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  • Largely arbitrary
  • As an indicator of infection the lower the temperature defined as abnormal the higher the sensitivity but the lower the specificity
  • As a general rule consider the possibility of infection in all ICU patients with temperature ³ 38.3° . NB. Infection without fever is not uncommon.

Diagnostic approach

History and examination

  • localizing complaints- ask the patient if possible. If not, look at notes.
  • allergy to drugs
  • duration of vascular cannulation
  • sputum, wound drainage
  • abdominal pain or tenderness

Physical examination

  • skin: rash, vasculitis (ie palpable purpura)
  • tender or inflammed IV site, ± purulence
  • wound dressings should be taken down after 24 hours.
  • legs for DVT, gout
  • head and neck: fundi for candida, oral herpetic lesions. Think of sinusitis.
  • lungs: auscultation may not be that useful, but a decrease in oxygenation, and CXR infiltrates may be more sensitive indicators of pneumonia, but not more specific.
  • cardiac: may have a friction rub associated with Dressler’s syndrome, or a murmur associated with endocarditis.
  • abdominal findings may be unremarkable in the elderly and those who are sedated/unconscious.
  • examination of the genitalia may reveal unsuspected epididymitis, prostatitis, prostatic abscess or perirectal abscess.


  • urinalysis and culture and 2-3 sets of blood cultures
  • CXR
  • sputum and gram stain
  • except in neurosurgical patients , meningitis is an uncommon nosocomial infection
  • joint fluid needs to be sampled if relevant. Look for crystals and gram stain and culture.
  • ± ultrasound or CT or radionuclide studies
  • in many cases the work-up will point towards a likely source and therefore the need or otherwise for antibiotics
  • in the acutely ill patient it may be necessary to change, broaden, or stop antibiotics.
  • negative cultures in a febrile patient who is clinically deteriorating may be a clue to fungal infection in high risk patient

Sites of infection

  • The most common sites of infection in ICU patients are intravascular lines, chest, abdomen, wounds and urinary tract
  • Other sites that need to considered include CNS and sinuses

Intravascular lines

See "Intravascular lines and infection"


See "Chest infection"

  • Many febrile ICU patients have small pleural effusions. It is not necessary to perform a diagnostic tap in all these patients.
  • A diagnostic tap is indicated if the effusion is big enough to allow safe aspiration and there is one of:
  • a suspicion of TB
  • possible contamination of pleural space by surgery, trauma or fistula
  • adjacent pulmonary infiltration on CXR


"See intra-abdominal infections"


"See intra-abdominal infections"


Common site of nosocomial infection


For operations in which a body cavity is entered wound is divided into superficial and deep components. The terms superficial and deep refer to the relationship to the layer of fascial closure

Clinical features

  • superficial infection: purulent drainage from incision or drain located above fascia
  • deep: purulent drainage from deep compartment but not from organ-space or spontaneous dehiscence of wound

Risk factors

  • ASA score of 3 or greater
  • Contaminated or dirty operation. Contaminated = major break in asepsis, gross spill of GI contents, entry into hollow organ containing infected contents. Dirty = acute purulent inflammation found, traumatic wounds requiring surgical repair, faeces or devitalized tissue in field of operation
  • Long procedure time. Definition of long procedure time depends on procedure that was performed.


  • In clean surgical procedures in which the GI, gynaecological and respiratory tracts have not been entered the usual organism is S. aureus
  • In all other situations polymicrobial mixed aerobic-anaerobic infection with organisms found in the normal flora of the surgically resected organ is common


  • Examine wound for erythema, purulence or tenderness
  • If infection is suspected wound should be opened
  • Gram stain and cultures should be performed on any expressed pus or material obtained from deep within wound site

Urinary tract

  • Bacteriuria is common but is often not clinically significant
  • If colony count is <104 cfu/ml or pyuria is absent in a non-neutropaenic patient with an indwelling catheter then it is unlikely that fever is due to urinary tract infection
  • Likely organisms: gram negative bacilli, Strep. faecalis, yeasts

Central nervous system

See "Meningitis", "Brain abscess", "Subdural empyema"

  • CNS infection rarely causes encephalopathy in absence of detectable focal abnormalities. However difficulty of carrying out a detailed neurological examination in ICU patients means that CNS infection must always be considered in febrile ICU patients.
  • Imaging and culture of CSF are central to the investigation of possible CNS infection. CT prior to LP is required in patients with focal neurological findings suggesting disease above foramen magnum. If bacterial meningitis is suspected and LP is delayed empirical antibiotic therapy should be started after blood cultures are taken.
  • Patients with suspected brain abscesses should not undergo LP because the bacteriological yield from CSF analysis in this setting is too low to justify the risk of herniation. Aspiration of the suspected abscess is the investigation of choice.
  • Basic tests to be performed on CSF include cell counts, glucose and protein concentration, gram stain and bacterial cultures. Additional tests such as testing for cryptococcal antigen, stains and culture for fungi, acid-fast smears and cultures and PCR for bacteria and HSV may be indicated in certain settings.
  • NB The upper limit of normal for protein concentration in CSF varies according to the site from which is was obtained:
    - ventricular fluid: 0.2 g/l
    – cisternal fluid: 2.5 g/l
    – lumbar fluid: 0.4 g/l


  • Most common risk factor for sinusitis in ICU is obstruction of ostia draining sinuses by nasogastric or nasotracheal tube
  • Relatively uncommon to document sinusitis as cause of fever with much certainty so investigation for sinusitis should only be undertaken after more likely causes have been excluded.


