Introduction

Catheter-related bloodstream infections (CRBSI) resulting from bacterial colonisation of an intravascular catheter are a significant clinical problem, magnified in recent years by the increasing use of intravascular catheters in intensive care, chemotherapy and total parental nutrition (TPN). In particular, central venous catheter-related infections are a common cause of bacteraemia and sepsis.

There are three routes by which infection can occur:

• Intraluminal
• Extraluminal
• Haematogenous.

Aetiology of CRBSI

The most common causative organisms associated with CRBSIs are:

Diagnosis of CRBSI

Clinical

The symptoms and signs of catheter-related infection may be localised to the insertion site or track of a tunnelled device. Alternatively, manifestations may be systemic and possibly complicated by bacteraemia.

Microbiology

The purpose of investigation is both to confirm that the catheter is the source of infection, and to identify and characterise the organism so that therapeutic decisions can be made.

Swab cultures taken from the insertion site or the catheter hub are unreliable for the diagnosis of CRBSI because of contamination with skin commensals, although they may be helpful in the diagnosis and management of site sepsis.

Several methods of microbiological investigation for CRBSI have been described.

Without removal of the catheter

• Paired blood cultures
• Endoluminal brushing

With removal of the catheter

• Catheter tip culture
• Other techniques

Management of CRBSI

Factors affecting the management of CRBSI include the type of catheter, severity of symptoms, any underlying disease and the potential pathogens involved.

There are two key decisions:

• Whether to remove the line
• Whether to treat with antibiotics.

Removal of the line

Line removal is the most reliable means of eliminating infection, but its benefits have to be balanced against disadvantages, which include the difficulties of managing patients without central venous access, and the risks of establishing alternatives. The risks associated with leaving the colonised line in situ include:

Indications for line removal include:

For immunocompetent patients with low-grade infections caused by relatively avirulent organisms such as coagulase-negative Staphylococcus spp. or diphtheroids, it may be sufficient to remove the line without giving systemic antibiotics. In other situations, antibiotics may be required following line removal in order to treat persistent bacteraemia or metastatic infection.    

Systemic antibiotics

If the severity of the CRBSI merits empirical treatment:

• Take blood cultures but do not wait for results before starting treatment
• Follow hospital guidelines where available and base initial treatment on local microbiology surveillance cultures and sensitivities. There are no data to support specific recommendations for empirical therapy, but suitable regimens include:
  • If MRSA is likely from a knowledge of local incidence patterns, a glycopeptide such as vancomycin, with or without another anti-staphylococcal antibiotic, can be used
  • If methicillin-sensitive Staphylococcus spp. are likely, an anti-staphylococcal penicillin, such as flucloxacillin
  • In some circumstances, for example if the patient is severely ill or immunocompromised, it may be appropriate to cover Gram-negative organisms.  Suitable agents include antipseudomonal cephalosporins, aminoglycosides, or carbapenems.
• Change to the most appropriate agent once sensitivities of the pathogen(s) are known
• IV antibiotics should be used initially, but the patient can be switched to oral therapy once the patient has stabilised .

If Staphylococcus aureus is isolated from a line tip following removal, but not from a peripheral blood culture, the patient should be closely monitored for evidence of metastatic infection but does not require specific antibiotics if they remain well.

If Staphylococcus aureus is isolated from blood culture, antibiotic therapy should be started immediately and the duration of therapy should be sufficient to prevent relapse or possible metastatic seeding and embolic complications.

Extended durations of treatment may be required for specific patients (eg. infection with coagulase-negative Staphylococcus spp., evidence of endocarditis or septic thrombosis, the immunosuppressed or those with a poor clinical response).

If yeasts are isolated from the line tip they should be treated with high-dose antifungal agents as candidaemia has a high mortality.

Antibiotic lock technique

The antibiotic lock technique may be an alternative to systemic antibiotics for treating CRBSI without removing the line.

Prevention of CRBSI

There is no reliable evidence that antimicrobial prophylaxis can prevent catheter-related infections and consequently this not recommended. However, several factors affect the risk of CRBSI including:

• Site of insertion
• Type of device
• Antimicrobial or silver/chlorhexidine impregnated devices
• Insertion technique
• Duration of catheterisation

Further information and guidelines for insertion and maintenance of intravascular catheters is covered in the following links.

Guidelines for preventing infections associated with the insertion and maintenance of central venous catheters.