Community medicine chapters
Nosocomial, iatrogenic and opportunistic infections
What counts as a hospital-acquired infection, the commonest types and organisms, how they spread and how to prevent them, plus iatrogenic and opportunistic infections and the patients at risk.
- A nosocomial (hospital-acquired) infection is one that was not present or incubating on admission and appears 48 hours or more after admission (or soon after discharge).
- The commonest are urinary tract infection (catheters), surgical site infection, pneumonia (especially ventilator-associated) and bloodstream infection (central lines).
- Hand hygiene is the single most important preventive measure; standard precautions apply to every patient.
On this page
Overview
Hospitals bring together sick people, invasive procedures and resistant organisms. Infections caught in hospital add to illness, deaths, length of stay and cost, and spread antibiotic resistance.
Definitions
- Nosocomial (hospital-acquired, healthcare-associated) infection: an infection that was not present or incubating at the time of admission and appears 48 hours or more after admission, or after discharge if it was acquired in hospital (for example a surgical site infection within 30 days of surgery).
- Iatrogenic infection: an infection caused by a medical procedure, treatment or health worker (for example hepatitis C from a reused syringe, or infection after an injection).
- Opportunistic infection: an infection by an organism that usually does not harm healthy people but causes disease in those with weakened immunity.
An infection is called nosocomial if it appears 48 hours or more after admission and was not incubating on admission.
Common types
| Type | Main risk factor |
|---|---|
| Urinary tract infection (commonest in classic teaching) | Urinary catheters |
| Surgical site (wound) infection | Contaminated operations, long surgery, poor technique, no prophylaxis when needed |
| Pneumonia (including ventilator-associated) | Mechanical ventilation, aspiration, immobility |
| Bloodstream infection | Central venous lines, IV cannulas |
| Diarrhoea (Clostridioides difficile) | Broad-spectrum antibiotics |
Common organisms
- Gram-positive: Staphylococcus aureus (including MRSA), coagulase-negative staphylococci, enterococci.
- Gram-negative: E. coli, Klebsiella, Pseudomonas aeruginosa, Acinetobacter: often multidrug-resistant.
- Clostridioides difficile; Candida.
- Viruses: hepatitis B and C, HIV (from blood), influenza, norovirus.
Sources and routes
- Endogenous: the patient's own flora entering a normally sterile site (for example gut organisms causing a catheter UTI).
- Exogenous: from health workers' hands (the commonest route), other patients, contaminated equipment, the environment, air, water and food.
Risk factors
- Host: extremes of age, diabetes, cancer, malnutrition, immunosuppression, burns.
- Procedures: catheters, ventilators, lines, surgery.
- Environment: overcrowding, poor cleaning, shortage of staff and supplies.
- Antibiotics: overuse selects resistant organisms.
Prevention and control
Hand hygiene
Hand hygiene is the single most important measure to prevent hospital infections.
The WHO "five moments": before touching a patient, before a clean or aseptic procedure, after exposure to body fluids, after touching a patient, and after touching the patient's surroundings. Alcohol hand rub is quick and effective; wash with soap and water when hands are visibly soiled or after caring for a patient with C. difficile diarrhoea.
Standard precautions
Apply to all patients, whether or not they are known to be infected, treating all blood and body fluids as potentially infectious:
- Hand hygiene.
- Personal protective equipment (gloves, gowns, masks, eye protection) as needed.
- Safe handling of sharps: no recapping; immediate disposal in a puncture-proof container.
- Safe injection practice: one needle, one syringe, one patient; auto-disable syringes.
- Respiratory hygiene (cough etiquette).
- Cleaning and disinfection of equipment and surroundings.
- Safe handling of linen and hospital waste.
Transmission-based precautions
Added for known or suspected infections: contact (MRSA, C. difficile), droplet (influenza, meningococcus) and airborne (TB, measles, chickenpox; N95 masks and negative-pressure rooms).
Other measures
- Care bundles for catheters, central lines and ventilators (insert only when needed, aseptic insertion, remove early).
- Surgical asepsis, correct antibiotic prophylaxis.
- Antibiotic stewardship.
- Surveillance of infection rates; an infection control committee and team.
- Immunisation of staff (hepatitis B, influenza).
Iatrogenic infections in Pakistan
Reuse of syringes and unnecessary injections have been major drivers of hepatitis B and C spread in Pakistan, and of HIV outbreaks (for example the 2019 outbreak among children in Ratodero, Sindh). Auto-disable syringes, fewer injections and safe blood transfusion are key.
Needlestick injury
Approximate risk of transmission after a needlestick from an infected patient (widely quoted figures):
| Virus | Risk |
|---|---|
| Hepatitis B | About 6–30% (higher if the source is HBeAg positive) |
| Hepatitis C | About 1.8% |
| HIV | About 0.3% |
Immediate action: let the wound bleed, wash with soap and water (do not squeeze or scrub with bleach), report, assess the source, and start post-exposure prophylaxis (HBV vaccine/immunoglobulin, HIV PEP) as per local protocol, ideally within hours.
Of the blood-borne viruses, hepatitis B carries the highest risk after a needlestick, which is why all health workers should be vaccinated.
Opportunistic infections
Seen in people with weak immunity: HIV/AIDS, cancer chemotherapy, organ transplant, long-term steroids, diabetes, malnutrition.
| Organism | Typical illness |
|---|---|
| Pneumocystis jirovecii | Pneumonia (PCP) in advanced HIV |
| Candida | Oral and oesophageal thrush |
| Mycobacterium tuberculosis | TB (the leading opportunistic infection in HIV in our region) |
| Cryptococcus | Meningitis |
| Cytomegalovirus | Retinitis, colitis |
| Toxoplasma | Brain abscesses |
Expect: the 48-hour definition, the commonest nosocomial infection and organisms, hand hygiene as the most important measure, standard precautions, iatrogenic vs opportunistic infections with examples, and the relative needlestick risks of HBV, HCV and HIV.
Quick revision
- Nosocomial: 48 hours or more after admission; not incubating on admission.
- Commonest: catheter-associated UTI; also surgical site, pneumonia, bloodstream.
- Hand hygiene is the most important prevention; standard precautions for all.
- Iatrogenic: caused by procedures (unsafe injections → HBV, HCV, HIV).
- Opportunistic: disease in the immunocompromised (PCP, candida, TB, CMV).
- Needlestick risk: HBV > HCV > HIV.
Written by The House Job from Excel Community Medicine and Park's Textbook of Preventive and Social Medicine (named in the UHS PGET syllabus), with infection-control practice following WHO guidance.
FAQ
What is a nosocomial infection?
An infection that was not present or incubating on admission and appears 48 hours or more after admission to hospital.
What is the most important measure to prevent hospital infections?
Hand hygiene.
What is an iatrogenic infection?
An infection caused by a medical procedure, treatment or health worker, such as hepatitis C from a reused syringe.
Which virus has the highest risk of transmission after a needlestick injury?
Hepatitis B.