secretion drainage, oral care (chlorhexidine is controversial), and avoiding unnecessary circuit changes.
• Surgical site infection: appropriate antibiotic prophylaxis (cefazolin 2 g, 3 g if over 120 kg, within 60 minutes before incision, repeated for prolonged surgery), hair clipping not shaving, chlorhexidine-alcohol skin prep, normothermia, glucose control (below 180 mg/dL), nasal decolonisation (mupirocin 2% twice daily for 5 days with chlorhexidine washes for S. aureus carriers), and oxygen optimisation.
• Environmental cleaning and disinfection (chlorine-based or sporicidal agents for C. difficile), water system safety (Legionella and Pseudomonas control), air handling in operating rooms, and construction controls.
• Antimicrobial stewardship: restrict broad-spectrum agents, de-escalate by culture results at 48 to 72 hours, limit duration, intravenous-to-oral switch, and local antibiograms. Reduces C. difficile and resistance.
• Screening and decolonisation: MRSA screening in high-risk settings, universal chlorhexidine bathing in ICU, and isolation of CPE and C. auris carriers.
• Vaccination of healthcare workers (influenza, hepatitis B, COVID-19, pertussis, varicella, MMR), occupational health, sharps safety, and staffing levels.

Treatment

• Remove or replace infected devices (central line, urinary catheter) promptly where possible. Control the source (drain abscess, debride wounds).
• Empirical antibiotics by local antibiogram and syndrome, then de-escalate with cultures:
• Hospital-acquired pneumonia and VAP: piperacillin-tazobactam 4.5 g IV every 6 hours, cefepime 2 g every 8 hours, or meropenem 1 g every 8 hours, with an antipseudomonal agent plus vancomycin 15 to 20 mg/kg every 8 to 12 hours or linezolid 600 mg every 12 hours if MRSA risk. Duration 7 days.
• CLABSI: vancomycin 15 to 20 mg/kg IV every 8 to 12 hours (trough-guided or AUC/MIC 400 to 600) plus an antipseudomonal beta-lactam if Gram-negative risk. Remove the line for S. aureus, Candida, Pseudomonas, or persistent bacteraemia. Duration 7 to 14 days for coagulase-negative staphylococci with the line removed (10 to 14 days with line retention), at least 14 days for S. aureus (4 to 6 weeks with complications or endocarditis), and 14 days after clearing cultures for Candida (echinocandin first line: caspofungin 70 mg loading then 50 mg daily, micafungin 100 mg daily, anidulafungin 200 mg then 100 mg daily).
• CAUTI: see UTI and pyelonephritis articles. Duration 7 days (14 if delayed response).
• Surgical site infection: opening and drainage of the wound, antibiotics for systemic signs or cellulitis (cefazolin 2 g every 8 hours or vancomycin), longer for deep infection, necrotising infections require urgent debridement.
• Carbapenem-resistant Enterobacterales: ceftazidime-avibactam 2.5 g IV every 8 hours, meropenem-vaborbactam 4 g every 8 hours, imipenem-relebactam, cefiderocol 2 g every 8 hours, or combinations with colistin (9 million units loading then 4.5 million units every 12 hours) or tigecycline 100 mg then 50 mg every 12 hours.
• Acinetobacter: sulbactam-durlobactam, high-dose ampicillin-sulbactam (9 g every 8 hours), colistin or tigecycline combinations.
• VRE: linezolid 600 mg twice daily or daptomycin 8 to 12 mg/kg daily.
• Candida auris: echinocandin, with infection control.
• C. difficile infection: stop the inciting antibiotic where possible. Fidaxomicin 200 mg twice daily for 10 days (preferred, lower recurrence) or vancomycin 125 mg orally four times daily for 10 days. Fulminant disease: vancomycin 500 mg orally or via nasogastric tube four times daily plus IV metronidazole 500 mg every 8 hours, rectal vancomycin if ileus, and surgical review (colectomy or loop ileostomy). Recurrence: fidaxomicin extended pulsed regimen, vancomycin taper, bezlotoxumab 10 mg/kg, and faecal microbiota transplantation after multiple recurrences. Avoid antimotility drugs and unnecessary PPIs.

Outbreak management

• Identify clusters promptly, implement cohorting, enhanced cleaning, screening of contacts, and review of practices. Report to infection prevention and public health authorities. Close wards or units if needed.

Surveillance and quality

• Monitor rates of CLABSI, CAUTI, VAP, SSI, MRSA bacteraemia and C. difficile, with feedback to clinical teams, and benchmark. Audit hand hygiene and bundle compliance.

Patient and family education on hand hygiene, device care and early reporting of symptoms.