Bloodstream Infections

Introduction

Bloodstream infections are serious infections where the bacteria or fungi are circulating in the bloodstream i.e. the bacteria or fungi can be isolated by doing a culture of blood. Laypersons may use the term “blood poisoning” to indicate blood stream infections. In general, presence of bacteria in the blood means there is bacteremia which has the following implications :

  • The infection is severe and has spread from the primary site of the infection into the bloodstream
  • The infection in the bloodstream can circulate to distant sites in the body causing bacteria seeding of these sites and result in satellite or metastatic infections

Bacteremia can be caused by Gram positive bacteria like Staphylococcus, Streptococcus, Enterococcus or Gram negative bacteria like Pseudomonas, Klebsiella, Enterobacter, E. coli, etc , Gram negative bacteremia is a significant cause of morbidity and mortality, when associated with septic shock, the mortality can be up to 38%.

Fungemia indicates the presence of fungi in the bloodstream and this is most commonly caused by Candida species ( candidemia ).

Epidemiology

Community acquired bloodstream infections are an uncommon occurrence and reflect the severity of the underlying infection. For example, severe pneumococcal pneumonia may be associated with pneumococcal bacteremia. Similarly, for patients with liver abscess due to Klebsiella species, the bacteria, Klebsiella may also be isolated from the blood.

Many hospitals keep statistics of “hospital acquired” bloodstream infections (BSI) in their institutions as a measure of success of their infection control efforts and to aid in planning of antibiotic stewardship programmes. Many of these hospital acquired BSI are device related. Certain bacteremias eg. MRSA or multi-drug resistant bacteremia often reflect the state of infection control or antibiotic misuse in the healthcare institution. Some of these bacteremias may be hospital acquired and a cluster occurrence may be a sign of a breach in infection control or even a batch contamination. ( eg drugs or infusates ).

Gram negative bacteremia may also be acquired in the hospital, accounting for up to 25% of all bloodstream infections. In addition to the severity of the infection, the bacteria associated with such infections may also be multi-drug resistant. Most ICU bacteremias are associated with devices such as central venous catheters, dialysis catheters, mechanical ventilation etc. The magnitude of the problem varies from hospital to hospital and follows geographic distribution as well. Latin America has a bigger problem (50%) than Europe ( 40%) than North America (35%).

Clinical Presentation

The clinical signs & symptoms of bacteremia are the same as those of sepsis :

  • Fever, shaking chills, rigors
  • Septic shock with hypotension in severe cases
  • Confusion, obtundation, multi-organ failure
  • Blood culture done will confirm presence of bacteria
  • Other sites of infection may be present as well (they may be the primary source of the infection or the site may have become secondarily involved as a result of bacteria or fungi circulating in the bloodstream)
  • If it is related to a central venous or dialysis catheter, line sites may show inflammation or pus discharge
  • In line sepsis complicated by endocarditis or heart valve infection, heart murmurs and heart failure may be a presenting sign , or peripheral embolic signs may be present ( Osler’s nodes, Janeway lesions )

Diagnosis

The most important test is a blood culture which is needed to confirm the presence of bacteria (sometimes fungi) in the bloodstream. If a line related infection is suspected, blood culture needs to be drawn from the line as well. If there are distant sites of infection, cultures from these sites should be obtained as well.

Other markers of infection may also be used :

  • Leucocytosis, in severe cases leucopenia may also occur
  • Neutrophilia, metabolic acidosis, raised lactate
  • Raised biomarkers such as CRP, procalcitonin

Risk factors for bacteremia

  • Hemopoietic stem cell transplant
  • Liver failure
  • Solid organ transplant
  • Diabetes mellitus
  • Pulmonary disease
  • Chronic hemodialysis
  • HIV infection
  • Steroid usage
  • Surgical procedures ( biopsy, ERCP )
  • Traumatic wounds
  • Low serum albumin < 30 g/L
  • Intravenous drug use
  • Prolonged stay in ICU
  • Multiple devices insertion /Lines/catheters, etc

Spontaneous bacteremia can occur in neutropenic patients (white cell count <1000) due to translocation of gut bacteria. This also occurs in splenectomised patients and those who have severe oral mucositis following chemotherapy.

Complications of uncontrolled bloodstream infection :

  • Progression to septic shock and multi-organ failure if not controlled quickly
  • Secondary bacterial/ fungal seeding of other body sites (heart valves, bones, joints, eyes,etc ) resulting in satellite infection
  • Prolonged antibiotic usage and development of resistance if suboptimally treated

Not to mention, financial strain on healthcare resources and healthcare system.

Treatment

The treatment is based on the antibiogram testing of the bacteria isolated. Usually, broad spectrum antibiotics are started before the results of the blood culture are available and the regimen is fine tuned accordingly thereafter. If there is a distant source or satellite source, this needs to be dealt with separately. Often, a persistent bacteremia may point to the following :

  • Inadequate source control. Sometimes, drainage of infected material from the source of infection is needed to control the infection
  • Sometimes, removal of lines, implants and foreign material may be necessary to clear the bacteremia
  • Re-evaluation of the bacteremia may be necessary as drug resistance can develop during the treatment and change of antibiotics may be needed
  • Unexplained recurrent bacteremia without a good explanation may sometimes point to self-inflicted aetiology as seen in factitious infection/ Munchausen’s syndrome

Prevention

Many of the hospital acquired bacteremia and Candidemia can be prevented by good infection control measures:

  • Line care
  • Antibiotic stewardship programmes
  • Minimise antibiotic misuse
  • Staff education
  • Use of bundles/ guidelines on prevention of nosocomial infection
  • Pre-operative prophylactic antibiotic use for implant /prosthesis surgery

 

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