A 45 year old gentleman has been in ICU for five days, recovering from some rib fractures sustained in the course of a fall (lateral fractures of right sided ribs 6-10, without a flail segment). He has required only high flow nasal prongs, a paravertebral block and a fentanyl PCA via his CVC.
He has now become febrile overnight, to 38.9º C. The night registrar has done some blood cultures, and they have come back as:
Gram positive cocci, resembling Staphylococci.
Identification pending.
How will you decide whether this patient needs antibiotics?
(This is not a real CICM viva)
Does this patient need antibiotics? The answer is "maybe" and more information is required.
There are several questions that first need to be answered:
- Are these cocci a real positive blood culture, or are they a contaminant?
- If these cocci are a contaminant, are they still a threat to the patient?
- i.e. is there a way that this patient could have a dangerous CONS bacteremia, do they have risk fac
- If they are a contaminant, and the patient is not at any great risk from a CONS bacteremia, then the question is, where is the fever coming from?
- If they are not a contaminant, they need to be treated, and a source needs to be found.
- In that case, the question that needs to be answered is, do we need vancomycin, or are these sensitive cocci?
The cocci in the culture are negative for coagulase. What does that mean?
Broadly, you group staphylococci into those which produce coagulase (S.aureus) and those which do not (all others). This group contains the following relevant members:
- S.epidermitis (IE)
- S. schleiferi (IE)
- S. lugdunensis (IE)
- S. haemolyticus (IE)
- S. saprophyticus (UTIs)
- S. warneri
- S. hominis
- S. capitis
Because they do no produce coagulase, they cannot coat themselves in a film of clotted blood, which is an important protective factor. As the result, all these CONS bugs are defenseless against phagocytosis, and are generally viewed as a low-virulence organism.
What sort of infections are normally caused by CONS?
Broadly:
- indolent ones
- superficial, usually confined to the skin
- related to breakdown of the skin barrier properties
- limited to areas which are sequestered from the immune system
- more common among immunocompromised hosts
- less likely to stimulate a vigorous immune response
Specific infections caused by these organisms:
- Urinary tract infections
- Central or peripheral venous catheter related infections,
- VP shunt infections
- Pneumonia,
- Endophthalmitis
- Surgical wound infections
- Mastitis or breast abscess
- Osteomyelitis
- Native and prosthetic valve endocarditis
- Prosthetic joint infections
- Infections of pacemaker leads
How will you decide whether this CONS culture represents a true bacteraemia?
Blood culture findings suggestive of a true CoNS bacteraemia:
- Number of positive cultures (more than one)
- Both bottles (aerobic and anaerobic)
- Simultaneous cultures: both grow the same CoNS.
- Rapid time to culture growth: time to positive culture of less than 16 hours
- Quantitative blood culture: a colony count <10 CFUs suggests contamination
(Kassis et al, 2009)
What empirical antibiotics will you give?
- Vancomycin: The Sanford Guide recommends this as empiric therapy.
- Flucloxacillin: Most CoNs (80-90%) are resistant to "classical" β-lactams, but sensitive to antistaphylococcal ones like flucloxacillin.
- Cephazolin and linezolid are alternatives.
- If a prosthetic device is infected but needs to remain in situ, rifampicin may be used over a long course.
The patient has a central line. It is only Day 5. How will you decide whether this central line is the source of this bacteraemia?
- This line should be removed and cultured. The patient only needs a PCA and antibiotics which may be administered via a peripheral cannula. The CVC tip culture will reveal whether this organism is originating from the CVC.
- If for whatever reason the CVC needs to remain in situ, one method of identifying whether the line is responsible is to culture the CVC lumens at the same time as the peripheral blood. In this fashion, if the CVC culture becomes positive first, it is most likely the source (i.e. the greatest inoculum is in the CVC lumen).
The central line is removed and cultured. The tip grows >100 CFU of CONS. What is the significance of this finding?
This is probably a CLABSI.
CLABSI is a laboratory-confirmed bloodstream infection in a patient where the central line was in place for over 48 hours on the date of the event, where the organism cultured from blood is not related to an infection at another site. The patient is febrile, which makes the diagnosis of infection more likely.
Prompt the trainee:
"How is this not just a colonised line?"
If there were no accompanying clinical features, the growth of >15 colony-forming units (semiquantitative) or 100 (quantitative) from a proximal or distal catheter segment would be just a colonised line.
But the patient is febrile. So.
What is the normal risk of infection from CVCs?
Risk of infection per 1000 catheter days:
| Peripheral cannula |
0.5 |
| Arterial line: |
1.7 |
| Normal central line |
2.7 |
| Tunneled CVC |
1.6 |
| PICC |
1.1 |
| PA catheter |
3.7 |
What factors increase the risk of CVC infection?
- Femoral site (as opposed to subclavian)
- Non-tunnelled line (tunneling is protective)
- Plain uncoated catheter
- Antibacterial coating reduces risk of infection
- Antiseptic coating reduces the risk of colonisation
- Multiple lumens
- Frequent line access
- Frequent dressing changes (or very infrequent)
- Insertion by inexperienced operator
How do they get infected?
- During insertion:
- Substandard sterile technique
- "Re-wiring" of an old line, rather than the insertion of a new line
- Use of contaminated site, eg. groin
- After insertion:
- Poor care for dressings
- Use of solutions prone to contamination (eg. propofol, lipid or TPN)
- Contamination of lumen by breaking of sterile line connection
- Poor line changing and port handling technique (one is supposed to use chlorhexidine-soaked gauze)
- Haematogenous contamination of intravascular portion
Broadly, how would you prevent CVCs from getting infected?
- Intelligent decisionmaking regarding the indication for CVC insertion
- Use subclavian lines.
- Minimum number of lumens.
- Use of dedicated lumens for lipid infusions.
- Immunosuppressed patients or those with burns should have antibiotic-coated lines.
- For insertion, use aseptic technique and maximal barrier precautions.
- 0.5% chlorhexidine in 70% alcohol is the preferred cleaning agent.
- Handle ends of administration sets with gauze soaked in chlorhexidine.
- Review the line site daily.
- Remove the line as soon as possible.
- Change lines early - however, there is no evidence for how many days one can safely wait. Oh's Manual recommends that "there is no indication for routine CVC line changing based on catheter days".
- Sterile, transparent semipermeable dressings
- Change dressings regularly (every 7 days for standard dressings)