College Answer

Aetiology: dependent on cause.   Combination of overgrowth of endogenous flora, immune suppression, impairment of natural defences (eg. endotracheol tube, invasive catheters), and cross contamination  with  pathogens.     Commonest  are  pneumonia  (thought  related  to  aspiration  of organisms colonising oro-pharyngeal and gastric contents, decreased gastric pH, exposure to water borne organisms), surgical wound infections (contamination at time of surgery), sinusitis (tubes, immobility, nasal congestion),  line related sepsis (entry site contamination,  blood borne contamination, contamination of intravenous lines).

Clinical  manifestations:  apart  from systemic  manifestations  of sepsis  (leukocytosis/leukopaenia, fever, etc) are dependent on cause.   Pneumonia (purulent secretions, impaired oxygenation, radiological   infiltrates  etc.),  sinusitis  (purulent  discharge),  line  related  (local  inflammation). Diagnostic techniques are specific to cause.

Possible prevention: consider general infection control measures (including surveillance, continuous quality improvement, avoid un-necessary immunosuppression [steroids, glucose control], avoid un- necessary antibiotics).   Decrease cross infection (standard precautions [esp. hand washing] and transmission based precautions; cleaning/disinfection and sterilization of equipment; avoiding reuse of single  use items).   Pneumonia  (eg. semi-recumbent  position,  aspiration  above  cuff,  possibly selective decontamination, infrequent changing of circuit).   Line related (eg. sterile insertion, antibiotic/antiseptic   impregnated   lines,  perhaps  tunneling,   surveillance,   change  according   to protocol).

Discussion

This question is painfully broad. A good article reporting on the epidemiology of nosocomial infection in American ICUs is available, and using this substrate, one can attempt to boil the answer down into a point-form list. A notable reference is Hatcher and Dhillon's chapter for Ohs' Manual(Ch 70, p. 724)

Aetiology of nosocomial infection in ICU:

• Pneumonia: VAP or HAP
• Central line associated bacteraemia
• UTI due to indwelling catheters
• Sinusitis due to nasogastric tubes
• Acalculous cholecystitis due to parenteral nutrition
• Pressure area infections
• Meningitis or ventriculitis due to EVD infection
• C.difficile infections due to broad-spectrum antibiotic use
• Surgical site infections

Clinical manifestations

• Broadly speaking, these depend on where the infection is.
• Fever
• Inflammatory marker elevation
• Shock and metabolic acidosis
• Purulent discharge (pulmonary, urinary, or nasal)
• Positive CSF gram stain and culture, decreased level of consciousness

Preventative measures

Non-specific measures

• Scrupulous handwashing
• Barrier precautions, gloves gowns and masks
• Surveillance for MROs
• Isolation precautions

Specific measures

• Regular oral hygiene
• Regular pressure area care
• Minimisation of the duration of ventilation
• Preventative strategies for VAP (eg. upright positioning)
• Preventative strategies for central line contamination
• Early removal of central lines
• Rationalisation of antibiotics to prevent C.difficile infection
• Control of hyperglycaemia
• Rationalisation of immunosuppressive therapies
• Perioperative antibiotics to prevent wound infection in high-risk patients