Infection is usually due to organisms that colonize the pharynx of critically ill patients. Gram negative bacilli constitute 60% of isolates. P. aeruoginosa is most common. S. aureus is most common gram positive. Fungi make up 5-10% of isolates

Clinical features

  • Presence of two major criteria or one major and two minor criteria for >7 days suggests the presence of acute bacterial sinusitis. Major criteria are cough and purulent nasal discharge while minor criteria are: periorbital oedema, headache, facial pain, tooth ache, earache, sore throat, foul breath, wheezing or fever.
  • In ICU patients many of these clinical features are difficult to elicit. Purulent nasal discharge is present in only 25% of ICU patients with proven sinusitis


  • plain radiographs, ultrasonograms, CT scans, and MRI scans can be obtained to diagnose acute sinusitis.
  • air fluid levels are sensitive for detecting sinusitis, but are not very specific.
  • in practice need a CT scan to improve the diagnostic yield
  • ultrasound is useful only as a screening tool as not very specific
  • definitive diagnosis by sampling is mandatory and provides the optimal means for tailoring antibiotic therapy.
  • disadvantages are that sampling is invasive and that samples are susceptible to contamination with normal nasal flora if rigorous technique is not used
  • Thus
  • If clinical findings suggest sinusitis CT should be performed
  • If findings are consistent then should do a puncture. Gram stain the puncture and culture for aerobic and anaerobic organisms as well as fungi to determine the causative pathogens

GI tract

- the only common enteric cause of fever in the ICU is Clostridium difficile which should be suspected in any patient with fever and diarrhoea who has received antibiotics or chemotherapy within 3 weeks of the onset of the diarrhoea

Evaluation for other pathogens:

- those with risk factors ie

  • HIV (salmonella, microsporidium, CMV, or perhaps MAIS.)
  • Recent travel (E.coli, ova, parasites and cyclospora, E. histolytica, and S. stercoralis)

Suggested workup and treatment:

  • Day 1: send one stool sample for C. difficile
  • If the first sample is negative, send an additional sample
  • If severe disease is present and rapid tests for C. difficile are negative or can’t be performed, then consider performing flexible sigmoidoscopy
  • If severe illness is present, consider empirical therapy, with metronidazole, while awaiting results of tests. Empirical therapy is generally not recommended if two samples are negative when a reliable assay has been used.

Stool cultures for other enteric pathogens are rarely indicated and should be done only if appropriate.

Postoperative fever

- fever is common is the first 48 hours postoperatively

- mostly non-infectious in origin

- after 96 hours likely to represent infection

Causes include

  • Atelectasis
  • UTI common due to the use of catheters
  • Haematoma
  • Wound infection: can develop 1-3 days after surgery
  • DVT
  • Suppurative phlebitis
  • PE
  • Catheter related infection
  • Pneumonia


  • Aggressive chest physiotherapy
  • Urine should be cultured if febrile for >72 hours
  • Surgical wounds should be examined daily-culture only if looks infected or suspect
  • Maintain a high level of suspicion for DVT, etc

Non-infectious causes of fever in the ICU

  • drugs and drug withdrawal
  • malignant hyperpyrexia, neuroleptic malignant syndrome
  • blood products
  • rapid killing of organisms eg Jarisch-Herxheimer reaction
  • tumour lysis syndrome
  • -cytokine related fever has occurred in association with infusion of IL-2, granulocyte-macrophage colony stimulating factor, and on occasion, G-CSF during the treatment of certain malignancy.
  • thrombophlebitis
  • deep vein thrombosis, pulmonary infarction
  • myocardial infarction
  • chronic/acute pancreatitis
  • endocrine causes
  • SAH
  • gout
  • fat emboli
  • organ transplant rejection

Further reading

O'Grady, N.P., Barie, P.S., Bartlett, J.G., Bleck, T., Garvey, G., Jacobi, J., Linden, P., Maki, D.G., Nam, M., Pasculle, W., Pasquale, M.D., Tribett, D.L., and Masur, H. Practice guidelines for evaluating new fever in critically ill adult patients. Clinical Infectious Diseases 26:1042-1059, 1998

© Charles Gomersall and Ross Calcroft November 1999

©Charles Gomersall, April, 2014 unless otherwise stated. The author, editor and The Chinese University of Hong Kong take no responsibility for any adverse event resulting from the use of this webpage.
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